ANATOMICAL LANDMARKS OF MAXILLARY AND MANDIBULAR ...

1

COLLEGE OF DENTISTRY; 4TH GRADE (2019-2020) DIJLAH UNIVERSITY

PROSTHODONTICS

Lec. 1 Dr. Salwan Sami

ANATOMICAL LANDMARKS OF MAXILLARY AND

MANDIBULAR EDENTULOUS ARCHES IN

RELATION TO THE REMOVABLE DENTURES

The foundation for dentures is made up of bone and covering soft tissues.

The denture base rests on the mucous membrane (mucosa and submucosa),

which serves as a cushion between the denture base and the supporting bone.

It is quite essential to have knowledge of the tissues that support the

maxillary and the mandibular dentures.There are certain tissue areas or regions

in the maxillary and mandibular edentulous foundations, which are better suited

to bear the stresses due to mastication, and are called as stress bearing areas.

While there are other tissue areas which are not quite suited to take up these

stresses, either due to their anatomy or due to the structures that lie beneath them

and are called stress relief areas. The structures which limit the extension of the

maxillary and mandibular complete dentures are called border-limiting areas.

ANATOMICAL LANDMARKS OF MAXILLA

Stress-bearing areas:

Primary stress-bearing areas in the maxilla are firm tuberosity and hard

palate on either side of palatal raphe, while the secondary stress-bearing areas

are the alveolar ridge and rugae area. The primary stress-bearing areas

generally have thicker mucosa and/or underlying bone that is less subject to

resorption because it is cortical bone. The residual ridge is generally a secondary

stress-bearing area as it is made up of cancellous bone and is subject to resorptive

remodeling after dental extraction and with long-term denture wear.

2


Hard palate

It is made up of two palatine processes of the maxillae (anteriorly) and the

palatine bone (posteriorly). The palatine process of the maxillae joins together at

the midline forming the medial palatal suture. The mucosa is keratinized

throughout the hard palate. Anterolaterally, the submucosa contains adipose

tissue, and posterolaterally, it contains minor salivary gland tissue. This tissue is

displaceable, and although it contributes to the support of the denture, the

horizontal portion of the hard palate lateral to the midline provides the primary

support area for the denture as it also undergoes least resorption.

Tuberosity

It is dense fibrous connective tissues with minimal compressibility. It is a

bulbous extension of the residual ridge in the second and third molar region. The

posterior part of the ridge and the tuberosity areas are considered as one of the

most important areas of support to the maxillary denture because they are least

likely to resorb. If maxillary teeth remain unopposed, the tuberosities and

posterior alveolar arch can hypererupt below the occlusal plane, interfering with

placement of the mandibular prosthetic dentition. When the maxillary teeth are

extracted, the need for a surgical tuberosity reduction should always be

evaluated. The problems associated with maxillary tuberosity that may

sometimes interfere with maxillary denture construction are:

a) Enlargement of the tuberosities.

b) The presence of bilateral undercuts.

c) The presence of pendulous tuberosities.

Palatal rugae area

It is raised areas of dense connective tissue radiating from the median suture

in the anterior one-third of the palate. In the area of the rugae, the palate is set at

3


an angle to the residual ridge and is rather thinly covered by soft tissue and is a

secondary stress-bearing area as it resists the anterior displacement of denture. It

should not be distorted during impression making.

Residual alveolar ridge

It is defined as “The portion of the alveolar ridge and its soft tissue covering

which remains following the removal of teeth.” The shape and size of the residual

alveolar ridge is dependent on the anatomic contour of the patient`s dentate arch.

Therefore U, V, and square arch forms are seen in the edentulous patient. After

dental extraction, the width and height of the residual alveolar ridge change. In

the first 6 to 12 months the resorption is greatest, but it continues at a reduced rate

throughout life.

The residual alveolar ridge crest is a secondary supporting area. The lateral

walls of the ridges are covered in the final denture because they give stability

against lateral displacement and create the peripheral seal.

Border-limiting areas:

These areas determine and confine the extent of the denture.

Labial Frenum

It appears as a fold of mucous membrane present in the midline extending

from the mucous lining of the lip to or towards the crest of residual ridge on the

labial surface. It has a configuration varying from single to multiple folds and

may be narrow or broad and is fan-shaped superiorly. It contains no muscle fibers

and has no action of its own. Hence it is a passive frenum. A V-shaped notch

should be recorded during impression making to accommodate the labial frenum.

The labial notch in the labial flange of the denture must be just wide enough and

just deep enough to allow the frenum to pass through it as the patient moves the

upper lip. If frenum is attached close to the crest frenectomy is done, failure of

4


which will lead to the denture border being placed on the bone tissue which will

cause decreased border seal.

Labial Vestibule

It is defined as, “That portion of the oral cavity which is bounded on one

side by the teeth, gingiva, and alveolar ridge (in the edentulous mouth, the

residual ridge) and on the other side by the lips and cheeks.” It runs from the

buccal frenum on one side to the other, on the labial side of the ridge. It is divided

into two compartments by a labial frenum namely the right and left. The vestibule

is covered by the lining mucosa.

Orbicularis oris is the main muscle of the lip. Its tone depends on the support

received from the labial flange of the denture and the position of artificial teeth.

Its fibers run horizontally and it has an indirect displacing effect on the denture.

The muscles in this region are thin and their influence is minimal. The main

support for the upper lip is obtained from the junction of acrylic to the teeth and

not from the periphery.

Buccal frenum

It forms the dividing line between the labial and buccal vestibules. The frena

may be a single or double fold or even a broad-fan shape. The levator anguli oris

muscle attaches beneath the frenum, affecting its position. The orbicularis oris

pulls the frenum forward, and the buccinator pulls it backward. These three

muscles influence the position of the buccal frenum thus it requires more

clearance in the denture for its action than the labial frenum does.

Buccal vestibule

It lies opposite the tuberosity and extends from the buccal frenum to the

hamular notch. The size of the buccal vestibule varies with the contraction of the

5


buccinator muscle, the position of the mandible, and the amount of bone lost

from the maxilla.

The size and shape of the distal end of the buccal flange of the denture must

be adjusted to the ramus and the coronoid process of the mandible and to the

masseter muscle. When the mouth is opened and the mandible is moved from

side to side, the width and height of this area is reduced. The stability and

retention of the denture is greatly increased when this area is recorded properly.

Hamular notch

It forms the distal limit of the buccal vestibule; it is situated between the

tuberosity and the hamulus of the medial pterygoid plate. It can be palpated with

a mouth mirror or T-shaped burnisher. The mucous membrane of the hamular

notch consists of a thick submucosa made up of loose areolar tissue.

The pterygomandibular raphe, covered by mucosa, extends from the

hamulus inferiorly into the retromolar pad of the mandible. The

pterygomandibular raphe represents the tendinous union of the buccinator and

superior pharyngeal constrictor muscle. The raphe moves forward when the

mouth is opened wide and creates a vertical indentation in the posterior border

of the denture distal to the tuberosities and may even flatten the denture border

immediately lateral to the notch. These tissues in the notch should be displaced

by the posterior palatal border of the denture to achieve a posterior palatal seal,

but overextension causes trauma to the mucosa.

Fovea Palatinae

These are two ductal openings. Each one formed by coalescence of the ducts

of several mucous glands. These act as an arbitrary guide to locate the posterior

6


border of the denture. The position of the fovea palatine also influences the

position of the posterior border of the denture.

Vibrating line

It is an imaginary line across the posterior part of the palate marking the

division between the movable and immovable tissues of the soft palate that

marks the beginning of motion in the soft palate when an individual says “ah,”

and the soft palate elevates. This motion is barely perceptible at the anterior of

this line and is made up of the aponeurosis and muscle fibers of the tensor veli

palatini muscles, glandular tissue, and mucosa, all of which can be displaced

with the denture. Moving a few millimeters posteriorly, there is more motion

and greater elevation of the soft palate. The vibrating line is more of an area

and is always on the soft palate. Its lateral border terminates through the

hamular notches. At the midline, it usually passes 1 to 2 mm anterior to the

fovea palatinae. The distal end of the denture should extend to the vibrating

line.(Aponeurosis is a flattened fibrous membrane, similar to tendon, that binds

muscles together or connects them to other body parts like skin or bone.)

Posterior palatal seal area

It is a soft tissue area limited posteriorly by the distal demarcation of the

movable and immovable tissues of the soft palate and anteriorly by the junction

of the hard and soft palates on which pressure, within physiologic limits, can be

placed. The posterior palatal seal of the denture (a portion of the intaglio surface

of a maxillary removable complete denture, located at its posterior border) should

cover and creating pressure on these area to ensure intimate contact of the denture

base to the soft palate and improves retention of the denture.

Stress relief areas:

Mid-Palatine Raphe

7


It is a soft tissue covering the medial palatal suture. In the region of the

medial palatal suture, the submucosa is extremely thin, with the result that the

mucosal layer is in close contact with the underlying bone. For this reason, this

soft tissue covering the medial palatal suture is nonresilient and may need to be

relieved in the impression or in the denture to avoid trauma from the denture

base.

Incisive Papilla

It is situated on a line immediately behind and between the central incisors.

It lies nearer to the crest of the ridge as resorption progresses. The incisive

foramen is located beneath the incisive Papilla. Thus the location of the incisive

papilla gives an indication as to the amount of resorption that has taken place.

The nasopalatine nerves and blood vessels pass through the foramen, and care

should be taken that the denture base does not impinge on them so that it should

be relieved in the impression or in the denture.

Torus palatinus

It is a hard bony enlargement that occurs in the midline of the roof of the

mouth in a small percentage of patients. The torus is covered by a thin layer of

mucous membrane that is easily traumatized by the denture base, unless the area

is relieved on the intaglio surface. Smaller tori require only being relieved

because they do not interfere in prosthetic construction.

Removal of maxillary tori indicated when there is speech interference,

denture instability due to fulcrum effect, undercut torus that traps food debris,

finally; if the torus extends posteriorly to the vibrating line that affects posterior

palatal seal and prevent adequate denture retention.

Other relief areas

8


The bilateral greater and lesser palatine foramina (Bilaterally located on

the palatal side of the alveolar ridge in the 2nd molar area) often have a

sharp, spiny overhanging edge that may irritate the soft tissues as a result

of pressure from the denture.

Cuspid eminence is a bony elevation on the residual alveolar ridge formed

after extraction of the canine. It is located between the canine and first

premolar region.

The root of the zygoma is located opposite the first molar region,

approximately distal to the buccal frenum and palpable superior to the

buccal vestibule. With increasing resorption of the residual ridge the

denture may require relief over this area to prevent soreness of the

underlying tissue.

9


ANATOMICAL LANDMARKS OF MANDIBLE

The mandible bone consists of:

Body of mandible: It is the curved horizontal horse shoe shaped portion

which carries the alveolar process.

The Rami: two in number forming the vertical portions & joining the body

posteriorly at more or less right angle; each ramus terminates at its upper

extremity in two processes they are: Coronoid and Condyle.

Stress-bearing areas:

Buccal shelf

It is the area between the mandibular buccal frenum and the anterior edge

of the masseter muscle.Medially it is bound by the crest of the ridge and laterally

by the bony external oblique ridge and distally by the retromolar pad. The

buccinator muscle fibers attach horizontally along the bony oblique ridge. As

resorption of the ridge occurs, the buccal shelf does not resorb because of its

muscle attachments on the posterior and lateral borders. The alveolar ridge of the

mandible is significantly medial to the inferior border of the mandible; therefore,

as the ridge resorbs, the denture-bearing surface becomes flatter and widens

towards the buccal shelf. The shelf is dense cortical bone and lies at right angles

to vertical occlusal forces, and is therefore a primary stress-bearing area for the

denture. With resorption of the ridge, the moveable lingual tissues can come to

lie on the superior aspect of the denture-bearing surface, making the adaptation

of the patient a priority to denture success.

Residual Alveolar Ridge

The slopes of the residual alveolar ridge may provide more support than

the crest in the mandible due to the nature of the underlying bone and the mucosa.

The crest of the residual alveolar ridge is covered by fibrous connective tissue,

10


but the underlying bone is cancellous made up of spongy trabeculae without a

good cortical plate covering it. The crest of the mandibular ridge is a secondary

stress-bearing area.

Border-limiting areas:

Labial Frenum

The mucolabial fold extends from the inner aspect of the lip to the

mandible. Unlike the maxillary labial frenum, it is active. The mentalis muscle

inserts very close to the crest of the ridge in this area and limits the border

extension in length and width. The frenum contains fibers of the orbicularis oris

muscle. Both of these two muscles are very active and opening the mouth wide

will thin the dimensions of the denture border.

Labial Vestibule

This is the space between the residual alveolar ridge and the lower lip,

extends from the labial frenum to the buccal frenum. The length and thickness of

the labial flange of the denture occupying this space is crucial in influencing lip

support and retention.

Buccal Frenum

It overlies the depressor anguli oris. The fibers of the buccinator are

attached to the frenum. It should be relieved to prevent displacement of the

denture during function.

Buccal Vestibule

It extends posteriorly from the buccal frenum till the retromolar pad. It is

bound by the residual alveolar ridge on one side and buccinator on the other side.

The buccinators muscle influences the extent of the buccal flange. The

distobuccal border of the buccal vestibule is bordered by the vertical fibers of the

11


masseter muscle, originating on the zygomatic arch, and attaching to the

mandible lateral to the buccinator fibers. Occlusal forces activate the masseter

muscle and cause a bulge in the buccinator muscle, creating the masseteric notch

in the posterior lateral denture border. During border molding this muscle can be

activated by pushing downward on the patient’s chin while the patient attempts

to close the mouth against this pressure.

Retromolar Pad

The retromolar pad is a triangular pad of tissue at the distal end of the

residual ridge. The anterior portion of the triangle is keratinized tissue of the

remnant gingiva of the third molar called the pear-shaped pad. The posterior

aspect of the triangle is composed of thin, non-keratinized epithelium; loose

connective tissue; glandular tissue; fibers of the temporalis tendon and of the

buccinator and superior constrictor muscles; and the pterygomandibular raphe.

The underlying bone is dense cortical bone because of the muscle attachments

and is resistant to resorption. The denture should cover the retromolar pad

because of the support and lack of long-term cortical bone resorption. To avoid

displacement of the denture, the muscles should be activated during border

molding by opening wide and closing against pressure.

Lingual Frenum

It is the anterior attachment of the tongue and overlies genioglossus muscle.

It should be accommodated as a notch in the mandibular denture.

Alveololingual Sulcus

It is the space between the tongue and the residual ridge and extends from

the lingual frenum to the retromylohyoid curtain. It accommodates the lingual

flange of the denture; this sulcus is divided into three regions:

12


1. Anterior region: Also called the sublingual crescent area or sublingual fold. It

extends from the lingual frenum to the premylohyoid fossa, where the

mylohyoid curves below the sulcus. The flange of the mandibular denture

should provide adequate space for the sublingual gland. This is achieved by

the flange sloping inwards, medially away from the lingual surface of the

mandible. The border should rest on the floor of the mouth below the tongue

to accommodate the sublingual gland when tip of the tongue touches the upper

incisors.

2. Middle region: It extends from the premylohyoid fossa to the distal end of the

mylohyoid ridge. This region is shallower than other parts of the sulcus. This

is due to the prominence of the mylohyoid ridge and action of the mylohyoid

muscle. The lingual flange should slope medially away from the lingual

surface of the mandible; parallel to the mylohyoid muscle fibers and towards

the tongue. This sloping helps in three ways:

The tongue rests over the flange stabilizing the denture.

Provides space for raising the floor of the mouth without displacing the

denture.

The peripheral seal is maintained during function.

3. Posterior region: The retromylohyoid fossa (The mandible is usually undercut

inferiorly and posteriorly to the posterior mylohyoid ridge and is called the

retromylohyoid fossa) is present here. This region is no longer influenced by

mylohyoid muscle. The denture flange in this region should turn laterally

towards the ramus of the mandible to fill up the fossa and complete the typical

S-form of the lingual flange of the lower denture as dictated by the

combination of the arch form of the lingual side of the mandible, projection

of mylohyoid ridge and retromylohyoid fossa. Finally, denture border should

be extended posteriorly to contact the retromylohyoid curtain when the tip of

the tongue is placed against the front part of upper residual ridge.

13


Retromylohyoid space: an anatomic area in the alveololingual sulcus just lingual

to the retromolar pad bounded anteriorly by the mylohyoid ridge, posteriorly by

the retromylohyoid curtain, inferiorly by the floor of the alveololingual sulcus,

and lingually by the anterior tonsillary pillar when the tongue is in a relaxed

position.

Retromylohyoid curtain: is formed by the mucous membrane and the superior

constrictor. The region of the retromylohyoid curtain influences the disto lingual

flange of the mandibular denture. Two muscles that influence the denture border

in the region of the retromylohyoid curtain are :Superior constrictor of pharynx

and Medial pterygoid.

The medial pterygoid muscle lies behind the superior constrictor muscle.

When the mandible is elevated the contracting medial pterygoid will push against

the fibers of the superior constrictor and will create a bulge in the wall of the

retromylohyoid curtain.

14


Stress relief areas:

The mylohyoid ridge

It is a bony prominence along the lingual aspect of the mandible; the

magnitude of the prominence varies among patients. Anteriorly the mylohyoid is

attached to the inferior border of the mandible, but continuing posteriorly the

mylohyoid is attached to this ridge and is nearer the level of the alveolar ridge.

The posterior aspect is usually most prominent near the retromolar pad and is

present on the mandible at the same level as the external oblique ridge. This

posterior prominence often requires relief in the denture and may require surgical

reduction if combined with a posterior torus.

The mental foramen

It lies between the first and second premolar region. The mental nerve exits

the mental foramen below the alveolar ridge, but with continued resorption of

the ridge, the mental foramen can become positioned at the crest of the ridge and

be compressed by the denture. This causes pain or even altered sensation in the

lip.

The genial tubercles

They are a dense cortical prominence at the inferior border of the mandible

at the lingual midline. They represent the muscle attachment of the genioglossus

muscles. They only become relevant in the denture border when there is

extensive resorption of the residual ridge.

Torus Mandibularis

They are lingual bilateral prominences of dense cortical bone in the

premolar area, but they may extend posterior to the molar area. They usually

require removal before a denture can be fabricated, or they will severely limit the

15


extension of the denture in the floor of mouth. Smaller tori may only require

relief in the denture.

Other relief areas

Crest of the residual alveolar ridge can sometimes be present as sharp,

spiny or knife-edged. Then it needs to be relieved.

RESORPTION PATTERN OF MAXILLARY AND

MANDIBULAR RIDGE:

The maxillary ridge usually resorbed at the expense of the crest and labial or

buccal aspect resulting in that the crest of the ridge moves in superior and palatal

direction (upwards & inwards) and that is why the maxillary arch has tendency

to become smaller.

16


The mandibular ridge resorbed at the expense of the crest of the ridge

(downwards), resulting in that the crest of the ridge moves in an inferior direction

due to flaring shape of mandible and that's why the mandibular arch has tendency

of becoming larger. The process of remodeling of bone affects particularly the

cortical bone, which is usually the labial and buccal cortical bone of maxilla and

lingual cortical bone of mandible.

The consequences of residual ridge resorption include:

1. Loss of width and depth of sulcus, we have a decreased in height of ridge so the

muscles will be near the denture.

2. Loss of occlusal vertical dimension and decreased in height of lower face.

3. The most important consequences are the change in inter alveolar ridge

relationship because of the resorption direction which is centripetal in maxilla

and centrifugal in the mandible, this resorption will cause a small upper jaw and

wide lower jaw and will affect the arrangement of teeth.

The end


1

PROSTHODONTICS


ANATOMY AND PHYSIOLOGY RELATED TO

PROSTHODONTICS. (MYOLOGY)

Muscles are related to prosthodontics classified into:

1. Muscles of facial expression.

2. Suprahyoid muscles.

3. Infrahyoid muscles.

4. Muscles of mastication.

5. Muscles of the tongue.

6. Muscles of the soft palate.

7. Pharyngeal muscles.

1. Muscles of facial expression

The muscles responsible for the expression seen in the lower half of the

face are: Zygomaticus major, Zygomaticus minor, Levator labii superioris,

Levator labii superioris alaeque nasi, Levator anguli oris, Mentalis, Depressor

labii inferioris, Depressor anguli oris, Risorius, Platysma, Incisivus superioris,

Incisivus inferioris, Orbicularis oris, Buccinators.

The actions of these muscles are responsible for various facial expressions

including smiling, laughing and frowning. Usually they act as a group of

muscles, upon the loss of teeth, the function of the entire group of muscles is

seriously impaired; therefore, the restoration of the lip to its original position

and contour is an extremely important function of the prosthetic appliance.


2

The perioral muscles of facial expression generally do not insert into

bone and need support from the teeth for proper function, their insertion around

the oral cavity opening is very important, where they partly insert into the

connective tissue of the skin and partly into the mucous membrane of the lips.if

these muscles are not properly supported either by natural teeth or by the

artificial teeth none of the facial expression will appear as normal, such as the

naso-labial sulcus, the philtrum, the commissures of the lips, as well as the

mento-labial sulcus.


3

When the perioral muscles are stretched during mouth opening, the

vestibular space between the muscles in the cheek and the slopes of the residual

alveolar ridges is restricted, so that, reduction of the bulk of the flange to

accommodate this action helps to prevent the denture from being dislodged

when the mouth is opened. The muscles of the perioral region are arranged in

distinct patterns, and there are various classification systems. Group I muscles

enter the modiolus, which is the area of convergence for the tendinous fibers of

muscles entering the lip. Group II muscles enter the upper lip, and Group III

muscles enter the lower lip.

Modiolus

The area of strong muscle activity in the lower labial sulcus is bounded

distally on each side by the modiolus, a decussation of muscle fibres at the

corner of the mouth connecting the facial muscles with the orbicularis oris

muscle. Narrowing of the lower denture base related to the modiolus is usually

necessary to avoid displacement .The muscles contributing to the modiolus are

able to move or fix the corner of the mouth in any required position during

function. The labial flanges of the maxillary and mandibular denture frequently

need to be reduced in thickness in the area of the modiolus. The contraction of

the modiolus presses the corner of the mouth against the premolars; the

premolars should be arranged on the crest of the residual ridge to avoid any

interference with this modiolus.


4

Mentalis Muscle

This muscle is found around the chin, it raises the lower lip that causing the

chin to winkle. The contraction of the mentalist raise soft tissues of the chin

thus reducing the depth and width of the labial sulcus .If there has been marked

resorption of the underlying bone, this muscle can exert a considerable pressure

on the labial flange of the denture resulting in posterior and upward

displacement.

Buccinator Muscle

This muscle provides support and mobility for the soft tissues of the cheek.

It is a wide; rather thin muscle arising from a horse shoe shaped line along the

outer surfaces of the maxillary and mandibular alveolar processes in the area of

the molar teeth. In addition, the buccinators originates from the

pterygomandibular raphe or ligament which serves as the junction between the

buccinators muscle and the superior constriction muscle of the pharynx .The

buccinators fibers arising from the mandible follow the external oblique line to

the mesial aspect of the first molar and then ascend slightly toward the corner

of the mouth. Buccinators fibers that originate from the maxillary alveolar

process in the area of the molar descend slightly toward the corner of the

mouth. Some of the fibers insert into the mucous membrane of the cheek in and


5

around the modiolus. The remaining fibers enter the upper and lower lips to

become a part of the orbicularis oris muscle. In the lower jaw it becomes part of

the denture bearing area. It has three heads:

a) Superiorly attached to the alveolar process of the maxilla in the molar area.

b) Inferiorly attached to the alveolar process of the mandible in the molar area.

c) Middle from the ramus.

The fibers of the buccinators muscle are arranged approximately

horizontally and parallel to the occlusal plane but they run perpendicular or at a

right angle to the fibers of the masseter muscle. It is not a true muscle of

mastication, but it aids in conjunction with the tongue in keeping the bolus of

food on the occlusal table during mastication.

Due to the direction of pull of this muscle fibers, by which the denture is

prevented from being dislodge by having its buccal flange resting on a portion

of the buccinators muscle.

The buccinators muscle alone does not dislodge the lower denture directly,

but when the masseter muscle is activated it pushes the buccinators medially

against the denture border in the region of the retromolar pad, so its action is

indirect. To avoid this dislodging action, the denture border should be

contoured in a manner to accommodate the interaction of the buccinators

muscle and masseter muscle. This contour is called the "masseter groove."

The vertical height of the distobuccal flange of the maxillary denture is

limited by the position of the buccinators muscle in the upper jaw.

Orbicularis Oris Muscle

It is the sphincter muscle of the mouth. It has no skeletal attachments

except through the attachments of the incisivus labii superioris and inferioris


6

muscles and the nasolabialis muscles. It composed not only of intrinsic fibers

but also of extrinsic fibers of many of the muscles that coverage at the

modiolus. The complex arrangement of the muscle fibers of different origins

facilitates the various movements of the lips.

The upper lip is supported by the six maxillary anterior teeth and not the

denture border. When the teeth are in occlusion, the superior border of the

lower lip is supported by the incisal third of the six maxillary anterior teeth .It

is important for the dentist to make sure that the actions of these muscles are

recorded when making impressions for the dentures. Also, the angles of the

mouth are easily irritated if the lips are stretched when an impression tray is

inserted.


7

2. Suprahyoid muscles

They are a group of muscles; their function is the elevation of the hyoid

bone, the elevation of larynx and at the same time depression of the mandible.

These muscles are the digastric, stylohyoid, mylohyoid and geniohyoid

muscles.

Mylohyoid Muscle

This muscle attached to the mylohyoid ridge and insert into the hyoid bone.

It limits the extension of the lingual flange of the mandibular denture. The

mylohyoid forms the muscular floor of the mouth. It elevates the hyoid bone,

the tongue, and the membranous floor of the mouth during swallowing. Over-

extension of the lower lingual flange below the mylohyoid line will impinge on

the mylohyoid muscle, thus can affect its action and can unseat the denture.

Geniohyoid Muscles

This muscle arises from the inferior mental spine (genial tubercle), which is

located on the inner aspect of the symphysis menti just above the anterior

attachment of the mylohyoid muscle. This muscle usually presents no problems

in complete denture construction unless there is extensive bone resorption in

this area where they will be high near the crest of the ridge causes pain when

pressure is applied.


8

3. Infrahyoid Muscles

These groups of muscles consist of sternohyoid, omohyoid, sternothyroid,

and thyrohyoid muscles. They have no particular significance in complete

denture construction with respect to denture borders, but having an effect on

mandibular movement by fixing the hyoid bone so that the Suprahyoid muscles

can act on the mandible.

4. Muscles of Mastication

The muscles that have been designated as the muscles of mastication are

the masseter, temporalis, medial pterygoid, and lateral pterygoid muscles. Their

origin is from bones of the skull and they are inserted into the mandible, they

are involved in the masticatory and non-masticatory movement of the

mandible. These muscles function as a group along with Suprahyoid,

Infrahyoid and other groups of muscles to produce the precise movements

necessary for mastication, deglutition, speech and respiration. These muscles

are very powerful, but only the masseter muscle can directly influence the

contour of the denture base.

The muscles of mastication are usually divided into two groups: the

elevator and the depressor. The elevator muscles are usually stronger than the

depressors where the muscles which are responsible for protruding and moving

the mandible from side to side are usually stronger than the retractors, their

effect is mainly manifested through the centric jaw relation recording made

with the aid of weak posterior fibers of temporalis muscle while the antagonist

is the stronger lateral pterygoid.

The elevator muscles are the medial pterygoid, masseter, anterior and

middle fibers of temporalis, the superior head of the lateral pterygoid

muscle, the posterior fibers of the temporalis elevate and retract.


9

The depressor muscles are the inferior head of the lateral pterygoid

which is responsible for protrusion as well.

Masseter Muscle

Its fibers run from the zygomatic arch downwards and backwards to the

outer surface of the ramus of the mandible. The primary action of this powerful

muscle is to elevate the mandible.

It has got an effect on the distobuccal corner of the mandibular impression,

when the masseter contracts it applies pressure against the buccinator which in

turn forms the distobuccal border.

Temporalis Muscle

It's a fan-shaped muscle, that's originated from the temporal fossa and

associated fascia on the lateral aspect of the skull. Its fibers are divided into

three groups based on the orientation of the fibers. The anterior fibers are

oriented vertically and form the bulk of the muscle, the middle fibers are

increasingly oblique, and the posterior fibers are almost horizontal in their

inclination. The temporalis inserts on the coronoid process and along the

anterior border of the ramus of the mandible down to the area of the third molar

tooth.

The anterior and middle fibers elevate the mandible, while the posterior

fibers elevate as well as retract the mandible. An indentation of the temporalis

muscles may be recorded on the posterior buccal flange of the maxillary

impression.

Medial Pterygoid Muscles

It runs essentially from the medial surface of the lateral pterygoid plate,

pyramidal process of the palatine bone, and the maxillary tuberosity, and


10

inserted into the medial surface of the ramus and angle of the mandible. Its

primary action is to elevate the mandible. Sometimes, indentation of this

muscle will be recorded at the posterior border of the buccal flange in the

maxillary impression.

Lateral Pterygoid Muscle

It is the fourth muscle of mastication, has no direct effect on the border of

the denture. The lateral pterygoid muscle has two heads; the superior head

arises from the infratemporal crest and the adjoining surface of the greater wing

of the sphenoid bone. The inferior head arises from the lateral aspect of the

lateral pterygoid plate. The superior head is the smaller and insert in part into

the anterior and medial surface of the articular disk with the bulk of its fibers

joining the inferior head to insert on the anterior surface of the neck of the

condylar process. The superior head appears to function during elevation of the

mandible, whereas the inferior head functions during depression and protrusion

of the mandible.


11

5. Muscles of the Tongue

The tongue is a powerful muscular structure composed of intrinsic and

extrinsic muscle fibers. Functions of the tongue are coordinated with those of

other muscles thus producing muscular movement that are necessary for

various functions such as mastication, deglutition and speech.

The tongue is located in the floor of the mouth and it is in intimated

contact with the lingual flanges of the mandibular denture. The denture flanges

must be contoured to allow the tongue to have its normal wide range of

functional movements. For example, the tip of the tongue is used to moisten the

lips many times a day; while during mastication, the tongue takes the food from

the floor of the mouth and the labial and buccal vestibule and places it on the

occlusal surfaces of the teeth.

According to the size of the tongue, there are three different sizes

which are:

Medium size (normal): Normal size tongue can usually adapted to

complete denture very easily that provided a well extended denture

flanges, properly contoured placing them in compatible positions with

the tongue and cheek, and ending up with the teeth placed in the neutral

zone.

Large size (macroglossia): Such a tongue may interfere with the

impression making.

Small size (Microglossia): Such a tongue will give a reduced support

interfering and lowering the amount of retention of the lower denture.

According to the height of the tongue, there are three different positions:

High: the tongue is higher than the level of the residual ridge.

Medium: the tongue is leveled with the residual alveolar ridge.


12

Low: the tongue is lower than the level of the residual alveolar ridge.

The tongue is usually forming a good landmark for successfully leveling

the lower occlusal plane. The occlusal plane of the lower denture should be

kept in low position allowing the lateral borders of the tongue to rest up on the

occlusal surface of the teeth, thus the mouth is widely opened and increasing

the lower complete denture stability.

The neutral zone forms a balanced position for the artificial teeth located

between the tongue lingually in one side and the muscles of the lips and cheeks

laterally and buccally in the other side contributing largely to the stability of the

lower complete denture.

The intrinsic muscles are originated and inserted within the tongue,

producing changes in the shape of the tongue (responsible for the change in

shape); on the other hand, the extrinsic muscles are originated from structures

other than the tongue and outside the tongue, they can move the tongue as well

as change in its shape. They include: Genioglossus, styloglossus, hyoglossus

and palatoglossus .

Palatoglossus Muscle

It limits the distal extension of the lingual flange of the mandibular

impression along with superior constrictor muscle.


13

6. Muscles of the soft palate

The tensor veli palatini, levator veli palatini, muscular uvulae,

palatoglossus and palatopharangeus are group of muscles forming the movable

curtain extending downwards and backwards into the pharynx.

Tensor Veli Palatini

It drops the soft palate; the denture restores a portion of this muscle in the

posterior palatal seal area.

Levator Veli Palatini

It elevates the soft palate.

7. Pharyngeal muscles

Include superior constrictor, middle constrictor and inferior constrictor

muscles.


14

The superior constrictor

It is one of the most interests in complete denture construction; it has

four sites of origin which are the posterior border of the medial pterygoid plate,

the pterygomandibular raphe, the posterior end of the mylohyoid line and the

side of the tongue. The action of this muscle exerts pressure against the distal

extremity of the mandibular denture, so that an over extension in this area will

be very painful to the patient as the denture perforate the tissue and create a

painful lesion.


15

Temporomandibular Joints (T.M.J)

Each temporomandibular joint involves the articulation of the condylar

process of mandible with the mandibular fossa (glenoid fossa) of the temporal

bone. The temporomandibular joints are synovial joints but differ from most

synovial joints in that the articular surfaces of the bony components are covered

with dense fibrous connective tissue instead of hyaline cartilage. In addition the

temporomandibular joint has a fibrous articular disc interposed between the

bony articular surfaces, which add to the complexity of the normally

functioning joint and to the diagnosis and treatment of the abnormally

functioning joint.

Movement of the mandible can be classified as masticatory and non-

masticatory. The masticatory movements are necessary for introduction,

grasping, crushing and grinding of food, as well as the swallowing of the

triturated mass. The non-masticatory movements include all of the other normal

mandibular movements, such as those used in speech and wetting the lips and

also habitual or abnormal movements such as bruxism, clenching, or tapping

the teeth together. It is important to note that the time spent each day for non-

masticatory movements exceeds the time used for masticatory movements.

A patient is considered suffering from "TMJ dysfunction syndrome" when

one of the following symptoms is present:

1. Pain and tenderness in one or more of the muscles of mastication.

2. Sounds (clicking) during condylar movements.

3. Limitations of the mandibular movements.

• A successful complete denture construction requires healthy

TMJs with both structural and functional harmony of the

osseous structures, as well as the intra-articular tissue and the

capsular ligaments.


16

• The presence of unhealthy TMJs will consequently affect the

process of impression making especially because of the need

of a big and wide mouth opening and the ability of mandible to

move from side to side and this will come true during centric

jaw relation recording.

Oral mucosa

The mucous membrane that covers the oral cavity acts as an intervening

cushioning material between the residual ridges and denture. This membrane

composed of mucosa and submucosa.

The submucosa is formed by connective tissue and makes up the bulk of

the mucous membrane. The submucosa varies in thickness and character from

dense to loose areolar connective tissue. The support and stability offered by

the mucosa to the denture depends on the thickness of submucosa and its


17

attachment to the underlying bone. A dense, firmly attached submucosa will

successfully withstand the pressure of the denture. A thin layer can be easily

traumatized, while a loosely attached layer is easily displaceable.

Depending on the oral mucosa location, it could be classified into:

1. The masticatory mucosa.

2. The lining Mucosa.

3. The specialized mucosa .

The masticatory mucosa

It is the mucosa that covering the hard palate and crest of the residual

ridge, it is a keratinized mucosa.

The lining mucosa

Cover in the lips, cheeks and vestibular spaces, other areas include the

alveololingual sulcus, the soft palate and the ventral surface of the tongue. This

type of mucosa is not firmly attached or in other words, it was loosely attached

to the underlying bone, this lining mucosa is a non-keratinized mucosa.

The specialized mucosa

Covers the dorsum of the tongue, this mucosa is keratinized including the

papillae on the upper surface of the tongue.

The soft tissues should be recorded when or during their resting condition.

Tissues tend to return to their normal form after a period of time after being

displaced, thus, creating an unstable denture, so that proper relief is sometimes

needed for proper recording of these tissues in their undistorted form.

The region of the median palatal suture exhibits a very thin submucosa

firmly attached to the underlying bone, that's why the covering tissues of this


18

suture is non-resilient. Here a very little or no stress can be subjected to this

area during the impression making procedure or rocking of the denture above

the center of the palate will occur.

Salivary glands

The major exocrine glands that secrete saliva are the paired parotid,

submandibular and sublingual glands, in addition to these 3 major glands, the

numerous minor salivary glands are distributed throughout the oral cavity in the

lips, cheeks, tongue and the palate.

The parotid gland empties its secretions into the oral cavity via a duct

which opens through the buccal mucosa near the maxillary second molar tooth.

The submandibular and the sublingual glands are located in the floor of the

mouth, also empty their secretions into the oral cavity via a duct, the position of

their ducts are very important for any overextension or pressure area exerted by

the lower flange on the openings of these ducts will cause blocking out of the

duct, where the patient will eventually complain of swelling under the chin, this

could be relieved immediately after removal of the lower dentures from the

mouth.

Saliva is a mixture of two types of primary secretions :

1. A serous secretion (thin, watery) containing the enzyme ptyalin for

the digestion of starchy foods.

2. A mucous secretion (viscid, sticky or adhesive) for lubrication

purposes

The parotid gland considered being serous, the submandibular glands are

mixed but mostly serous secretions; and, the sublingual glands are mixed but

mostly mucous secretions.


19

Saliva possesses the following functions in the edentulous patient:

Denture retention – saliva is an essential component in the physical

retention of complete dentures.

Lubrication – the glycoproteins in saliva facilitate movement of the soft

tissues during speech, mastication and the swallowing of food.

Cleansing – saliva physically washes food and other debris from the soft

tissues and from the polished surfaces of prostheses.

Taste – flavours are perceived only when substances are in solution in

saliva or other fluids.

Digestion – digestion begins during mastication when salivary amylase

starts to break down glucose.

Antimicrobial – there are antimicrobial components, such as antibodies,

in saliva which help to maintain a normal balance of the oral flora.

Some of the pathologic conditions that decrease salivation are atrophy of

the salivary glands with aging, fibrosis of glands following irradiation therapy

of head and neck tumors and diseases of the brain stem that directly depress

activity in the salivatory nuclei and block salivation, other conditions include

some types of encephalitis, poliomyelitis, diabetes mellitus, diabetes insipidus,

diarrhea caused by bacteria of food, elevated temperature from acute infectious

diseases, and vitamin deficiency particularly vitamin A, numerous drugs used

to treat these and other conditions can alter the quantity and quality of saliva.

Xerostomia or dry mouth is the case of insufficient saliva may cause loss

of retention, and the mucosa will not tolerate dentures so that such a problem

should be discussed with the patient and it may be necessary to limit denture

use to short periods and to restrict the diet to moist foods that are relatively soft

or even liquid.


20

Pathologic conditions that may be accompanied by increased salivation

are digestive tract irritants and painful lesions of the oral cavity. These may be

due to a vitamin deficiency, surgical trauma, an ill-fitting denture, or inadequate

inter-occlusal distance when artificial dentures are made.

Some patients may have excessive salivary secretions, affecting the

process of impression making and even may cause a gagging reflex. Excessive

salivation, particularly by the submandibular and sublingual glands, presents a

problem in impression making. When this problem exists, appropriate drugs

can be administered orally before making the impression. Excessive secretions

of mucus from the palatal glands may distort the impression material in the

posterior two thirds of the palate. To counteract this problem the palate may be

massaged to encourage the glands to empty, the mouth may be irrigated with a

stringent mouth wash just before inserting the impression material, or the palate

may be wiped with gauze.

Lastly, the viscosity of the saliva is very important a thick saliva is good for

retention of the denture, but may cause gagging, on the other hand can be of

bad effect on the efficiency of denture seal.

The end


1

PROSTHODONTICS


DIAGNOSIS & TREATMENT PLANNING OF

REMOVABLE PARTIAL DENTURES (R.P.Ds).

The steps for R.P.D. construction are:

1. Diagnosis and treatment plan for R.P.D.

2. Preparation of the mouth for R.P.D.

3. Impression procedure for R.P.D.

4. Occlusal relationship for R.P.D.

5. Trial stage for R.P.D.

6. Initial placement, adjustment and servicing of R.P.D.

Diagnosis: the determination of the nature of a disease.

Treatment plan: the sequence of procedures planned for the treatment of a

patient after diagnosis.

The delineation of each patient’s uniqueness occurs through the patient

interview and diagnostic clinical examination process.

PATIENT INTERVIEW

The interview, an opportunity to develop rapport with the patient,

involves listening to and understanding the patient’s chief complaint or concern

about his or her oral health. This can include clinical symptoms of pain,

difficulty with function, concern about appearance, problems with an existing

prosthesis, or any combination of symptoms related to the teeth, periodontium,


2

jaws, or previous dental treatment. It is important to listen carefully to what the

patient has stated is the reason for presenting for evaluation.

Although formats for sequencing the patient interview and clinical

examination vary, so that the dentist should follow a sequence that includes:

1. Chief complaint and its history.

2. Medical history review.

3. Dental history review, especially related to previous prosthetic

experience.

4. Patient expectations.

CLINICAL EXAMINATION

A. Objectives of Prosthodontic Treatment

The objectives of any prosthodontic treatment may be stated as follows:

(1) the elimination of disease; (2) the preservation, restoration, and maintenance

of the health of the remaining teeth and oral tissues (which will enhance the

removable partial denture design); and (3) the selected replacement of lost

teeth; for the purpose of (4) restoration of function in a manner that ensures

optimum stability and comfort in an esthetically pleasing manner.

B. Extra-oral examination.

It includes a general look at the patient as a whole "his head and face

particularly", so we look for any symptoms or deformity of the face. We have

to see position of the lips and whether it is short or long also the opening of the

mouth. We should examine the facial symmetry, T.M.J with mandibular

movement and muscles of mastication.


3

C. Intra-oral examination.

A complete oral examination should precede any treatment decisions. It

should include visual and digital examination of the teeth and surrounding

tissues with a mouth mirror, explorer, and periodontal probe, vitality tests of

critical teeth, and examination of casts correctly oriented on a suitable

articulator. Clinical findings are augmented by and correlated with a complete

intraoral radiographic survey.

Sequence for Oral Examination:

1. Relief of pain and discomfort and caries control by placement of

temporary restorations.

A preliminary examination is conducted to determine the need for

management of acute needs and whether a prophylaxis is required to conduct a

thorough oral examination.

2. A thorough and complete oral prophylaxis.

An adequate examination can be accomplished best with the teeth free of

accumulated calculus and debris. A complete oral examination should be

deferred until the teeth have been thoroughly cleaned.

3. Complete intraoral radiographic survey.

The objectives of a radiographic examination are:

a. To locate areas of infection and other pathosis that may be present.

b. To reveal the presence of root fragments, foreign objects, bone

spicules, and irregular ridge formations.

c. To reveal the presence and extent of caries and the relation of

carious lesions to the pulp and periodontal attachment.


4

d. To permit evaluation of existing restorations as to evidence of

recurrent caries, marginal leakage, and overhanging gingival

margins.

e. To reveal the presence of root canal fillings and to permit their

evaluation as to future prognosis (the design of the removable

partial denture may hinge on the decision to retain or extract an

endodontically treated tooth).

f. To permit evaluation of periodontal conditions present and to

establish the need and possibilities for treatment.

g. To evaluate the alveolar support of abutment teeth, their number,

the supporting length and morphology of their roots, the relative

amount of alveolar bone loss suffered through pathogenic

processes, and the amount of alveolar support remaining.

4. Impressions for making accurate diagnostic casts to be mounted for

occlusal examination.

5. Examination of teeth, investing structures, and residual ridges.

The teeth, periodontium, and residual ridges can be explored by

instrumentation and visual means. Recording of relevant patient history and

clinical data on diagnosis charts is important to document features important to


5

clinical presentation. These can be recorded on electronic or paper charts for

future reference .Visual examination will reveal many of the signs of dental

disease. Consideration of caries susceptibility is of primary importance. The

number of restored teeth present, signs of recurrent caries, and evidence of

decalcification should be noted.

At the time of the initial examination, periodontal disease, gingival

inflammation, the degree of gingival recession, and mucogingival relationships

should be observed. The number of teeth remaining, the location of the

edentulous areas, and the quality of the residual ridge will have a definite

bearing on the proportionate amount of support that the removable partial

denture will receive from the teeth and edentulous ridges.

6. Vitality tests of remaining teeth.

Vitality tests should be given particularly to teeth to be used as abutments

and those having deep restorations or deep carious lesions. This should be done

through both thermal and electronic means.

7. Determination of the height of the floor of the mouth to locate inferior

borders of lingual mandibular major connectors.

Mouth preparation procedures are influenced by the choice of major

connectors. This determination must precede altering contours of abutment

teeth.

D. Diagnostic Casts

A diagnostic cast is a life-size reproduction of a part or parts of the oral

cavity and/or facial structures for the purpose of study and treatment planning.

It should be an accurate reproduction of all the potential features that aid

diagnosis. These include the teeth locations, contours, and occlusal plane


6

relationship; the residual ridge contour, size, and mucosal consistency; and the

oral anatomy delineating the prosthesis extensions.

The diagnostic cast can be obtained by taking an impression which is

usually made with an irreversible hydrocolloid (alginate) in a stock (perforated

or rim lock) impression tray.

Diagnostic casts serve several purposes as an aid to diagnosis and treatment

planning. Some of these are as follows:

1. Diagnostic casts are used to supplement the oral examination by

permitting a view of the occlusion from the lingual, as well as from the

buccal aspect.

2. Diagnostic casts are used to permit a topographic survey of the dental

arch that is to be restored by means of a removable partial denture. The

cast of the arch in question may be surveyed individually with a cast

surveyor to determine the parallelism or lack of parallelism of tooth

surfaces involved, and to establish their influence on the design of the

removable partial denture.

3. Diagnostic casts are used to permit a logical and comprehensive

presentation to the patient of present and future restorative needs, as well

as of the hazards of future neglect.

4. Individual impression trays may be fabricated on the diagnostic casts, or

the diagnostic cast may be used in selecting and fitting a stock

impression tray for the final impression.

5. Diagnostic casts may be used as a constant reference as the work

progresses. Penciled marks indicating the type of restoration, the areas of

tooth surfaces to be modified, the location of rests, and the design of the

removable partial denture framework, as well as the path of placement


7

and removal, all may be recorded on the diagnostic cast for future

reference.

6. Unaltered diagnostic casts should become a permanent part of the

patient’s record because records of conditions existing before treatment

are just as important as are preoperative radiographs.

DIAGNOSTIC FINDINGS

The information gathered in the patient interview and clinical examination

provides the basis for establishing whether treatment is indicated, and if so,

what specific treatment should be considered.

A. Interpretation of Examination Data

As a result of the oral examination, several diagnoses are made that are

related to the various tissues, conditions, and clinical information gathered. The

integration of these diagnoses serves as the basis for decisions that will

ultimately identify the suggested treatment. The treatment decision reflects a

confluence of several aspects of the patient’s past, present, and potential oral

health status. These are as follows:

1. Radiographic Interpretation

It is important to verify by clinical examination disease found through

radiographic interpretation. Also, if the clinical examination reveals dental

caries and/or periodontal disease, its severity can be confirmed by radiographic

interpretation.

The quality of the alveolar support of an abutment tooth is of primary

importance because the tooth will have to withstand greater stress loads when

supporting a dental prosthesis. Abutment teeth providing total abutment support

to the prosthesis, whether fixed or removable, will have to withstand a greater


8

load and especially greater horizontal forces. Abutment teeth adjacent to distal

extension bases are subjected not only to vertical and horizontal forces but to

torque as well because of movement of the tissue-supported base.

The morphologic characteristics of the roots determine to a great extent

the ability of prospective abutment teeth to resist successfully additional

rotational forces that may be placed on them. Teeth with multiple and divergent

roots will resist stresses better than teeth with fused and conical roots, because

the resultant forces are distributed through a greater number of periodontal

fibers to a larger amount of supporting bone.

Unerupted third molars should be considered as prospective future

abutments to eliminate the need for a distal extension removable partial

denture. The increased stability of a tooth-supported denture is most desirable

to enhance the health of the oral environment.


9

2. Periodontal Considerations

An assessment of the periodontium in general and abutment teeth in

particular must be made before prosthetic restoration. One must evaluate the

condition of the gingiva, looking for adequate zones of attached gingiva and the

presence or absence of periodontal pockets. The ideal periodontal condition is a

disease-free periodontium with adequate attached mucosa in regions at or

adjacent to removable partial denture component parts that cross the gingival

margins to best resist the mechanical challenges posed as the result of function

and use.

3. Caries Risk Assessment Considerations

Caries activity in the mouth, past and present, and the need for protective

restorations must be considered. Frequent consumption of sugars can lead to

carious involvement of roots, caries around restorations, or caries associated

with clasps of removable partial dentures.


10

4. Evaluation of the Prosthesis Foundation—Teeth and Residual Ridge

An evaluation of the prosthesis foundation is required to ensure that an

appropriately stable base of sound teeth and/ or residual ridge(s) is provided to

maximize prosthesis function and patient comfort.

5. Surgical Preparation

The need for pre-prosthetic surgery or extractions must be evaluated. The

same criteria apply to surgical intervention in the partially edentulous arch as in

the completely edentulous arch.

Extraction of teeth may be indicated for one of the following three reasons:

If the tooth cannot be restored to a state of health, extraction may be

unavoidable

A tooth may be removed if its absence will permit a more serviceable

and less complicated removable partial denture design. Teeth in extreme

malposition (lingually inclined mandibular teeth, buccally inclined

maxillary teeth, and mesially inclined teeth posterior to an edentulous

space) may be removed if an adjacent tooth is in good alignment and if

good support is available for use as an abutment.

A tooth may be extracted if it is so unesthetically located as to justify its

removal to improve appearance.

6. Analysis of Occlusal Factors

From the occlusal analysis made by evaluating the mounted diagnostic

casts, the dentist must decide whether it is best to accept and maintain the

existing occlusion or to attempt to improve on it by means of occlusal

adjustment and/or restoration of occlusal surfaces. It must be remembered that

the removable partial denture can supplement the occlusion that exists only at

the time the prosthesis is constructed. The dominant force that dictates the


11

occlusal pattern will be the cuspal harmony or disharmony of the remaining

teeth and their proprioceptive influence on mandibular movement. The goal of

artificial tooth placement is to harmonize with the functional parameters of the

existing occlusion providing bilateral, simultaneous functional contact.

7. Fixed Restorations

There may be a need to restore modification spaces with fixed restorations

rather than include them in the removable partial denture.

Generally any unilateral edentulous space bounded by teeth suitable for use

as abutments should be restored with a fixed partial denture cemented to one or

more abutment teeth at either end. The length of the span and the periodontal

support of the abutment teeth will determine the number of abutments required

to restore with fixed partial denture.

Two specific contraindications for the use of unilateral fixed restorations

are known. One is a long edentulous span with abutment teeth that would not

be able to withstand the trauma of the occlusal forces. The other is abutment

teeth, which exhibit reduced periodontal support due to periodontal disease,

which would benefit from cross-arch stabilization.

Usually any missing anterior teeth in a partially edentulous arch (anterior

modification spaces) are best replaced by means of a fixed restoration. There

are exceptions. Sometimes a better esthetic result is obtainable when the

anterior replacements are supplied by a removable partial denture. This is also

true when excessive tissue and bone resorption necessitates placement of the

pontics in a fixed partial denture too far palatally for good esthetics or for an

acceptable relation with the opposing teeth.


12

8. Orthodontic Treatment

Occasionally, orthodontic movement of malposed teeth followed by

retention through the use of fixed partial dentures makes possible a better

removable partial denture design mechanically and esthetically than could

otherwise be used.

9. Need for Determining Type of Mandibular Major Connector

One of the criteria used to determine the use of the lingual bar or linguoplate

is the height of the floor of the patient’s mouth when the tongue is elevated.

10. Need for Reshaping Remaining Teeth

The clinical crown shapes of anterior and posterior teeth are not capable of

supporting a removable partial denture framework without appropriate

modification. Without the required modifications, the prosthesis does not

adequately benefit from the support and stability offered by the teeth and

consequently will not be comfortable to the patient.

B. Indications for Removable Partial Dentures

Although a removable partial denture should be considered only when a

fixed restoration is contraindicated, there are several specific indications for the

use of a removable restoration:

1. Distal Extension Situations

The most common partially edentulous situations are the Kennedy Class I

and Class II which have an edentulous space on the opposite side of the arch is

often conveniently present to aid in required retention and stabilization of the



13

2. After Recent Extractions

The replacement of teeth after recent extractions often cannot be

accomplished satisfactorily with a fixed restoration. When relining will be

required later, or when a fixed restoration using natural teeth or implants will be

constructed later, a temporary removable partial denture can be used.

3. Long Span

A long span edentulous area may be totally tooth supported if the abutments

and the means of transferring the support to the denture are adequate, and if the

denture framework is rigid.

4. Need for Effect of Bilateral Stabilization

The removable partial denture, on the other hand, may act as a periodontal

splint through its effective cross-arch stabilizing of teeth weakened by

periodontal disease.

5. Excessive Loss of Residual Bone

Whenever excessive resorption has occurred, teeth supported by a denture

base may be arranged in a more acceptable buccolingual position than is

possible with a fixed partial denture. A removable partial denture will permit

the location of the replaced teeth in a favorable relation to the lip and opposing

dentition regardless of the shape of the residual ridge.

6. Unusually Sound Abutment Teeth

Sometimes the reasoning for making a removable restoration is the desire

to see sound teeth preserved in their natural state and not prepared for

restorations.


14

7. Abutments with Guarded Prognoses

The questionable tooth may then be included in the original design and, if

subsequently lost, the removable partial denture can be modified or remade.

Most removable partial denture designs do not lend themselves well to later

additions, although this eventuality should be considered in the design of the

denture.

8. Economic Considerations

A prosthesis that is made to satisfy economic considerations alone may

provide only limited success and result in more costly treatment in the future.

The end


1

PROSTHODONTICS


PREPARATION OF THE MOUTH FOR


The preparation of the mouth is fundamental to a successful removable

partial denture service. Mouth preparation, perhaps more than any other single

factor, contributes to the philosophy that the prescribed prosthesis not only

must replace what is missing but also must preserve the remaining tissues and

structures that will enhance the removable partial denture.

In general, mouth preparation includes procedures in four categories:

1. Oral surgical preparation,

2. Conditioning of abused and irritated tissues,

3. Periodontal preparation, and

4. Preparation of abutment teeth.

The objectives of the procedures involved in all four areas are to return the

mouth to optimum health and to eliminate any condition that would be

detrimental to the success of the removable partial denture.

Naturally, mouth preparation must be accomplished before the impression

procedures are performed that will produce the master cast on which the

removable partial denture will be fabricated. Oral surgical and periodontal

procedures should precede abutment tooth preparation and should be completed

far enough in advance to allow the necessary healing period.


2

Oral Surgical Preparation

All pre-prosthetic surgical treatment for the removable partial denture

patient should be completed as early as possible. The longer the interval

between the surgery and the impression procedure, the more complete the

healing and consequently the more stable the denture-bearing areas.

A variety of oral surgical techniques can prove beneficial to the clinician in

preparing the patient for prosthetic replacements.

Extractions

Planned extractions should occur early in the treatment regimen but not

before a careful and thorough evaluation of each remaining tooth in the dental

arch is completed. Extraction of nonstrategic teeth that would present

complications or those that may be detrimental to the design of the removable

partial denture is a necessary part of the overall treatment plan.

Removal of Residual Roots

All retained roots or root fragments should be removed. Removal of root

tips can be accomplished from the facial or palatal surfaces without resulting in

a reduction of alveolar ridge height or endangering adjacent teeth.

Impacted Teeth

All impacted teeth, including those in edentulous areas, as well as those

adjacent to abutment teeth, should be considered for removal. The periodontal

implications of impacted teeth adjacent to abutments are similar to those for

retained roots. These teeth are often neglected until serious periodontal

implications arise.


3

Malposed Teeth

The loss of individual teeth or groups of teeth may lead to extrusion,

drifting, or combinations of malpositioning of remaining teeth. Orthodontics

may be useful in correcting many occlusal discrepancies.

Cysts and Odontogenic Tumors

Panoramic roentgenograms of the jaws are recommended to survey the

jaws for unsuspected pathologic conditions. When a suspicious area appears on

the survey film, a periapical roentgenogram should be taken to confirm or deny

the presence of a lesion. All radiolucencies or radiopacities observed in the

jaws should be investigated.

Exostoses and Tori

The existence of abnormal bony enlargements should not be allowed to

compromise the design of the removable partial denture. The removal of

exostoses and tori is not a complex procedure, and the advantages to be realized

from such removal are great in contrast to the deleterious effects that their

continued presence can create.

Hyperplastic Tissue

Hyperplastic tissues are seen in the form of fibrous tuberosities soft

flabby ridges, folds of redundant tissue in the vestibule or floor of the mouth,

and palatal papillomatosis. All these forms of excess tissue should be removed

to provide a firm base for the denture. Although hyperplastic tissue has no great

malignant propensity, all such excised tissue should be sent to an oral

pathologist for microscopic study.


4

Muscle Attachments and Frena

As a result of the loss of bone height, muscle attachments may insert on or

near the residual ridge crest. The mylohyoid, buccinator, mentalis, and

genioglossus muscles are most likely to introduce problems of this nature.

Appropriate ridge extension procedures can reposition attachments and remove

bony spines, which will enhance the comfort and function of the removable

partial denture. The maxillary labial and mandibular lingual frena are the most

common sources of frenum interference with denture design. These can be

modified easily through any of several surgical procedures.

Bony Spines and Knife-Edge Ridges

Sharp bony spicules should be removed and knifelike crests gently

rounded. These procedures should be carried out with minimum bone loss.

Polyps, Papillomas, and Traumatic Hemangiomas

All abnormal soft tissue lesions should be excised and submitted for

pathologic examination before a removable partial denture is fabricated.

Hyperkeratoses, Erythroplasia, and Ulcerations

All abnormal white, red, or ulcerative lesions should be investigated,

regardless of their relationship to the proposed denture base or framework.

Dentofacial Deformity

Patients with a dentofacial deformity often have multiple missing teeth as

part of their problem. Correction of the jaw deformity can simplify the dental

rehabilitation. Several dental professionals (prosthodontist, oral surgeon,

periodontist, orthodontist, general dentist) may play a role in the patient’s

treatment.


5

Osseointegrated Devices

A number of implant devices to support the replacement of teeth have

been introduced to the dental profession. These devices offer a significant

stabilizing effect on dental prostheses through a rigid connection to living bone.

Implants are carefully placed using controlled surgical procedures and, in

general, bone healing to the device is allowed to occur before a dental

prosthesis is fabricated. Long-term clinical research has demonstrated good

results for the treatment of complete and partially edentulous dental patients

using dental implants.

Augmentation of Alveolar Bone

Considerable attention has been devoted to ridge augmentation with the

use of autogenous and alloplastic materials, especially in preparation for

implant placement.


6

Conditioning of Abused and Irritated Tissues

Many removable partial denture patients require some conditioning of

supporting tissues in edentulous areas before the final impression phase of

treatment begins because the tissue contour may change according to tissue

healing. Patients who require conditioning treatment often demonstrate the

following symptoms:

1. Inflammation and irritation of the mucosa covering denture-bearing areas

2. Distortion of normal anatomic structures, such as incisive papillae, rugae,

and retromolar pads

3. A burning sensation in residual ridge areas, the tongue, and the cheeks

and lips

These conditions are usually associated with ill-fitting or poorly occluding

removable partial dentures. However, nutritional deficiencies, endocrine

imbalances, severe health problems (diabetes or blood dyscrasias), and bruxism

must be considered in a differential diagnosis.

If the use of a new removable partial denture or the relining of a present

denture is attempted without first correcting these conditions, the chances for

successful treatment will be compromised because the same old problems will

be perpetuated. The patient must be made to realize that fabrication of a new

prosthesis should be delayed until the oral tissues can be returned to a healthy

state. If there are unresolved systemic problems, removable partial denture

treatment will usually result in failure or limited success.

The first treatment procedure should consist of immediate institution of a

good home care program. A suggested home care program includes rinsing the

mouth three times a day with a prescribed saline solution; massaging the

residual ridge areas, palate, and tongue with a soft toothbrush; removing the


7

prosthesis at night; and using a prescribed therapeutic multiple vitamin along

with a prescribed high-protein, low-carbohydrate diet. Some inflammatory oral

conditions caused by ill-fitting dentures can be resolved by removing the

dentures for extended periods. However, few patients are willing to undergo

such inconveniences.

If the denture is the problem, patient is advised by removing them till the

tissues return to normal as see it in previous details. If this is not resolved,

tissue conditioners are used to provide a soothing and cushioning effect on the

irradiated mucosa till mucosa becomes normal.

Use of Tissue Conditioning Materials

The tissue conditioning materials are elastopolymers that continue to flow

for an extended period, permitting distorted tissues to rebound and assume their

normal form. These soft materials apparently have a massaging effect on

irritated mucosa, and because they are soft, occlusal forces are probably more

evenly distributed. Their use is limited to reversible tissue changes like tissue

abrasion and ulceration; these materials have not any direct effect on

irreversible tissue changes like tissue hyperplasia and hyperatrophy.

Tissue conditioners are soft and should be of adequate thickness at least

2mm. Tissue conditioners are composed of powder containing a poly ethyl

methacrylate and a liquid containing a mixture of aromatic ester and ethyl

alcohol up to 30% of the main constituent which is volatile material. Within a

few days the tissue conditioners will become stiffer as a result of the alcohol

loss.

Mode of action of tissue conditioners are:

Evenly distributes the occlusal load over the tissues.

Produces an intimate tissue contact massaging the soft tissues.


8

Reduces the inflammation by increasing blood flow to the abused tissues.

Maximum benefit from using tissue conditioning materials may be

obtained by (1) eliminating deflective or interfering occlusal contacts of old

dentures (by remounting in an articulator if necessary); (2) extending denture

bases to proper form to enhance support, retention, and stability; (3) relieving

the tissue side of denture bases sufficiently (2 mm) to provide space for even

thickness and distribution of conditioning material; (4) applying the material in

amounts sufficient to provide support and a cushioning effect; and (5)

following the manufacturer’s directions for manipulation and placement of the

conditioning material.

The conditioning procedure should be repeated until the supporting tissues

display an undistorted and healthy appearance. Many dentists find that intervals

of 4 to 7 days between changes of the conditioning material are clinically

acceptable. Improvement in irritated and distorted tissues is usually noted

within a few visits, and in some patients a dramatic improvement will be seen.

Usually three or four changes of the conditioning material are adequate, but in

some instances additional changes are required. If positive results are not seen

within 3 to 4 weeks, one should suspect more serious health problems and

request a consultation from a physician.


9

Periodontal Preparation

Periodontal preparation of the mouth usually follows any oral surgical

procedure and is performed simultaneously with tissue conditioning

procedures. In any situation, periodontal therapy should be completed before

restorative dentistry procedures are begun for any dental patient. The

periodontal health of the remaining teeth, especially those to be used as

abutments, must be evaluated carefully by the dentist and corrective measures

instituted before a removable partial denture is fabricated.

The objective of periodontal therapy is the return to health of supporting

structures of the teeth, creating an environment in which the periodontium may

be maintained. The specific criteria for satisfying this objective are as follows:

1. Removal and control of all etiologic factors contributing to periodontal

disease along with reduction or elimination of bleeding on probing.

2. Elimination of, or reduction in, the pocket depth of all pockets with the

establishment of healthy gingival sulci whenever possible.

3. Establishment of functional atraumatic occlusal relationships and tooth

stability.

4. Development of a personalized plaque control program and a definitive

maintenance schedule.

Abutment Teeth Preparation

Equipped with the diagnostic casts on which a tentative removable partial

denture design has been drawn, the dentist is able to accomplish preparation of

abutment teeth with accuracy. The information at hand should include the

proposed path of placement, the areas of teeth to be altered and tooth contours

to be changed, and the locations of rest seats and guiding planes.


10

During examination and subsequent treatment planning in conjunction with

a survey of diagnostic casts, each abutment tooth is considered individually as

to what type of restoration is indicated.

Classification of abutment teeth preparation:

The subject of abutment preparations may be grouped as follows:

(1) Those abutment teeth that require only minor modifications to their coronal

portions,

(2) Those that are to have restorations other than complete coverage crowns,

(3) Those that are to have crowns (complete coverage).


11

Sequence of Abutment Preparations on Sound Enamel or Existing

Restorations:

1. Proximal surfaces parallel to the path of placement should be prepared to

provide guiding planes.

2. Tooth contours should be modified, lowering the height of contour so

that:

(a) The origin of circumferential clasp arms may be placed well below the

occlusal surface, preferably at the junction of the middle and gingival

thirds;

(b) Retentive clasp terminals may be placed in the gingival third of the

crown for better esthetics and better mechanical advantage; and

(c) Reciprocal clasp arms may be placed on and above a height of contour

that is no higher than the cervical portion of the middle third of the

crown of the abutment tooth.

3. After alterations of axial contours are accomplished and before rest seat

preparations are instituted, an impression of the arch should be made in

irreversible hydrocolloid and a cast formed in a fast-setting stone. This

cast can be returned to the surveyor to determine the adequacy of axial

alterations before proceeding with rest seat preparations. If axial surfaces

require additional axial recontouring, this can be performed during the

same appointment and without compromise.

4. Occlusal rest areas should be prepared that will direct occlusal forces

along the long axis of the abutment tooth. Mouth preparation should

follow the removable partial denture design that was outlined on the

diagnostic cast at the time the cast was surveyed and the treatment plan

confirmed. Proposed changes to abutment teeth should be made on the

diagnostic cast and outlined in colored pencil to indicate the area,

amount, and angulation of the modification to be done.


12

Form of the Occlusal Rest and Rest Seat for abutment teeth preparations:

1. The outline form of an occlusal rest seat should be a rounded triangular

shape with the apex toward the center of the occlusal surface.

2. It should be as long as it is wide, and the base of the triangular shape (at

the marginal ridge) should be at least 2.5 mm for both molars and

premolars.

3. The marginal ridge of the abutment tooth at the site of the rest seat must

be lowered to permit a sufficient bulk of metal for strength and rigidity of

the rest and the minor connector. This means that a reduction of the

marginal ridge of approximately 1.5 mm is usually necessary.

4. The floor of the occlusal rest seat should be apical to the marginal ridge

and the occlusal surface and should be concave, or spoon shaped.

5. The angle formed by the occlusal rest and the vertical minor connector

from which it originates should be less than 90 degrees. Only in this way


13

can the occlusal forces be directed along the long axis of the abutment

tooth. An angle greater than 90 degrees fails to transmit occlusal forces

along the supporting vertical axis of the abutment tooth.

Abutment Preparations Using Crowns:

All abutment teeth to be restored with castings can be prepared at one

time intraoral and an impression made that will provide an accurate stone

replica of the prepared arch.

Wax patterns may then be refined on separated individual dies or

removable dies.

All abutment surfaces facing edentulous areas should be made parallel to

the path of placement by the use of the surveyor blade. This technique

will provide proximal surfaces that will be parallel without any further

alteration in the mouth, will permit the most positive seating of the

removable partial denture along the path of placement, and will provide


14

the least amount of undesirable space beneath minor connectors for the

lodgments of debris.

Guiding planes are extended from the marginal ridge to the junction of

the middle and gingival thirds of the tooth surface involved.

After the guiding planes are parallel and any other contouring to

accommodate the removable partial denture design is accomplished,

occlusal rest seats are carved in the wax pattern. Regardless of the type of

crown used, preparation should be made to provide the appropriate depth

for the occlusal rest seat. This is best accomplished by altering the axial

contours of the tooth to the ideal before preparing the tooth and creating a

depression in the prepared tooth at the occlusal rest area.

The end

COLLEGE OF DENTISTRY; 4TH GRADE (2019-2020) DIJLAH UNIVERSIT

1

PROSTHODONTICS


IMPRESSION PROCEDURES FOR


Impression: is an imprint or negative likeness of the teeth and other

adjacent structures for use in dentistry.

An impression of the partially edentulous arch must record accurately the

anatomic form of the teeth and surrounding tissues. This is necessary so that the

prosthesis may be designed to follow a definite path of placement and removal

and so that support, stability, and retention derived from the abutment teeth

may be precise and accurate.

An Impression registration for construction of RPD must fulfill the

following two requirements:

1. The anatomical form and the relationship of the remaining teeth in the

dental arch as well as surrounding soft tissue must be recorded accurately so

that the denture will not exert pressure on those structures beyond their

physiologic limits and its retention and stabilizing components maybe properly

placed.

2. The supporting form of the soft tissue underlying the distal extension

base of partial denture should be recorded so that firm areas are used as primary

stress bearing areas and remaining displaceable tissue are not over loaded only

in this way can maximum support of partial denture base be obtained.


2

Generally, impressions can be classified into anatomical form and

functional form impressions.

Anatomical form Impressions

Anatomical form is the surface contour of the ridge when it is not under

any occlusal load. Generally anatomic impressions are indicated for tooth

supported partially edentulous arches (Kennedy’s class III and most class IV

cases). Most maxillary distal extension bases can be recorded with this

technique.

For tooth supported partially edentulous arches, the anatomic form

impression is a one-stage impression method using an elastic impression

material in a custom or stock tray that will produce a master cast that records

the teeth and soft tissues in their anatomic form.

Anatomical impressions are contraindicated for distal extension cases due

to the following reason: under occlusal load, the rest in the direct retainer will

prevent the tissue-ward movement of that part of the denture near the abutment

tooth. However, the distal end of the denture will show tissue-ward movement

and compress the tissues under occlusal load and produce lever action. This

will lead to weakening of the abutment teeth due to torsional forces acting on it

and residual ridge resorption.


3

Functional form Impressions

Functional form is the form of the residual ridge recoded under some

loading or compression. These impressions are recorded under functional load

(pressure), that is, the tissue surface is recorded in the compressed form this can

be achieved by occlusal loading, finger loading, especially designed individual

trays or consistency of impression material. Since the soft tissues are recorded

in the compressed form, the denture will not exert additional stress on the

abutment teeth during functional loading; by this procedure, the occlusal load

can be evenly distributed between the soft tissues and the abutment teeth. This

prevents the concentration of deleterious forces on the abutment teeth.

Functional impressions are required only to record edentulous saddles.

These impressions are indicated for distal extension bases for tooth-tissue

supported partial dentures (Kennedy’s class I and class II cases) especially in

the mandibular arch. Another indication a long span anterior edentulous base

(normally including at least the six anterior teeth), where the ridge must supply

some support for the prosthesis.

For tooth-tissue supported partial edentulous arches, functional

impressions require a special tray to closely adapt to the distal extension

edentulous area and provide adequate space for even thickness of the material.

As we do not require a functional impression of the dentulous area, we prefer to

limit the functional impression to the saddle area. The remaining areas are

recorded with an anatomic impression using a stock tray. This cannot be

accomplished on a master cast made from a single impression. Instead, a dual

impression technique is used; the impression of the teeth is made with a

material that captures the teeth in their anatomic positions and the impression of

the residual ridge must record the soft tissues in their functional form.


4

IMPRESSION MATERIALS FOR RPDs:

Classification of impression materials:

1. Rigid Materials:

A- Plaster of Paris

B- Metallic oxide paste.

2. Thermoplastic materials:

A- Modeling plastic.

B- Impression waxes and Natural resins.

3. Elastic impression materials:

A- Hydrocolloids:

Reversible Hydrocolloids (Agar-Agar)

Irreversible Hydrocolloids (alginate)

B- Elastomers impression materials:

• Polysulfide impression materials.

• Condensation silicone impression materials.


5

• Addition silicon impression materials.

• Polyether impression materials.

Materials that could be permanently deformed by removal from tooth or

tissue undercuts should not be used. The thermoplastic impression materials

and metallic oxide pastes are therefore excluded for recording the anatomic

form of the dental arch. Plaster of Paris and modeling plastic are capable of

recording tissue detail accurately, but they must be sectioned for removal and

subsequently reassembled, which often leads to permanent deformation.

Rigid Materials

These impression materials get set to a rigid consistency. They may be

capable of recording tooth and tissue details accurately; but they cannot be

removed from the mouth without fracture and reassembly. Rigid (Inelastic)

materials were initially used for taking final impressions for edentulous

patients. Most inelastic materials have been replaced for this purpose by elastic

materials, overcoming the former materials’ inability to be withdrawn from

undercut areas without fracture.

Plaster of Paris (impression plaster)

Impression plaster was used as a “mucostatic” impression material for

making final impressions for edentulous patients because it does not compress

and displace tissues during seating of the tray. The technique is applicable to

patients with displaceable soft tissues that should be recorded in a passive state.

Metallic Oxide Paste

These materials are usually some form of a zinc oxide–eugenol

combination. They are not used as primary impression materials and should


6

never be used for impressions that include remaining natural teeth. They also

are not to be used in stock impression trays.

Uses of metallic oxide past:

• Secondary impression material for complete denture and for distal

extension denture base of RPD.

• It should be used with custom acrylic tray (special tray).

• It can be used as impression for relining distal extension denture

bases.

Thermoplastic materials

These materials become plastic at higher temperature and they return to

their original form when temperature has become lowered. It cannot record

minute details accurately because they undergo permanent distortion during

withdrawal from tooth and tissue undercuts.

Modeling plastic

Impression compound, also called modeling plastic, is a thermoplastic

material that is supplied in the form of cakes (red) or sticks (green, grey, or

red), with the colors representing different fusing temperatures. The material is

softened by heat over a flame or in a temperature-controlled water bath to the

required softening temperature. The cast should be poured as soon as possible,

at least within the first hour, to minimize any distortion due to relaxation of the

impression compound. A common error in the use of modeling plastic is that it

is often subjected to higher temperatures than intended by the manufacturer. It

then becomes too soft and loses some of its favorable working characteristics.

Modeling plastic types are:


7

Type I (Lower Fusing Material)

• Cakes: As an impression material for completely edentulous patients,

also is most often used for border correction (border molding) of

custom impression trays for Kennedy Class I and Class II removable

partial denture bases.

• Sticks: As a border molding material for the custom tray, the material

is used before making the final impression.

Type II (Higher Fusing Material)

Type II compound is used as a tray adaptation material, which requires

more viscous properties. It is used for making a primary impression of the soft

tissues and then used as a tray to support a thin layer of a second impression

material, such as ZOE paste, hydrocolloids, or elastomers.

Impression waxes and Natural resins

Those impression waxes and resins commonly spoken of as mouth-

temperature waxes. The most familiar of these have been the Iowa wax and the

Korecta waxes, all of which were developed for specific techniques. Its uses:

• It used in recording the edentulous area.

• It may be used to correct the borders of impression made of more

rigid materials.

Elastic impression materials

Those impression materials remain in an elastic flexible state after they

have been removed from the mouth. They are only ones that can be withdrawn

from tooth and tissue undercuts without permanent deformation, forming the

most suitable impression material for recording any irregular contours of oral


8

both hard and soft tissue and therefore most generally used for making

impressions for RPDs, immediate dentures and crowns, and fixed partial

dentures when tooth and tissue undercut and surface details must be recorded

with accuracy.

Hydrocolloid impression material

Reversible (agar-agar) hydrocolloids

These materials are fluid at higher temperatures and gel upon reduction in

temperature, are used primarily as impression materials for fixed restorations.

They demonstrate acceptable accuracy when properly used; however, the

reversible hydrocolloid impression materials offer few advantages over the

irreversible (alginate) hydrocolloids when used as a removable partial denture

impression material. Present-day irreversible hydrocolloids are sufficiently

accurate for making master casts for removable partial dentures. However,

border control of impressions made with these materials is difficult.

Disadvantages of Agar:

1. Must be introduced into the mouth while warm enough to become a sol,

to be converted into an elastic gel on cooling thus there is a danger of

burning the oral tissue.

2. Requires warming and tempering equipment that is thermoelastically

controlled necessitates the use of water-jacketed impression tray for

cooling.

Irreversible (Alginate) hydrocolloids

These materials are used for making diagnostic casts, orthodontic treatment

casts, and master casts for removable partial denture procedures. Because they

are made of colloid materials, neither reversible nor irreversible hydrocolloid

impressions can be stored for any length of time, but must be poured


9

immediately. These materials have low tear strength, provide less surface detail

than other elastic materials and are not as dimensionally stable as other elastic

materials.

They can, however, be used in the presence of moisture (saliva); are

hydrophilic; pour well with stone; have a pleasant taste and odor; and are

nontoxic, non-staining, and inexpensive. The hydrocolloids can be acceptably

disinfected with a spray solution of 2% acid glutaraldehyde.

Advantages of alginate impression materials:

1. Simplicity of equipment.

2. Ease of manipulation.

3. Little discomfort to the patient.

4. Short chair time.

5. Accurate reproduction of undercut areas.

The principal differences between reversible and irreversible hydrocolloids

are as follows:

1. Reversible hydrocolloid converts from the gel form to a sol by the

application of heat. It may be reverted to gel form by a reduction in

temperature. This physical change is reversible.

2. Irreversible hydrocolloid becomes a gel via a chemical reaction as a

result of mixing alginate powder with water. This physical change is

irreversible.

All hydrocolloids are dimensionally stable for only a brief period after

removal from the mouth. If exposed to the air, they rapidly lose water content,

with resulting shrinkage and other dimensional changes. If immersed in water,

they imbibe water, with accompanying swelling and dimensional changes. All

hydrocolloid impressions should be poured immediately, but if they must be


10

stored for a brief period, they should be in a saturated atmosphere rather than

immersed in water. This can be accomplished simply by wrapping the

impression in a damp paper towel or sealing it in a plastic bag.

Important Precautions to be observed in the handling of hydrocolloid

impressions are as follows:

1. The impression should not be exposed to air because some syneresis or

dehydration will inevitably occur and result in shrinkage.

2. The impression should not be immersed in water or disinfectants because

some imbibition will inevitably result, with an accompanying expansion.

3. The impression should be protected from dehydration by placing it in a

humid atmosphere or wrapping it in a damp paper towel until a cast can

be poured. To avoid volume change, this should be done within 15

minutes after removal of the impression from the mouth.

4. Exudate from the hydrocolloid has a retarding effect on the chemical

reaction of gypsum products and results in a chalky cast surface. This can

be prevented by pouring the cast immediately or by first immersing the

impression in a solution of accelerator if an accelerator is not included in

the formula.

Step by step procedure for making a hydrocolloid impression

The step by step procedure and important points to observe in the making

of a hydrocolloid impression are as follows:

1. Tray selection: Stock trays for dentulous and partially edentulous arches

are of different types (perforated, non-perforated and rimlock) and

materials (metal and non-metal). Select a suitable, sterilized impression


11

tray that is large enough to provide 4-5 mm thickness of the impression

material between the teeth and tissue, and the tray to avoid tears in the

impression. The selection of proper size and shape of the tray to take the

advantages of dimensional accuracy of the impression material and to

include all the anatomical landmarks in the impression and will permit its

easy insertion and removal from the patient mouth.

2. Tray modification: Build up the palatal portion of the maxillary

impression tray with wax or modeling plastic to ensure even distribution

of the impression material and to prevent the material from slumping

away from the palatal surface.

The palate may be swabbed with topical anesthesia, this will anaesthetize

the minor salivary glands and mucous gland of the palate to prevent secretion,

also to prevent gag reflex.

If gelation occurs next to the tissues while the deeper portion is still fluid,

distorted impression of the palate may result which cannot be detected in the

finished impression, this may result in the major connector of the finished

casting not being in contact with the underlying tissues.

The maxillary tray has to be extended posteriorly to include the tuberosity

and vibrating line region of the palate, such an extension also aids in correctly

orienting the tray in the patient mouth when the impression is made.

The lingual flange of the mandibular tray may need to be lengthened with

wax in the retromylohyoid area or to be extended posteriorly, but it rarely ever

needs to be lengthened elsewhere. Wax may need to be added inside the

distolingual flange to prevent the tissues of the floor of the mouth from rising

inside the tray.

3. Position of dentist and patient: Place the patient in an upright position,

with the involved arch nearly parallel to the floor. For mandibular


12

impressions, The dentist position should be in front of the patient on the

right and the patient`s mouth is at the level of dentist`s shoulder. For

maxillary impressions, the dentist position should be behind the patient

and the patient`s mouth is at the level of dentist`s elbow.

4. When irreversible hydrocolloid (alginate) is used, place the measured

amount of water in a clean dry rubber mixing bowl. Add the correct

measure of powder, spatulate rapidly against the side of the bowl with

short stiff spatula. This should be accomplished in less than 1 min. The

P/W ratio should be accurate not too thin or too thick, according to

manufacturer instructions. The patient should rinse his mouth with cool

water to eliminate excess saliva while the impression material is being

mixed and the tray is being loaded.

5. Loading the material in the tray, try to avoid entrapping air. Have the

first layer of material look through the perforations of the tray or rim-

lock to prevent any dislodgment after gelation.

6. After loading the tray, quickly place some of the impression material on

any critical areas with the finger, such as rest preparations and abutment

teeth. If maxillary impression is being made, place material in the highest

aspect of the palate and over the rugae.

7. Use a mouth mirror or index finger to retract the cheek away from you as

the tray rotated into the mouth from the near side.

8. Seat the tray first on the side away from you, next on the anterior area,

while reflecting the lip, and then on the near side with the mouth mirror

or finger for cheek retraction. Ensure that the lip is draping naturally over

the tray.

9. Be careful not to seat the tray too deeply, leaving a room for thickness of

material over the occlusal and incisal surfaces.

10. After insertion the tray inside the patient's mouth loaded with impression

material it should be held immobile for 3 minutes with light finger


13

pressure over the left and right premolar area. To avoid internal stresses

in the finished impression, do not allow the tray to move during gelation;

do not allow the patient or the assistant to hold the tray in position. Some

movement of the tray is inevitable during the transfer, and at the critical

time of gelation movement will produce an inaccurate impression. Wait

2-3 minutes after gelation, this extra time will improve properties of

impression (the compressive strength of alginate nearly doubles in the

first 4 minutes after gelation, and its elasticity improves over time). Do

not remove the impression from the mouth until impression material has

completely set.

11. After complete setting of impression material, remove the tray with one

snap movement in line with the long axis of the teeth to avoid tearing or

other distortion. The tear strength of alginate increases with the rate at

which a stress is applied; thus it is desirable to rapidly remove the

impression from the mouth. Avoid twisting or torqueing the impression.

12. Rinse the impression from free saliva with slurry water, and then

examine it critically. Spray the impression with a suitable disinfectant

and cover it immediately with a damp paper towel.

The cast should be poured immediately into a hydrocolloid impression to

avoid dimensional changes and syneresis. Alginates are dimensionally unstable.

The impression can undergo syneresis and imbibition when exposed to air and

water. Circumstances often necessitate some delay, but this time lapse time

should be kept to a minimum. The delay of 15 minutes is satisfying, but the

delay should not exceed 15 minutes if the impression is kept in humid

atmosphere.


14

Step by Step procedure for making a stone cast from hydrocolloid

impression

1- A more abrasive-resistant type IV stone should be used to form removable

partial denture casts. Have the measured dental stone at hand, along with

the designated quantity of room temperature water, as recommended by

the manufacturer. A clean 600-mL rubber mixing bowl, a stiff spatula, and

a vibrator complete the preparations. A No. 7 spatula also should be within

reach.

2- First, pour the measure of water into the mixing bowl and then add the

measure of stone. Spatulate thoroughly for 1 minute, remembering that a

weak and porous stone cast may result from insufficient spatulation , then

place the mixing bowl on the vibrator and knead the material to permit the

escape of any trapped air.

3- After removing the impression from the damp towel, gently shake out

surplus moisture and hold the impression over the vibrator, impression

side up, with only the handle of the tray contacting the vibrator. The

impression material must not be placed in contact with the vibrator

because of possible distortion of the impression.

4- with a small spatula add the first cast material to the distal area away from

you , allow this first material to be vibrated around the arch from tooth to

tooth toward the anterior part of the impression , continue to add small

increments of material at this same distal area with each portion of added

stone pushing the mass ahead of it, this avoid the entrapment of air when

the impression of all teeth have been filled, continue to add artificial stone

in large portion until the impression is completely filled..

5- The filled impression should be placed on a supporting jig and the base of

the cast completed with same mix of stone, the base of the cast should be

16-18mm.


15

6- As soon as the cast material has developed sufficient body, trim the excess

from the side of the cast. Wrap the impression and cast in wet paper towel

or place humid until the initial set of the stone has taken place, the

impression thus prevent from losing water by evaporation which might

deprive the cast material of sufficient water for crystallization.

7- After 30 minute is sufficient for initial setting, any stone that interferes

with separation from the tray must be trimmed away with knife.

8- Clean the impression tray immediately while the used impression material

is still elastic.

9- Trimming of the cast should be deferred until final setting has occurred.

The sides of the cast then may be trimmed to be parallel, and any blebs or

defects resulting from air bubbles in the impression may be removed.

Possible causes of inaccurate and/ or a weak cast of dental arch

1. Distortion of the hydrocolloid impression

(a) By use of an impression tray that is not rigid ;

(b) By partial dislodgment from the tray ;

(c) By shrinkage caused by dehydration;

(d) By expansion caused by imbibition

(e) By attempting to pour the cast with stone that has already begun to

set.

2. A ratio of water to powder that is too high. Although this may not cause

volumetric changes in the size of the cast, it will result in a weak cast.

3. Improper mixing. This also results in a weak cast or one with a chalky

surface.

4. Trapping of air, either in the mix or in pouring, because of insufficient

vibration.


16

5. Soft or chalky cast surface that results from the retarding action of the

hydrocolloid or the absorption of necessary water for crystallization by

the dehydrating hydrocolloid.

6. Premature separation of the cast from the impression.

7. Failure to separate the cast from the impression for an extended period.

The control of gagging during making impression:

The gag reflex is a normal, healthy defense mechanism, which prevents

foreign bodies from entering the trachea. It can be triggered by tactile

stimulation of the soft palate, posterior part of the tongue and the fauces.

Sight, taste, noise and psychological factors can also produce gagging.

Procedures that will help to prevent gagging include :

1- The dentist should:

a) Not mention the subject of gagging

b) Ask whether the patient has had impressions made previously.

2- Before the impression is made:

a) Ask the patient to use astringent mouth rinse and cold-water

rinses.

b) Prescribing a combination of atropine and a mild sedative

medication.

c) Seat the patient in an upright position with the occlusal plane

parallel with the floor.

d) Ask the patient to take a deep breath and hold the breath while the

dentist quickly checks the size and fit of the tray.


17

e) Correct the maxillary tray with modeling plastic and leaving

sufficient unrelieved modeling plastic at the posterior border.

3- The impression material must:

a) Have the consistency of thick whipped cream

b) Fast-setting alginate. Set up to a rubbery consistency in few

minutes.

4- During the impression procedure:

a) Not overfill the tray with impression material.

b) Seat the posterior part of the tray first and then rotate the tray into

position.

c) Force excess alginate in an anterior direction.

d) Ask the patient to:

Keep the eyes opened and focused on some small object.

Breathe through the nose.

The "leg lift" procedure is used before and during the making of

the impression.

Giving all instructions to the patient in a firm, controlled manner.

The end


1

PROSTHODONTICS


SUPPORT FOR THE DISTAL EXTENSION


Support: is the resistance to forces directed toward the basal tissue or

underlying structures.

In a tooth-supported removable partial denture, the support comes

entirely from the abutment teeth at either end of that span through the direct

transfer of occlusal forces to the abutment teeth through the occlusal rests.

Support may be augmented by splinting and by the use of additional abutments,

but in any event the abutments are the sole support of the removable

restoration. The tooth-supported base is secured at either end by the action of a

direct retainer and is supported at either end by a rest.

In a tooth-supported removable partial denture, the residual ridge beneath

the base is not called on to aid in the support of the removable partial denture.

Therefore the resiliency of the ridge tissues, the ridge configuration, and the

type of bone that supports these tissues are not factors in denture support.

An impression (and resultant stone cast) records the anatomic form of the

teeth and their surrounding structures and is needed to make a tooth-supported

removable partial denture. The impression should also record the moving

tissues that will border the denture in an unstrained position, so the relationship

of the denture base to those tissues may be as accurate as possible. An under-

extended base may lead to food entrapment and inadequate facial contours,

particularly on the buccal and labial sides.


2

In distal extension removable partial denture, the support is obtained

from both the abutment teeth and the residual ridge (soft tissue overlying bone).

The distal extension removable partial denture must depend on the residual

ridge for some support, stability, and retention. Indirect retention, to prevent the

denture from lifting away from the residual ridge, should also be incorporated

in the design.

Resilient tissues, which are distorted or displaced by occlusal load, are

unable to provide support for the denture base comparable with that offered by

the abutment teeth. Ridge tissues recorded in their resting or nonfunctioning

form are incapable of providing the composite support needed for a denture that

derives its support from both hard and soft tissue.

Three factors must be considered in the acceptance of an impression

technique for distal extension removable partial dentures: (1) the material

should record the tissues covering the primary stress–bearing areas in their

supporting form; (2) tissues within the basal seat area other than primary

stress–bearing areas must be recorded in their anatomic form; and (3) the total

area covered by the impression should be sufficient to distribute the load over

as large an area as can be tolerated by the border tissues.

Factors Influencing the Support of a Distal Extension Base:

Support from the residual ridge becomes more important as the distance

from the last abutment increases and will depend on the following several

factors:

1. Contour and quality of the residual ridge.

2. Extent of residual ridge coverage by the denture base.

3. Type and accuracy of the impression registration.


3

4. Accuracy of the fit of the denture base.

5. Design of the removable partial denture framework.

6. Total occlusal load applied.

Contour and Quality of the Residual Ridge

The ideal residual ridge to support a denture base would consist of cortical

bone that covers relatively dense cancellous bone, with a broad rounded crest

with high vertical slopes, and is covered by firm, dense, fibrous connective

tissue. Such a residual ridge would optimally support vertical and horizontal

stresses placed on it by denture bases. Unfortunately this ideal is seldom

encountered.

The crest of the bony mandibular residual ridge is most often cancellous.

Loss of firm mucosa overlying the residual ridge is common following tooth

extraction in the posterior mandible. Pressures placed on tissues overlying the

crest of the mandibular residual ridge usually result in irritation of these tissues,

accompanied by the sequence of chronic inflammation. Therefore the crest of

the mandibular residual ridge cannot be a primary stress-bearing region. The

buccal shelf region (bounded by the external oblique line and the crest of the

alveolar ridge) seems to be better suited for a primary stress-bearing role

because it is covered by relatively firm, dense, fibrous connective tissue

supported by cortical bone. In most instances this region bears more of a

horizontal relationship to vertical forces than do other regions of the residual

ridge.

The crest of the bone of the maxillary residual ridge may consist primarily

of cancellous bone. Unlike in the mandible, oral tissues that overlie the

maxillary residual alveolar bone are usually of a firm, dense nature (similar to

the mucosa of the hard palate) and capable of resisting occlusal forces. The


4

crest of the maxillary residual ridge is the primary supporting region for the

maxillary distal extension denture base for vertically directed forces. Some

resistance to these forces may be obtained by the buccal and lingual slopes of

the ridge. The buccal slope does, however, resist lateral forces relatively well.

Relief must be provided for the incisive papilla and the median palatal raphe,

especially if tissues covering the palatal raphe are less displaceable than those

covering the crest of the residual ridge.

Extent of Residual Ridge Coverage by the Denture Base

The broader the residual ridge coverage, the greater is the distribution of the

load, which results in fewer loads per unit area. A denture base should cover as

much of the residual ridge as possible and should be extended the maximum

amount within the physiologic tolerance of the limiting border structures or

tissues. Maximum coverage of denture-bearing areas with large, wide denture

bases is of the utmost importance in withstanding both vertical and horizontal

stresses.


5

Type and Accuracy of the Impression Registration

The residual ridge may be said to have two forms: the anatomic form and

the functional form. The anatomic form is the surface contour of the ridge when

it is not supporting an occlusal load. The functional form of the residual ridge is

the surface contour of the ridge when it is supporting a functional load.

However, many dentists believe that certain regions of the residual ridge(s)

in a partially edentulous patient are more capable of supporting dentures than

other regions. Their impression methods are directed to place more stress on

primary stress-bearing regions with specially constructed individual trays and at

the same time record the anatomic form of other basal seat tissues, which

cannot assume a stress-bearing role. The form of the residual ridge recorded

under some loading, whether by occlusal loading, finger loading, specially

designed individual trays, or the consistency of the impression material, is

called the functional form. This is the surface contour of the ridge when it is

supporting a functional load.

Many of the requirements and advantages that are associated with the

distributed stress denture apply equally well to the functionally or

physiologically based denture. Some of these requirements are

(1) Positive occlusal rests;

(2) An all-rigid, nonflexible framework;

(3) Indirect retainers to add stability; and

(4) Well-adapted, broad coverage denture bases.

Those who do not accept the theory of physiologic basing, should use some

form of stress breaker between the abutment and the distal extension base to

avoid the possible cantilever action of the distal extension base against the

abutment teeth.


6

Accuracy of the Fit of the Denture Base

Support of the distal extension base is enhanced by intimacy of contact of

the tissue surface of the base and the tissues that cover the residual ridge. The

tissue surface of the denture base must optimally represent a true negative of

the basal seat regions of the master cast.

Design of the Removable Partial Denture Framework

Some rotation movement of a distal extension base at the distal abutment is

inevitable under functional loading.

It must be remembered that the extent to which abutments are subjected to

rotational and torqueing forces that result from masticatory function is directly

related to the position and resistance of the food bolus. The longer the

edentulous area covered by the denture base, the greater the potential lever

action on the abutment teeth.


7

Rotational forces passing through the most posterior clasp assemblies can

be controlled using appropriate components. The most efficient method of

controlling rotational movement is the use of one or more indirect retainers

anterior to the fulcrum line. The indirect retainer is most often in the form of a

rest attached to the major connector by a minor connector. They have suggested

that occlusal rests may be moved anteriorly to better use the residual ridge for

support without jeopardizing either vertical or horizontal support of the denture

by occlusal rests and guiding planes. If the distal extension denture is bilateral,

one indirect retainer should be used on each side of the arch. If the distal

extension base is unilateral, only one indirect retainer is needed. This indirect

retainer is positioned anterior to the fulcrum line and on the opposite side of the

arch from the distal extension ridge.

Maximum contact of the proximal plate minor connector with the guiding

plane produces a more horizontal distribution of stress to the abutment teeth.

Minimum contact or disengagement allows rotation around the fulcrum located

on the mesio-occlusal rest, producing a more vertical distribution of stress to

the ridge area. Finally, Minor connector contact with the guiding plane from the

marginal ridge to the junction of the middle and gingival thirds of the abutment

tooth distributes load vertically to the ridge and horizontally to the abutment

tooth.


8

Total Occlusal Load Applied

The number of artificial teeth, the width of their occlusal surfaces, and

their occlusal efficiency influence the total occlusal load applied to the

removable partial denture. The reduction of the size of the occlusal table

reduces the vertical and horizontal forces that act on the removable partial

dentures and lessens the stress on the abutment teeth and supporting tissues.

Methods for Obtaining Functional Support for the Distal

Extension Base

A thorough understanding of the characteristics of each of the impression

materials and impression methods leads to the conclusion that no single

material can record the anatomic form of the teeth and tissues in the dental arch

and, at the same time, the functional form of the residual ridge. Therefore, some

secondary or corrected impression method must be used.

Methods for obtaining functional support should satisfy the two

requirements for providing adequate support to the distal extension removable

partial denture base. These are (1) that it records and relates the supporting soft

tissue under some loading, and (2) that it distributes the load over as large an

area as possible.

There are two categories of impression techniques available to record a

distal extension denture base. These categories may be defined as physiologic

impression techniques and selected pressure techniques.

These two categories of impression making are most commonly used for

the mandibular distal extension partially edentulous arch (Kennedy Class I and

Class II arch forms) due to their greater variation in tissue mobility and tissue

distortion or displaceability, which requires some tissue placement to obtain the


9

desired support from these tissues. This variability in tissue mobility is

probably related to the pattern of mandibular residual ridge resorption.

These two categories are seldom used in the maxillary distal extension

partially edentulous arch because of the nature of the masticatory mucosa and

the amount of firm palatal tissue present to provide soft tissue support. These

tissues seldom require placement to provide the required support. If excessive

tissue mobility is present, it is often best managed by surgical resection, as this

is a primary supporting area.

The other indication for these two categories is a long-span anterior

edentulous base (normally including at least the six anterior teeth), where the

ridge must supply some support for the prosthesis. Improving the accuracy of

the cast with a secondary impression and defining the peripheral extension of

the anterior flange can be helpful in distributing forces that act against a weaker

portion of the dental arch.

Physiologic impression techniques record the ridge portion of the cast in

its functional form by placing an occlusal load on the impression tray during

the impression procedure. The physiologic impression procedures are

presented: McLean’s method and Hindle’s modification of McLean’s method;

the functional reline method; and the fluid wax method.

A custom-made impression tray is fabricated over the edentulous areas of

the preliminary cast. A functional impression of the edentulous ridge is made

by using the custom-made tray. The second impression is made over the

functional impression and it records the structures in their anatomic form by

using large stock tray. The second impression is also known as the pick-up

impression because it covers, and picks up the functional impression (first

impression) along with itself. The master cast is poured and all following

procedures, including the metal framework, are carried out on this final cast.


10

The common techniques employed to record a pick-up impression are

McLean’s method and Hindle’s modification of McLean’s method.

Selected pressure impression techniques are intended to equalize the

support between the abutments and the soft tissues and to direct forces to the

portions of the ridge that are most capable of withstanding such forces. This is

accomplished by relieving the tray in some areas while allowing the impression

tray to contact the ridge in other areas. Areas where relief is provided are

minimally displaced during impression procedures. In those areas where relief

is not provided, greater soft tissue displacement occurs. Thus the impression

tray contacts the tissues only over the areas that were not relief (stress-bearing

areas). Since the tray contacts only the stress-bearing areas during impression

making, only these areas are compressed (recorded functionally) while making

the impression.


11

Selected pressure impression technique as follow:

1. Firstly; primary impression making for pouring a master cast in

anatomical form impression to the teeth and residual ridge; then,

design planning, and framework fabrication.

2. Check the framework intra-orally; should be fitted in all positions.

3. Use of disclosing media to identify interferences to completely

seating the removable partial denture framework.

4. Adjusting the seated framework to the opposing occlusion.

5. Use the frame work as a special tray, so the edentulous area on the

cast is outlined by a pencil and wax spacer is adapted over the

outlined ridge.

6. A cold cure acrylic resin is adapted on distal extension part of the

framework (covering the edentulous ridge).

7. After setting of acrylic, the framework is removed from the cast and

trimmed to be under-extended 2-3 mm.

8. A tracing compound is added to the borders of flanges and makes

border molding.

9. Impression material (Zinc oxide-Eugenol paste) mixed and loaded

into the intaglio surface, and the framework precisely seated in the

patient mouth until impression set. Pressing on occlusal rest seat and

indirect retainer. Pressure should not be applied on the acrylic saddle.

10. The impression must be thoroughly inspected and any cause for

rejection carefully considered. Any impression exhibiting a void or

underextension should be rejected. In addition, any evidence that the

framework was not seated completely, such as the presence of

impression material beneath rests, is reason to remake the impression.

If any doubt exists, the impression must not be accepted.


12


13

In the functional reline method, the fluid wax technique and the selected

pressure technique, an impression of the edentulous ridge is made using an

impression tray attached to the framework. The master cast is altered to

accommodate the secondary impression, and a corrected or altered cast is

generated. For this reason, the technique is often referred to as a corrected cast

or altered cast procedure.

Altered cast: is a final cast that is revised in part before processing a

denture base; and is called also corrected cast, modified cast.

Altered-cast procedure:

1. Outline the master cast for removal of the edentulous ridge area; the

edentulous area in the anatomical master cast is cut away with a saw.

The cast is sliced using two cuts one buccoloingual and one

anteroposterior.

2. The buccolingual cut is made 1 mm behind the terminal abutment

across the edentulous area.

3. The anteroposterior cut is made 1 mm lingual or medial to the lingual

sulcus. The lingual sulcus should be cut away along with the

edentulous ridge. Vertical grooves are prepared on the cut walls of the

cast.

4. The framework along with the functional impression is placed over

the cut anatomical master cast. Since the edentulous areas are cut

away from the cast, the edentulous areas of the impression will be

projecting in free space.

5. The framework is sealed to the master cast using sticky wax to avoid

displacement during boxing and pouring. The cast is inverted along

with the framework. Now the functional impression attached to the


14

framework will be seen projecting underneath the cut areas of the

cast.

6. The impression is beaded and boxed in continuity with the cast. The

cast is soaked in slurry water for 10 minutes before pouring the

impression.

7. Pour the impression by dental stone after boxing it. After setting of

stone, remove boxing wax and framework, and then we get a new

master cast (altered master cast) with corrected edentulous area.

The end


1

PROSTHODONTICS


OCCLUSAL RELATIONSHIPS FOR


Occlusion: the static relationship between the incising or masticating

surfaces of the maxillary or mandibular teeth or tooth analogues.

The treatment of patients with removable partial dentures is the

establishment of a functional and harmonious occlusion. Occlusal harmony

between a removable partial denture and the remaining natural teeth is a major

factor in the preservation of the health of their surrounding structures.

Balanced occlusion is desirable with complete dentures because

unbalanced occlusal stresses may cause instability of the dentures and trauma to

the supporting structures. These stresses can reach a point that causes

movement of the denture bases. In removable partial dentures, however,

because of the attachment of the removable partial denture to the abutment

teeth, occlusal stresses can be transmitted directly to the abutment teeth and

other supporting structures, resulting in sustained stresses that may be more

damaging than those transient stresses found in complete dentures.

In establishing occlusion on a removable partial denture, the influence of

the remaining natural teeth is usually such that the occlusal forms of the teeth

on the removable partial denture must be made to conform to an already

established occlusal pattern. Occlusal adjustment or restoration may have

altered this pattern. However, the pattern present at the time the removable

partial denture is made dictates the occlusion on the removable partial denture.


2

The establishment of a satisfactory occlusion for the removable partial

denture patient should include the following:

(1) Analysis of the existing occlusion;

(2) Correction of existing occlusal disharmony;

(3) Recording of centric relation or an adjusted centric occlusion;

(4) Harmonizing of eccentric jaw movements for a functional eccentric

occlusion; and

(5) Correction of occlusal discrepancies created by the fit of the framework

and during processing of the removable partial denture.

Desirable Occlusal Contact Relationships for Removable Partial

Dentures

The following occlusal arrangements are recommended to develop a

harmonious occlusal relationship among removable partial dentures and to

enhance stability of the removable partial dentures:

1. Simultaneous bilateral contacts of opposing posterior teeth must occur in

centric occlusion.

Note: (Centric occlusion: the occlusion of opposing teeth when the mandible is

in centric relation; this may or may not coincide with the maximal intercuspal

position.)

(Centric relation: a maxillomandibular relationship, independent of tooth

contact, in which the condyles articulate in the anterior-superior position

against the posterior slopes of the articular eminences; in this position, the

mandible is restricted to a purely rotary movement; from this unstrained,

physiologic, maxillomandibular relationship, the patient can make vertical,


3

lateral or protrusive movements; it is a clinically useful, repeatable reference

position.)

(Maximal intercuspal position: the complete intercuspation of the opposing

teeth, independent of condylar position.)

2. Occlusion for tooth-supported removable partial dentures (CL III and

CL IV) may be arranged similarly to the occlusion seen in a harmonious

natural dentition.

3. Bilateral balanced occlusion in eccentric positions should be formulated

when a maxillary complete denture opposes the removable partial

denture.

Note :( Balanced occlusion: The bilateral, simultaneous occlusal contact of the

anterior and posterior teeth in excursive movements).

(Excursive movement: movement occurring when the mandible moves away

from maximal intercuspal position).

4. Working side contacts should be obtained for the mandibular distal

extension denture. These contacts should occur simultaneously with

working side contacts of the natural teeth to distribute the stress over the

greatest possible area.

Note :( Working-side: the side toward which the mandible moves in a lateral

excursion).

5. Simultaneous working and balancing contacts should be formulated for

the maxillary bilateral distal extension removable partial denture

whenever possible such an arrangement will compensate in part for the

unfavorable position the maxillary artificial teeth must occupy in

relation to the residual ridge, which is usually lateral to the crest of the

ridge.


4

Note :( Balancing side: that side of the mandible that moves toward the medial

line in a lateral excursion).

6. Only working contacts need to be formulated for the maxillary or

mandibular unilateral distal extension removable partial denture.

Balancing side contacts would not enhance the stability of the denture

because it is entirely tooth supported by the framework on the balancing

side.

7. In the Kennedy Class IV removable partial denture configuration,

contact of opposing anterior teeth in the planned intercuspal position is

desired to prevent continuous eruption of the opposing natural incisors,

unless they are otherwise prevented from extrusion by means of a

lingual plate or auxiliary bar, or by splinting.

8. Artificial posterior teeth should not be arranged farther distally than the

beginning of a sharp upward incline of the mandibular residual ridge or

over the retromolar pad. To do so would have the effect of shunting the

denture anteriorly. The buccal cusps, however, must be favorably placed

to direct stress toward the buccal shelf, which is the primary support

area in the mandibular arch. In such positions, the denture is not

subjected to excessive tilting forces.

On the other hand, the artificial teeth of the bilateral, distal extension,

maxillary removable partial denture often must be placed lateral to the crest of

the residual ridge to enhance the stability of the denture so that it seems logical

to provide simultaneous working and balancing contacts in these situations if

possible.


5

Methods for Establishing Occlusal Relationships

Five methods of establishing interocclusal relations for removable partial

dentures will be briefly described:

1. Direct Apposition of Casts.

2. Interocclusal Records with Posterior Teeth Remaining.

3. Occlusal Relations Using Occlusion Rims on Record Bases.

4. Jaw Relation Records Made Entirely on Occlusion Rims.

5. Establishing Occlusion by the Recording of Occlusal Pathways.

Direct Apposition of Casts

The first method is used when sufficient opposing teeth remain in contact

to make the existing jaw relationship obvious, or when only a few teeth are to

be replaced on short denture bases and no evidence of occlusal abnormalities is

found. With this method, opposing casts may be occluded by hand. The

occluded casts should be held in apposition with rigid supports attached with

sticky wax to the bases of the casts until they are securely mounted in the

articulator.


6

Interocclusal Records with Posterior Teeth Remaining

A second method, which is a modification of the first, is used when

sufficient natural teeth remain to support the removable partial denture

(Kennedy Class III or IV) but the relation of opposing natural teeth does not

permit the occluding of casts by hand. In such situations, jaw relations must be

established as for fixed restorations with some type of interocclusal record.

The least accurate of these methods is the interocclusal wax record. The

bulk, consistency, and accuracy of the wax will influence the successful

recording of centric relation with an interocclusal wax record after chilling.

Therefore a definite procedure for making interocclusal wax records is given as

follows:

•A uniformly softened, metal-reinforced wafer of baseplate or set-up wax is

placed between the teeth, and the patient is guided to close in centric relation.

Correct closure should have been rehearsed before placement of the wax so that

the patient will not hesitate or deviate in closing. The wax then is removed and

immediately chilled thoroughly in room-temperature water. It should be

replaced a second time to correct the distortion that results from chilling and

then again chilled after removal.

•All excess wax should now be removed with a sharp knife. It is most

important at this time that all wax that contacts mucosal surfaces be trimmed

free of contact. The chilled wax record again should be replaced to make sure

that no contact with soft tissue occurs.

A wax record can be further corrected with a freely flowing occlusal

registration material, such as a metallic oxide paste, which is used as the final

recording medium. Some of the advantages of using a metallic oxide paste over

wax as a recording medium for occlusal records include:


7

(1) uniformity of consistency;

(2) ease of displacement on closure;

(3) accuracy of occlusal surface reproduction;

(4) dimensional stability;

(5) the possibility of some modification in occlusal relationship after

closure, if it is made before the material sets; and

(6) Less likelihood of distortion during mounting procedures.

Three important details to be observed when one uses such a material are as

follows:

(1) Make sure that the occlusion is satisfactory before making the

interocclusal record.

(2) Be sure that the casts are accurate reproductions of the teeth being

recorded.

(3) Trim the record with a sharp knife wherever it engages undercuts, soft

tissue, or deep grooves.

Occlusal Relations Using Occlusion Rims on Record Bases

A third method is used when one or more distal extension areas are

present, when a tooth-supported edentulous space is large, or when opposing

teeth do not meet. In these instances, occlusion rims on accurate jaw relation


8

record bases must be used. Simple wax records of edentulous areas are never

acceptable. Any wax, however soft, will displace soft tissue. It is impossible to

accurately seat such a wax record on a stone cast of the arch.

With this method, the recording precedes much the same as with the

second method, except that occlusion rims are substituted for missing teeth. It

is essential that accurate bases be used to help support the occlusal relationship.

Record bases may be made from an auto-polymerizing acrylic-resin, visible

light-cured resin (VLC) and other record bases include the use of cast metal and

compression molded or processed acrylic resin bases for jaw relation records.

Relative to the third method, some mention must be made of the ridge on

which the record bases are formed. If the prosthesis is to be tooth supported or

if a distal extension base is to be made on the anatomic ridge form, the bases

will be made to fit that form of the residual ridge. But if a distal extension base

is to be supported by the functional form of the residual ridge, it is necessary

that the recording of jaw relations be deferred until the master cast has been

corrected to that functional form. Record bases must be as nearly identical as

possible to the bases of the finished prosthesis.

Jaw relation records made by this method accomplish essentially the same

purpose as the two previous methods. The fact that record bases are used to

support edentulous areas does not alter the effect. In any method, the skill and

care used by the dentist in making occlusal adjustments on the finished

prosthesis will govern the accuracy of the resulting occlusion.

Methods for Recording Centric Relation on Record Bases:

Centric relation may be recorded in many ways when record bases are

used. The least accurate is the use of softened wax occlusion rims. Modeling

plastic occlusion rims, on the other hand, may be uniformly softened by

flaming and tempering, resulting in a generally acceptable occlusal record. This


9

method is time proved, and when competently done, it is equal in accuracy to

any other method.

When wax occlusion rims are used, they should be reduced in height until

just out of occlusal contact at the desired vertical dimension of occlusion. A

single stop is then added to maintain their terminal position as a jaw relation

record is made in some uniformly soft material, which sets to a hard state.

Quick-setting impression plaster, bite registration paste, or auto-polymerizing

resin may be used. With any of these materials, opposing teeth must be

lubricated to facilitate easy separation. Whatever the recording medium, it must

permit normal closure into centric relation without resistance and must be

transferable with accuracy to the casts for mounting purposes.

Jaw Relation Records Made Entirely on Occlusion Rims

The fourth method is used when no occlusal contact occurs between the

remaining natural teeth, such as when an opposing maxillary complete denture

is to be made concurrently with a mandibular removable partial denture. It may

also be used in those rare situations in which the few remaining teeth do not

occlude and will not influence eccentric jaw movements. Jaw relation records

are made entirely on occlusion rims when either arch has only anterior teeth

present.


10

In any of these situations, jaw relation records are made entirely on

occlusion rims. The occlusion rims must be supported by accurate jaw relation

record bases. Here, the choice of method for recording jaw relations is much

the same as that for complete dentures. Either some direct interocclusal method

or a stylus tracing may be used. As with complete denture fabrication, the use

of a facebow, the choice of articulator, the choice of method for recording jaw

relations, and the use of eccentric positional records are optional, based on the

training, ability, and desires of the individual dentist.


11

Establishing Occlusion by the Recording of Occlusal Pathways

The fifth method of establishing occlusion on the removable partial denture

is the registration of occlusal pathways and the use of an occluding template

rather than a cast of the opposing arch.

Methods described previously may be applied to the fabrication of

removable partial dentures in both arches simultaneously, whereas the

registration of occlusal pathways necessitates that an opposing arch be intact or

restored. If removable partial dentures are planned for both arches, a decision is

necessary as to which denture is to be made first and which is to bear a

functional occlusal relation to the opposing arch. Generally the mandibular arch

is restored first and the maxillary removable partial denture is occluded to that

restored arch.

Regardless of the method used for recording jaw relations, when one arch

is completely restored first, that arch is treated as an intact arch even though it

is wholly or partially restored by prosthetic means. The dentist must consider at

the time of treatment planning the possible advantages of establishing the final

occlusion to an intact arch.

Step-by-Step Procedure for Registering Occlusal Pathways:

After the framework has been adjusted to fit the mouth, the technique used for

the registration of occlusal pathways is as follows:

1. Support the wax occlusion rim with a denture base that has the same

degree of accuracy and stability as the finished denture base. Place a film

of hard sticky wax on the base before the wax occlusion rim is secured to

it. The wax used for the occlusion rim should be hard enough to support

biting stress and should be tough enough to resist fracture. Hard inlay

wax has proved to be suitable for most patients.


12

2. Inform the patient that the occlusion rim must be worn for 24 hours or

longer. It should be worn constantly, including at night time, except for

removal during meals. With wearing and biting into a hard wax

occlusion rim, a record is made of all extremes of jaw movement.

3. After 24 hours, the occlusal surface of the wax rim should show a

continuous gloss, which indicates functional contact with the opposing

teeth in all extremes of movement. Any areas deficient in contact should

be added to at this time.

4. After a second 24- to 48-hour period of wear, the registration should be

complete and acceptable. The remaining teeth that serve as vertical stops

should be in contact, and the occlusion rim should show an intact glossy

surface representing each cusp in all extremes of movement.

The completed registration is now ready for conversion to an occluding

template. This is usually done by boxing the occlusal registration with

modeling clay after it has been reseated and secured onto the master or

processing cast. Only the wax registration and areas for vertical stops are left

exposed. It is then filled with a hard die stone to form an occluding template.

It is necessary that stone stops be used to maintain the vertical relation

rather than relying on some adjustable part of the articulating instrument, which

might be changed accidentally. Also, by using stone stops and by mounting


13

both the denture cast and the template before separating them, a simple hinge

articulator may be used.

The end


1

PROSTHODONTICS


INITIAL PLACEMENT, ADJUSTMENT, AND

SERVICING OF REMOVABLE PARTIAL

DENTURES (R.P.Ds).

Initial placement of the completed removable partial denture is the final

steps for the removable partial dentures construction

The objectives of this appointment are: (1) to place the prosthesis and make

it as comfortable as possible by evaluate and correct the fit of the denture base,

correct the occlusion, and adjust the retentive clasps.(2) to teach the patient how

to use the prosthesis.(3) to instruct the patient how to maintain the prosthesis

and oral cavity. The first objective should be completed in order so that the

occlusion should not be evaluated until the denture base has been adjusted to fit

the edentulous ridge and surrounding tissues. Adjustment of retentive clasps

should not be considered until occlusal adjustments have been finalized.

The term adjustment has two connotations, each of which must be

considered separately. The first is adjustment of the denture bearing and

occlusal surfaces of the denture made by the dentist at the time of initial

placement and thereafter. The second is the adjustment or accommodation by

the patient, both psychologically and biologically, to the new prosthesis.

The timing of initial placement appointment:

1. The initial placement of the prosthesis should be early in the morning to

have time for a double check after the patient used the prosthesis for

several hours.


2

2. This appointment should not be placed in the last day of the week. It is

important to give the patient the chance for a second appointment the day

after.

3. Instruct the patient not being in a position to transact an important

business or attend social engagements immediately after the insertion.

INITIAL PLACEMENT AND ADJUSTMENT PROCEDURE

Checking the Framework and inspecting the prosthesis

The tissue surface or intaglio surface of the prosthesis should be checked

extraorally for blebs, bubbles, blisters or artifacts in acrylic base due to the

processing procedure. Cast metal bases are not subject to the difficulties

associated with polymerization shrinkage and usually doing not require

adjustment during the insertion appointment. Any correction to a cast metal

base should have been performed at the framework try-in appointment.

Borders of the prosthesis should be smooth and rounded, if not, checked to

detect sharp edges and corrected its.

Checking the fit of denture base

The prosthesis should be seated gently in the patient`s mouth along the

determined path of placement. The prosthesis should be propriocepted (felt) for


3

any resistance to insertion due to the presence of undercuts. The prosthesis

should be relieved in the undercut areas. The pressure points, which require

relief, are detected with the help of pressure indicating paste (PIP).

Altering bearing surfaces to perfect the fit of the denture to the supporting

tissue should be accomplished with the use of some kind of indicator paste. The

paste must be one that will be readily displaced by positive tissue contact and

that will not adhere to the tissue of the mouth. Several pressure indicator pastes

are commercially available. These pressure indicator pastes consist principally

of zinc oxide powder combined with a medium-consistency vegetable fat or

shortening. Other ingredients are added to improve the flavor and consistency

of the paste.

The paste should be applied by the dentist in a thin layer over the bearing

surfaces. A stiff-bristled brush is used to coat the surface with a thin layer of

pressure-indicating paste. The brush marks should be visible. The material

should be rinsed in water so it will not stick to the soft tissue, and then digital

pressure should be applied to the denture in a tissue-ward direction.

The patient cannot be expected to apply a heavy enough force to the new

denture bases to register all of the pressure areas present. The dentist should

apply both vertical and horizontal forces with the fingers in excess of what

might be expected of the patient. The denture is then removed and inspected.

Any areas where pressure has been heavy enough to displace a thin film of

indicator paste should be relieved and the procedure repeated with a new film

of indicator until excessive pressure areas have been eliminated. Therefore only

those areas that show through an intact film of indicator paste should be

interpreted as pressure areas and relieved accordingly.

The decision to relieve an area of pressure must consider whether the

pressure is in a primary, secondary, or non-supportive denture bearing area. The


4

primary denture bearing areas should be expected to show greater contact than

other areas.

Pressure areas most commonly encountered are as follows :

In the mandibular arch

(1) The lingual slope of the mandibular ridge in the premolar area ,

(2) The mylohyoid ridge ,

(3) The border extension into the retromylohyoid space, and

(4) The distobuccal border in the vicinity of the ascending ramus and the

external oblique ridge.

In the maxillary arch

(1) The inside of the buccal flange of the denture over the tuberosities ,

(2) The border of the denture lying at the malar prominence

(3) The point at the pterygomaxillary notch where the denture may impinge

on the pterygomandibular raphe or the pterygoid hamulus .

The amount of relief necessary will depend on the accuracy of the

impression, the master cast, and the denture base. Despite the accuracy of

modern impression and cast materials, many denture base materials leave much

to be desired in this regard, and the element of technical error is always present.

It is therefore essential that discrepancies in the denture base are detected and

corrected before the tissues of the mouth are subjected to the stress of

supporting a prosthetic restoration.


5

Checking the peripheral denture base extensions

Maximum flange extension, within physiologically tolerable limits

provides optimal support and stability for the prosthesis. Extension of denture

flanges into the facial vestibules and lingual sulci enhances resistance to

horizontal displacement. Therefore, acrylic resin denture base flanges should

not be arbitrarily reduced. Rather, they should be critically evaluated and

adjusted only when physiologic limits have been exceeded.

Overextensions of denture base flanges may cause the following:

The muscles and frena will tend to dislodge the prosthesis during

function; the resultant dislodging force may be destructive to the

abutment teeth especially in tooth-tissue supported removable partial

denture.

Overextensions interfere with the complete seating of the prosthesis.

Overextensions may cause ulceration, pain and swelling of the vestibular

tissues, if not corrected over a period time, a redundant tissue form in

these tissues as a response to chronic irritation.

Overextensions may cause muscle impingement that interfere with the

muscle function.

Underextensions of denture base flanges may cause the following:

Underextensions affect the support of the prosthesis due to inadequate

distribution of masticatory force.

Underextensions affect the stability of the prosthesis due to inadequate

resistance to the lateral or horizontal stresses.

Foods entrapments beneath the denture base of the prosthesis.

Visual and digital evaluation of the resin flanges should be performed

during the placement appointment. The extension of the peripheral borders is


6

determined by performing border-moulding movements and checking for

lifting of denture. Overextensions are easily detectable due to the displacement

of the prosthesis during function. Disclosing wax can be placed on denture base

flanges to help identify areas of overextension.

In general, posterior denture base flanges should be at least 2mm thick

and should display rounded borders. Flanges should be slightly thinner at the

distolingual aspects of mandibular extension base removable partial dentures

and distofacial aspects of maxillary extension base removable partial dentures.

Decreased flange thickness in these areas provides additional tongue space in

the mandibular arch and freedom of movement for the coronoid processes in

the maxillary arch. The leading edges of maxillary and mandibular posterior

denture base flanges also should be thinned. This helps to disguise the presence

of the flange when the patient is viewed from the front during normal

conversation and while smiling. Thick leading edges of posterior denture base

flanges are often esthetically unattractive.

When designing a denture base for the anterior portion of the mouth,

consideration must be given to the esthetic requirements of the patient. Careful

evaluation of the pressure indicator paste often will reveal excessive tissue

contact along the border of the denture base. Correction of this interference

involves vertical reduction of the flange length to the point of contact with the

edentulous ridge. Once the anterior denture base flange has been adjusted to

permit complete seating of the prosthesis, the superior and lateral margins of

the flange are beveled to produce thin borders. This will permit a smooth

transition from the denture base to the soft tissues, thereby producing a natural

and esthetic effect.

The frena should be relieved appropriately; the notch like frenum relief is

inspected in the denture to ensure adequate clearance, the margins of the relief


7

should also be examined to avoid tissue injury, and finally excessive frenum

relief will allow air entry between the denture and the tissues leading to loss of

peripheral seal.

Following adjustment, the pressure indicator paste and grinding residue are

wiped from all denture surfaces and fresh paste is applied. This procedure is

repeated until the removable partial denture can be completely seated without

encountering resistance, producing blanching of the soft tissues, or causing

patient discomfort.

Correcting the Occlusal Contacts

Correction of occlusal contacts must not be initiated until the removable

partial denture can be completely and comfortably seated in the patient’s

mouth. Attempting to correct occlusal errors before establishing adequate fit of

the denture base is inappropriate. Faulty occlusion can produce severe tissue

reaction like excessive ridge resorption, damage to the temporomandibular

joint.

The criteria to be followed before adjusting occlusion:

It is best to consider one arch as an intact arch so that the other one can

be adjusted according to the intact arch.

If one partial denture is tooth supported and the other tissue supported,

the tooth-supported arch is first adjusted and is considered as the intact

arch for adjustment of the tissue supported denture.

If both partial dentures are entirely tooth borne, the one occluding with

the most natural teeth is adjusted first, and considered as the intact arch.

If both dentures are tissue supported, the final adjustment of occlusion on

opposing tissue-supported base is usually done on the mandibular

denture, since this is the moving member. Hence, even if the mandibular


8

denture opposes more natural teeth and is considered as the intact arch,

the final occlusal adjustments are made only on it.

One should have a clear idea about the source of occlusal interference

before treating such conditions. Sources for occlusal interference include:

1. Denture extension.

2. Occlusal Interference from Denture Framework.

3. Contact between the natural and artificial teeth (occlusion).

Denture extension

The heel is the last part of the posterior acrylic denture base extension.

Denture`s heel should be examined for interference with each other or the

tuberosity. In such cases, the acrylic resin of the maxillary denture base should

be reduced first without thinning or weakening the structure. If the interference

still exists, the mandibular extension should be adjusted and shortened till there

is no interference.

Occlusal Interference from Denture Framework

Any occlusal interference from occlusal rests and other parts of the

denture framework should have been eliminated before or during the

establishment of occlusal relations. The denture framework should have been

tried in the mouth before a final jaw relation is established, and any such


9

interference should have been detected and eliminated. Much of this need not

occur if mouth preparations and the design of the removable partial denture

framework are carried out with a specific treatment plan in mind.

Contact between the natural and artificial teeth (occlusion).

The goals of occlusal evaluation and correction during the insertion

appointment are (1) maintenance of existing natural tooth contacts and (2)

establishment of occlusal harmony in all centric and eccentric positions. Failure

to achieve these goals may result in the patient’s inability to wear a new


From a practical standpoint, the clinical techniques used to evaluate

occlusal errors may be classified as either intraoral or extraoral procedures. The

choice of procedure is primarily determined by the stability and support of the

removable partial denture in the patient’s mouth. A fairly large percentage of

new removable partial dentures may be evaluated using an intraoral approach.

However, for those patients in whom denture stability and support are

compromised, use of the extraoral (or remount) procedure is most appropriate.

The remount procedure includes patients with (1) removable partial dentures

displaying long extension bases, (2) extension base removable partial dentures

covering extremely mobile soft tissues, and (3) removable partial dentures

opposed by conventional complete dentures.

Intraoral procedure:

There are two clinical methods commonly used to correct occlusal

discrepancies in the prosthesis. Each one has been described as follows:

First method: It basically involves using, either an articulating paper or

occlusal indicator wax to check for the interferences:


10

1. Occlusal indicator wax or two strips of 28- gauge soft green wax (casting

wax) is placed between opposing dentition.

2. The strips are folded in the center to form a V-shaped structure. The V-

shaped band of wax is now placed in-between the teeth and the patient is

guided to close in centric occlusion two or three times.

3. The wax is removed and inspected under transillumination for

perforations.

4. All perforated areas are either premature contacts or excessive contacts.

5. The excessive contacts can also be identified by using the wax record as

reference and relieved accordingly.

Second method:

1. Wax strips are placed on the occlusal surface of the teeth. The strips are

folded over the buccal and lingual surfaces of the teeth for retention.

2. Next, the patient is guided to close in centric relation twice or thrice. The

wax over the occlusal surface is examined for perforation. The areas of

the tooth, which produced perforations on the wax, are marked with a

waterproof pencil through the wax perforations.

3. The wax is removed from the teeth and the pencil marks present on the

teeth indicate the excessive or premature contacts. The occlusal surface is

relieved in the marked areas.


11

Extraoral procedure (remount procedures):

Extraoral correction represents an alternative to intraoral procedures. When

using the extraoral technique, the removable restoration or restorations are

mounted on a dental articulator using a facebow transfer and interocclusal

records. Occlusal contacts are then marked, evaluated, and adjusted in the dry,

well-illuminated environment of the dental laboratory.

To remount removable partial dentures in an articulator, it is necessary to

secure casts of both the dental arch restored by the removable partial denture

and the opposing arch. An irreversible hydrocolloid impression is made with

the removable partial denture completely seated in the patient’s mouth. In most

instances, the prosthesis will remain in the impression when the impression is

removed from the mouth. If the prosthesis remains in the mouth, it must be

retrieved and carefully repositioned in the impression. Undercuts within the

removable partial denture are then blocked out using baseplate wax, clay, wet

paper towels, or wet facial tissues. Dental stone is mixed and vibrated into the

impression. When the dental stone has hardened, the cast is recovered and

trimmed in preparation for mounting procedures. A cast of the opposing

dentition must also be fabricated. If the opposing arch is restored with a

conventional complete denture, the denture itself may be remounted on the

articulator. If this is not the case, an alginate impression of the arch is made and

a cast is generated.

At this stage of the procedure, the maxillary cast is mounted on the

articulator using a facebow record. The mandibular cast is mounted using jaw

relation records. Before continuing, the accuracy of the mounting is verified

using additional jaw relation records. Upon completion of the verification

process, occlusal evaluation and correction procedures are initiated in the

articulator outside the patient mouth.


12

The techniques and goals used in extraoral correction procedures are similar

to those described for the intraoral method. The adjustment of denture teeth is

continued until simultaneous contact of opposing occlusal surfaces has been

achieved. In turn, eccentric occlusion is adjusted. After the occlusion of the

removable partial denture has been refined on the articulator, appropriate

occlusal anatomy is restored using fine burs and a low-speed handpiece.


13

Adjusting Retentive Clasps

Retention provided by clasps should be just adequate to maintain the

denture in position and should not exert undesirable forces on the abutment.

After all the other corrections are completed, the clasps are adjusted finally.

Wrought wire clasps are adjusted to increase contact with tooth. Plier

No.139 is used for this purpose which is a tapered cylindrical beak is opposed

by flat surface of a triangular beak. The round beak of plier is placed on inner

aspect of clasp at point marked where adjustment is needed. Denture is rotated

with opposite hand towards round beak of pliers. Small adjustments are made at

a time and denture is returned to mouth for observation and process is repeated

until complete contact between tooth and clasp has been reestablished.

Cast circumferential clasps are adjusted in one plane only inward

perpendicular to the flat surface of clasp or in the opposite direction. Technique

is similar to that for wrought wire clasp and same pliers are used.

Vertical projection clasps can be adjusted inward or outward

perpendicular to flat side of approach arm. Procedure is again similar to the

above two clasps and the same pliers are used.


14

INSTRUCTIONS TO THE PATIENT AND FOLLOW-UP

SERVICES

The placement and removal of the prosthesis

Finally, before the patient is dismissed, Patients should be instructed in the

proper placement and removal of the removable partial denture. They should

demonstrate that they can place and remove the prosthesis themselves. The

patient should be informed about the importance of path of insertion. Therefore,

the first insertion and removal of the prosthesis should be performed by the

clinician while the patient observes the process. After that, the mirror is held by

the dentist and the patient tries carefully to insert and remove the prosthesis into

the mouth. Insertion of a removable partial denture is generally less of a

problem than is denture removal. Seating the denture with biting pressure

should be discouraged because damage to the denture, natural teeth, or soft

tissues can easily result. The patient should secure the perfect seat of the

prosthesis by applying pressure along the incisal and/ or occlusal surfaces of

the artificial teeth.

After the patient has observed insertion of the removable partial denture, its

removal also should be demonstrated. The most convenient method for

engaging the prosthesis is to position a fingernail or thumbnail apical to a facial

clasp arm on each side of the dental arch and to move the clasp occlusally. This

method is acceptable when cast circumferential clasps are readily available.

However, if only wrought-wire clasps are available, this technique should be

avoided. Wrought-wire clasps are easily distorted using this technique. When

wrought-wire clasps are present, the patient should grasp the acrylic resin

denture bases on each side of the arch and carefully withdraw the removable

partial denture from the mouth.


15

Patients should be advised that some discomfort or minor annoyance

might be experienced initially in the first few days. Patients must be advised of

the possibility of the development of soreness despite every attempt on the part

of the dentist to prevent its occurrence. Patients mostly like to know that these

difficulties can be solved easily in the control appointments. It is vital to inform

the patients about the importance of periodic recalls.

Discussing phonetics with the patient in regard to the new dentures may

indicate that this is a unique problem to be overcome because of the influence

of the prosthesis on speech. With few exceptions, which usually result from

excessive and preventable bulk in the denture design, contour of denture bases,

or improper placement of teeth, the average patient will experience little

difficulty in wearing the removable partial denture. Most hindrances to normal

speech will disappear in a few days.

Oral hygiene and prosthesis care

The patient must understand that meticulous home care is a prerequisite to

removable partial denture success. Inadequate home care will hasten the

destruction of the remaining teeth. Emphasis should be given to physically

brushing the denture on a daily basis, rather than relying on a cleaning or

soaking agent to remove debris. The use of common toothpastes should be

avoided since these pastes often contain abrasive particles. Scouring powders

and abrasive household cleaners should also be avoided because of their

potential for damaging both acrylic resin and metal components of a removable

partial denture. The patient must understand that the denture should never be

brushed while in the mouth. Instead, the prosthesis should be removed to

permit access to all surfaces. The patient should also be instructed to clean the

denture over a partially filled basin of water so that if the denture is dropped,

little harm will be done. A denture-cleaning solution can be used for extra


16

cleaning especially for older and handicapped patients. Soaking the prosthesis

15 minutes daily in this solution helps not only to keep the denture clean but

also to disinfect the surfaces.

The patient should also be instructed to remove the prosthesis before going

to bed at night. The soft tissues covered by the denture bases and the major

connectors must be given the opportunity to recover from constant mechanical

stresses applied when the prosthesis is in place. The risk of enamel

decalcification and soft tissue inflammation is greatly increased when the

prosthesis is worn for long periods of time. Extraorally, the patient should also

be told to store the prosthesis in a container and covered with water to prevent

its dehydration and subsequent dimensional change. About the only situation

that possibly justifies wearing removable partial dentures at night is when

stresses generated by bruxism would be more destructive because they would

be concentrated on fewer teeth. Broader distribution of the stress load, plus the

splinting effect of the removable partial denture, may make wearing the denture

at night advisable.

Written instructions

It is impractical to expect that patients will remember all of the instructions

provided at the insertion appointment. Providing the patient with written

instructions will permit the patient an opportunity to review the instructions at

home.

Follow-up services

The patient with a removable partial denture should not be dismissed as

completed without at least one subsequent appointment for evaluation of the

response of oral structures to the restorations and minor adjustment if needed.

This should be made at an interval of 24 hours after initial placement of the

denture.


17

The dentist should examine the mouth and the denture depends on the oral

and physical condition of the patient. Patients who are caries susceptible or who

have tendencies toward periodontal disease or alveolar atrophy should be

examined more often. Every 6 months should be the rule if conditions are

normal.

The future development of denture rocking or looseness may be the result

of a change in the form of the supporting ridges rather than lack of retention.

This should be detected as early as possible after it occurs and corrected by

relining or rebasing.

The patient should be advised that maximal service may be expected from

the removable partial denture if the following rules are observed:

1. Avoid careless handling of the denture, which may lead to

distortion or breakage.

2. Protect teeth from caries with proper oral hygiene, proper diet, and

frequent dental care.

3. Prevent periodontal damage to the abutment teeth by maintaining

tissue support of any distal extension bases.

4. Accept removable partial denture treatment as something that

cannot be considered permanent, but partial dentures must receive

regular and continuous care by both the patient and the dentist.

The end


1

PROSTHODONTICS


RELINING, REBASING, REPAIRS AND

ADDITIONS TO REMOVABLE PARTIAL

DENTURES (R.P.DS).

Relining is the resurfacing of the tissue of a denture base with new

material to make it fit the underlying tissue more accurately.

Rebasing is the replacement of the entire denture base with new material.

The artificial teeth may need to be replaced in a rebase procedure.

Relining removable partial dentures is a common occurrence in many

dental practices; however, rebasing is not indicated as often.

Both relining and rebasing needs a new impression and uses the existing

denture base with modifications. With a tooth-supported prosthesis, the

impression method (open- or closed-mouth) is not as critical. In deciding

between a closed-mouth and an open-mouth impression method for relining a

distal extension removable partial denture, a major consideration is the

resiliency of the mucosa covering the residual ridge. Both techniques should

guard against framework movement during the impression procedure. Before

relining or rebasing is undertaken, the oral tissue must be returned to an

acceptable state of health.

To accomplish relining or rebasing, the original denture base must have

been made of a resin material that can be relined or replaced. Ordinarily, a

metal base, with its several advantages, is not used in a tooth-supported area in

which early tissue changes are anticipated. A metal base should not be used


2

after recent extractions or other surgery or for a long span when relining is

anticipated to provide secondary tissue support.

RELINING

Two methods can be used for relining which are:

Indirect (Conventional or laboratory) relines method

In this method, an impression is made by using the partial denture that

needs to be relined. Heat-cure acrylic resin is added in the laboratory using the

conventional flasking method or the metal reline jig. This method is commonly

used in tooth-tissue supported denture bases and long span tooth-supported

denture bases.

Direct (chairside) reline method

In this method, self-cure acrylic resin is used to reline the denture base

directly in the mouth. This method is commonly used in tooth-supported

denture bases.

Despite the time and cost savings of the direct technique, the advantage of

the indirect technique is a harder, denser, and more completely cured resin

relines compared with direct reline materials. The materials used for direct-

reline procedures are more porous and flexible and less color stable.

Additionally, direct-reline materials comprise a greater risk because of less

polymerization that lead to more residual monomer which may be cytotoxic to

particular patients.

Before starting the relining procedures, the oral mucosa should be returned

to an acceptable state of health that may require a period of function without the

RPD or using the RPD with a tissue conditioner after relief of the RPD in the

effected regions.


3

Relining Tooth-Supported Denture Bases:

Tissue changes that occur beneath tooth-supported denture bases do not

affect the support of the denture because the support for that restoration is

derived entirely from the abutment teeth at each end of each edentulous span;

therefore relining or rebasing is usually done for reasons that include

unhygienic conditions and the trapping of debris between the denture base and

the residual ridge; or patient discomfort associated with lack of tissue contact

that arises from open spaces between the denture base and the tissue.

Commonly, tooth-supported removable partial denture bases are made of

metal as part of the cast framework. These generally cannot be satisfactorily

relined, although they sometimes may be altered by drastic grinding to provide

mechanical retention for the attachment of an entirely new resin base, or some

of the new resin bonding agent may be used. Because the tooth-supported

denture base cannot be depressed beyond its terminal position with the occlusal

rests seated and the teeth in occlusion, and because it cannot rotate about a

fulcrum, a closed-mouth impression method is used. Ordinarily, an

impression material is used that will record the anatomic form of the oral tissue.

When relining in the mouth with a resin reline material is done with an

appropriate technique, the results can be highly satisfactory, with complete

bonding to the existing denture base, good color stability, permanence, and

accuracy.

The procedure for applying a direct or chairside relines of an existing resin

base is as follows:

1. Generously relieve the tissue side of the denture base. Lightly relieve the

borders. This not only provides space for an adequate thickness of new

material but also eliminates the possibility of tissue impingement caused by

confinement of the material.


4

2. Apply lubricant or tape over the polished surfaces from the relieved border

to the occlusal surfaces of the teeth to prevent new resin from adhering to

the preserved bases and teeth.

3. Mix the powder and the liquid in a suitable container according to the

proportions recommended by the manufacturer.

4. While the material is reaching the desired consistency, ask the patient to

rinse the mouth with cold water. At the same time, wipe the fresh surfaces

of the dried denture base with a cotton pellet or small brush saturated with

some of the reline resin monomer. This facilitates bonding and ensures that

the surface is free of any contamination.

5. When the material has first begun to thicken, but while it is still quite fluid,

apply it to the tissue side of the denture base and over the borders.

Immediately place the removable partial denture in the mouth in its

terminal position, and have the patient lightly close into occlusion. Be sure

that no material flows over the occlusal surfaces or alters the established

vertical dimension of occlusion.

Then, with the patient’s mouth open, manipulate the cheeks to turn the excess

at the border and establish harmony with bordering attachments. If a

mandibular removable partial denture is being relined, have the patient move

the tongue into each cheek and then against the anterior teeth to establish a


5

functional lingual border. It is necessary that the direct retainers be effective to

prevent displacement of the denture while molding of the borders is

accomplished. Otherwise the denture must be held in its terminal position with

finger pressure on the occlusal surfaces while border molding is in progress.

6. Immediately remove the denture from the mouth and, with fine curved

scissors, trim away gross excess material and any material that has flowed

onto proximal tooth surfaces and other components of the removable partial

denture framework. While doing this, have the patient again rinse the

mouth with cold water. Then replace the denture in its terminal position to

bring the teeth into occlusion. Repeat the border movements with the

patient’s mouth open. By this time, or soon thereafter, the material will

have become firm enough to maintain its form out of the mouth.

7. Remove the denture, quickly rinse it in water, and dry the relined surface

with compressed air. Apply a generous coat of glycerin with a brush or

cotton pellet to prevent frosting of the surface caused by evaporation of the

monomer. Allow the material to polymerize in a container of cold water.

This will eliminate any patient discomfort and tissue damage that could

have resulted from exothermic heat or prolonged contact of the tissue with

unreacted monomer. Although it is preferable for 20 to 30 minutes to elapse

before trimming and polishing, it may be done as soon as the material

hardens. Polymerization may be expedited and made denser by placing the

denture in warm water in a pressure pot for 15 minutes at 20 psi. Regular

finishing and polishing is done.

When properly done, a direct reline is entirely acceptable for most tooth-

supported removable partial denture bases made of a resin material, except

when some tissue support may be obtained for long spans between abutment

teeth. In the latter situation, a reline impression in tissue conditioning material

or other suitable elastic impression material may be accomplished. The denture


6

may then be flasked, and a processed reline may be added for optimal tissue

contact and support.

Relining Distal Extension Denture Bases:

A distal extension removable partial denture derives its major support from

the tissue of the residual ridge, requires relining much more often than does a

tooth-supported denture. Because of this, distal extension bases are usually

made of a resin material that can be relined to compensate for loss of support

caused by tissue changes. The primary reason for relining a distal extension

base is to reestablish tissue support for that base. The need for relining a distal

extension base is determined by evaluating the stability and occlusion at

reasonable intervals after initial placement of the denture.

The indications of the need for relining a distal extension R.P.D are:

1. Loss of occlusal contact between opposing dentition or between the

denture and the opposing natural dentition may be evident.

2. Loss of tissue support that causes rotation and settling of the distal

extension base is obvious when alternate finger pressure is applied on

either side of the fulcrum line.

The need for relining is assessed by visual examination of the loss of

support from the supporting tissue:

Using alginate: A thin mix of alginate is made (one scoop of powder with

2 measures of hot water). This provides a mix, which is thin enough to

prevent displacement of soft tissues, yet sets quickly. The thin mix of

alginate is loaded under the denture base and the partial denture is seated

in the mouth. The position is maintained until the alginate sets. The

amount of alginate is clinically evaluated. If two or more millimeters of

alginate are present, then this is a good indication for relining.


7

Using finger pressure: Finger pressure is applied to the retromolar pad

area of the distal extension denture base. If there is loss of supporting

tissues, then the anterior indirect retainer will lift from its rest

preparation. The amount of space under the indirect retainer is clinically

evaluated. If the indirect retainer lifts two or more millimeters, then the

patient is a candidate for relining.

The procedure for applying an indirect or conventional or laboratory

relines for distal extension denture base is as follows:

The clinical stage:

1. A uniform amount of resin is removed from the tissue side of the denture

base. This is done for two reasons:

Space must be created so that the impression material does not displace

the soft tissues.

The tissue surface of the denture base should be removed so that the new

resin can bond to the underlying dense, uncontaminated resin in the

existing denture.

2. The reduced denture base is used as a special tray to make an impression

of the edentulous ridge. The impression material of choice varies for

individual cases depend on the type of soft tissue:

• Zinc-oxide eugenol impression material is used when mobile tissue is

present on the crest of the ridge.

• Polysulphide rubber, silicone, mouth temperature wax are used on dense

firm tissue of the edentulous ridge.

• Tissue conditioners can be used for either cases but they distort the

tissues.

3. The most important factor to be preserved during relining procedure is

the maintenance of tooth-framework relationship. This is accomplished


8

by holding the framework against the abutment teeth until the reline

material sets. So that, an opened-mouth impression method is used.

4. Before the completed reline impression is removed from the mouth, the

framework is moved around its fulcrum to verify whether the reline has

restored the desired support to the denture base.

5. Make an over-impression with alginate impression material over the

completed reline impression (pick-up or dual impression) to obtain a

complete arch cast.

6. Pour the impression with dental stone to make a definitive cast, but do

not separate it from the cast after setting, and then the impression with

the cast is forwarded to the laboratory for processing.


9

The laboratory stage

7. The removable partial denture with the reline impression in the cast is

directly flasked in the laboratory. After the plaster in the flask is set, the

flask is opened up. The denture base area should be completely cleared

of impression material.

8. A separating medium is applied in the mould space. The heat-activated

denture base resin is kneaded and placed in the flask. Tight closure of

flask is necessary.

9. After the resin is completely polymerized, deflasking is done.

10. Another laboratory technique involves the removable partial denture

with the relined impression in the cast is directly mounted on a

duplicating device (metal reline jig). The entire partial denture should be

in the top half of the duplicating device. Auto-polymerizing denture base

resin is used with this device.

11. The relined removable partial denture is finished and polished.

Methods of Reestablishing Occlusion on a Relined

Removable Partial Denture:

Occlusion on a relined removable partial denture may be reestablished by

several methods, depending on whether the relining results in an increase in the

vertical dimension of occlusion or in lack of opposing occlusal contacts. In

either instance, it is usually necessary to make a remounting cast for the relined

removable partial denture so the denture can be correctly related to an opposing

cast or prosthesis in an articulator .

If the artificial teeth to be corrected are resin, the occlusion can be

reestablished by adding autopolymerizing or light-activated resin to occlusal

surfaces, or by fabricating gold occlusal surfaces, which can be attached to the

original replaced teeth. The original teeth may also be removed from the


10

denture base and replaced by new teeth arranged to harmonize with the

opposing occlusal surfaces .

REBASING

Rebasing is a laboratory technique similar to relining wherein the bulk of

denture base material is removed along with the impression material and

replaced by new resin.

Indications of the rebasing:

• When the denture borders do not extend to cover all the supporting

tissue.

• When the denture is fractured in the denture base.

• When the artificial teeth are to be replace or rearrange.

• When the denture is stained or discolored so that needs to replace for

esthetic reason.

Rebasing technique is:

The clinical stage:

1. The tissue surface of the denture base is relieved and trimmed to provide

space for re-adaptation of borders with modelling plastic impression

material.

2. Border moulding is done. After border moulding, a final impression is

made using the framework. An over-impression with alginate impression

material to obtain a complete arch cast. A cast is poured against the

rebase impression.

The laboratory stage:

3. The modelling plastic and the final impression material are scrapped

away from the denture base.


11

4. The denture base extending over the area to be rebased should be

trimmed leaving just about 2-3 mm adjacent to the base of the teeth.

5. The tissue surface of the denture resin is trimmed to provide space for the

new resin. This trimming should stop short of the denture teeth.

6. When the anterior teeth are involved, the junction of the new resin and

the existing denture base should be kept in an area that is not visible.

7. Now the framework with the trimmed denture base will not contact the

edentulous ridge.

8. The contour of the denture base is re-established by adding small

amounts of base plate wax. This gives a finished contour to the processed

rebase and reduces the finishing time.

9. Flasking is done. A boil-out procedure is done to soften the wax and

modelling plastic.

10. Acrylization with heat-activated denture base resin and processing is

done as usual.

11. The denture is de-flasked. Finishing and polishing is done.

REPAIRS AND ADDITIONS

The frequency of the need for repairing or adding to a removable partial

denture occurrence should be held to a minimum by careful diagnosis,

intelligent treatment planning, adequate mouth preparations, and the carrying

out of an effective removable partial denture design with proper fabrication of

all component parts. Any need for repairs or additions will then be the result of

unexpected complications that arise in abutment or other teeth in the arch,

breakage or distortion of the denture through accident, or careless handling by

the patient, rather than faulty design or fabrication. On the other hand, if

fracture has occurred because of structural defects, or if it occurs a second time


12

after the denture has been repaired once before, then some change in the

design—by modification of the original denture or with a new denture—may be

necessary.

The results of breakage or distortion of the denture:

1. From an accident.

2. Poor design.

3. Faulty fabrication.

4. Use of the wrong material for given situation.

Repairing or adding to a removable partial denture needs a new impression

with the removable partial denture in its terminal position in the patient`s

mouth, an impression is made in irreversible hydrocolloid and then is removed,

with the removable partial denture remaining in the impression. The dental

stone is poured into the impression and is allowed to set. Finally, the removable

partial denture is placed in the cast where the repair done.

Broken Clasp Arms

Reasons for breakage of clasp arms:

1. Breakage may result from repeated flexure into and out of too severe an

undercut .

If the periodontal support is greater than the fatigue limit of the clasp arm,

failure of the metal occurs first. Otherwise the abutment tooth is loosened and

eventually is lost because of the persistent strain that is placed on it. With an

accurate survey of the master cast, we can prevent this type of breakage by

locating clasp arms only where an acceptable minimum of retention exists.


13

2. Breakage may occur as a result of structural failure of the clasp arm itself .

A cast clasp arm that is not properly formed or is subject to careless

finishing and polishing eventually will break at its weakest point. This can be

prevented by providing the appropriate taper to flexible retentive clasp arms

and uniform bulk to all rigid non-retentive clasp arms.

3. Breakage may occur because of careless handling by the patient.

Any clasp arm will become distorted or will break if subjected to

excessive abuse by the patient. The most common cause of failure of a cast

clasp arm is distortion caused by accidental dropping of the removable partial

denture.

A broken retentive clasp arm, regardless of its type, may be replaced with

a wrought-wire retentive arm embedded in a resin base or attached to a metal

base by soldering. Often this avoids the necessity of fabricating an entirely new

clasp arm.

Fractured Occlusal Rests

Breakage of an occlusal rest almost always occurs where it crosses the

marginal ridge. Improperly prepared occlusal rest seats are the usual cause of

such weakness: an occlusal rest that crosses a marginal ridge that was not

lowered sufficiently during mouth preparations may be made too thin or may

be thinned by adjustment in the mouth to prevent occlusal interference.

Soldering may repair broken occlusal rests. In preparation for the repair, it

may be necessary to alter the rest seat of the broken rest or to relieve occlusal

interferences.


14

Distortion or Breakage of Other Components —Major and

Minor Connectors

When major and minor connectors were originally made with adequate

bulk, distortion usually occurs from abuse by the patient. All such components

should be designed and fabricated with sufficient bulk to ensure their rigidity

and permanence of form under normal circumstances. Major and minor

connectors occasionally become weakened by adjustment to prevent or

eliminate tissue impingement. Such adjustment at the time of initial placement

may from faulty design or fabrication of the casting. Such a restoration should

be remade instead of further weakening the restoration by attempting to

compensate for its inadequacies by relieving the metal.

A new restoration must be made, or that part must be replaced by casting

a new section and then reassembling the denture by soldering. The cost and

probable success must then be weighed against the cost of a new restoration.

Generally the new restoration is advisable.

Loss of Teeth Not Involved in Support or Retention of the

Restoration

Additions to a removable partial denture are usually simply made when the

bases are made of resin. The addition of teeth to metal bases is more complex

and necessitates casting a new component and attaching it by soldering or

creating retentive elements for the attachment of a resin extension. In most

instances when a distal extension denture base is extended, the need should be

considered for subsequent relining of the entire base. After the denture base has

been extended, a relining procedure for both the new and the old base should be

carried out to provide optimum tissue support for the restoration.


15

Loss of an Abutment Tooth

In the event of a lost abutment, the next adjacent tooth is usually selected

as a retaining abutment, and it generally will require modification or a

restoration. Any new restoration should be made to conform to the original path

of placement, with proximal guiding plane, rest seat, and suitable retentive area.

Modifications to the existing tooth should be done the same as during any other

mouth preparations, with proximal recontouring, preparation of an adequate

occlusal rest seat, and any reduction in tooth contours necessary to

accommodate retentive and stabilizing components. A new clasp assembly may

be cast for this tooth and the denture reassembled with the new replacement

tooth added.

Other Types of Repairs

Other types of repairs may include the replacement of a broken or lost

prosthetic tooth, the repair of a broken resin base, or the reattachment of a

loosened resin base to the metal framework.

Repair procedure to the denture resin base is:

1. Accurately reassemble the fractured pieces, any differences may cause

the denture either not fit or does not occlude correctly.

2. Sticky wax applied to the fractured pieces along the fracture line, to

maintain them in a correct position.

3. A wooden match stick can added on either side along the occlusal

surfaces of the teeth attaching them with sticky wax. To reinforce the

fractured pieces.

4. Block any severe tissue undercuts; a cast is poured with plaster.

5. After the cast is set. Separate the fractured R.P.D pieces, removing the

sticks or the sticky wax. Apply separating medium to the cast.


16

6. The fractures edges are to be beveled towards the polished surface which

should be reduced with grooves of (8-10 mm) zig—zig, the pieces are

then re-assembled on the cast.

7. An auto-polymerized denture base resin is applied, over filling to allow

an excess amount for adequate polishing and thus compensating for

expected shrinkage. The repaired R.P.D is completed by curing in a

pressure pot followed by finishing and polishing in the usual manner.

Replacement procedure to the denture artificial teeth is:

1. An accurate opposing cast and a jaw relation record is necessary.

2. The tooth of the same mould and shade is selected and set in the space

produced by the missing tooth.

3. Access should be gained by opening through the lingual surface. The

labial or buccal denture base should be preserved.

4. The ridge-lap area should be relieved to allow at least 2 mm of repair

resin to bind the tooth to the base.

5. The tooth is attached to the framework with sticky wax.

6. Auto-polymerized denture base resin is added with a fine brush. The

repair is completed by curing in a pressure pot followed by finishing and

polishing.

7. If multiple teeth are to be replaced, a mounting cast is poured against the

tissue-surface of the R.P.D. This cast is articulated with the opposing

cast. Teeth to be replaced are positioned and finally the denture base is

relieved. Gingival contours are waxed and the denture is flasked, packed

and processed.


17

THE CAUSES OF REMOVABLE PARTIAL DENTURE

FAILURE:

1. Inadequate diagnosis and improper treatment planning.

2. Improper mouth preparation.

3. Failure to provide sufficient support for distal extension denture base.

4. Failure to use proper clasp design.

5. Improper occlusion.

6. Failure of the dentist to provide the technician with proper design and

instructions.

7. Failure of the technician to follow the instruction of the dentist.

8. When the patient does not accept the treatment.

9. Failure to provide the patient with proper instruction.

10. Inadequate cooperation with patients.

11. Uneducated and uncooperative patient.

The end


1

PROSTHODONTICS


THE DIFFERENCES BETWEEN TOOTH-

SUPPORTED AND TOOTH&TISSUE-

SUPPORTED REMOVABLE PARTIAL

DENTURES (R.P.Ds).

Certain points of difference are present between Kennedy Class I and Class

II types (tooth and tissue-supported) of partial dentures on the one hand and the

Class III and Class IV types (tooth-supported) of partial denture on the other.

The first difference is the manner of support.

Support is the resistance to forces directed toward the basal tissue or

underlying structures.

In a tooth-supported removable partial denture, a metal base or the

framework that supports an acrylic-resin base is connected to and is part of a

rigid framework that permits the direct transfer of occlusal forces to the

abutment teeth through the occlusal rests. The residual ridge beneath the base is

not called on to aid in the support of the removable partial denture. The Class

III and Class IV types derive all of its support from the abutment teeth.

The distal extension removable partial denture does not have the advantage

of total tooth support because one or more bases extends for covering the

residual ridge distal to the last abutment. Therefore it is dependent on the

residual ridge for a portion of its support. Distribution of this load over a

maximum area of bone is a prime requisite in preventing trauma not only to the

tissues of the extension base areas but also to the abutment teeth. The Class I


2

type and the distal extension side of the Class II type derive their primary

support from tissues underlying the base and secondary support from the

abutment teeth.

The second difference is the method of impression registration

required for each type.

An impression registration for the fabrication of a partial denture must fulfill

the following two requirements:

1. The anatomic form and the relationship of the remaining teeth in the

dental arch, as well as the surrounding soft tissues, must be recorded

accurately so that the denture will not exert pressure on those structures

beyond their physiologic limits.

The anatomic form impression is a one-stage impression method using an

elastic impression material that will produce a cast that does not represent a

functional relationship between the various supporting structures of the

partially edentulous mouth. It will represent only the hard and soft tissues at

rest.

2. The supporting form of the soft tissues underlying the distal extension

base of the partial denture which should be recorded so that firm areas

are used as primary stress-bearing areas and readily displaceable tissues


3

are not overloaded, only in this way can maximum support of the partial

denture base be obtained.

A removable partial denture fabricated from a one-stage impression, which

records only the anatomic form of basal seat tissues, places more of the

masticatory load on the abutment teeth and the bone that underlies the distal

end of the extension base. The result will be a traumatic load to the bone

underlying the distal end of the base and to the abutment tooth, which in turn

can result in bone loss and loosening of the abutment tooth. A properly

prepared, individualized impression tray can be used to record the primary

stress-bearing areas in a functional form and the non–stress-bearing areas in an

anatomic form, just as is often accomplished in making impressions for

complete dentures.

The third difference is in the clasp design.

This difference between the two main types of partial dentures lies in their

requirements for direct retention.

The tooth-supported partial denture is retained and stabilized by a clasp at

each end of each edentulous space. The only requirement of such clasps is that

they flex sufficiently during placement and removal of the denture to pass over

the height of contour of the teeth in approaching or escaping from an undercut

area. During its terminal position on the tooth, a retentive clasp should be

passive and should not flex except when engaging the undercut area of the

tooth for resisting a vertical dislodging force.

Cast retentive arms are generally used for this purpose. These may be of the

circumferential type, arising from the body of the clasp and approaching the

undercut from an occlusal direction, or of the bar type, arising from the base of

the denture and approaching the undercut area from a gingival direction. Each

of these two types of cast clasps has its advantages and disadvantages.


4

In tooth and tissue–supported RPD, the direct retainer adjacent to a distal

extension base must perform still another function in addition to that of

resisting vertical displacement. Because of the lack of tooth support distally, the

denture base will move tissueward under function proportionate to the quality

(displaceability) of the supporting soft tissues, the accuracy of the denture base,

and the total occlusal load applied. Because of this tissue-ward movement,

those elements of a clasp that lie in an undercut area mesial to the fulcrum for a

distal extension (as is often seen with a distal rest) must be able to flex

sufficiently to dissipate stresses that otherwise would be transmitted directly to

the abutment tooth as leverage. On the other hand, a clasp used in conjunction

with a mesial rest may not transmit as much stress to the abutment tooth

because of the reduction in leverage forces that results from a change in the

fulcrum position. This serves the purpose of reducing or “breaking” the stress,

hence the term stress-breakers, and is a strategy that is often incorporated into

partial denture designs through various means. Some dentists strongly believe


5

that a stress-breaker is the best means of preventing leverage from being

transmitted to the abutment teeth. Others believe just as strongly that a wrought

wire or bar-type retentive arm more effectively accomplishes this purpose with

greater simplicity and ease of application.

A retentive clasp arm made of wrought wire can flex more readily in all

directions than can the cast half-round clasp arm. Thereby, it may more

effectively dissipate those stresses that would otherwise be transmitted to the

abutment tooth.

Only the retentive arm of the circumferential clasp, however, should be

made of wrought metal. Reciprocation and stabilization against lateral and

torquing movement must be obtained through use of the rigid cast elements that

make up the remainder of the clasp. This is called a combination clasp because

it is a combination of cast and wrought materials incorporated into one direct

retainer. It is frequently used on the terminal abutment for the distal extension

partial denture and is indicated where a mesiobuccal but no distobuccal

undercut exists, or where a gross tissue undercut, cervical and buccal to the

abutment tooth, exists.

It must always be remembered that the factors of length and material

contribute to the flexibility of clasp arms. From a materials physical property


6

standpoint, a short wrought wire arm may be a destructive element because of

its reduced ability to flex compared with a longer wrought-wire arm.

However, in addition to its greater flexibility compared with the cast

circumferential clasp, the combination clasp offers the advantages of

adjustability, minimum tooth contact, and better esthetics, which justify its

occasional use in tooth-supported designs.

The amount of stress transferred to the supporting edentulous ridge and the

abutment teeth will depend on:

(1) The direction and magnitude of the force;

(2) The length of the denture base lever arm;

(3) The quality of resistance (support from the edentulous ridges and

remaining natural teeth); and

(4) The design characteristics of the partial denture.

The location of the rest, the design of the minor connector as it relates to its

corresponding guiding plane, and the location of the retentive arm are all

factors that influence how a clasp system functions.

The fourth difference is the indirect retention.

The need for some kind of indirect retention exists in the distal extension

type of partial denture, whereas in the tooth-supported (Class III and Class IV

types) there is no extension base to lift away from the supporting tissues

because of the action of sticky foods and movements of the tissues of the mouth


7

against borders of the denture. This is because each end of each denture base is

secured by a direct retainer on an abutment tooth. Therefore the tooth-supported

partial denture does not rotate about a fulcrum as does the distal extension

partial denture.

Indirect retainer is the component of a removable partial denture that assists

the direct retainer in preventing displacement of the distal-extension denture

base by functioning through lever action on the opposite side of the fulcrum

line when the denture base attempts to move away from the tissues in pure

rotation around the fulcrum line.

Indirect retainer components should be placed as far as possible from the

distal extension base, which provides the best leverage advantage against

dislodgment. For the sake of clarity in discussion of the location and functions

of indirect retainers, fulcrum lines should be considered the axis about which

the denture will rotate when the bases move away from the residual ridge.

An indirect retainer consists of one or more rests and the supporting minor

connectors. The proximal plates, adjacent to the edentulous areas, also provide

indirect retention. It should be remembered that the rest is actually the indirect

retainer united to the major connector by a minor connector. An indirect


8

retainer should be placed as far from the distal extension base as possible in a

prepared rest seat on a tooth capable of supporting its function.

The fifth difference is the material of the denture base.

The manner in which the distal extension type of partial denture is supported

often necessitates the use of a denture base material that can be relined to

compensate for tissue changes. Acrylic resin is generally used as a base

material for the distal extension bases. Because the tooth-supported base has an

abutment tooth at each end on which a rest has been placed, future relining or

rebasing may not be necessary to reestablish support. Relining is necessary

only when tissue changes have occurred beneath the tooth-supported base to the

point that poor esthetics or accumulation of debris results. For these reasons

alone, tooth-supported bases made soon after extractions should be of a

material that permits later relining.


9

FORMS OF REMOVABLE PARTIAL

DENTURES

Removable partial dentures are defined as any prostheses that replace

some teeth in a partially dentate arch. It can be removed from the mouth and

replaced at will. Basically there are two types of removable partial dentures:

1. Acrylic removable partial dentures: These are made of acrylic resin with

clasps of wrought wire. In spite of the fact that they are considered as a

temporary solution, many people keep this type of appliance for many

years because as long as they are properly maintained, they look

outwardly as good as the more expensive permanent cast removable

partial dentures.

2. Cast removable partial dentures: These are mainly fabricated by the lost

wax casting method and hence the name. Modern frameworks are cast

from an extremely strong alloy called chrome cobalt which can be cast

very thin and they are much less likely to break. They are also much less

noticeable to the tongue. The teeth and denture base are made of acrylic

resin.


10

Some forms of removable partial dentures:

TEMPORARY REMOVABLE PARTIAL DENTURES

It is defined as “A dental prosthesis to be used for a short interval of time

for aesthetics, mastication, occlusal support or convenience or to condition the

patient to the acceptance of an artificial substitute for missing natural teeth until

more definitive prosthetic therapy can be provided “. There are three types of

Temporary partial dentures, which are:

• Interim partial denture.

• Transitional partial denture.

• Treatment partial denture.

Interim partial denture: It is defined as a removable dental prosthesis

designed to enhance esthetics, stabilization, and/or function for a limited period

of time, after which it is to be replaced by a definitive dental or maxillofacial

prosthesis.

The interim denture is worn till the patient becomes suitable for definitive

prosthesis. Interim dentures are also used as an intermediate therapy until the

permanent prosthesis is fabricated. After fabricating the permanent prosthesis,

these dentures are used as spare dentures.

Indications:

• When age, health or lack of time precludes a more definitive treatment.

• In young patients with an anterior or posterior edentulous space and

where a fixed prosthesis cannot be given.

• In people (Geriatric or others) who have health limitations and cannot

undergo lengthier appointments.

• For economic reasons.


11

• For a person who had an unexpected tooth loss and wants a denture

within a short span of time.

Transitional partial denture: It is defined as a removable partial denture

serving as an interim prosthesis to which artificial teeth will be added as natural

teeth are lost and that will be replaced after post-extraction tissue changes have

occurred; a removable transitional denture may become an interim complete

removable prosthesis when all of the natural teeth in the dental arch have been

extracted.

Indications:

It is given when some or all the remaining teeth have periodontal poor

prognosis but immediate extraction of all teeth are not indicated for

physiological and psychological reasons.

Basically transitional dentures are used as a supportive therapy when the

patient is expected to transit from a partially edentulous condition to a

completely edentulous condition due to poor periodontal prognosis of the

existing teeth.

Treatment Partial Denture: It is defined as “A dental prosthesis used for the

purpose of treating or conditioning the tissues which are called upon to support

and retain a denture base”.

Indications:

• As a vehicle to carry tissue treatment material

• To increase or restore the vertical dimension on a temporary basis.

• As a splint following oral surgical procedures.

• As a night-guard to protect the teeth from trauma due to oral habits.


12

IMMEDIATE REMOVABLE PARTIAL DENTURES

It is defined as “Any removable partial denture constructed for placement

immediately following the removal of natural teeth”. They are given in cases

having teeth with poor prognosis. The denture is placed on the day of

extraction.

Advantages:

• It is more aesthetic (improves patient psychology).

• Prevents supra-eruption, and drifting of the opposing and adjacent teeth

respectively.

• Hemorrhage and swelling is controlled because it acts like a splint over

the surgical site.

Disadvantages:

• More patient visits are required during the first few months due to tissue

changes.

• Because of changes in the tissues after removal of the teeth, immediate

dentures usually need to be re-fitted by a dentist within several months so

that need relining to compensate for bone resorption.

• Because some of teeth are still in place, the patient cannot see how the

dentures will look in mouth until after the natural teeth have been

removed (no try-in stage).

• Immediate dentures are usually more expensive because of the additional

time required for their construction.

The end


1

PROSTHODONTICS


DIAGNOSIS AND TREATMENT PLANNING

OF COMPLETE DENTURES.

DIAGNOSIS for prosthodontics care requires the use of general diagnostic

skills and accumulated knowledge from other aspects of dentistry and its

supporting science. During diagnosis the dentist should have a worthy

knowledge about:

1. Patient expectations.

2. Patient attitude.

3. Medical history.

4. Dental history.

Successful treatment also requires an understanding of the patient’s

general health and their dental history, as well as a thorough appreciation of the

status of the oral and perioral tissues and any existing prostheses, be they

successful or unsatisfactory. The collection of medical and dental histories and

their careful analysis, coupled with a thorough orofacial examination, are an

essential and integral part of prosthodontic management and cannot be

overemphasized. They are necessary to ensure the selection of an optimal

treatment protocol with an associated favorable clinical outcome.

TREATMENT PLANNING is the process of matching treatment options

with a patient’s specific needs as determined by careful diagnosis. Detailed

observations that allow the dentist to move from general to specific knowledge


2

of the patient being examined, will lead to both a diagnosis and identification of

any factors that have the potential to prevent desirable treatment.

Key information that facilitate choice of treatment options are:

1. History: The Patient’s Story

Social and behavioral information.

Psychological considerations.

Systemic health status.

2. Dentist’s Specific Observations

Extraoral evaluation:

Temporomandibular joints

Lips and cheeks

Intraoral examination:

Mucosa

Tongue

Saliva

Residual ridge morphology and ridge relations

Tori, undercuts, enlarged tuberosities

Teeth (when present)

Existing prostheses and their occlusal relationship.

Radiographic and Photographic imaging.

Diagnostic / Study casts.

SOCIAL AND BEHAVIORAL INFORMATION

Success in prosthodontic treatment is only partially dependent on the

dentist’s skills and is also heavily dependent on matching patients’ expectations

to realistic treatment outcomes.

The warning to beware of patients who have a “bag of dentures” is widely

known, and reflects an unfavorable balance between these factors. The dentist


3

should refrain from treating such a patient, unless it is possible to determine

ways in which new prostheses can significantly improve on their predecessors.

PSYCHOLOGICAL CONSIDERATIONS

Dentists are in significant agreement that success or failure in fabricating

dentures is not exclusively predicated on a patient’s oral anatomy or the skills

of the dental team, but also on the patient’s attitude toward their prostheses. All

patients may be regarded as psychologically prepared for treatment. The

problem for the dentist is to determine if that preparation is positive or

negative.

SYSTEMIC HEALTH STATUS

Dentist must be aware of each patient’s general health, especially

conditions that might influence the choice of treatment, or that can be

aggravated by a clinical intervention. Knowledge of all medications that a

patient is taking is important to avoid any conflict in therapy. Some systemic

diseases have direct relation to the denture success even though no local

manifestations are apparent.

Debilitating diseases: like diabetes, tuberculosis, or blood diseases should be

under medical care. These patients require extra instructions in oral hygiene,

also frequent recall appointments should be arranged because the supporting

bone may be affected so that the denture bases adapted and the occlusion

corrected if need.

Cardiovascular diseases: patients with such disease may require consultation

with cardiologist as some denture procedures may be preferable. Such patient

must be controlled before dental treatment.

Joint diseases: joint involvement particularly osteoarthritis present different

problems. If the disease involved the tempromandibular joint, alteration in the


4

treatment plan may be essential. In extreme conditions, a special impression

tray and technique are often necessary because of the limited access from

reduced ability to open the jaws; furthermore, jaw relation records are difficult

and occlusion correction must be made often because of subsequent changes in

the joint.

Neurological disorders: some neurological involvement as Bell`s palsy or

Parkinson`s disease requires some attention, dentist have to deal with some

problem related to denture retention, maxillomandibular records and supporting

musculature.

Skin diseases: many of dermatological diseases may have oral manifestations

such as pemphigus. Medical support mostly needed because these oral lesions

are painful that prevent proper dental work.

After history taking and the preceding general observations, the dentist

begins the specific extraoral and intraoral examinations that also will be

supplemented by a radiographic one.

EXTRAORAL EXAMINATION

Extraoral examination is concerned principally with facial contours and

symmetries, the appearance of the teeth and their relationships with the lips in

rest, and function and patterns of jaw movement. It also may be supplemented

by palpation of the temporomandibular joints (TMJs) and of the submandibular

and cervical lymph nodes. Facial asymmetries, plus disparities in jaw size,

should be noted early on since they may require special accommodation in a

treatment plan. The vertical dimensions of the face at rest and with the teeth in

occlusion, as well as anteroposterior jaw relations, should be estimated during

diagnosis to permit provision for their acceptance or correction being included

in the treatment plan. It has been noted previously that the extraoral

examination should include the exposed head and neck; however, before


5

carrying out such an examination, its purpose and nature should be explained to

the patient to avoid misunderstanding.

TEMPOROMANDIBULAR JOINT

The dentist may need to explore the TMJs and masticatory muscles. The

TMJs should be healthy before new dentures are made. Unhealthy TMJs

complicate the registration of jaw relation records since centric relation depends

on the structural and functional harmony of osseous structures, the intraarticular

tissue, and the capsular ligaments. If these are absent, the patient will be unable

to position the mandible in a correct and repeatable centric relation.

CHEEKS AND LIPS

The external form of the cheeks and lips is dependent on their internal

structure and underlying support, which may be provided by the natural teeth

and ridges or their artificial replacements. The muscles of the cheeks and lips

have a critical function in the successful use of dentures, the flanges of which

must be suitably shaped to aid in maintaining the prostheses in place without

conscious effort by the patient. This involves the development of the correct

arch form and tooth positions, as well as the shape of the polished surfaces and

the thickness of the denture borders.

INTRAORAL EXAMINATION

The surface quality and contours of the soft and hard tissues are the objects

of a careful visual examination of the mouth. Complete dentures are entirely

dependent for support on soft tissue (mucoperiosteum) and underlying hard

tissue (bone). The health and quality of these tissues are therefore very

important determinants of success in the wearing of complete dentures.

MUCOSA

Diagnosis of abnormalities of the mucosa requires the recall of the normal

appearance. Shape, color, and texture are significant characteristics. The color

of the mucosa reveals much about its health. The differences in appearance


6

between a healthy, pink mucosa and red, inflamed tissue will be apparent. The

cause of any inflammation must be determined. Abrasions, cuts, or other sore

spots may be found in any location under the basal seats of the existing

dentures or at the borders. They may be the result of overextended or even

underextended borders. Incorrect occlusion is also a major source of tissue

trauma.

INFECTION

Although infections may arise from a variety of sources, oral fungal

infections are common in edentulous patients, particularly in maxillary denture-

related stomatitis. Concomitant inflammation of the corners of the mouth which

is called an angular cheilitis, it should raise suspicions of Candida albicans

infection.

Soft tissue hyperplasia associated with ill-fitting dentures is a common

finding and is observed in relation to edentulous ridges and border tissues as a

reaction either to trauma or to the resorption of supporting bone.

Papillary hyperplasia is cauliflower-like in appearance and tends to occur on

the anterior region of the palate in long-term denture wearers. Although the

infection must be treated before new dentures are made, recurrence is likely

unless the hyperplastic tissue is removed.

TONGUE

The tongue plays an important role in determining denture success or

failure, with its size and activity being the main concerns. The tongue will

expand into any edentulous space(s) by a reorientation of its intrinsic

musculature and become habitually active within its extended boundaries. The

introduction of a new denture will then be met with dislodging competition

from the tongue. An edentulous patient who has not been wearing a mandibular

denture often uses the tongue as an antagonist for the maxillary arch during

mastication. In these situations, the tongue can become enlarged and also very


7

strong, making prosthetic treatment and subsequent denture use challenging for

the dentist and the patient.

Tongue position and coordination are significant in functioning with a

mandibular denture. Normally, the tongue should be expected to rest in a

relaxed position on the lingual flanges, which, if properly contoured, will allow

the tongue to help retain the denture.

SALIVA

The quality and quantity of saliva are crucial factors in a patient’s ability to

tolerate dentures since both the flow rate and the viscosity are important to

denture success. Normal resting salivary flow is about 1 mL/min. A flow of

medium viscosity at this rate lubricates the mucosa and assists retention of

complete dentures.

Many factors can affect the flow rate, but aging is no longer considered to

be a primary factor in diminished flow. Many patients of denture-wearing age,

however, take medications that can reduce salivary flow. Patients who have

received radiation therapy in the region of the salivary glands usually have

glandular tissue destruction with a resulting reduction in salivary flow. The

glands themselves may be diseased or ducts blocked.

Thick, ropey saliva tends to dislodge dentures, and thin saliva or low

salivary flows tend to provide an insufficient film for their retention or

lubrication of the mucosa.

BONE RIDGE MORPHOLOGY

Residual ridges are best examined visually and by palpation, an assessment

that should extend to the adjacent structures. A sensitive finger will detect

abnormalities such as displaceable structures, discontinuities, and enlargements

of structures. It can reveal textural differences and unusual contours and

although a light touch should be used for most of the examination, the patient’s

response to pressure also can be helpful.


8

Many variations in residual ridge morphology will be found. Some will

present no special problems; others will require accommodation in impression

making while still others may require surgical correction. While surgical

reduction is tempting and sometimes indicated, the reduction in ridge height

adversely affects the stability of a denture. It may therefore sometimes be

preferable to retain the ridge for its contribution to denture stability if it is

relieved of direct pressure by using a selective pressure impression technique

that gains support for the denture from other areas.

Severe resorption frequently results in the mental foramina coming to lie

superficially near to or on the crest of the mandibular residual alveolar ridge.

Relief of the denture over the nerve must be provided but is not always

completely effective because of denture movement in function. However, the

predictable stabilization of dentures that results from implant support has

effectively overcome this problem.

TORI

These are benign bony enlargements found in some patients at the midline

of the hard palate or on the lingual aspect of the mandible in the premolar

region. They vary in size. Small ones may be accommodated by relief of the

denture base. Others are so large that their interference with denture design

warrants consideration for their surgical removal.

BONY UNDERCUTS

These can be found on maxillary and mandibular residual alveolar ridges.

Typical examples are posterolingual mandibular undercuts and lateral posterior

maxillary ones. Maxillary buccal undercuts are frequently the result of

exostoses and may need to be surgically removed if they cannot be

accommodated by suitable relief areas in the overlying acrylic flanges.

ARCH RELATIONS

The available amount of support for complete dentures is directly related to

the size of the residual ridges in both the mandible and the maxillae. The arch


9

forms, as demonstrated by the edentulous ridges as they appear from an

occlusal viewpoint, should be noted since arch form can be used as a factor in

tooth selection. It also may assist in decisions on the arrangement of teeth. If

the arches are asymmetric, problems of tooth arrangement and occlusion may

occur.

The ideal ridge has broad top and parallel sides. As the ridge becomes

narrower, it becomes sharper and consequently is less able to withstand as

much occlusal pressure as a broader ridge. The relationship between the

maxillary and mandibular support areas also changes because of resorption

after teeth have been lost. The bone of the maxillae resorbs primarily from the

occlusal, buccal, and labial surfaces. Thus the maxillary residual ridge loses

height, and the maxillary arch becomes narrower from side to side and shorter

anteroposteriorly. On the other hand, the mandibular ridge resorbs primarily

from the occlusal surface. Because the mandible is wider at its inferior border

than at the residual alveolar ridge in the posterior part of the mouth, resorption,

in effect, moves the distal ridges progressively farther apart. The mandibular

arch thus appears to become wider and the maxillary arch narrower.

The relationship also will be obvious on mounted diagnostic/study casts,

which will readily reveal the inter-arch separation. This is important

information because a lack of space can lead to denture failure from improperly

positioned teeth. Excessive space usually is related to severe ridge reduction

with a resulting instability that also limits denture success.

ENLARGED MAXILLARY TUBEROSITIES

When the maxillary tuberosity is so large that they prevent the correct

location of the occlusal plane, require the omission of some teeth, or prevent

the correct distal extensions of the denture bases, then they could be surgically

reduced.


10

TEETH (WHEN PRESENT)

Some patients seeking denture treatment will have a number of remaining

teeth in one or both arches and are unsure about the outcomes of the different

therapeutic possibilities available to them. They will require diagnosis and

treatment planning that offers considered alternative options to complete

dentures. The following considerations for either arch should retain such

patients’ entire or partial dentitions are:

1. Using traditional dental interventions—periodontal, restorative,

prosthodontic, and surgical—the health of the dentition may be restored.

2. Those teeth that are regarded as having poor prognoses may be extracted

while retaining others that offer a good prognostic outcome.

3. Alternatively, specific teeth can be selected as potential abutments for

overdenture treatment with or without adjunctive implant support.

4. Extraction of all remaining teeth with immediate denture replacement is

another option.

EXISTING DENTURES

The patient’s existing dentures can convey a wealth of information and

should be carefully examined both outside and inside the mouth. The objective

is to determine the effects of time-dependent functional on the denture base and

artificial teeth, as well as evidence of denture hygiene procedures and chemical

staining. The presence of reinforcing metallic components also should be noted

because this may reflect a history of repairs before denture breakages.

Examination of old prostheses, coupled with discussion with the patient,

also can reveal much about what the patient likes and dislikes and can or cannot

tolerate. It is important to note characteristics such as the arch form of the teeth

relative to the arch form of the residual alveolar ridge, the orientation of the


11

occlusal plane, the relationship of the anterior teeth to the lips, denture base

extensions, the thickness and contours of the flanges, and wear patterns.

The occlusion can have a profound effect on denture stability, lack of which is

often ascribed to errors in the fitting surfaces. Tissue trauma and a patient’s

inability to successfully use dentures can frequently also be traced to errors of

an inadequate occlusion.

An intraoral evaluation of a denture’s fit will determine its adaptation to

the denture-bearing area, how well the flanges fill the sulci, the correctness of

the border extensions, and the location of the posterior palatal seal.

RADIOGRAPHS & PHOTOGRAPHS MEASUREMENTS

Radiographs are important aids in the evaluation of submucosal conditions

in patients seeking prosthodontic care. They provide information about the

presence or absence of pathoses or abnormalities, as well as insights into the

quantity and, to a limited extent, the quality of bony tissues. Intraoral

radiography is the most frequently used format in dentistry, with the periapical

approach. Panoramic dental radiography provides a general survey of a

patient’s denture foundation and surrounding structures and is readily available

for the convenient examination of both dentulous and edentulous patients.

Preextraction photographs can be useful for determining teeth selection

and arrangement. Observations on face form and jaw relations also can be

made.

DIAGNOSTIC / STUDY CASTS

Diagnostic or study casts offer a versatile and three-dimensional analogue

of both available denture-bearing areas and currently used prostheses. They

provide accurate information on tooth size and arrangement, and when

articulated, also can reveal jaw relationships and interarch tooth relationships.


12

They provide accurate information on arch size and symmetry; interarch

space; arch concentricity; antero-posterior jaw relationship; and lateral jaw

relationships. They assist in making decisions on preprosthetic surgery.

Undercuts may be observed in the diagnostic casts. Even soft tissue disease

may be more obvious on a cast than intraorally when saliva and color may

obscure information. Tissue displacement from the pressure of an old ill-fitting

denture also may be more obvious on a dry cast than in the mouth.

After all the intraoral and general physical and dental conditions have been

recorded and radiographs, casts, and other visual aids are in hand, they can be

interpreted and the treatment plan developed. The details of the specific

observations determine the details of the treatment required.

The end


1

PROSTHODONTICS


PREPROSTHETIC SURGERY FOR

COMPLETE DENTURES.

Preprosthetic surgery is defined as surgical procedures designed to

facilitate fabrication of prosthesis or to improve the prognosis of prosthodontic

care.

Preprosthetic surgery is an important procedure done prior to prosthetic

replacements in compromised condition of the hard and the soft tissues

supporting the complete denture. Its aims are to facilitate retention and stability

of the denture, and to improve the condition of the supporting tissues.

Requirements of an ideal alveolar residual ridge:

1. No evidence of intraoral or extraoral pathologic conditions.

2. Proper jaw relationship in the anteroposterior, transverse and vertical

dimensions.

3. Alveolar processes that are as large as possible and of the proper

configuration (the ideal shape of the alveolar process is a broad U-shaped

ridge with vertical components as parallel as possible).

4. No bony or soft tissue protuberances or undercuts.

5. Adequate attached keratinized mucosa in the primary denture bearing

area.

6. Adequate vestibular depth.

7. Have no muscle fibers or frena that mobilize the prosthesis.

8. Have no neoplastic lesions.


2

Treatment methods to improve the patient’s denture foundation and ridge

relations are usually either nonsurgical or surgical in nature but can be a

combination of both methods.

PREPROSTHETIC NONSURGICAL METHODS

Dentures can apply excessive forces to the supporting tissues because of

poor fit or occlusal errors. These loads may be localized or generalized and can

cause accelerated bone resorption, inflammation, and hyperplasia. The latter

soft tissue conditions must be treated before denture construction and can often

be improved significantly by nonsurgical procedures.

Preprosthetic nonsurgical methods include:

1. Managing traumatized tissues.

2. Occlusal correction of old prostheses.

3. Good nutrition.

4. Conditioning the patient's musculature.

Managing traumatized tissues.

Rest for the denture-supporting tissues can be achieved by removal of the

dentures from the mouth for an extended period or the use of temporary soft

liners inside the old dentures. Both procedures allow deformed tissue of the

residual ridges to return to normal form.

Clinical reports and experience also support the merits of regular finger or

toothbrush massage of denture-bearing mucosa after denture removal,

especially of those areas that appear edematous and enlarged. This usually can

be readily achieved by removing the dentures for 48 to 72 hours before the

impressions are made for the construction of new dentures. Many dentures fail


3

because the impressions or registrations of the relations are made when the

tissues are distorted by the old dentures.

The temporary soft liners which also-called “tissue conditioning materials”

provide an interim cushioning stage and allow the tissues to recover their

unstressed shape. Their softness is maintained for several days while the tissues

recover, and they have been widely used in dentistry for many years. They offer

expanded scope for short-term resolution of patients’ problems in removable

prosthodontics.

Occlusal correction of the old prostheses.

It has been demonstrated that tissue abuse caused by improper occlusion

can be corrected by (1) withholding the faulty dentures from the patient, (2)

adjusting/correcting the occlusion and refitting the denture by means of a tissue

conditioner, and (3) substituting properly made dentures once the denture-

bearing tissues have recovered.

An attempt should first be made to restore an optimal vertical dimension of

occlusion to the dentures presently worn by the patient with an interim resilient

lining material. This step enables the dentist to predict the amount of vertical

dimension. The tissue treatment material also permits some movement of the

denture base, so its position becomes compatible with the existing occlusion, in

addition to allowing the displaced tissues to recover their original form.

Consequently, ridge relations are improved, and this improvement facilitates

the dentist’s eventual relation registration procedures.

Good Nutrition.

A good nutritional program must be emphasized for each edentulous

patient. This program is especially important for the geriatric patient whose

metabolic and masticatory efficiency may be compromised.


4

Conditioning of the Patient’s Musculature.

The use of jaw exercises can permit relaxation of the muscles of

mastication and strengthen their coordination and help prepare the patient

psychologically for the prosthetic service. If at the initial appointment the

dentist observes that the patient responds with difficulty to instructions for

relaxation and coordinated mandibular movement, a program of mandibular

exercises may be prescribed. Clinical experience indicates that such a program

may be beneficial and the subsequent registration of jaw relations facilitated.

PREPROSTHETIC SURGICAL METHODS

Infrequently, certain conditions of the denture-bearing tissues require

surgical interventions. These conditions may be the result of unfavorable

morphological variations of the denture-bearing area, or more commonly, they

result from long-term wear of ill-fitting dentures. It must be emphasized that

these interventions are infrequently mandatory. It is often far easier to

accommodate the morphological conditions by making alterations in the

prosthetic techniques and materials used than to subject the patient to a surgical

intervention.

Objectives of preprosthetic surgical prescriptions are:

1. Correcting conditions that preclude optimal prosthetic function.

2. Enlargement of denture-bearing areas.

3. Provision for placing tooth root analogues by means of osseointegrated

dental implants.


5

Surgical correction of conditions that preclude optimal prosthetic

function.

Hyperplastic Ridge, Epulis Fissuratum, and Papillomatosis

The mobile tissues (e.g., a hyperplastic ridge) that interfere with optimal

seating of the denture, localized enlargement of peripheral tissues (an epulis),

or tissues that readily harbor microorganisms (a papillomatosis) are not

conducive to firm, healthy foundations for complete dentures. Whenever

possible, these tissues should be rested, massaged, or treated with an antifungal

agent before their surgical excision. This often results in a considerable

reduction in the edema, making the surgical procedure simpler and less

extensive. Healing is faster, scarring reduced, patient comfort improved, and a

better prosthodontic result achieved. If the patient’s health or a personal choice

precludes surgical intervention, then the impression technique and design of the

denture base have to be modified to accommodate the mobile tissue and

minimize its distortion.

Frenular Attachments and Pendulous Maxillary Tuberosities

If the frenum is close to the crest of the bony ridge, it may be difficult to

obtain the ideal extension and border of the flange of the denture. The

frenectomy can be carried out either before prosthetic treatment is begun or at

the time of denture insertion when the new prosthesis can act as a surgical


6

template. The former is preferred because the patient will not have to contend

with postoperative discomfort along with adjustment to the dentures.

Pendulous fibrous maxillary tuberosities are frequently encountered. They

occur unilaterally or bilaterally and may interfere with denture construction by

excessive encroachment on or obliteration of the interarch space. Surgical

excision is the treatment of choice, but occasionally maxillary bone must be

removed.

Bony Prominences, Undercuts, Spiny Ridges, and Tori

Exostoses may occur on both jaws but are more frequent on the buccal

sides of the posterior maxillary segments. They may create discomfort if

covered by a denture and usually are excised. It must be emphasized that

routine excision of all mandibular exostoses is rarely recommended. Frequently

the denture can be easily relieved to accommodate the exostosis, or a so-called

permanent soft liner can be used.

Maxillary tori are rarely removed because satisfactory dentures can be

made over most of them by careful relief of the palatal denture-base material.

Sometimes the genial tubercles are extremely prominent as a result of

advanced ridge reduction in the anterior part of the body of the mandible. If the

activity of the genioglossus muscle has a tendency to displace the lower denture


7

or if the mucosa over the tubercle cannot tolerate the pressure or contact of the

denture flange in this area, then it may have to be removed and the

genioglossus muscle detached.

Residual alveolar ridge undercuts are rarely excised as a routine part of

improving a patient’s denture foundations because considerable evidence exists

that any residual ridge surgery causes excessive bone resorption. Moreover, a

path of insertion and withdrawal of the prosthesis can be readily determined

together with careful adjustment of a denture flange, which enables the dentist

to use the undercuts for extra stability. Alternatively, one undercut area can be

relieved in the denture to permit engagement of the remaining undercut area for

retentive purposes.

Discrepancies in jaw size relationships

The patient with prognathism frequently places considerable stress and

unfavorable leverages on the maxillary basal seat under a complete denture.

This may cause excessive reduction of the maxillary residual ridge. A

mandibular osteotomy in these cases can create a more favorable arch

alignment and improve the appearance as well.

Pressure on the Mental Foramen

If bone resorption in the mandible has been extreme, the mental foramen

may open near or directly at the crest of the residual bony process. Pressure


8

from the denture on the mental nerve exiting the foramen and over this sharp

bony edge will cause pain and sometimes paresthesia in its area of distribution.

Pain also can occur in the oral mucosa overlying the sharp bone as it is pinched

by the denture. The most suitable way of managing this is to adjust the denture

to relieve the pressure. However, in rare instances, it may be necessary to

reposition the mental foramen more inferiorly.

Ridge Parallelism

A lack of parallelism between the maxillary and mandibular ridges can be

encountered and, on occasion, may require surgical correction. This lack of

parallelism may be caused by failure to trim the tuberosity and ridge behind the

last maxillary tooth when it was removed or may be the result of jaw defects,

unequal ridge reduction, or abnormalities of growth and development. Most

clinicians favor parallel ridges for their denture foundations because the

resultant forces generated are directed in a way that tends to seat the dentures

rather than dislodge them. Also, the height of the occlusal plane of the upper

denture can be elevated posteriorly to improve the denture esthetically.

Virtually all the surgical procedures described necessitate the use of a

surgical template. The patient’s old dentures usually can be modified and

lined with a tissue conditioner to function as such. In fact, clinical experience

indicates that careful prosthetic technique and design frequently can preclude a

surgical intervention. The obvious exception to this observation is the use of

implants, which have significantly improved treatment outcomes for patients

with a maladaptive denture experience.

Enlargement of denture-bearing areas

For many years, heavily resorbed alveolar ridges and the associated

shallow sulci were considered major causes of difficulties in the use of

complete dentures.


9

Over the years, an expanding interest in preprosthetic surgery led to the

development of techniques designed to enlarge the denture-bearing areas. These

involved either extending the sulcus (vestibuloplasty) or enlarging the ridge by

bone grafting. The former technique also sometimes involved the use of skin or

mucosal grafts to maintain the patency of the newly acquired sulcular depth.

Vestibuloplasty

The reduction of alveolar ridge size is frequently accompanied by an

apparent encroachment of muscle attachments on the crest of the ridge. These

so-called high (mandibular) or low (maxillary) attachments serve to reduce the

available denture-bearing area and to undermine denture stability.

The anterior part of the body of the mandible is the site most frequently

involved with the labial sulcus virtually obliterated, and the mentalis muscle

attachments appearing to “migrate” to the crest of the residual ridge. Myoplasty

accompanied by sulcus deepening was proposed as a method of extending the

denture-bearing area and improving denture retention. The operation involves

detaching the origins of muscles on either the labial or lingual, or both, sides of

the edentulous residual ridges. This allows for an increase in the vertical

extensions of the denture flanges.

The use of customized acrylic resin templates or the modified previous

denture to support vestibuloplasty in the mandible is essential. These templates

may have to be fastened to the mandible with circummandibular wires for 1

week or longer. This protocol ensures the patency of most of the recovered

vestibular depth.

All of these preprosthetic surgical procedures have now been virtually

eclipsed by routine implant placement and advances in bone grafting combined

with implant prescriptions.


10

Ridge Augmentation

For many years oral and maxillofacial surgeons have attempted to restore

advanced jaw residual ridge resorption by placing onlay bone grafts, or

inserting synthetic materials. These procedures are rarely preferable alternatives

to implant placement, principally because of their surgically extensive nature

and uncertain outcomes and benefits. Nevertheless, current surgical

developments and reports suggest promise for combining some types of grafts

with implants to rectify serious residual ridge resorption problems, particularly

in the maxillae.

Replacement of tooth roots with osseointegrated dental implants

Three decades of extensive and rigorous studies about treatment outcomes

with osseointegration have provided evidence to support this type of treatment.

The denture-bearing area is no longer the prime or exclusive source of support,

and the focus has now shifted to an endosseous one. While dental implant

treatment is not limitless in its applicability, it has greatly extended the range

and quality of prosthodontic interventions.

For the edentulous patient this often means the option of treatment with

implant-stabilized fixed or removable prostheses using various numbers and

locations of dental implant bodies. The combination of osseointegrated implants

and complete denture fabrication skills have now expanded patient

management scope and enhanced favorable outcomes in a very compelling

manner.

The end


1

PROSTHODONTICS


TMJ ANATOMY

AND MANDIBULAR MOVEMENTS

Temporomandibular joint (TMJ) is the articulation of the condylar

process of the mandible and the intraarticular disk with the mandibular fossa of

the squamous portion of the temporal bone. Movement in the upper joint

compartment is mostly translational, whereas that in the lower joint

compartment is mostly rotational. The joint connects the mandibular condyle to

the articular fossa of the temporal bone with the temporomandibular disk

interposed.

The temporomandibular joint is a bilateral, synovial, ginglymoarthrodial

joint. Bilateral meaning a single bone crosses the midline and the joints on

either side of the body and work in synchronization with each other. Synovial

meaning it contains synovial fluid. Ginglymoarthrodial (Ginglymus meaning

a hinge joint and arthrodia meaning a joint permitting gliding motion. Hence, it

permits both hinge and gliding movements).

The TMJ consists of the following parts:

1. The mandibular or glenoid fossa.

2. The condyle or head of the mandible.

3. The articular disc or Meniscus which is found between the condyle

and the glenoid fossa. It divides the synovial joint or TMJ into upper

(superior) and lower (inferior) compartment.

4. Synovial cavity.

5. Joint capsule and mandibular ligaments.


2

The joint has a capsule and an articulating disc. The glenoid fossa of the

temporal bone and the condyle of the mandible form the articulating surfaces.

The joint cavity is divided into the upper and lower compartments by the

articular disc. Hence, the joint exhibits two types of movements namely,

rotation (hinge movement) and translation (gliding movement). The upper

compartment shows anteroposterior gliding movement. When this movement

takes place, the condyle and the disc move as a single unit against the glenoid

fossa. The lower compartment shows hinge movement. During hinge

movement the condyle moves against the articular disc and the glenoid fossa,

which together act as a single unit. The structure of the temporomandibular

joint is complex and is capable of functional and parafunctional movements.

The TMJ is enclosed in a capsule that is attached at the borders of the

articulating surfaces of the mandibular fossa and eminence of the temporal

bone and to the neck of the mandible. The anterolateral side of the capsule may

be thickened to form a band referred to as the temporomandibular ligament.

Accessory ligaments of the TMJ, including the stylomandibular and

sphenomandibular ligaments, are considered a part of the masticatory


3

apparatus. The function of the ligaments is to stabilize the joints by limiting the

movements, ligaments do not stretch but it could be elongated and the

elongation of the ligament could compromise normal joint function.

DETERMINANTS OF MANDIBULAR MOVEMENTS

The major factors that determine the mandibular movements in general are:

• Condylar guidance

• Incisal guidance

• Neuromuscular factors.

Condylar Guidance (Posterior Determinant)

Condylar guidance can be defined as, “Mandibular guidance generated by

the condyle and articular disc traversing the contour of the glenoid fossa”. It is

nothing but the path of movement taken by the condyle in the glenoid fossa.

The glenoid fossa and the condyle are the articulating surfaces of the

temporomandibular joint. The condyle moves along the surface of glenoid fossa

during mandibular movement. Hence, the surface of the glenoid fossa

determines the path of movement of the condyle. The slope of the glenoid fossa

is not straight, instead it is ‘S’ bend. Hence the condyle also moves along ‘S’

shaped path. This shape of the glenoid fossa, which determines the path of

movement of the condyle, is called the condylar guidance.

Incisal Guidance (Anterior Determinant)

It is defined as “The influence of the contacting surfaces of the mandibular

and maxillary anterior teeth during mandibular movements”. When the

mandible moves forward (protrusion), the incisal edge of the lower anterior

teeth slide along the slope of the lingual surface of the upper anterior teeth

before reaching edge to edge contact. The slopes of the lingual surface of the


4

upper anterior teeth determine the path along which the mandible moves during

protrusive movement. In other words, the lingual surface of the maxillary

anterior guides the mandible during protrusive movement and is called the

Incisal guidance.


5

Neuromuscular Factors

The muscles of mastication are the most important determinants of

mandibular movements. In a normal patient, the muscles function in a

coordinated smooth manner. But when there is hypertrophy or dysfunction of

one group of muscles, the movement of the mandible is uncoordinated and

asymmetrical. Similarly, the tone of the muscle also determines the freedom of

movement. Muscular dysfunction should be evaluated before performing jaw

relation. The muscles that control the movement of the mandible could be

considered in 3 groups:

1. Closing muscles.

The masseter, temporalis and medial pterygoid muscles supply the

power for pulling the mandible against the maxillae (elevating and closing

mandible).

2. Gliding muscles.

The lateral pterygoid muscles connect the mandible to the lateral

pterygoid plate and act to protrude the jaw or to move it laterally (gliding).

3. Opening muscle.

The muscles that depress the mandible (open) consist of four groups,

suprahyoid muscles, infrahyoid muscles, platysma muscles and lateral

pterygoid muscles.

MANDIBULAR AXES

Axis is a line around which a body may rotate or about which a structure

would turn if it could revolve. There are three axes around which the

mandibular movements take place in horizontal, sagittal and frontal planes.

These axes include the followings:


6

1. Hinge axis or transverse horizontal axis:

It is an imaginary line around which the mandible may rotate within the

sagittal plane. Rotation around this axis is seen during protrusive and mouth-

opening movements.

2. Sagittal axis:

It is an imaginary anterioposterior line around which the mandible may

rotate when view in the frontal plane. Rotation around this axis is seen in

association with lateral movements.

3. Vertical axis:

It is an imaginary line around which the mandible may rotate through the

horizontal plane. The mandible rotates around this vertical axis during the

lateral movements.

MANDIBULAR MOVEMENTS

As any other movement in space, complex three dimensional mandibular

movements can be divided into two basic components: translation, in which all

points within a body have identical motion, and rotation, in which the body is

turning about an axis.


7

Every possible three-dimensional movement can be described in terms of

these two components. It is easier to understand mandibular movement when

the components are described as projections in three perpendicular planes:

sagittal, horizontal, and frontal.

Reference Planes:

Horizontal plane is any plane passing through the body at right angles to

both the median and frontal planes, thus dividing the body into upper and

lower parts; in dentistry, the plane passing through a tooth at right angles

to its long axis.


8

Frontal plane is any plane parallel with the long axis of the body and at

right angles to the median plane, thus dividing the body into front and

back parts. So that it called because this plane roughly parallels the

frontal suture of the skull.

Sagittal plane is any vertical plane or section parallel to the median plane

of the body that divides a body into right and left portions.

Mandibular movements can be classified into the followings:

Based on the type of movement:

Hinge movement (opening and closing movement).

Protrusive and Retrusive movement.

Lateral movement.


9

Based on the extent of movement:

Border movements

Functional movements

Parafunctional movements

Border movements

Border movement is the mandibular movement at the limits dictated by

anatomic structures, as viewed in a given plane. As the definition suggests

border movements are recorded in three different planes. A pantograph is

required to record all border movements. The pantograph is an extraoral tracing

device. Posselt in 1952 was the first to describe the border movement. All

possible mandibular movements occur within this limits which are the most

extreme positions to which the mandible is able to move in any direction.

Mandibular movements are limited by TMJs and the ligaments, the

neuromuscular system, and the teeth.

These border movements are measured in all three dimensions (horizontal,

frontal, and sagittal planes). In the sagittal plane, the border movements are

subdivided into:

Anterior border movements: which appear as one arc, the condyles rotate

and translate in its.

Posterior border movements: which appear as two arcs, the condyles

rotate in the opening and closing up to the point of terminal hinge

opening then translate to the point of maximum opening.

In the sagittal plane, the mandibular position in centric occlusion (CO) is

depicted in (1). And centric relation (CR) or the most retruded position (B) in

(2). Rotation, the terminal hinge movement (3) takes place between B and C,

from which the translation phase of the posterior opening occurs to D, the

maximum opening position (4). The most protrusive closure from D ends in E,


10

maximum protrusion with tooth contacts (5) the postural rest position (PR) and

the habitual closure (H) are located well inside the borders.

When we combine the border movements of all the three planes, we get a

three-dimensional space within which mandibular movement is possible. This

three-dimensional limiting space is called the envelope of motion. It was first

described by Posselt in 1952.


11

Functional movements

Functional mandibular movement is defined as all normal, proper, or

characteristic movements of the mandible made during speech, mastication,

yawning, swallowing, and other associated activities. Most functional

movement of the mandible (as occurs during mastication and speech) takes

place inside the physiologic limits established by the teeth, the TMJs, and the

muscles and ligaments of mastication; therefore, these movements are rarely

coincident with border movements.

Parafunctional movements

Parafunctional movements of the mandible may be described as sustained

activities that occur beyond the normal functions of mastication, swallowing,

and speech. There are many forms of parafunctional activities, including

bruxism, clenching, nail biting, and pencil chewing. Parafunction is typically

manifested by long periods of increased muscle contraction and hyperactivity.

The two most common forms of parafunctional activities are bruxism and

clenching.


12

Four mandibular movements of prime importance to complete denture service

are:

1. Hinge like movement used in the opening and closing the mouth for the

introduction of food.

2. A protrusive movement used in the grasping and incision of food.

3. Right or left lateral movements used in the reduction of fibrous as well as other

types of food.

4. Bennett movement which is the bodily side shift of the mandible which may be

recorded in the region of the translating condyle of the non-working side during

the lateral movement.

The end

Date post:	18-Dec-2021
Category:	Documents
Upload:	others
View:	17 times
Download:	0 times

ANATOMICAL LANDMARKS OF MAXILLARY AND MANDIBULAR ...

Documents