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INTRODUCTION,
CLASSIFICATION & BIOMECHANICS
of PARTIALLY
EDENTULOUS arches
DR. ANUSHA SINGH
CONTENTS:
Indication against use of FPD Indication for RPD Parts of RPD Steps in the treatment of an RPD patient Advantages and disadvantages of RPD Requirements of an acceptable classification Classifications mechanical principles applicable in removable
prosthodontics forces acting on partial dentured Causes of failure of RPD Conclusion References
The art and science of replacing absent body parts is termed prosthetics , and any artificial part is called a prosthesis.
The term prosthesis and appliance are often confused & interchangeable.
Appliance is correctly used only to refer to a device worn by a patient in the course of treatment, such as a orthodontic appliance, surgical appliance.
PROSTHODONTICS
FIXED
REMOVABLE MAXILLOFACIAL
complete Partial
extracoronal Intacoronal
REMOVABLE PARTIAL DENTURE
‘‘ Any prosthesis that replaces some teeth in a partially dentate arch . It can be removed from mouth and placed at will.’
- GPT 8
INDICATIONS AGAINST USE OF FIXED PARTIAL DENTURES
Youth Patient large dental pulps and lack of clinical crown height.
Advanced Age Reduced life expectancy and Frequently failing general health
contraindicate the expensive and tedious dental procedures
Long edentulous span
Excessive loss of bone As they are unable to support a fixed prosthesis
and it is necessary to provide support for the lips or cheek or to obtain proper tooth position for the artificial tooth
INDICATIONS FOR RPD
Long edentulous span :contraindicates use of fixed partial denture
No abutment tooth posterior to edentulous space
Reduced periodontal support of remaining teeth: loss of bony support so unable to support a fixed prosthesis.
Need for cross-arch stabilization: The fixed partial denture can provide excellent an anterioposterior stabilization but limited lateral, or buccolingual, stabilization.
Physical or emotional problem of the patient :The lengthy preparation and construction for fpd can be tiring
Esthetics of primary concern in replacement of multiple missing anterior teeth :Three-dimensional denture tooth on a denture base may have a more lifelike appearance than some pontics
After recent extraction : teeth immediately following extraction are replaced with temporary removable partial dentures that can be relined as resorption occurs.
Patient desire :To avoid operative procedures on sound, healthy teeth and for eco nomic reasons.
ADVANTAGES OF RPD Does not sacrifice sound healthy tooth Economic
Easier to repair
A properly designed partial denture will assist in support of existing teeth
help to balance bite. This means better chewing and a healthier jaw joint.
Add support to the cheeks & lips.
existing natural teeth extracted for any reason, new teeth can be added
DISADVANTAGES OF RPD Low patient acceptance.
The clasps sometimes show when the patient smiles.
The bar across the palate interferes
with taste. It may feel bulky and may cause the patient to gag at first.
food collects under it during eating. It should be removed from the mouth and cleaned after every meal and at night.
As the partial is repeatedly taken in and out, it can wear anchor teeth and loosen them.
Caries may develop under clasp component especially if patient fails to keep the prosthesis and abutment clean.
PARTS OF A REMOVABLE PARTIAL DENTURE
The components of a removable partial denture are:
1. Major connector2. Minor connector3. Rest4. Direct retainer5. Indirect retainer6. Denture base7. Artificial tooth replacement
MAJOR CONNECTOR Def: The major connectors connect the parts of
the prosthesis located on one side of the arch with those on the opposite side. All other parts of the partial denture are attached to it either directly or indirectly.
Properties: Be rigid Provide vertical support and protect the soft
tissues Provide a means of obtaining indirect retention
where indicated
MINOR CONNECTOR
Def: The connecting link between the major
connector or base of a rpd and the other units of the prosthesis, such as clasp assembly, indirect retainers, occlusal rests, or cingulum rests.
Functions : To transfer functional stress to the abutment
teeth. To transfer the effect of the retainers, rests,
and the stabilizing components to the rest of the denture.
REST A rest is a rigid extension of a partial denture that
contacts a remaining tooth (or teeth) to dissipate functional forces.
DIRECT RETAINER
A clasp or attachment placed on an
abutment tooth for the purpose of holding a removable denture in position.
INDIRECT RETAINER
A part of RPD which assists the direct
retainers in preventing displacement of distal extension denture bases by functioning through lever action on the opposite side of the fulcum line.
DENTURE BASE AND TOOTH REPLACEMENTS
Denture base is the part of the denture that forms the tissue surface of the denture over the edentulous area.
o helps to distribute the forces acting on the denture over the entire residual ridge.
o It holds the tooth replacements in position.
Tooth replacements reproduce the contour and function of the missing teeth.
PARTIAL DENTURE SERVICE DIVIDED INTO SIX PHASES
first phase patient education.
second phase diagnosis, treatment planning, design of the partial denture framework, treatment sequencing, and execution of mouth preparations.
third phase provision of adequate support for the distal extension denture base.
fourth phase establishment and verification of harmonious occlusion
fifth phase involves initial placement procedures and a review of instructions given the patient to optimally maintain oral structures and the provided restorations.
sixth phase follow-up services by the dentist through recall appointments for periodic evaluation of the responses of oral tissue to restorations and of the acceptance of the restorations by the patient.
FIRST PHASE: Patient education
"The process of informing a patient about a health matter to secure informed consent, patient cooperation, and a high level of patient compliance.“
give written suggestions to reinforce the oral presentations.
SECOND PHASE: diagnosis , treatment planning n mouth prep.
thorough medical and dental histories.
The complete oral examination including both clinical and radiographic interpretation
Evaluation of the occlusal plane, the arch form, and the occlusal relations of the remaining teeth accomplished by clinical visual evaluation and diagnostic mounting.
The surveyor is instrumental in diagnosing and guiding the appropriate tooth preparation and verifying mouth preparation
THIRD PHASE: provision of support for distal extension
primary supporting area should be recorded or related under some loading so that the base may be made to fit the form of the ridge when under function.
distal extension base must be made as equal to and compatible with the tooth support as possible.
FOURTH PHASE:
For the distal extension base, however, jaw relation records should be made only after verifying the fit of the framework to the abutment teeth and opposing occlusion
FIFTH PHASE :
occurs when the patient is given possession of the removable prosthesis.
occlusal harmony be ensured
the processed bases must be reasonably perfected to fit the basal seats.
ascertained that the patient understands the suggestions and recommendations given by the dentist
SIXTH PHASE: Periodic recall
Periodic re-evaluation of the patient is critical .
These examinations must monitor the condition of the oral tissue, the response to the tooth restorations, the prosthesis, the patient's acceptance, and the patient's commitment to maintain oral hygiene.
6-month recall period is adequate for most patients,
CLASSIFICATION
Need for classification:
Formulate a good treatment plan
Anticipate difficulties for the design
Communication
Designing according to occlusal load
REQUIREMENTS
1. Allow visualization of the type of
partially edentulous arch being
considered
2. Permit differentiation between tooth-
supported and tissue-supported partial
dentures
3. Serve as a guide to the type of design to
be used
4. Be universally acceptable
CUMMER’S CLASSIFICATION
Proposed by Cummer in 1920
First professionally recognized
classification
Based upon choice of number and position
of direct retainer
CLASS I
Partially dentulous arch in which two
diagonally opposite teeth are chosen as
abutment for direct retainers with an
indirect retainer as auxillary attachment
CLASS II Partially dentulous arch in which two
diametrically opposite teeth are chosen as
abutments for attachment of direct
retainer with an indirect retainer as
auxillary attachment
CLASS III Partially dentulous arch in which one or
more teeth on the same side are chosen
as abutments for attachment of direct
retainer with or without indirect retainer
CLASS IV Partially dentulous arch in which three or
more teeth are chosen as abutments for
attachment of direct retainer without use
of indirect retainer
KENNEDY CLASSIFICATION
Dr.Edward Kennedy (1925)
Most widely used
Original classification contains 4 classes
based on relationship of edentulous spaces
to abutment teeth
Class I
Bilateral edentulous areas located
posterior to the remaining natural teeth
(most common)
CLASS I I
Unilateral edentulous area located
posterior to the remaining natural teeth
CLASS III
Unilateral edentulous area with natural
teeth both anterior and posterior to it
CLASS IV
Single,bilateral edentulous area located
anterior to the remaining natural teeth
(least common)
Dr. O.C. Applegate (1960) modified Kennedy classification by including 2 more classes:
CLASSV Edentulous area bounded anteriorly and
posteriorly by natural teeth but in which anterior abutment (lateral incisor)is not suitable for support
CLASS VI Teeth adjacent to the space are capable of
total support of required prosthesis
APPLEGATES RULES RULE 1 Classification should follow rather than
precede any extractions of teeth that might alter the original classification.
RULE 2 If a third molar is missing and not to be
replaced, it is not considered in the classification.
RULE 3 If a third molar is present and is to be used
as an abutment, it is considered in the classification.
RULE 4 If a second molar is missing and is not to be
replaced, it is not considered in the classification .
RULE 5 The most posterior edentulous area/areas
always determine the classification.
RULE 6 Edentulous areas other than those determining
the classification are referred to as modifications and are designated by their number.
RULE 7 The extent of the modification is not
considered, only the number of additional edentulous areas.
RULE 8 There can be no modification areas in Class IV
arches.
BAILYN’S CLASSIFICATIONProposed by Bailyn Based on whether the prosthesis is tooth-
borne, tissue-borne ,or a combination of the two.
RPD
Saddle areas anterior Saddle areas posterior
to First premolar to canine
ANTERIOR(A) POSTERIOR(P)
SUB-DIVISIONS:
CLASS I :Bounded Saddle(not more than three teeth missing. Tooth-supported
CLASS II: Free end saddle(there is no distal abutment tooth). Tooth Tissue-supported
CLASS III: Bounded saddle (more than three teeth missing ). Tooth Tissue-supported
MAUK’S CLASSIFICATION By Mauk in 1942
Based on : - number and position of the
remaining teeth - number ,length and position of
the spaces
CLASS IBilateral space with no teeth posterior to it
CLASS II Bilateral
space with teeth
present posterior to one
space
CLASS IIIBilateral space with teeth present posterior to both spaces
CLASS
IV Unilateral
posterior space with or
without teeth
posterior to it
CLASS VAnterior space withUnbroken posteriorarch
CLASS VI
Irregular spaces around
the arch
BECKETT’S SYSTEM
Proposed by Beckett in 1953
3 classes
Based on whether the denture base is tooth-borne, tissue-borne or a combination of the two
Widely used in Australia
CLASSI Saddles(denture bases ) which are tooth-borne
CLASS 2 saddles(denture bases)
which are mucosa-borne
CLASS 3inadequate abutments and mucosa to support the saddle
FRIEDMAN’S SYSTEM
Introduced by Friedman in 1953
Based on three segments types : ‘A’ Anterior space ‘B’ Bounded posterior
space ‘C’ Cantilever
‘A’ anterior space
‘B’ bounded posterior
space
‘C’ CantileverPosterior free –end space
‘C-A-B’space
CRADDOCK CLASSIFICATION
By Craddock in 1954
CLASSI : saddles supported on both sides by substantial abutment teeth
CLASSII: vertical biting forces applied to denture resisted entirely by soft tissues
CLASSIII: tooth –supported at only one end of the saddle
SKINNER’S SYSTEM
Given by C.N Skinner in 1957
Based upon the relationship of the abutment teeth to the supporting residual alveolar ridge
Classified into 5 classes
CLASSI Teeth present both anterior and posterior to denture base
CLASS II RPDs –teeth are
posterior to
denture base
CLASS IIIabutment teeth are related anterior to denture base
CLASS IV denture base both
anterior and posterior
to remaining teeth
CLASS V abutment teeth are unilateral to denture base
WATT etal CLASSIFICATION IN 1958
Based on type of support derived1. Entirely tooth-borne: denture rests on
abutment teeth2. Entirely tissue-borne: denture rests on soft
tissue3. Partially tooth-borne and Partially tissue-
borne: rest both on tissue and teeth
APPLEGATE-KENNEDY SYSTEM
By O.C Applegate in 1960
Is a modification of Kennedy classification
Based on : - ability of boundary teeth to supply
abutment facilities for the partial denture -the location of the edentulous spaces in
relation to the teeth which remain
CLASS I All remaining teeth are anterior to bilateral
edentulous space Most frequently occurring Mandible(highest incidence)
CLASS II Remaining teeth of either right or left side are
anterior to unilateral edentulous ridge
CLASS IIIEdentulous space bounded by teeth both
anteriorly and posteriorly
CLASS IV Edentulous space lies anterior to the remaining
teeth which bound it both to right and left of median line
CLASS V -Edentulous space bounded anteriorly and
posteriorly by teeth but the anterior boundary tooth not
suitable for abutment service-Mostly in maxillary arch
CLASSVIEdentulous space bounded anteriorly and
posteriorly by teeth and where boundary teeth are capable of
total support
SWENSON CLASSIFICATION
Proposed by Swenson and Terkla
4 classes based on relationship of edentulous spaces to abutment
CLASS IArch with one free end denture base
CLASS II arch
with two free end
denture base
CLASS IIIEdentulous space posteriorly on one or both sides but with teeth present anteriorly and posteriorly to each space
CLASS IV anterior
edentulous space with 5 or
more anterior teeth
missing
COSTA’S CLASSIFICATION By Eugene Costa in 1974 (Romania)
Based on describing the partially edentulous spaces
Terminologies used Anterior- edentulous space in anterior dental
arch Lateral- edentulous space bounded both
mesially and distally by remaining teeth Terminal- edentulous space not bounded distally by remaining teeth Spaces identified starting from right to left
‘A’ Anterior
‘L’ Lateral
‘T’ Terminal
OSBORNE-LAMMIE system
Proposed in 1974
-CLASS I: mucosa-borne-CLASSII: tooth-borne-CLASSIII: combination of I & II
WILD’S CLASIFICATION 3 classes: CLASS I –Interruption of dental arch(bounded)
CLASSII-Shortening of dental arch(free end)
CLASS III-Combination of I & II
Not well known in English literature
MC GARRY CLASSIFICATION
Developed by The American College of
Prosthodontists(ACP) in 2002 ,McGarry et al
Based on diagnostic finding and treatment planning
Class I This class is characterized by ideal or
minimal compromise in the location and
extent of edentulous area (which is
confined to a single arch), abutment
conditions, occlusal characteristics, and
residual ridge conditions.
Class II This class is characterized by moderately
compromised location and extent of edentulous
areas in both arches, abutment conditions
requiring localized adjunctive therapy, occlusal
characteristics requiring localized adjunctive
therapy, and residual ridge conditions.
Class III This class is characterized by substantially
compromised location and extent of edentulous
areas in both arches, abutment condition requiring
substantial localized adjunctive therapy, occlusal
characteristics requiring reestablishment of the
entire occlusion without a change in the occlusal
vertical dimension, and residual ridge condition.
Class IV This class is characterized by severely
compromised location and extent of edentulous
areas with guarded prognosis, abutments requiring
extensive therapy, occlusion characteristics
requiring reestablishment of the occlusion with a
change in the occlusal vertical dimension, and
residual ridge conditions.
20.ICKClassification System partially edentulous arches incorporating
implants placed or to be placed in the edentulous spaces for an RPD
The classification begins with the phrase "Implant-Corrected Kennedy (class)," followed by the description of the classification. It can be abbreviated as :
(i) ICK I, for Kennedy class I situations,(ii) ICK II, for Kennedy class II situations,(iii) ICK III, for Kennedy class III situations, and(iv) ICK IV, for Kennedy class IV situations.
Sulieman S. Al-Johany, & Carl Andres , 2008
BIOMECHANICAL CONSIDERATIONS
Biomechanics basically deals with application of mechanical principles to biological tissues.
designing an RPD should be based on thorough understanding of the various forces that will act on RPD : direction and magnitude of these forces,
one can select the components of the RPD and position them to counteract, control or minimize these stresses, without compromising the health.
An understanding of simple machines should enhance our rationalization of the design of R.P.D’s to accomplish the objective to preserve oral structures.
Machines can be divided into 2 general categories: simple and complex.
The six simple machines are: lever, wedge, screw, wheel and axle, pulley and inclined plane.
‘lever’ and ‘inclined plane’ deserve most of our attention in designing a R.P.D.
Mechanical principles applicable in Removable
Prosthodontics
Lever principle
Inclined plane
Snowshoe principle
L beam effect
Lever: A simple machine consisting of a rigid bar pivoted on a fixed point and used to transmit force, as in raising or moving a weight at one end by pushing down on the other.
The support point of the lever is called the fulcrum,
Fulcrum line of a removable partial denture: (GPT-8): a theoretical line around which a removable partial denture tends to rotate
Three classes of levers (based on location of fulcrum, resistance and direction of effort (force).
Class IClass IIClass III
Class I lever
Fulcrum lies in the centre, Resistance is at one end and force at the other.
This type of lever can occur in patients with distal extension partial dentures.
The Direct retainer will be - Fulcrum,
Effort end lies on the point- Area where the artificial teeth are located
Load is the region of the Anterior end of the major connector.
Using AN ADDITIONAL REST (INDIRECT RETAINER) TO SHIFT THE FULCRUM LINE PREVENTS LEVER ACTION IN THESE DENTURES.
A cantilever is a beam supported at only one end and can act as a first class lever. A cantilever design should be avoided.
When force is directed against unsupported beam, cantilever can act as a first class lever.
Mechanical advantage is in favour of effort arm
Cast circumferential direct retainer engages mesiobuccal undercut and is supported by disto occlusal rest. If rigidly attached to abutment it may impart detrimental first class lever force to abutment
Mesial rest concept for distal extension removable partial denture
Distal occlusal rest: Gingival extremity of denture base adjacent to posterior abutment tends to move in an arc towards the tooth
Mesial rest Mesial rest is to alter the fulcrum
position and the resultant clasp movement,
disallowing harmful engagement of the abutment tooth
Bar type of retainer, minor connector contacting guiding plane on distal surface of premolar, n mesio occlusal rest used to reduce cantilever force when denture rotates towards residual ridge
Tapered wrought wire retentive arm,minor connector contacting guiding plane on the distal surface of premolar, and mesio occlusal rest.
This design is applicable when distobuccal undercut cannot be found or created or when tissue undercut contraindicates placing bar type retentive arm.
Class II lever
Fulcrum is at one end effort at the opposite end and resistance in the centre.
This type of lever action occurs in indirect retention of a rpd.
when a displacing force tends to lift a denture from one end(effort), the anterior most point of the major connector will act as the axis of rotation (fulcrum), the intermediate zone of the denture, which is lifted by the force, will form the resistance of the lever.
Class III lever
Fulcrum is at one end, resistance at opposite end and effort is in the centre. this type of lever action does not occur in partial dentures.
Inclined plane
Forces against an inclined plane may result in
•deflection of that which is applying the forces or• •may result in movement to the inclined plane,
• neither of these is desirable.
If angle greater than 90 degrees
Forces not along long axis
Slippage of prosthesis away from the abutment
Orthodontic like forces
Abutment severely tilted
Snowshoe principle
This principle is based on distribution of forces to as large an area as possible.
A partial denture should cover maximum area possible within the physiologic limits so as to distribute the forces over a larger area.
L beam effect : This principle is applicable to the antero-
posterior palatal bar or strap major connector.
In this component there are two bars /strap lying perpendicular to each
other. The ant. and post. bars are joined by flat longitudinal elements on each side of the lateral slopes of the palate.
The two bars lying in two different planes produce a structurally strong L beam effect that gives excellent rigidity to the prosthesis.
FORCES ACTING ON PARTIAL DENTURE
Distal extension rpd will rotate when force is directed on the denture base.
Differences in displaceability of the periodontal ligament of the supporting abutment teeth and soft tissue covering the residual ridge permit this rotation.
This rotation is in combination of directions rather than unidirectional
1. Fulcrum on horizontal plane:
Extends through the principle abutments.
Rotational movement of the denture in the sagittal plane.
Greatest in magnitude n most damaging
Force on abutment mesio-apical or disto-apical
(greatest vector in apical direction)
a) Denture base moves away from supporting tissues:
Counteracted by: direct retainer and indirect retainer
b) Denture base moves towards the supporting tissues:
Counteracted by:
• Occlusal rest• Tissues of supporting ridge
2. Fulcrum on the sagittal plane:
• Less in magnitude but can be damaging
extends through the occlusal rest on the terminal abutment and along the crest of the residual ridge on one side of the arch
Counteracted by:
Rigidity of major and minor connector and their ability to resist torque.
Close adaptation of the denture base along the lateral slopes and the buccal slopes of the palate and ridge.
Direct retainer design
3. Fulcrum located in midline just lingual to the anterior teeth (fulcrum is
vertical)
Rotational movement of denture in horizontal plane or flat circular movements of the denture
Counteracted by :
Stabilizing components (reciprocal arm and minor connector)
Rigid major connector
close adaptation of denture base
CAUSES OF FAILURE OF CLASP RETAINED PARTIAL DENTURES:
Diagnosis and treatment planning1. Inadequate diagnosis2. Failure to use a surveyor properly during treatment planningMouth preparation procedures1. Failure to properly sequence mouth preparation procedures2. Inadequate mouth preparations3. Failure to return supporting tissue to optimum health before
impression procedures4. Inadequate impressions of hard and soft tissueDesign of the framework1. Failure to use properly located and sized rests2. Flexible or incorrectly located major and minor connectors3. Incorrect use of clasp designs4. Use of cast clasps that have too little flexibility, are too broad
in tooth coverage, and have too little consideration for esthetics
Laboratory procedures
1. Problems in master cast preparation a. Inaccurate impression b. Poor cast-forming procedures c. Incompatible impression materials and gypsum products
2. Failure to provide the technician with information to enable the technician to execute the design
3. Failure of the technician to follow the design and written instructions
Support for denture bases
1. Inadequate coverage of basal seat tissue
2. Failure to record basal seat tissue in a supporting form
Occlusion
1. Failure to develop a harmonious occlusion
2. Failure to use compatible materials for opposing occlusal surfaces
Patient-dentist relationship
1.Failure of the dentist to provide adequate dental health care information
2. Failure of the dentist to provide recall opportunities on a periodic basis
3. Failure of the patient to exercise a dental health care regimen and respond to recall
CONCLUSION
A removable partial denture designed and fabricated so that it avoids the errors and deficiencies listed is one that proves the partial denture can be made functional, esthetically pleasing, and long lasting without damage to the supporting structures. The success or failure of a partial denture will depend more than anything else upon the design used. The design should conform to the requirement.
BIBLIOGRAPHY1.Mc Cracken;Removable Partial Prosthodontics 11th
edn.
2.Stewart; clinical removable partial prosthodontics 2nd edn.
3. Miller EL: Systems for classifying partially dentulous arches. J Prosthet Dent 1970;24:25-40
.4.Applegate O.C: The Rationale of Partial Denture Choice J Prosthet Dent 1960;10:891-907
5. Skinner C: A classification of removable partial denture based upon the principles of anatomy and physiology. J Prosthet Dent 1959;9:240-246
6. Costa E: A simplified system for identifying partially edentulous dental arches. J Prosthet Dent 1974;32:639-645
7. McGarry TJ, Nimmo A, Skiba JF, et al : Classification system for partial edentulism. J Prosthodont 2002;11:181-193
9 . Avant: universal classification for removable partial denture situations .J prosth dent 1960;16:533
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