Introduction to Occlusion

Abdel Rahman M.A.Demonstrator, Fixed prosthodontic department, Faculty of dental medicine, Al-Azhar University, Cairo, Egypt.

Part 1

Content

• Analysis of Occlusion• TMJ• Occlusion Musculature• Static Occlusion• Dynamic Occlusion• Ideal Occlusion • Vertical Dimension

Why occlusion Is important in dental practice ?

• The masticatory system in general consists of three main component: Teeth, periodontal tissues and occlusion or articulatory system.• When we say, “masticatory system," does this mean that this

system is a “true system”?• is a “true system”? By going to the definition of 'system', we

found that it means ‘An assemblage that is connected or interdependent, in order to form complicated unity ‘

PRINCIPLEThe ultimate goal for every patient should be maintainable health for the total masticatory system.

• In other words, any system should have interrelated components, which can’t act individually but with the aid of the other components• Back to the masticatory system we found that the changes

in one component necessarily affect the other components. Therefore, the masticatory system: teeth, occlusion and periodontal tissues are considered as a true system.

Goals of studying occlusion system

• Therefore, the first goal of studying occlusion system is to achieve the concept of complete dentistry

• GOALS FOR COMPLETE DENTISTRY:• Freedom from disease in all masticatory system structures• Maintainable healthy periodontium• Stable TMJs• Stable occlusion• Maintainable healthy teeth• Comfortable function• Optimum esthetics

PRINCIPLE Whether general practitioner or specialist, practicing without a comprehensive understanding of occlusal principles exacts a costly penalty in missed diagnoses, unpredictable treatment results, and lost production time

Design of the masticatory system

PRINCIPLE The design of the masticatory system requires balanced equilibrium of all its parts.

Temporomandibular Joint

Peter E. Dawson

PrincipleAll occlusal analysis starts at the temporo mandibular joints (TMJs).

TMJ Anatomy

The Articulating Surfaces

UNDERSTANDING CONDYLE DISK ALIGNMENT• Medial and lateral distal ligaments • Posterior ligament

• Superior elastic stratum • Superior lateral pterygoid muscle

HOW MUSCLE CONTROLS DISK ALIGNMENT• Opening • Maximum opening

• Closing • Closed

THE TEMPOROMANDIBULAR LIGAMENT

THE ARTERIOVENOUS SHUNT.

• If the TMJs are not stable, the occlusion will not be stable, so it is a risky proposition to undertake occlusal changes without knowing the condition of the TMJs.

Neuro-muscular control

PrincipleWhen bone and muscle war, muscle never loses. “Harry Sicher”

Masticatory Musculature

• Muscles of mastication• Masseter muscle• Temporalis muscle• Medial pterygoid muscle• Lateral Pterygoid muscle.

• Supra hyoid muscles.• Digastric muscle• Mylohyoid muscle• Geniohyoid muscle.

Coordinated muscle function during jaw opening

Coordinated muscle function during jaw closure

Coordinated muscle function at maximum intercuspation

Disharmony between the occlusion and the TMJs

Incoordinated muscle function

Muscle Response to Occlusal Interference

Muscle Response to Posterior Disclusion

• At the moment of separation of the posteriorteeth, almost all of the elevator muscles shut off. This has three beneficial effects: It greatly reduces the horizontal forces

against the anterior teeth, which are the only teeth in contact duringexcursions.

It reduces the compressive loading forces on the TMJs.

It makes it impossible to overload or wear the posterior teeth, even if the patient bruxes.

Muscle Incoordination as aCausative Factor in Disk Derangements

The ligament must be stretched

The ligament must be torn

The attachment of the ligament must

migrate.

Analysis of occlusion

Static occlusion

• Static occlusion refers to the position of teeth while the mandible is static in position

whether teeth are present “centric occlusion”or absent “centric relation”

Centric Occlusion

• Centric occlusion can be defined as the relation between maxillary and mandibular teeth while the teeth are contacting each other in maximum intercuspation, it’s also called the inter cuspation position (ICP) or the habitual bite.

Centric relation

• Centric relation is the relationship of the mandible to themaxilla when the properly aligned condyle-disk assemblies are in the most superior position against the eminentiae irrespective of vertical dimension or tooth position.

“Peter E.Dawson”• For better understanding Centric relation can be described

in three levels: • Anatomically• Conceptually• Mechanically

• Anatomically

Centric relation describes the relation of the mandible to the maxilla when the discin its normal position, and the condyle is in the most superior ‘upmost’ and mostanterior ’foremost’ position in the glenoid fossa as stated by Okeson’s AAOPguidelines.

• Conceptually

it’s the position of the mandible in the neutral zone between the elevator anddepressor muscles of the mandible.The importance of this concept coming from it gives an introduction to the ideal occlusion at one level.

Peter E.Dawson

• Mechanically

Centric relation describes the part of mandibular movements around a fixed axis.

What is the importance of centric relation ?

Does centric relation is the only relation that is dependable in occlusion ?

• Centric relation is the accepted term for defining the condylar axis position of intact, completely seated, properly aligned condyle-disk assemblies. A TMJ that is structurally deformed with a misaligned or displaced disk cannot be described as in centric relation because it does not fulfill the critical requirement of a properly aligned disk.

• Adapted centric posture is the manageably stable relationship of the mandible to the maxilla that is achieved when deformed TMJs have adapted to a degree that they can comfortably accept firm loading when completely seated at the most superior position against the eminentiae.

• The mandible is in adapted centric posture if five criteria are fulfilled:

1. The condyles are comfortably seated at the highest point against the eminentiae.

2. The medial pole of each condyle is braced by bone. (The disk may be partially interposed.)

3. The inferior lateral pterygoid muscles have released contraction and are passive.

4. The condyle-to-fossa relationship is manageably stable.5. Load testing produces no sign of tension or tenderness in either

TMJ.

So

Where is the difference between the two positions?

• There is no difference in the procedure for determining either centric relation or adapted centric posture. Both should be confirmed by load testing to verify that the joint is completely seated and the lateral pterygoid muscle is released.

• What is different is that a deformed joint that has adapted to a comfortable capacity to accept loading is not as stable as an intact TMJ. So patients should always be advised in advance of any occlusal treatment that there will be a need for periodic occlusal correction to maintain harmony with the changing joint position.

Centric Freedom

Dynamic Occlusion.

• Dynamic occlusion is a term refer to any contacts between teeth while the mandible is moving.

• The mandible has two guidance systems controlling its movement,

the posterior guidancethe anterior guidance.

Posterior guidance

• Posterior guidance is the controlled by the condylar system.• The posterior guidance is not influenced by the presence or

absence of teeth. It’s affected only by the joint compartments.

• Working side.• Non-Working side .• Condylar path.• Condylar angle.• Bennit angle.• Bennit movement.

• Working Condyle.• Non- Working condyle.

Impact of posterior determinant on the occlusal form of restorations

Posterior Determinant Variable Effect on restorations

Inclination of the articular eminence

Steeper Posterior cusps must be taller

Flatter Posterior cusps must be shorter

Medial wall of the glenoid fossa

Allow more lateral translation

Posterior cusp must be shorter

Allow less lateral translation

Posterior cusp may be taller

Anterior guidance

• Wherever the mandibular movements are associated with occlusal interference this is called “Anterior guidance”.• No matter how far posteriorly the tooth is, it’s located

anterior to the condyle.• anterior guidance became more ideally when occurring at

the most anterior teeth as far as possible anteriorly from the TMJ.

• Bilateral balanced occlusion .• Group functional occlusion.• Canine guidance or canine protected occlusion.

• Working side interferences.• Non-Working side

interferences.

Ideal Occlusion

Ideal occlusion

• When defining the ideal occlusion we must consider the ideality at variable levels. Ideal occlusion is defined for:

the tooth level, the articulatory system level and the patient level.

• The tooth level:

Multiple harmonious contactsSimultaneous centric stop No cusp to cusp or cuspal incline contacts. Occlusal contacts directed toward the long axis of the teeth.Smooth shallow guidance.

• The articulatory system level:

Centric occlusion occurs in centric relation.Centric freedom.No posterior interferences in protrusive and lateral

movements.

• The patient level:

The ideal occlusion should fall within the neuromuscular tolerance for the patient throughout life.

Introduction to Occlusion

Abdel Rahman M.A.Demonstrator, Fixed prosthodontic department, Faculty of dental medicine, Al-Azhar University, Cairo, Egypt.

Part 2

Content

• Some clarification about the centric relation.• Vertical Dimension.• Determining Centric Relation or Adapted centric posture.• Verification of Centric Relation.• Recording Centric Relation.

Some Clarification about Centric Relation

PrincipleIf a single concept must be learned about occlusion, that will be the concept of centric relation.

1

32

46

5

1

2

34 5

7

6

Maximum intercuspation

Centric relation

Remember that

• Centric Relation is a bony Not muscle braced position.• Centric relation is a repeatable and reproducible. Why ?• TMJ is a load bearing joint.• In centric relation medial pole rotate while lateral pole translate.• The inferior belly of the lateral pterygoid muscle is almost always

completely in active during clenching in the retrusive position.

Question:Why the condyle doesn’t fit into concave disk as a perfect

ball in socket?

Determining centric relation or adapted centric posture

Principledetermining centric relation is the single most important procedure a dentist should learn. Peter

E.Dawson

• Although centric relation is a routinely used physiologic position, it’s a mistake to use unguided closure to determine the correct centric relation.• This because in an unguided closure the patient has a

tendency to close toward the maximal inter cuspation position.• That is the reason why the mandible should be manipulated

to close in centric relation.

Methods for determining centric relation:• Bilateral manipulation• Anterior bite stops

Directly fabricated Anterior deprogramming deviceThe panky jigThe best-bite applianceThe lucia jig.NTI ( Nociceptive Trigeminal Inhibition)Leaf Gauge

• Bilateral manipulation:• Why use bilateral manipulation?

Kantor ME, Silverman SI, Garfinkel L. Centric-relation recording techniques--a comparative investigation. J Prosthet Dent. 1972 Dec;28(6):593-600.

McKee JR. Comparing condylar position repeatability for standardized versus nonstandardized methods of achieving centric relation. J Prosthet Dent. 1997 Mar;77(3):280-4.

• Bimanual manipulation is the most consistently accurate method and the most repeatable as proved by studies.• Bilateral manipulation is fast , uncomplicated.• Bilateral manipulation provides a quick verification of:

1. The correctness of the position.2. The alignment of the condyle-disk assembly.3. The integrity of the articular surfaces.

Gilboe DB. Centric relation as the treatment position. J Prosthet Dent. 1983 Nov;50(5):685-9.

Procedure:

Step one: Recline the patient all the way back Step two: Stabilize the

head.

Step three: After the head is stabilized, lift the patient’s chin

again to slightly stretch the neck.

Step four: Gently position the four fingers of each hand on

the lower border of the mandible.

Step five: Bring the thumbs together to form a C with each hand.

Ensure that the fingers are properly positioned.

Step six: With a very gentle touch, manipulate the jaw so

it slowly hinges open and closed.

OTHER METHODS FOR DETERMINING CENTRIC RELATION OR ADAPTED CENTRIC POSTURE

• Anterior Bite Stops• The value of anterior bite stops is primarily in their usefulness as

muscle deprogrammers. They do this by separating the posterior teeth so deflective posterior interferences cannot influence the musculature to displace the condyles.

• All of these appliances require a bite material for the posterior teeth after centric relation has been achieved.

Types of Anterior Bite Stops

Directly Fabricated Anterior Deprogramming Device

The Pankey Jig

The Best-bite Appliance The Lucia Jig

Leaf guage

• Disadvantages of anterior bite stop:• Am improperly made anterior stop can displace the condyle

distally.

Verification of Centric relation

PrincipleIf the temporomandibular joints (TMJs) are not completely comfortable when firmly loaded, they are not in centric relation.

Peter E.Dawson

• One of the most significant procedures in the diagnostic process is the verification of centric relation through load testing of the TMJ.

WHY?

• Load testing is not only an essential step in the verification of centric relation, it is a critical step in the differential diagnosis of intracapsular TMJ disorders.• One of the most practical uses for load testing is that it is a

fast, simple, and safe procedure for determining whether an intracapsular structural disorder is or is not a source of orofacial pain.

• To understand this concept we should re mention that: If the TMJs are in centric relation, all forces go through avascular non innervated structures, and the inferior lateral pterygoid muscles have completely released their contraction.

--

• Orofacial pain can be the result of either:

• Occluso-muscle dysfunction.

• Intracapsular disorder.

Procedure:

• PROPER LOAD TESTING MUST BE DONE IN INCREMENTS.

Gentle Loading Moderate Loading

Firm Loading

• Response to Gentle Loading can be a sign of:• TMD.• Muscle spasm.

Tip Use the anterior deprogrammer to

differentiate between occluso muscle pain and intra capsular disorder.

• Response to Moderate Loading in usually described in “tension” or “ tenderness” and in most instanced is an indication of muscle bracing rather than intra capsular disorder.

• Response to firm loading is most likely is a response to muscle bracing.

Common Mistakes

• Applying too much pressure soon.• Not applying enough upward loading forces

Recording Centric Relation

PrincipleThe price for inaccurate bite records is wasted time, compromised results, and a lack of predictability.

Peter E.Dawson

• CRITERIA FOR ACCURACY:The bite record must not cause any movement of teeth of

displacement or soft tissue.It must be possible to verify the accuracy of the interocclusal record

in the mouth.The bite record must fit the casts as accurately as it fits the mouthIt must be possible to verify the accuracy of the bite record on the

castThe bite record must not distort during storage or transportation to

the lab.

• Causes of error in recording centric relation:• Improper manipulation of the mandible.• No verification of centric relation.• Use of rubber material for recording the centric relation.• Too deep indentation in the bite record.• Use of soft waxes.• Too shallow indentation.• Use of unstable bite recording material.

Wax bite technique:

Anterior stop technique

Relating casts to the condylar axis

• There is very little, if any, value in studying unmounted casts, because the primary purpose of analyzing diagnostic casts is to observe tooth-to-tooth relationships in centric relation at the correct vertical dimension.• A correct axis allows changes in vertical dimension of

occlusion (VDO) up or down without displacement from centric relation.

• Since it would create a considerable error to open the jaw on one hinge axis (for a bite record) and then close the casts on another hinge axis (on the articulator), the condylar axis must be located on the patient and transferred to the articulator. The facebow is used for this purpose.

Face bow transfer

Vertical dimension

PrincipleThe repetitive contracted length of the elevator muscles determines the vertical dimension of occlusion.

“Peter E.Dawson”

UNDERSTANDING VERTICALDIMENSION• There are four misconceptions about vertical dimension. You

need to know:

1. We determine vertical dimension based on whether the patient is comfortable.

2. Measuring the freeway space is an accurate way to determine the correct vertical dimension of occlusion (VDO).

3. Determining the rest position of the mandible is a key to determining vertical dimension.

4. Lost vertical dimension is a cause of temporomandibular disorders (TMDs).

If altering the VDO does not cause discomfort and does not cause TMDs, why should we even be concerned about the VDO ?

• Answer: We should be concerned because failure to understand the physiology and biomechanics of vertical dimension has led to inappropriate overtreatment and has resulted in iatrogenic damage to dentitions and missed diagnosis of TMD, and because failure to understand the true nature of vertical dimension affects a major amount of the decisions every dentist must make in practice.

The key point to understand vertical dimension• The Key point to understand the concept of vertical dimension is to

understand that teeth continue to erupt through out life by the force of passive eruption.

• This eruptive force continue until it meet resistance

• Usually this resistance coming from contacting the opposing dentition.

• The space through which the eruptive force cause the teeth and the supporting alveolar bone to move with in it is gained and maintained by the contracted length of the elevator muscle fibers.

Vertical dimension of occlusion (VDO)

• Is the vertical position of the mandible in relation to the maxilla when the upper and lower teeth are intercuspated at the most closed position.

• Even though the VDO occurs when the teeth are fully articulated, the teeth are not the determinants of vertical dimension. Rather, their position is determined by the vertical dimension of the space available between the fixed maxilla and the muscle-positioned mandible

• the vertical position of each tooth is adaptable to the space provided, not vice versa, and that the capacity of the teeth to erupt or intrude is present throughout life.

• even severe abrasion of teeth does not cause a loss of vertical dimension.

Vertical dimension at rest (RVD)

• When a muscle is neither hypotonic nor hypertonic, it is said to be “at rest.”

Fact:The rest position is not consistent even in the same patient.

• Attempts to determine a consistent rest position have been pursued using transcutaneous electrical nerve stimulation (TENS).

• However, The muscle contracted position is unrelated to any consistent comparison with the resting musculature, regardless of how resting length is determined.

• The practical approach is to concentrate on accurately recording the VDO and allowing the dimensions of the freeway space to be the natural result of the difference between the optimum length of contracted muscles and the length of the muscles at rest.

Increase or not increase the Vertical dimension ?

• Any disharmony in the system provokes adaptive responses designed to return the system to equilibrium. There is always some price to pay for adaptation, and even though the adaptive process may be beneficial, it is not always predictable.

• Adaptive responses to increased vertical dimension may simply cause the lengthened teeth to intrude into the alveolar bone to regain the original jaw-to jaw relationship, or there may be an attempt to wear away the increased dimension by bruxing.

• and if the added compression of the supporting tissues exceeds their capacity to remodel acceptably, we will see hypermobility of the teeth and a lowered resistance in the periodontal structures.

• if it is not necessary, it is not advisable to disturb the equilibrium in the first place.

• The goal of occlusal therapy is to minimize the requirements for adaptation.

• Unnecessary increases in vertical dimension do the opposite. They increase the requirements for adaptation, and once the adaptive process is in accelerated activity, it is not always completely predictable.

WHEN THE VERTICAL DIMENSIONMUST BE CHANGED.• There are some problems of occlusion that would be very

difficult to solve without increasing the vertical dimension.

Extremely worn occlusion ( Increase VD Vs perform multiple pulp extirpation)

In some aesthetic cases ( increase VD Vs CLS ).Some orthodontic treatment can’t be performed without

temporarily increase the VD

Do all changes in vertical dimension lead to eventual problems in the dentition or its supporting

structures?

• showed that adult orthodontic patients whose vertical dimension had been increased up to 8 mm had reverted to their pretreatment vertical dimension within one year. He also observed that decreases in vertical dimension of up to 7 mm regained the lost vertical dimension within one year!

McAndrews I: Presentation to Florida Prosthodontic Seminar, Miami, Florida 1984. Also personal communication, 2001.

• There is more interesting findings regarding McAndrews observations:

the change back to the original vertical dimension did not adversely affect the corrected arch alignments or the intercuspal relationships.

changes in vertical dimension were the result of alveolar bone remodeling was the observation that the cementoenamel junction of the teeth retained the same relationship to the crest of bone.

• Of great significance in the McAndrews study is the attention paid to achieving holding contacts for all teeth in centric relation.

Conclusion:• What this study seem to indicate is that it is permissible to alter

the vertical dimension when necessary for achieving an improved occlusal relationship as long as all teeth are properly intercuspated at a correct centric relation.

Precaution:• Before increasing any vertical dimension, one should

evaluate the alveolar bone. Dense sclerotic bone with numerous exostoses does not have the same capacity to remodel as alveolar bone with normal trabeculae. Increasing vertical dimension in such unchangeable bone is contraindicated.