Fundamentals Of Occlusion

Fahim VohraSDS 333

Fundamentals Of Fixed ProsthodonticsChap 2, Pg 11-23.

Outline

• Definitions

• Mandibular movement

• Normal vs Pathological Occlusion

• Occlusal Interferences

• Schemes of Occlusion

• Determinants of Occlusion

The Temporo-Mandibular Joints

Why Is Occlusion Important ?• Assist in diagnosis• Planning in restorative care To minimize failure Ensure predictable outcome by minimising loads on teeth

Managing the environment so that we get the minimal amount of surprises (Similar to wearing a car seatbelt), the less the patient has to adapt the better.

Definitions

OCCLUSION

A relationship between the masticatory surfaces of the maxillary and mandibular teeth

The relationship between tooth contacts and mandibular movements

Centric Occlusion

Relationship of the mandible to the maxilla when the teeth are in maximum occlusal contact, irrespective of the position or alignment of the condyle-disk assemblies.

The relationship between the maxilla and mandible when the teeth are maximally meshed with themandible in its most cranial position

Centric Relation

A relationship of the mandible to the skull where the condyle is in an anteriorly, superiorly braced position along the articular eminence of the glenoid fossa, with the articular disc interposed between the Condyle and eminence.

Mandibular Movements

• Mandibular movements occur around three axes

a) Horizontal axis b) Vertical axis c) Sagittal axis

Horizontal Axis (Rotation)

This movement occurs in the sagittal plane when the mandible in centric relation makes a purely rotational opening and closing border movement around the transverse horizontal axis, which extends through both condyles.

Vertical axis (Rotation)

This movement occurs in the horizontal plane when the mandible moves into a lateral excursion. The center for this rotation is a vertical axis extending through the rotating or working-side condyle.

Working side• The side towards which the mandible moves during excursion

OR Mandible moving toward the cheek• Working side condyle pivots within the socket and is better

supported.

Balancing side (Non working side)• The side opposite to the direction in which the mandible

moves OR Mandible moving toward the tongue • Balancing side condyle has a downward orbiting path and is

more prone to injury or damage.

Balancing SideCondyle has downward path

Mandible and TMJ

Working SideCondyle pivots

Movement direction

Sagittal Axis

This movement occurs when mandible moves to working side, the condyle on the opposite side (Non working side) travels forward and downwards simultaneously. When viewed in the frontal plane, this produces a downward arc on the non working side, rotating about an anteroposterior (sagittal) axis passing through the other condyle

Pure Hinge Movement

It occurs as the result of the condyles rotating in the lower compartments of the temporomandibular joints within a 10- to 13-degree arc, which creates a 20- to 25-mm separation of the anterior teeth

• Occurs when the mandible moves forward (protrusion) • Teeth, condyles, and rami, all move in the same direction and

to the same degree. • Occurs within the superior cavity of the joint

Translation Movement

Maximum Opening(Translation & Rotation)

Occurs in the upper compartment of the joint as the mandible drops down farther . Then the horizontal axis of rotation shifts to the area of the mandibular foramen, as the condyles translate forward and downward while continuing to rotate.

Protrusive Position

When the mandible slides forward so that the maxillary and mandibular anterior teeth are in an end-to-end relationship, it is in a protrusive position.

Bennett Movement

It is defined as “the bodily lateral movement/ lateral shift of mandible resulting from movements of condyles along lateral inclines of mandibular fossa during lateral jaw movement”Dr Norman Bennett

Bennett Angle

The angle formed between the sagittal plane and the average path of advancing condyle as viewed in the horizontal plane during lateral mandibular movements. Average range is 7.5-12.8 degree

WSCBSC

Sagittal plane

Bennett angle

Posterior Determinant of OcclusionTMJ – Temporomandibular Joint

Bony surfaces

The dentist has no control on the posterior determinants i.e. TMJ

Anterior Determinant of OcclusionTeeth

• Incisors• Canines• Premolars• Molars

Posterior teeth Provide vertical stops Guide mandible to CO

Anterior teeth Guide mandible in protrusive, retrusive and lateral

excursions

The closer the tooth located to a determinant , more it will be influenced by it.

Anterior Determinants Of Occlusion

Occlusal Interferences

• Interferences are undesirable occlusal contacts that may produce mandibular deviation during closure to maximum intercuspation or may hinder smooth passage to and from the intercuspal position .

• These can be of following types

a) Centricb) Working c) Non working d) Protrusive

Centric Interferences

It is a premature contact that occurs when the mandible closes with the condyles in their optimum position in the glenoid fossae (CR) . It will cause deflection of the mandible in a posterior, anterior, and/or lateral direction

Working Side Interference

It occurs when there is contact between the maxillary and mandibular posterior teeth on the same side of the arches as the direction in which the mandible has moved. If that contact is heavy enough to dis-occlude anterior teeth, it is an interference .

• It is an occlusal contact between maxillary and mandibular teeth on the side of the arches opposite the direction in which the mandible has moved in a lateral excursion .

• It has the potential for damaging the teeth, PDL, MOM and TMJ due to changes in the mandibular leverage, the placement of forces outside the long axes of teeth and disruption of normal muscle function.

Non-Working Side Interference

Protrusive Interference• It is a premature contact occurring between the mesial

aspects of mandibular posterior teeth and the distal aspects of maxillary posterior teeth .

• The proximity of the teeth to the muscles and the oblique forces make them potentially destructive.

• They also interfere with the patient's ability to incise properly

Ideal vs PathologicOcclusion

Ideal Occlusion

An ideal occlusion should provide comfort and function in a predictable way.

1) Ideal occlusion at tooth level Cusp tip to fossa or cusp to marginal ridge contact – i.e no incline

contacts

2) Ideal occlusion at articulatory system level Posterior stability, Anterior guidance, Lack of posterior

interferences.

3) Ideal occlusion at patient level Within the adaptability of the rest of the articulatory system.

Features Of Ideal Occlusion

A) Anterior Guidance:

• In lateral excursions of the mandible, working-side contacts (preferably on the canines) disocclude or separate the nonworking teeth instantly.

• In protrusive excursions, anterior tooth contacts will disocclude the posterior teeth.

Protrusive Guidance

Excursive Guidance

Features Of Ideal OcclusionB) Posterior stability:

Enough posterior teeth in each arch with solid and stable contacts in appropriate positions to evenly distribute loads and to allow the mandible to close in a reproducible CO. Posterior teeth contact more heavily than anterior teeth

It is enhanced by tall cusp – deep fossa Maintains teeth position CO or ICP is easily reproduced Increased masticatory function

Signs of lack of PS, drifting, fremitus, fractured rest, mobility & wear

Lack Of Posterior Stability

C) Absence of posterior interferences

Features Of Ideal Occlusion

The non-working side

D) Centric Occlusion is achieved at centric relation position

E) Occlusal loads are axially transmitted through the teeth

Features Of Ideal Occlusion

Organization Of Occlusion

• There are three recognized concepts that describe how teeth should contact in various mandibular positions

1. Bilateral balanced occlusion2. Unilateral Balanced occlusion (Group function)3. Mutually protected occlusion (Canine protected)

Bilateral Balanced Occlusion

• It dictates that a maximum number of teeth should contact in all excursive positions of the mandible.

• Use for complete denture occlusal scheme as contacts on non-working side prevent tipping of the denture

• Not used for fixed prosthodontics, as very difficult to achieve

Unilateral Balanced Occlusion

• Also called group function• It requires teeth on the working side to be in

contact in lateral excursion and teeth on the non-working side are free of any contact.

• Avoids destructive , oblique forces on the non-working side.

• Prevents wear of maxillary palatal and mandibular buccal cusps

Mutually Protected Occlusion• Also called canine protected occlusion• Anterior teeth overlap prevents the posterior teeth

from making any contact on either the working or the nonworking sides during mandibular excursions.

• Anterior teeth bear all the load and the posterior teeth are dis-occluded during excursions. Protecting the posterior teeth

• In CO, posterior teeth direct forces through their long axis and anterior teeth are slightly in or out of contact. Protecting the anterior teeth.

Guidance

Describes the influenced path the mandible takes as a result of the contacting surfaces of the teeth. Depending on the contact and shape of the teeth they should be in harmony

Protrusive Guidance

Influenced path the mandible takes as aresult of a forward thrust

Lateral Guidance

• Canine• Describes the way in which lateral

excursions are affected by tooth to tooth contacts involving the canine teeth only resulting in disclusion of the posterior teeth

Lateral Guidance

• Group function• When lateral

excursions are guided by more than one tooth other than the canines

Hanau’s Quint

By modifying the following five factors, a scheme of occlusion can be developed that will suit a particular patient best.

1. Condylar guidance 2. Incisal guidance 3. Occlusal plane orientation 4. Compensating curves 5. Height of the Cusp

Except for the condylar guidance, all other factors can be modified during thefabrication of a prosthesis and the anterior guidance plays a predominant role.

Anterior Guidance

• Guidance produced by the teeth themselves and not the temporomandibular joint (can be on any tooth)

• The influence of contacting surfaces of anterior teeth on mandibular movements.

• The influence of contacting surfaces of the guide pin and anterior guide table on articulator movements.

• The fabrication of a relationship of the anterior teeth preventing the posterior tooth contact in all eccentric mandibular movements.

Effects Of Anatomic Determinants Of Occlusion

Protrusive Incisal Path

The track of the incisal edges of the mandibular teeth from maximum intercuspation to edge-to-edge occlusion.

Protrusive Incisal Path Angle

The angle formed by the protrusive incisal path and the horizontal reference plane is the protrusive incisal path inclination. It ranges from 50 – 70 degrees and is often 5-10º steeper than the sagittal condylar guidance.

Incisal Guide Angle

The angle formed with the horizontal plane of occlusion and a line in the sagittal plane between the incisal edges of maxillary & mandibular central incisors when the teeth are in maximum intercuspation.

The angle formed in the sagittal plane between the horizontal plane and the slope of the incisal guide table.

Importance of Anterior Guidance

Opening and closing of the mandible is simply a rotation of the condyles in the articular fossae.

Importance of Anterior Guidance

As anterior guidance is normally steeper than the condylar guidance, the anterior teeth guide the mandible downwards during protrusive or lateral

movement and ..

Importance of Anterior Guidance

(during protrusive movement).. produces dis-occlusion or separation of the posterior teeth.

Importance of Anterior Guidance(during lateral movement)

Importance of Anterior Guidance

Anterior guidance is linked to the combination of horizontal & vertical overlap of the anterior teeth

and can affect the occlusal surface morphology of

the posterior teeth.

Inter-relationship with Vertical & Horizontal Overlap of the Anterior teeth

Anterior guidance can be made steeper by either increasing the vertical overlap (overbite) ‘A-B’, or by reducing the horizontal overlap (over jet) ‘C-A’ of the anterior teeth.

Anterior guidance can be made shallow by either decreasing the overbite ‘B-A’ or increasing the over jet ‘A-C’ of the ant. teeth.

Condylar Guidance & Posterior tooth Morphology(without considering the role of A.G.)

Shallow condylar guidance normally requires shallow cusp angle or short cusp height and steeper condylar guidance

requires steep cusp angle or longer cusp height.

Condylar side-shift & Posterior tooth Morphology (without considering the role of A.G.)

‘side shift +’ ‘No side shift’Similarly, in the presence of an immediate lateral side shift during lateral

movement (Bennett’s movement) the cusp height and cusp angle should be shallow.

Influence of Anterior Guidance on Posterior tooth Morphology

Influence A.G. on Posterior tooth Morphology(Effect of Overbite)

Greater overbite produces more disocclusion hence permits longer cusp height

Less overbite – less disocclusion – shorter Cusp height.

Influence of A.G. on Posterior tooth Morphology(Effect of Over jet)

Greater over jet necessitates shorter cusp height.

Less over jet allows for long cusp height.

Influence of A.G. on Posterior tooth Morphology

Summarizing,

greater anterior guidance allows posterior teeth to have longer cusp height

&

smaller anterior guidance requires posterior teeth to have shorter cusp height.

Influence of A.G. on Posterior tooth Morphology

By increasing the anterior guidance angle to compensate for inadequate or shallow condylar guidance, it is possible to

increase the cusp height of the posterior teeth.

Influence of A.G. on Posterior tooth Morphology

Similarly, increasing the anterior guidance will permit lengthening of the cusp that otherwise have to be shorter in the presence of

pronounced immediate lateral translation of the condyles.

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