8 -fundamentals of occlusion

7/30/2019 8 -Fundamentals of Occlusion

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Fundamentals ofocclusion

Reference: ShillingburgFunamentals of Fixed

Prosthodontics, third editionchapter two


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Objective

Appreciate the importance of occlusion

The ability to diagnose and treat simple occlusaldisharmonies

To produce restorations that will avoid the creation of

iatrogenic disease


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Centric Relation The maxillomandibular relationship in which the condyles articulate with the

thinnest avascular portion of their respective disks with the complex in theanterior-superior position against the shapes of the articular eminencies. Thisposition is independent of tooth contact. This position is clinically discernible

when the mandible is directed superior and anteriorly. It is restricted to a purely

rotary movement about the transverse horizontal axis (GPT-5)


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Only hinge rotationmovement of the condyletakes place in centricrelation position


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Inter-cuspal position (ICP)Also called maximum intercuspation MIC

The position of maximum intercuspation betweenteeth

The most cranial position of the mandible


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Maximum Intercuspation


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Mandibular MovementSeries of motions occurring around three axes:

Horizontal axis

Vertical axis Sagittal axis


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Horizontal Axis

This Movement in the sagittal plane, happens when themandible in centric relation makes a purely rotationalopening and closing border movement around theterminal hinge axis


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Purehingerotation

translation


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Vertical Axis

This movement occurs in the horizontal plane whenthe mandible moves into a lateral excursion.


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Sagittal Axis

This movement occurs in the frontal plane during alateral excursion around an anteroposterior axis


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Protrusion


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Laterotrusion and mediotrusion Condyle in non working

Side moves forward

and medially Condyle in working

Side moves laterally

And Slightly posteriorly

WorkingsideNon Workingside


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Bennett angleThe angle formed in the horizontal plane, between the

pathway of the non working condyle in a mandibularlateral translation, and the sagittal plane.

NWS

NWS WS

WS


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Bennett

angleBennett

movement


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The determinants of mandibularmovement

Contacting teethTwo condyles


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The determinants of mandibular

movements Two condyles: Condylar guidance,Bennett angle (the

dentist has no control over the posterior

determinants.)

Contacting teeth: posterior and anterior teeth


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Condylar guidance

The angle formed in the sagittal plane, between the condylarpath during protrusion, and the horizontal plane


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Contacting teeth

Posterior teeth: Provide vertical stops for mandible closure

Guide the mandible into the position of maximumintercuspation

Anterior teeth: Guide the mandible into right and left lateral excursive

movement.

Guide the mandible in the protrusion movement.

Why are the anterior teeth more suitable to carry theguidance in excursions??


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During protrusive movement of the mandible , the incisaledges of the mandibular anterior teeth move forward anddownward along the lingual concavities of the maxillaryanterior teeth

Anterior guidance


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Anterior guidance The track of the incisal edges from max.

intercuspation to edge-to-edge

occlusion is called the protrusive incisalpath

The angle formed between theprotrusive incisal path and thehorizontal reference plane is called theprotrusive incisal path inclination


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In a healthy occlusion, the anterior guidance is 5 to 10degrees steeper than the condylar guidance


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Affect occlusal surface morphology of the posterior teeth:

Vertical overlap

Horizontal overlap

Anterior guidance


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One of the objectives of restorative dentistry is to placethe teeth in harmony with TMJ. This will result in min.stress on the teeth and joint


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Interferences


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Occlusal interferences

Contacts that may produce mandibulardeviation during closure to maximumintercuspation or may hinder smooth passage to

and from the intercuspal position:1. Centric

2. Working

3. Non-working4. Protrusive


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1.Centric interference

Premature contact that occurs when the mandiblecloses with the condyles in their optimum position inthe glenoid fossae


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2.working interferenceAn occlusal contact between the maxillary and

mandibular posterior teeth on the same side of thearches as the direction in which the mandible has

moved


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3.nonworking interference

An occlusal contact between maxillary and mandibularteeth on the side of arches opposite to the direction in

which the mandible has moved


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Consequences of pathologic occlusion Trauma to TMJ

Parafunctional jaw activities (bruxism andclenching)

Muscle fatigue or spasm

Facets and wear of teeth

Teeth mobility


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Optimum occlusion

Minimum adaptation by the patient

Criteria for optimum occlusion


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Organisation of the occlusion

Bilateral balanced occlusion

Unilateral balanced occlusion

Mutually protected occlusion


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Bilateral balanced occlusion Prosthetic concept : (not frequently used)

max. number of teeth contact in all excursivepositions of the mandible

useful in complete denture construction

in which contact on the non working side is needed


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Unilateral balanced occlusion Commonly known as group function :

(Widely used)

working side : all teeth are in contact

nonworking side : teeth are free of any

contact


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Unilaterally balanced occlusion Contacts betweenopposing posteriorteeth on the working

side only duringlateral excursion(group function lateralguidance)

Incisors and caninescarry the protrusiveguidance


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Also known as canine protected occlusion:

ease of fabrication, greater tolerance by patients

anterior teeth protecting the posterior teeth in

mandibular excursions

post. teeth protecting anterior teeth at the intercuspal

position


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- Posterior teethcome in contact onlyin intercuspalposition acting asvertical stops

- Canines on theworking side carrythe lateral guidance

- Incisors and caninescarry protrusiveguidance


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Thats it

8 -fundamentals of occlusion

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