Occlusion Fixed 1

7/31/2019 Occlusion Fixed 1

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Occlusion


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Occlusion is the relationship between all the componentsof the masticatory system (teeth and their supporting

structures, the jaws and the tempromandibular joint, andthe muscles including lips and tongue) in natural functionand dysfunction. Occlusion includes morphologicalfeatures of contacting surfaces of opposing teeth and

restorations

Occlusion of teeth can be considered under two headings

Static occlusion: refers to any position in which the upper

and the lower teeth come together in contact when themandible is not moving

Functional occlusion

Refers to the contact between the upper and lower teeth

during the functional movement of the mandible


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To understand occlusion and the mandibularmovements we must understand the anatomy

of the tempromandibular joint Some of the components of the

tempromandibular joint consist of :

glenoid fossae

mandibular condyle(C in the picture thatfollows)

Articular disc(D in the picture that follows)

Articular eminance(A in the picture thatfollows)


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Important definitions

Maximum intercuspation: occlusal position of themandible in which the cusps of the teeth in one archinterpose themselves with the cusps of the teeth of the

opposing arch


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For example in normal occlusion and when themandible is closed the mandibular buccal cusps fall inthe central fossae of the maxillary posterior teeth andthe lingual cusps of the maxillary posterior fall in thecentral fossae of the mandibular posterior teeth

Functional cusps: are the cusps that do the grinding ofthe food and bear the load. the functional cusps in themaxilla are the lingual cusps while in the mandible are

the buccal cusps


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Centric relation: is the relationship between maxilla and

the mandible when the condyles in optimum position-superoanterior position-with the disc interposedbetween the condyles and the articular eminance

Centric occlusion: is the relationship of opposingocclusal surfaces (maximum intercuspation), it shouldexist when the mandible is in centric relation. It is toothto tooth relation while centric relation is bone to bone

relation


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In a healthy joint the condyle is in thesuperanterior position in the fossa with the

articular disc interposed when the tooth are inmaximum intercuspation


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Dysfunctional joint


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In the initial stage of opening (in the healthy joint)the condyle rotates in place with the discremainining unmoved.


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In maximum opening the condyle translates forward with the discstill interposed


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The mandibular movements are series ofmotions around different axes:

The mandible can perform opening andclosing

Can perform lateral movements such asmoving to the left or right side (excursive

movements) Can perform protrusive movement (anteriorly)

Can also perform retrusive movements

(posteriorly)


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When the mandible moves to one side, this sideis called the working or the laterotrusive side,and the other side is called the non working sideor mediotrusive

In this, the condyle of the non working side willarc forward and medially, while the condyle of

the working side will move laterally andposteriorly


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When the mandible slides forward so that themaxillary and mandibular teeth are in end- to

end, it is called a protrusive movement, in itthe mandibular anterior teeth travel a pathguided by contacts with maxillary anterior withcomplete disocclusion of the posterior teeth


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Determinant of mandibular movements:

They influence the mandibular movements

They are 1. posterior determinant :Tempromadibular

joint

2, the anterior deteminant (teeth) 3. the neuromuscular system

Dentist has no control on thetemperomandibular joint, it is unchangeable

but influence the mandibular movements bythe paths that the condyles must travel whenthe mandible is moving (condyler guidance)


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Measurements and reproduction of thosecondylar guidance is the basis for use in

articulators Anterior determinant, (teeth) provides guidance

to the mandible in several ways

Posterior teeth provides stops during closureand they guide the mandible into the maximumintercuspation position

Anterior teeth (canine to canine) help to guide

the mandible in lateral excursive and protrusivemovements


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Dentist has direct control over anterior determinantby 1. orthodontic movement of the teeth and 2.

restoration of anterior teeth or posterior occlusalsurfaces 3. selective grinding in any teeth that arenot in a harmonious relationship


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Occlusal interferences:

Undesirable occlusal contacts that may produce

mandibular deviation during closure to maximumintercuspation or may hinder the smoothpassage during lateral excursive movements

1.Centric interferences: premature contact thatoccurs when the mandible closes with thecondyles in their optimum position in the glenoidfossae, it will cause deflection of the mandible in

a posterior, anterior and/or lateral direction


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2. Working interference: when there is contactbetween the maxillary and mandibular posterior

teeth at the same side the mandible is moving to, ifthe contact is heavy enough to cause disocclusionof the anterior teeth, it is an interference


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3. A non working interference is an occlusal contactbetween maxillary and mandibular teeth on the oppositeside to the one the mandible is moving to, it is very

destructive, it damages the masticatory apparatus byplacing forces outside the long axis of the teeth and bydisruption of normal muscle function


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4. Protrusive interference: premature contact occursbetween the mesial aspect of mandibular posterior teeth

and the distal aspect of maxillary posterior teeth


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Arrangement of teeth in function comes in three types oforganization, these describe the manner in which teethshould or should not contact in the various movement of the

mandible :1.Bilateral balanced occlusion:Maximum number of teeth in both sides should contactduring all excursive movements of the mandible

It is useful in complete denture construction to avoid tippingof the denture,It was also used in complete occlusal rehabilitation onnatural dentition (full mouth fixed prosthesis) to reduce theand share the load on as many teeth as possible, howeverdue to the multiple tooth contact, it caused excessivefrictional wear


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2.Unilateral balanced occlusion:

Also called group functionIt is widely accepted

Began by observing the destructive nature of contacton the non-working side, it was noticed that this muchcontact in the natural teeth is not needed, thus all toothcontact in the non working side was eliminatedIt requires all teeth in working side to be in contact

during lateral excursion, in this way the occlusal load isdistributed on posterior teeth and prevents the teeth onthe non working side from the destructive obliqueforces


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This also saves the functional cusps (mandibularbuccal cusps and maxillary lingual cusps) fromexcessive wear

3.Mutually protected occlusion:

Also called canine protected or organic occlusion

In mouths of healthy periodontium and minimum

wear, the teeth are arranged so that the overlap ofthe anterior teeth prevented the posterior teeth onthe working side and the non working side from

contact during lateral excursion


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The separation between posterior teeth is calleddisocclusion

The result is that anterior teeth bear the loadduring the lateral excursive movements while theposterior teeth are disoccluded

During maximum intercuspation the posterior teeth

are fully occluded while the anterior teeth are inlight contact or out of contact thus posterior teethprotect the anteriors during the maximumintercuspation while the anteriors protect theposterior teeth during the lateral excursivemovements


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Therefore it is the most widely accepted occlusionform

However, to achieve this type of occlusion theremust be anterior teeth with healthy periodontium

In the absence of canines or in the case of anteriorbone loss group function must be achieved

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Occlusion Fixed 1