DeterminantsDeterminantsofof

Occlusion MorphologyOcclusion Morphology

Structures control Structures control mandibularmandibular movement movement

•• Posterior controlling factor : TMJPosterior controlling factor : TMJ•• Anterior controlling factor : anterior teethAnterior controlling factor : anterior teeth

•• Posterior teethPosterior teeth–– are positioned between these twoare positioned between these two

controlling factorscontrolling factors–– can be affected by both to varyingcan be affected by both to varying

degreesdegrees

Posterior controlling factorsPosterior controlling factorsCondylarCondylar guidance guidance

–– is the angle at which the is the angle at which the condylecondyle moves movesaway from a horizontal reference planeaway from a horizontal reference planefrom CR along the from CR along the articulararticular eminence of eminence ofthe the mandibularmandibular fossafossa

–– depends on the steepness of the depends on the steepness of the articulararticulareminenceeminence

–– considered to be fixed factor, unalterableconsidered to be fixed factor, unalterable

CG angle when the mandible move laterally isCG angle when the mandible move laterally isgreater than when greater than when mandibulemandibule protrudes protrudes

straight forward due to medial wall of thestraight forward due to medial wall of themandibularmandibular fossafossa is generally greater than is generally greater than

articulararticular emineneceeminenece anterior to anterior to condylecondyle..

Anterior controlling factorsAnterior controlling factors•• Anterior guidanceAnterior guidance

–– the the incisalincisal edges of the edges of the mandibularmandibular teeth teethocclude with lingual surface of the maxillaryocclude with lingual surface of the maxillaryteeth as mandible protrude or move laterallyteeth as mandible protrude or move laterally

–– The steepness of these lingual surfaceThe steepness of these lingual surfacedetermines the amount of vertical movementdetermines the amount of vertical movementof mandibleof mandible

–– The anterior guidance consider to be aThe anterior guidance consider to be avariable rather can be variable rather can be alteratedalterated during by during bydental proceduredental procedure

•• The morphologic characteristics of each posteriorThe morphologic characteristics of each posteriortooth must be in harmony with those of its opposingtooth must be in harmony with those of its opposingtooth to teeth during all eccentric tooth to teeth during all eccentric mandibularmandibularmovements.movements.

•• Therefore the exact morphology of the tooth isTherefore the exact morphology of the tooth isinfluenced by the pathway it travel across itsinfluenced by the pathway it travel across itsopposing tooth to teeth.opposing tooth to teeth.

•• Nearer the tooth is to the TMJ, the more the moreNearer the tooth is to the TMJ, the more the morejoint influences its movement.joint influences its movement.

OcclusalOcclusal surface of posterior teeth surface of posterior teeth

can be effected by the significance of thecan be effected by the significance of theanterior and anterior and condylarcondylar guidance in two guidance in twomannersmanners

–– factors influences factors influences vertical componentsvertical components(Height)(Height)

–– factors influences factors influences horizontal componentshorizontal components(Width)(Width)

Vertical determinants ofVertical determinants ofocclusalocclusal morphology morphology

Influences the heights of cusps and the depths ofInfluences the heights of cusps and the depths offossaefossae

1. The 1. The anterior controlling factoranterior controlling factor of ofmandibularmandibular movement movement (i.e., anterior guidance)(i.e., anterior guidance)

2. The 2. The posterior controlling factorposterior controlling factor of ofmandibularmandibular movement movement (i.e., (i.e., condylarcondylar guildanceguildance))

3. The 3. The nearessnearess of the cusp to these controlling of the cusp to these controllingfactors.factors.

Posterior centric cuspsPosterior centric cusps•• are generally developed to are generally developed to contact in thecontact in the

intercuspalintercuspal position position but to but to disoccludedisocclude during duringeccentric eccentric mandibularmandibular movements movements

•• must be long enough to contact in themust be long enough to contact in theintercuspalintercuspal position but not so long that they position but not so long that theycontact during eccentric movements.contact during eccentric movements.

Angle of Angle of articulararticular eminence eminence(Effect of (Effect of condylarcondylar guidance on cusp height) guidance on cusp height)•• Protrusion: the Protrusion: the condylecondyle descends along the descends along the

steepness of the steepness of the articulararticular eminence. eminence.•• more steepnessmore steepness

–– more the more the condylecondyle is forced to move is forced to moveinferiorly as it shifts inferiorly as it shifts anteriorlyanteriorly–– greater vertical movement of greater vertical movement of condylecondyle,,

mandible, mandible, mandibularmandibular teeth teeth

4545o o & 45& 45oo

6060o o & 60& 60oo

Effect of anterior guidance on cusp heightEffect of anterior guidance on cusp height

•• Anterior guidance is a functionalAnterior guidance is a functionalrelationship between the maxillary andrelationship between the maxillary andmandibularmandibular anterior teeth. anterior teeth.

•• Anterior guidance is consisted ofAnterior guidance is consisted of–– vertical overlap of anterior teeth.vertical overlap of anterior teeth.–– horizontal overlaps of anterior teeth.horizontal overlaps of anterior teeth.

Examples of anterior guidanceExamples of anterior guidance

Same vertical overlap, varying horizontal overlapSame vertical overlap, varying horizontal overlap

Increase in horizontal overlap leads to aIncrease in horizontal overlap leads to adecreased anterior guidance angle, lessdecreased anterior guidance angle, lessvertical component to vertical component to mandibularmandibularmovement, and flatter posterior cusps.movement, and flatter posterior cusps.

Same horizontal overlap, varying vertical overlapSame horizontal overlap, varying vertical overlap

Increase in vertical overlap produced anIncrease in vertical overlap produced anincreased anterior guidance angle, moreincreased anterior guidance angle, morevertical component to vertical component to mandibularmandibularmovement, and steep posterior cuspsmovement, and steep posterior cusps

Effect of plan of occlusion on cusp heightEffect of plan of occlusion on cusp height

•• Plane of occlusion id an imagination linePlane of occlusion id an imagination linetouching touching incisalincisal edges of maxillary anterior edges of maxillary anteriorteeth and the cusps of the posterior teeth.teeth and the cusps of the posterior teeth.

•• The relationship of the plan to the angle ofThe relationship of the plan to the angle ofthe the articulararticular eminence influences the eminence influences thesteepness of the cuspssteepness of the cusps

Effect of curve of Effect of curve of SpeeSpee on cusp height on cusp height

•• the curve of the curve of SpeeSpee is is anteroposterioranteroposterior curve curveextending from the tip of the extending from the tip of the mandibularmandibularcanine along the canine along the buccalbuccal cusp tips of cusp tips ofmandibularmandibular posterior teeth posterior teeth

•• Its curvature can be Its curvature can be decribeddecribed in terms of the in terms of thelength of the radius of the curvelength of the radius of the curve

A short radius theA short radius thecurve is more acutecurve is more acutethat with a longerthat with a longerradiusradius

Orientation of curve of Orientation of curve of SpeeSpee

To be continuedTo be continued

Effect of Effect of mandibularmandibular lateral lateraltranslation movement on cusp heighttranslation movement on cusp height

•• Bennett movement:Bennett movement: MandibularMandibular lateral translation lateral translationmovement is a movement is a bodily bodily sideshiftsideshift of the mandible that of the mandible thatoccurs during lateral movements.occurs during lateral movements.

•• During a lateral excursion the During a lateral excursion the orbiting orbiting condylecondylemoves downward and forward, and inwardmoves downward and forward, and inward

•• Opposite Opposite condylecondyle rotate around axes in rotate around axes in mandibularmandibularfossafossa ( (rotating rotating condylecondyle))

•• TM ligamentTM ligament of ofthe rotatingthe rotatingcondylecondyle is very is verytight tight and theand themedial wallmedial wall is isclose close to theto theorbiting orbiting condylecondyle

•• a pure arcinga pure arcingmovement ismovement ismade around themade around theaxis of rotationaxis of rotationcondylecondyle

Degree of inward movement ofDegree of inward movement ofcondylecondyle for lateral translation for lateral translation

Determined by 2 factorsDetermined by 2 factors

–– morphology of the morphology of the medial wallmedial wall of the of themandibularmandibular fossafossa

–– inner horizontal portion of the inner horizontal portion of the TMTMligamentligament, which attaches to the, which attaches to thelateral pole of the rotating lateral pole of the rotating condylecondyle..

•• looseness of thelooseness of theTM ligament &TM ligament &the medial wall ofthe medial wall ofthe the mandibularmandibularfossafossa lies medial lies medialto an arc aroundto an arc aroundthe axis of thethe axis of therotating rotating condylecondyle

•• condylecondyle is moved is movedinwardly to theinwardly to themedial wall andmedial wall andproduces aproduces amandibularmandibularlateral translationlateral translationmovement.movement.

Effect of Effect of mandibularmandibular lateral translation lateral translationmovement on cusp heightmovement on cusp height

•• Effect of the Effect of the amount of lateral translationamount of lateral translationmovement on cusp heightmovement on cusp height

•• Effect of the Effect of the direction of lateral translationdirection of lateral translationmovement on cusp heightmovement on cusp height

•• Effect of the Effect of the timing of lateral translationtiming of lateral translationmovement on cusp heightmovement on cusp height

Effect of the Effect of the amount of lateralamount of lateraltranslationtranslation movement on cusp height movement on cusp height

The greater the lateral translation movement, theThe greater the lateral translation movement, theshorter is the posterior cuspshorter is the posterior cusp

The greater the lateral translation movement,The greater the lateral translation movement,the shorter is the posterior cuspthe shorter is the posterior cusp

Effect of the Effect of the direction of lateraldirection of lateraltranslationtranslation movement on cusp height movement on cusp height• determined by the morphology and

ligamentous attachments of the TMJundergoing rotation– Movement occurs within a 60-degree (or less)

cone whose apex is located at the axis ofrotation

– More superior the lateral translationmovement, the shorter is the posterior cusp

movement occurs within a 60-degree (or less) conewhose apex is located at the axis of rotation

More superior the lateral translation movement,More superior the lateral translation movement,

the shorter is the posterior cuspthe shorter is the posterior cusp

Effect of the Effect of the timing of lateraltiming of lateraltranslationtranslation movement on cusp height movement on cusp height

• lateral translation movement– occurs early, a shift is seen even before the

condyle begins to translate from the fossa. Thisis called an immediate lateral sideshift

– it occurs in conjunction with an eccentricmovement, the movement is known as aprogressive lateral translation movement orprogressive sideshift.

1. Immediate 1. Immediate sideshiftsideshift, shorter posterior cusp, shorter posterior cusp2. progressive 2. progressive sideshiftsideshift, longer cusp, longer cusp

Horizontal determinants of Horizontal determinants of occlusalocclusal morphology morphology

•• distance from rotating distance from rotating condylecondyle on ridge and groove on ridge and groovedirectiondirection

•• distance from distance from midsagittalmidsagittal plane on ridge and groove plane on ridge and groovedirectiondirection

•• distance from rotating distance from rotating condylescondyles and from and from midsagittalmidsagittalplane on ridge and groove directionplane on ridge and groove direction

•• Effect of Effect of mandibularmandibular lateral translation movement on lateral translation movement onridge and groove directionridge and groove direction

•• intercondylarintercondylar distance on ridge and groove direction distance on ridge and groove direction

•• relationship between anterior and posterior controllingrelationship between anterior and posterior controllingfactorsfactors

Effect of distance from rotating Effect of distance from rotating condylecondyleon ridge and groove directionon ridge and groove direction

•• The greater the distance of the tooth from theThe greater the distance of the tooth from therotating rotating condylecondyle, the , the wider is the anglewider is the angleformed by the formed by the laterotrusive laterotrusive and and mediotrusivemediotrusivepathways.pathways.

A = A = Mediotrusive pathwayMediotrusive pathway, B = , B = LaterotrusiveLaterotrusive pathway pathway

MandibularMandibular teeth teeth

A = A = Mediotrusive pathwayMediotrusive pathway, B = , B = LaterotrusiveLaterotrusive pathway pathway

Maxillary teethMaxillary teeth

Effect of distance from Effect of distance from midsagittalmidsagittalplane on ridge and groove directionplane on ridge and groove direction

•• The greater the distance of the tooth from theThe greater the distance of the tooth from themidsagittalmidsagittal plane, the wider the angle formed plane, the wider the angle formedby the by the laterotrusivelaterotrusive and and mediotrusivemediotrusivepathways. (both maxillary and pathways. (both maxillary and mandibularmandibularteeth)teeth)

Effect of distance from rotating Effect of distance from rotating condylescondyles and from and frommidsagittalmidsagittal plane on ridge and groove direction plane on ridge and groove direction

•• More anterior theMore anterior thetooth in the dentaltooth in the dentalarch, the wider is thearch, the wider is theangle formed by theangle formed by thelaterotrusivelaterotrusive and andmediotrusivemediotrusivepathwayspathways

Effect of Effect of mandibularmandibular lateral translation lateral translationmovement on ridge and groove directionmovement on ridge and groove direction

•• As the amount of lateral translationAs the amount of lateral translationmovement increases, the angle between themovement increases, the angle between themediotrusivemediotrusive and and laterotrusivelaterotrusive pathways pathwaysgenerated by the centric cusp tips increases.generated by the centric cusp tips increases.(both maxillary and (both maxillary and mandibularmandibular teeth) teeth)

Effect of Effect of anterolateralanterolateral and and posterolateralposterolateraltranslation movement of the rotating translation movement of the rotating condylecondyle

•• The more The more anteriolateralanteriolateral the movement of the the movement of therotating rotating condylecondyle, the smaller is the angle, the smaller is the angleformed by the formed by the mediotrusivemediotrusive and and laterotrusivelaterotrusivepathways.pathways.•• The more The more posterolateralposterolateral the movement of the the movement of the

rotating rotating condylecondyle, the wider is the angle, the wider is the angleformed by the formed by the mediotrusivemediotrusive and and laterotrusivelaterotrusivepathwayspathways•• (both maxillary and (both maxillary and mandibularmandibular teeth) teeth)

IntercondylarIntercondylar distance on ridge and distance on ridge andgroove directiongroove direction

Relationship between anterior andRelationship between anterior andposterior controlling factorsposterior controlling factors

Relationship between anterior andRelationship between anterior andposterior controlling factorsposterior controlling factors

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