DETERMINANTS OF OCCLUSAL MORPHOLOGY

© Dr Keson B C TanBDS (Hons), MSD

DETERMINANTS OF

OCCLUSAL MORPHOLOGY


DETERMINANTS OF

OCCLUSAL MORPHOLOGY





DETERMINANTS OF OCCLUSAL MORPHOLOGY

Occlusal Anatomy

Harmony

Controlling Structures



• TMJs• Anterior Teeth

Mandibular Movement Patterns -Controlling Structures



• Posterior portion of mandible• Anterior portion of mandible


Influence movement of


• Condylar Guidance


Posterior Controlling Factors

Anterior Controlling Factors• Anterior Guidance


• Fixed factor• altered only by trauma, pathosis,

or surgery


Condylar Guidance


• Steepness of lingual surfacesof Maxillary incisors

• Amount of vertical overlap• Variable factor• Altered by

• Dental procedure - orthodontia, restorations, extractions

• Pathology - caries, habits, tooth wear

DETERMINANTS OF OCCLUSAL MORPHOLOGYAnterior Guidance



CONTROLLING FACTORS

• Proximity of tooth to Controlling Factor

Posterior Controlling Factor (PCF)vs

Anterior Controlling Factors (ACF)





• Vertical • Horizontal


Controlling Factors


• Cusp Height & Fossa Depth


Vertical Determinants

Horizontal Determinants• Ridge & Groove Direction


VERTICAL DETERMINANTS

a. Anterior Controlling Factorsb. Posterior Controlling Factorsc. Proximity of Cusps to ACF or PCF

Cusp Length and Fossa Depth

Posterior centric cusps- Disclude in Eccentric Movements- Contacts in MI



1. Condylar Guidance2. Anterior Guidance3. Occlusal Plane4. Curve of Spee5. Lateral Translation Movement


• Angle at which the condyle moves away from a horizontal reference plans.

• Condylar Guidance Angle of Nonworking Condyle > Straight Protrusion

• Medial wall of mandibular fossa steeper than articular eminence directly anterior to the condyle.

• = Fischer angle


Condylar Guidance Angle



Condition : SteeperEffect : Steeper posterior cusps

Condylar Guidance





Condition : GreaterEffect : Taller posterior cusps

Anterior GuidanceVertical Overlap

Horizontal OverlapCondition : GreaterEffect : Shorter posterior cusps




• Plane that passes through incisal edges of max anterior and cusps of max posterior.

• Occlusal Plane vs. Horizontal Reference Plane

Plane of Occlusion


Condition : More parallel to condylar guidance

Effect : Shorter posterior cusps


Plane of Occlusion


• A-P Curve• Tip of Mand canine along

buccal cusp tips of mandibular posteriors

• Curvature• Orientation of curve to

horizontal reference plane


Curve of Spee


Condition : More acute curvature

Effect : Shorter posterior cusps


Curve of Spee


• Bodily sideshift of mandible• Nonworking condyle inward movement

1. Morphology of medial wall of mandibular fossa

2. Inner horizontal portion of TM ligament(attached to lateral pole of Working condyle).

VERTICAL DETERMINANTSLateral translation movement


• Amount• Direction• Timing


Lateral translation movement


• Inner horizontal portion TM ligament• Medial wall of mandibular fossa


Amount

Lateral translation movement -




Condition : Greater magnitudeEffect : Shorter posterior

cusps

Amount




• Working condyle - morphology & ligamentousattachments

• Superior• Inferior• Anterior• Posterior


DirectionLateral translation movement -


Condition : More superiorEffect : Shorter posterior

cusps


Direction



• Immediate Sideshift (ISS)• Lateral translation immediately condyle

begins to translate from fossa

• Progressive Sideshift (PSS)• In conjunction with eccentric movement


Timing




Condition : Greater ISSEffect : Shorter posterior cusps


TimingLateral translation movement -

If sideshift occurs late

- Cusps beyond functional range- Amount and direction - no

influence !


HORIZONTAL DETERMINANTS

1. Distance from rotating condyle2. Distance from midsagittal plane3. Lateral Translation Movement4. Intercondylar distance


• Ridge and groove direction• Cusp position

HORIZONTAL DETERMINANTSInfluence

Centric cusp pathways• Laterotrusive• Mediotrusive• Arcs around Working

(Rotating) condyle


Condition : Greater distanceEffect : Wider angle between W and NW pathways

HORIZONTAL DETERMINANTSDistance from Working Condyle


Condition : Greater distanceEffect : Wider angle between W and NW

pathways

HORIZONTAL DETERMINANTS

Distance from Mid-sagittal Plane




Condition : Greater ISSEffect : Wider angle between W and NW pathways

HORIZONTAL DETERMINANTSLateral translation movement -Amount



Condition : Greater distanceEffect : Narrower angle between W and NW

pathways

HORIZONTAL DETERMINANTSIntercondylar distance



Relationship between ACF and PCF

• Complete denture balanceTheory that ACF and PCF are correlated

Scientific evidence• Articular eminence angle not correlated

to any specific occlusal relationship • ACF independent of PCF• Alteration of ACF possible in

therapeutic occlusal specifications


A Positive Surface Error is one which occurs when the articulator under-compensates for the mandibular movement, resulting in a positive feature existing on the occlusal surface where that feature should be smaller or non-existent.


• A Negative Occlusal Surface Error is one which occurs when the articulator over-compensates for a mandibular movement.

• This results in a negative feature such as a groove or fossa that is wider than ideal or conversely a positive feature such as a ridge or cusp that is somewhat narrower than ideal.

• Such posterior teeth are allowed to disclude more freely when the mandible moves.

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DETERMINANTS OF OCCLUSAL MORPHOLOGY