occlusion part(iii) / orthodontic courses by indian dental academy
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OCCLUSION (PART III) INDIAN DENTAL ACADEMY
Leader in continuing dental education www.indiandentalacademy.com
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Contents
Introduction Posterior controlling factors Anterior controlling factors Understanding the controlling
factors
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Vertical determinants of occlusal morphology (on cusp height)
Horizontal determinants of occlusal morphology (on ridge and groove direction)
Summary References
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Introduction
The occlusal anatomy of the teeth must function in harmony with the structures controlling the movement patterns of the mandible.
To maintain harmony of the occlusal condition, the posterior teeth must pass close to but must not contact their opposing teeth during mandibular movement
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Posterior controlling factors
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The angle at which the condyle moves away from horizontal reference plane is referred to as the condylar guidance angle.
Two TMJ’s –posterior controlling factors
Fixed factors
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Anterior controlling factors
Vertical overlap and horizontal overlap
Variable factor (altered by dental procedures)
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Understanding the controlling factorsIf the criteria for optimum functional occlusion has to be fulfilled, the morphologic characteristics of each posterior tooth must be in harmony with those of its opposing tooth or teeth during all eccentric mandibular movements.
The relationship of a posterior tooth to the controlling factors influences the precise movement of that tooth.
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Therefore, the significance of the anterior and condylar guidances lies in how they influence posterior tooth shape.
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Occlusal surface of the posterior teeth can be affected in 2 manners
1. Height
2. Width
Factors that influence the heights of cusps and depths of fossae are the vertical determinants of the occlusal morphology
Factors that influence the direction of ridges and grooves on the occlusal surfaces are considered the horizontal determinants of the occlusal morphology www.indiandentalacademy.com
Vertical determinants of occlusal morphology (on cusp height)
a) Effect of condylar guidance b) Effect of anterior guidance
c) Effect of plane of occlusion
d) Effect of curve of Spee
e) Effect of mandibular lateral translation movement www.indiandentalacademy.com
a) Effect of condylar guidance
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b) Effect of anterior guidance
It is a function of the relationship between the maxillary & mandibular anterior teeth.
Anterior guidance = Overjet X overbite
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c) Effect of plane of occlusion
It is an imaginary line extending from cusp tip of mandibular canine to distobuccal cusp of lower second molar
Relationship of this plane to the angle of articular eminence influences the steepness of the cusps.
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As the plane of occlusion becomes more nearly parallel to the angle of the articular eminence, the posterior cusps must be made shorter.
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d) Effect of curve of Spee
3 components affecting the cusp height are:
a) Length of the radius of the curve
b) Degree of curvature of the curve of Spee
c) Orientation of curve of Speewww.indiandentalacademy.com
Length of the radius of the curve
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Degree of curvature of the curve of Spee
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Orientation of curve of Spee
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e) Effect of mandibular lateral translation movement
Bennett movement- A bodily side shift of the mandible that occurs during lateral movements.
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The degree of medial movement of orbiting condyle depends on two factors :
a.Morphology of medial wall of the fossa.
b. Inner horizontal portion of the Temporomandibular ligament (which attaches to the lateral pole of the rotating condyle)
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Lateral translation movement has 3 attributes
1. Amount
2. Direction
3. Timing
Amount and Timing are dependent on medial wall of fossa and TM ligament.
Direction depends on the direction taken by the rotating condyle.
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Effect of amount of lateral translation movement on cusp height
Greater the amount of lateral translation movement, shorter is the posterior cusp
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Effect of the direction of lateral translation movement on cusp height
Determined by the morphology and ligamentous attachments of the TMJ undergoing rotation.
The movement occurs within a 60 degree cone whose apex is located at the axis of rotation.
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Effect of timing of lateral translation movement on cusp height
Dependent on the medial wall of fossa and TM ligament.
Immediate side shift – when the lateral translation movement occurs early
Progressive side shift – if movement occurs in conjunction with an eccentric movement
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Horizontal determinants of occlusal morphology
Influences the direction of ridges and grooves on the occlusal surfaces
Each centric cusp tip generates both laterotrusive and mediotrusive pathways across its opposing tooth
Each pathway represents a portion of the arc formed by the cusp rotating around the rotating condyle
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Horizontal determinants of occlusal morphology (on ridge and groove
direction)a) Effect of distance from rotating condyle
b) Effect of distance from mid-Sagittal plane
c) Effect of distance from rotating condyle and from mid-Sagittal plane
d) Effect of mandibular lateral translation movement
e) Effect of inter-condylar distance www.indiandentalacademy.com
a)Effect of distance from rotating condyle
Greater the distance – wider the anglewww.indiandentalacademy.com
b) Effect of distance from mid-Sagittal plane
More the distance – wider the anglewww.indiandentalacademy.com
c) Effect of distance from rotating condyle and from mid-Sagittal plane
The combination of the two positional relationships is what determines the exact pathways of the centric cusp tips
Because of the curvature of the dental arch; as the distance of tooth from rotating condyle increases – distance from midsagittal plane decreases, but distance from rotating condyles increases FASTER than decrease in distance from midsagittal plane.
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Therefore, the teeth toward the anterior region (e.g. premolars) have larger angles than posterior teeth (e.g. molars).
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d) Effect of mandibular lateral translation movement
influences the directions of ridges and grooves
Movement depends on 2 factors:
1. Amount
2. Direction
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Effect of amount of lateral translation movement on ridge and
groove direction
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Effect of direction of lateral translation movement on ridge and
groove direction
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e) Effect of inter-condylar distance
As inter condylar distance increases – distance between the condyle and the tooth increases – wider angles
(in a given arch configuration)
As inter condylar distance increases – the tooth is placed nearer the mid-sagittal plane relative to the rotating condyle-midsagittal plane distance – decrease in the angle generated
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Increase in inter-condylar distance – decrease in angle between mediotrusive and laterotrusive pathways
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Summary Vertical determinants of occlusal morphology (on cusp height and fossa depth)
Horizontal determinants of occlusal morphology (on ridge and groove direction)
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Factor Condition Effect
Condylar guidance
Steeper Taller
Anterior guidance
More overbiteMore Overjet
Taller Shorter
Plane of occlusion
More parallel Shorter
Curve of Spee
More acute Shorter
Lateral translation
Greater movementMore superior Greater immediate shift
Shorter ShorterShorter
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Factor Condition Effect
Distance from rotating condyle
Greater Wider the angle
Distance from midsagittal plane
Greater Wider the angle
Lateral translation Greater Wider the angle
Intercondylar distance
Greater Smaller the angle
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References Occlusion series in BDJ, 2001;191:6-7 Okeson JP. Management of Temporomandibular Disorders and Occlusion, ed. 4th, 1998; Mosby Ash MM and Ramfjord S. Occlusion, ed. 4th, 1966; WB Saunders Company, Michigan
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Santos JD. Occlusion Principles and Concepts, ed. 2nd, 1999; Ishiyaku EuroAmerica, Inc. U.S.A. Shillingburg HT. Fundamentals of Fixed Prosthodontics, ed.3rd, 1997;Quintessence
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Thank you
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