4/10: Determinants of Occlusal Morphology Flashcards
What are the factors that determine the patterns of mandibular movements?
The TMJ’s and the anterior teeth
Where should the posterior teeth pass to maintain harmony?
Pass close to but NOT contact the opposing teeth during mandibular movement
What are structures that control mandibular movement?
- structures that influence the movement of the posterior portion of the mandible (TMJs)
- structures that influence the movement of the anterior portion of the mandible (anterior teeth)
What are posterior controlling factors (condylar guidance)?
- the angle at which the condyle moves away from a horizontal reference plan
- the condylar guidance
What is the condylar guidance angle?
The angle at which the condyle moves away from a horizontal reference plane
What is the condylar guidance angle considered to be?
A “fixed factor”, since in the healthy patient it is unalterable
What determines how the anterior portion of the mandible moves?
Anterior teeth
What happens as the mandible protrudes or moves laterally?
The incisal edges of the mandibular anterior teeth occlude with the lingual surfaces of the maxillary anterior teeth
What determines the amount of vertical movement of the mandible?
The steepness of the lingual surfaces
What kind of factor is anterior guidance considered to be?
Variable rather than a fixed factor
How can anterior guidance be altered?
By pathologic conditions (caries, wear, etc), or dental procedures
What must be in harmony during all mandibular eccentric movements?
The morphologic characteristics of each posterior tooth with its opposing tooth or teeth
What is the morphology of the teeth influenced by?
The pathway it travels across its opposing tooth or teeth
What are components of mandibular movements?
Vertical component (supero-inferior movement)
Horizontal component (antero-posterior movement)
What is the vertical component a function of?
Superio-inferior movement
Where do we want posterior teeth to pass close to in the vertical component?
Close to but not contact opposing teeth during mandibular movement (occlusal harmony)
The length of the cusp and the distance it extends into the depth of an opposing fossa depends on?
- Anterior controlling factor of mandibular movement
- Posterior controlling factor of mandibular movement
- The nearness of the cusp to those controlling factors
What do vertical determinants control?
The function of the superior-inferior movement (cusp height, fossae depth)
What do horizontal determinants influence?
The direction of grooves and ridges on the occlusal surfaces, and the placement of the cusps in the horizontal plane
What are vertical determinant factors?
Height of cusps
Depths of fossae
Condylar guidance (posterior controlling factor)
Anterior guidance (anterior controlling factor)
Nearness of the cusp to the controlling factor
Plane of occlusion
Curve of spee
What are posterior controlling factors?
Fixed factors
Condylar guidance
The two TMJs
What happens to the condyle when the mandible is protruded?
The condyle descends along the articular eminence
What is condylar guidance?
The angle at which the condyle moves away from the horizontal reference plane
What happens to the condylar guidance angle when the mandible makes a lateral movement?
Greater than when the mandible makes a protrusive movement
The steeper the eminence the…
The more the condyle must move inferiorly
There is greater vertical movement
It allows for steeper posterior cusps
What are anterior controlling factors?
Anterior teeth
Anterior guidance
What do anterior teeth determine?
How the anterior portion of the mandible moves
What is anterior guidance altered by?
Restorations
Orthodontics
Extractions
Caries
habits
Tooth wear
Anterior guidance is a ________ rather than a _______ factor
Variable; fixed
What is the anterior guidance angle?
The angle formed by the intersection of the horizontal plane and the disclusive pathway of the anterior teeth
What is the anterior guidance angle influenced by?
Vertical overlap (VO)
Horizontal overlap (HO)
What does VO overlap do to the anterior guidance angle?
Increases the anterior guidance angle
What does HO overlap do to the anterior guidance angle?
Decreases the anterior guidance angle
What does increased anterior guidance angle do?
More vertical component
Allows for steeper posterior cusps
What happens when a tooth is nearer to the TMJ?
The more the joint anatomy will influence its eccentric movement and the less the anterior teeth influence its movement
What are other factors that influence cusp height?
Plane of occlusion
Curve of spee
Mandibular lateral translation movement
What is the plane of occlusion?
An imaginary surface that touches the incisal edges of the incisors and cusp tips of the occluding surfaces of the posterior teeth
What happens to the posterior cusps as the plane of occlusion becomes more parallel to the angle of eminence?
Posterior cusp tips must be made shorter
Where does the curve of spee go?
Anteroposterior
Where does the curve of spee extend?
From the tip of the mandibular canine along the buccal cusp tips of the mandibular posterior teeth
What is curvature described in?
Terms of length of radius of the curve
What happens to the curve with a short radius?
More acute than with a longer radius
The flatter the plane of occlusion, the ________ the cusp height
Greater
What is the radius of the curve of spee?
Short radius
Describe the short radius of the curve of spee
the ANGLE at which the mandibular teeth move away from the maxillary teeth WILL BE LESS THAN WITH A LONG RADIUS, therefore the CUSPS will need to be SHORTER
What happens if the plane of occlusion is rotated more anterior?
- more teeth anterior to perpendicular line
- taller cusps
What happens if the plane of occlusion is rotated more posterior?
- more teeth posterior to perpendicular reference line
- shorter cusps
What is bennett movement?
Effect of mandibular translation movement on cusp height
What kind of movement is mandibular lateral translation?
Bodily sideshift of the mandible during lateral movements
What does inward movement depend on?
- morphology of the medial wall of the fossa on the orbiting side
- inner portion of the TM ligament attached to the lateral pole of the rotating condyle
Is the temporomandibular ligament tight?
Yes, very
- not common
What kind of movement occurs around the rotating condyle?
Pure arcing movement
Describe the translation of the mandible in the temporomandibular ligament?
No lateral translation of the mandible
The more medial the medial wall is from the condyle, the _____________________________
More lateral translation movement
What is lateral translation movement described in?
- amount
- timing
-direction
The greater the amount of lateral translation, the ___________________________ the cusps must be
Shorter
Describe the movement of the rotating condyle
May move in a combination of movements
- laterosuperior
- lateroinferioposterior
etc
What does laterosuperior movement require?
Shorter posterior cusps
What does inferior movement allow?
Taller cusps
What has the greatest influence on occlusal morphology?
Lateral translation timing
How can translation movement occur?
Early
late
What is early translation called?
Immediate lateral translation (or immediate sideshift)
What is late lateral translation called?
Progressive lateral translation (or progressive sideshift)
When is immediate lateral translation seen?
Before the condyle begins to translate from the fofsa
The more the immediate movement, the ________ the cusps must be
Shorter
Graph of vertical determinants of occlusal morphology
