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***NOTE: When the mandible is opened beyond the point where the condyle begins to translate, the meniscus glides downward and forward on the articular eminence •Opening the mouth maximally from retruded position causes the Mn to rotate, then translate Direction of Motion 3 Planes Degree of movement Clinical significance of movements Each pt may have different relationships Mandible is a Class III leverFulcrum – Condyle Force – Muscles Workload – Teeth Functional Occlusion All contacts during chewing, swallowing, or normal actions Parafunctional Those made outside normal range, may create wear facets or attrition Bruxing, clenching, nail biting, thumb sucking, cheek biting Jaw closure in parafunction varies from masticatory function in the following ways: •Teeth seldom, if ever, contact in mastication •Teeth are in tight contact during parafunction •Masticatory cycles are vertical and cyclic Border Movements LOOK OVER PULLINGER’S HANDOUT
41 Sagittal Plane – Posselt’s Envelope (ABOVE) The final movement of the Mn in tooth closure is directed by the cusp-fossa relationship of opposing teeth The maximum intercuspal position is the most superior point #3 Postural or rest position is that black dot right under #3,4 Retruded contact position is #4 Terminal Hinge axis is #6 Masticatory Cycle of mandibular central incisor is #5 Curve #7 is the pathway for a maximum opening – both rotatory & translational (NOTa border movement) From which point to which point is there a the greatest change in anterior guidance? I think from 3 2 (OR from CR (3) to Edge to Edge Contact (2) Intercuspal position is determined almost exclusively by tooth contact The maximum opening position is the most inferior In a normal diagram in the sagittal plane, initial occlusal contact in RCP occurs at a more inferior position than ICP at #4 Mastication of food occurs primarily in lateral contacting movement In 90% of the population, the average distance from 3→4 is ~1.25mm (ICP is anterior to RCP) In the other 10%, 3=4 (RCP = ICP) The left border above is the protrusive opening path Frontal Plane Viewed anteriorly, chewing stroke (masticatory movement) vertical & tear drop in appearance (RIGHT) In Frontal Plane there is Posterior contacts only on “A” Canines are cusp tip to cusp tip on “B” Horizontal Plane (Gothic Arch) This records the position of the Mn anterior teeth, in assessing condylar movement via the lateral pterygoids The diamond shape results from 1) L lateral, 2) L lateral w/ protrusive, 3) R lateral, 4) R lateral w/ protrusive Points 5 & 6 in the figure on the right (below) represent the R & L lateral contacting positions, respectively The apex of the horizontal plane Gothic arch tracing represents CR (OR POINT 1 Below) Diagram shows (1999 Q 197 – SEE RIGHT) •Horizontal component of movement from retruded contact position (1) to ICP (2) •Anterior component of movement from ICP (2) to maximum protrusive position (4) •Lateral component of movement from retruded contact position (1) to ICP (2) •