DETERMINANTS OF OCCLUSAL MORPHOLOGY Dr. Pauline Hayes Garrett Dr. Patricia W. Kiln Dr. Michael Tabacco Department of Endodontics, Prosthodontics, and Operative Dentistry University of Maryland, Baltimore .

Line drawings adapted from: Okeson, J. P. (2003) Line drawings adapted from: Okeson, J.P. (2003). Management of Temporomandibular Disorders and Occlusion, 5th Ed. , St. Louis, MO: Mosby

Determinants of Occlusion “In health the occlusal anatomy of the teeth functions 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.” Okeson, J.P. (2003). Management of Temporomandibular Disorders and Occlusion ,5th Ed. , St. Louis, MO: Mosby, Chapter 6, pg.127. Posterior disocclusion Guidance Canine

Controlling Forces Vertical Posterior Controlling Forces The two Temporomandibular Joints Vertical Anterior Controlling Forces Anterior Teeth

Vertical Posterior Controlling Forces: Temporomandibular Joint Rule: THE STEEPER THE WALLS THE TALLER THE CUSPS

The articulating structures (1. glenoid fossa and 2 The articulating structures (1.glenoid fossa and 2.articular eminence) are part of the squamous portion of the temporal bone. The glenoid (mandibular) fossa is a depression on the inferior aspect of the temporal bone and its anterior wall is formed by an elevation known as the articular eminence ( 5 to 15 mm in height).

Anterior Controlling Forces Anterior Teeth (Overbite /Angle) Remember: Harmony! Illustration modified and Reprinted from: Okeson, J.P. (2003). Management of Temporomandibular Disorders and Occlusion, 5th Ed. , St. Louis, MO: Mosby, Chapter 3.with permission from Elsevier. Pg. 132.

Anterior Protection Horizontal overlap (overjet) - The projection of teeth beyond their antagonists in the horizontal plane. Vertical overlap (overbite) - The distance teeth lap over their antagonists as measured vertically; especially the distance the maxillary incisal edges extend below those of the mandibular teeth, when the teeth are in maximum intercuspation. In general, the greater the vertical overlap and the less the horizontal overlap of the anterior teeth, the greater the protection afforded posterior teeth by the anterior teeth. **Click on pictures to start movie Please note posterior protection (posterior dis-occlusion) as mandible moves in protrusion.

Overlap and Overjet Vertical overlap =overbite Horizontal overlap

The Greater the Vertical Overlap: The Taller the Cusps Can Be Click on image! Illustration above on the right modified and Reprinted from: Okeson, J.P. (2003). Management of Temporomandibular Disorders and Occlusion, 5th Ed. , St. Louis, MO: Mosby, Chapter 3.with permission from Elsevier. Pg. 134. **When the patient goes into protrusive with greater vertical overbite, there is a greater vertical space in posterior, allowing for taller cusps/teeth in the posterior. Also, Note the relationship of the condylar angle to the Vertical Overbite and cusps: THE STEEPER THE Articular eminence and medial WALLS of the mandibular fossa THE TALLER THE CUSPS

Looking at this another way… RULE The steeper the condylar inclination, the steeper the cusps may be Artificially making a steeper condyle with a wax insert, will allow more room in the molar area for steeper cusps during the Protrusive Movement

Increase overbite (VO) = increase cusp height (which increases vertical dimension during protrusion) Again: Illustrations modified and Reprinted from: Okeson, J.P. (2003). Management of Temporomandibular Disorders and Occlusion, 5th Ed. , St. Louis, MO: Mosby, Chapter 3.with permission from Elsevier. Pgs. 132 & 133. ** Note the relationship of the condylar angle to the cusp: THE STEEPER THE Articular eminence and medial WALLS of the mandibular fossa THE TALLER THE CUSPS can be.

Anterior Controlling Forces Overjet = Horizontal Overlap

The Greater the Overjet (HO): The Shorter the Cusps MUST Be

Illustration modified and Reprinted from: Okeson, J. P. (2003) Illustration modified and Reprinted from: Okeson, J.P. (2003). Management of Temporomandibular Disorders and Occlusion, 5th Ed. , St. Louis, MO: Mosby, Chapter 3.with permission from Elsevier. Pg. 134. So…The Greater the Overjet: The Shorter the Cusps MUST Be since there is less space in the posterior (less vertical dimension) during protrusion which only allows for short cusps less of vertical dimension

“Flatter” the plane (Curve), longer the cusp height can be Vertical Determinant Plane of Occlusion (Curve of Spee) “Flatter” the plane (Curve), longer the cusp height can be

THE EFFECT OF PLANE OF OCCLUSION, CURVES OF SPEE AND WILSON The curves are based on an arbitrary four-inch radius sphere This sphere typically touches at the same time the condylar surface, posterior cusp tips, and the “incisal point”

THE EFFECT OF PLANE OF OCCLUSION, CURVES OF SPEE AND WILSON A tangent to this curve in general terms establishes the PLANE OF OCCLUSION Variance in both the Plane of Occlusion and the corresponding curves influence cusp height

“The Flatter” the Occlusal plane or the Curve of Spee, taller the cusp height can be. Illustration modified and Reprinted from: Okeson, J.P. (2003). Management of Temporomandibular Disorders and Occlusion, 5th Ed. , St. Louis, MO: Mosby, Chapter 3.with permission from Elsevier. Pg. 136. Flat Curve of Spee Note: A “flatter" plane has a long radius and so as the mandibular teeth move away from a horizontal reference plane at a greater angle and so the cusps can be taller.

Vertical Determinants Lateral Translation Movement Immediate Side Shift

Bennet Angle THE BENNET MOVEMENT A bodily side shift of the condyle on the working side in conjunction with rotation. BENNET ANGLE The angle made by the Sagittal plane and a line drawn from the point of origin of the balancing condyle to the final position. Illustration modified and Reprinted from: Ramfjord & Ash (1971), Occlusion, W. B. Saunders Company., Philadelphia, Pa. with permission from Elsivier, Pg. 75

The Greater the Side Shift, the Shorter the Cusps Will Be BENNET ANGLE (Non- Working side) The angle formed by the protrusive movement and the condylar path along the medial wall of the condyle Mediotrusive Path Protrusive path

Determinants of Occlusal Morphology Fundamentally the Determinants of Occlusal Morphology represent an understanding of GEOMETRY and Three-Dimensional Movement that occurs with every jaw movement Waterpik (Hanau) Modular Articulator