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Criteria for Optimum Functional Occlusion Dr. Pauline Hayes Garrett Dr. Patricia W. Kiln Department of Endodontics, Prosthodontics and Operative Dentistry University of Maryland, Baltimore This material is taken from: Okeson, J.P. (2003). Management of Temporomandibular Disorders and Occlusion 6th Ed. , St. Louis, MO: Mosby, Chapter 5 Wheeler’s Dental Anatomy, Physiology and Occlusion, Ash, Eighth Edition, Saunders, 2003, Chapter15, pgs. 421-433 Objectives! • Explain and describe the criteria for optimum function of the masticatory system. • Identify and explain optimum occlusal contacts and function in the absence of pathology. The masticatory system consists of an extremely complex and interrelated group of muscles, bones, ligaments, teeth and nerves Illustration 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.31 The mandible is a bone suspended from the skull by ligaments and a muscular sling. The elevator muscles (masseter, medial pterygoid, and temporalis) raise the mandible. When force is applied, contact is made in three places…the two TMJs and the dentition. These forces are potentially quite heavy so damage could occur at all three sites. Anatomic structures of the TMJ (temporomandibular joint): Articular disc – dense fibrous connective tissue; no nerves or blood vessels so it can endure heavy forces without damage or pain. Illustrations 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.113 The articular disc separates, protects and stabilizes the condyle in the mandibular fossa during functional movements. Fibers from the upper head of the Lateral Pterygoid pull the disk down and forward. ARTICULAR DISC - SHAPE , ATTACHMENTS AND FUNCTION Peripherally the disc is attached to the fibrous capsule and the superior head of lateral pterygoid (anteriorly). Fig. A Medially and laterally the disc is tightly attached to the head of the condyle by the medial and lateral collateral (discal) ligaments. (figure B) They are composed of collagenous connective tissue. These ligaments function to restrict the disc from moving away from the condyle and permit the disc to move anteriorly and posteriorly together with the condyle (as a condyle-disc unit) during translation. They also function during the rotation of the TMJ. Illustrations Reprinted from: Okeson, J.P. (2003). Management of Temporomandibular Disorders and Occlusion, 5th Ed. , St. Louis, MO: Mosby, Chapter 3.with permission from Elsevier. (Fig. A ,pg 113),( Fig B, Pg.14) Positional stability of TMJ • Determined by muscles pulling across the joint to prevent dislocation • Major stabilizing muscles – Masseter – Medial pterygoid – Temporalis – Superior head of the lateral pterygoid CENTRIC RELATION: Most musculoskeletally stable position of the TMJ Optimum functional tooth contacts: Maximum Intercuspation • When closing in Centric Relation results in a cusp tip to cusp tip occlusal position. • The neuromuscular system can possibly slide the condylar position (via a Centric Slide) so that a cusp tip to fossa relationship was attained. Optimum functional tooth contacts • To be in harmony, all must be stable • Stable occlusion leads to both effective functioning AND minimal damage to all components Optimum functional tooth contacts • The musculoskeletal system is capable of applying much more force than necessary for effective function …so… • It’s important to establish occlusal conditions to accept heavy forces without damage while still being efficient Optimum functional tooth contacts • Optimum occlusal conditions, then, require even and simultaneous contact of all possible teeth. • This maximizes the stability of the mandible…and • Minimizes the amount of force on each tooth With only two posterior contacts, all force is loaded on that side causing the muscle system to pull the condyle on the unopposed side further into the mandibular fossa. This causes an unnatural shift and possible damage to one or both sides of the TMJ. With two posterior contacts on each side, the same load is more equally distributed and the mandible is more stable and balanced. As the number of occluding teeth increases, the force to each tooth decreases since the load is distributed over a greater area. This new information allows us to redefine the criteria for optimum functional occlusion: This new information allows us to redefine the criteria for optimum functional occlusion: Centric Relation coincides with maximum intercuspation = optimum functional occlusion = Centric Occlusion. Centric Occlusion may or may not = Maximum intercuspation • The first Tooth Position when the condyles are in centric relation = Centric Occlusion – The occlusion of opposing teeth when the mandible is in centric relation. This may or may not coincide with the maximal intercuspal position. Direction of force placed on teeth • Osseous tissue does not tolerate pressure forces • Pressure forces exerted on bone, cause bone to resorb (go away) • The periodontal ligament helps control these forces and provide stimulation – Pressure = bad – Tension = good • The periodontal ligament converts a destructive force (pressure) into an acceptable force (tension). Periodontal Ligament Bone Periodontal ligament accepts various directions of occlusal force • Cusp tip or fossa contact – Force is directed vertically through the long axis – Force is well accepted due to the alignment of the periodontal ligament fibers Periodontal ligament accepts various directions of occlusal force • Contacts on inclines – A horizontal component causes tipping – Some areas of the periodontal ligament (PL) are compressed while others are elongated – Forces are not effectively dissipated to the bone Criteria for optimum functional occlusion… • The definition must now include the concept that each tooth should contact in such a manner that the forces of closure are directed through the long axis of the tooth – This is also know as Axial Loading Forces applied along the long axes of teeth are generally well tolerated • Axial Loading: the process of directing occlusal forces through the long axis of the tooth • Compare to pounding the top of a fencepost • With proper contact, posterior teeth receive force along the vertical or long axis in MI Forces applied at an angle to the long axis have potential to cause harm • Compare to forces used to remove a fence post • May cause mobility, wear, or fracture Axial loading accomplished in two ways: • Development of tooth contacts on cusp tips or flat surfaces, perpendicular to the long axis of the tooth (marginal ridges, bottom of fossae). • Tripodization – each cusp contacting a fossa in such a way that three contacts points are made • Both of these methods eliminate off-axis forces, allowing the PL to reduce forces to the bone Which teeth can best accept horizontal forces? • Damaging horizontal forces of eccentric movement must be directed to the anterior teeth, positioned furthest from the fulcrum • Examining all anterior teeth, it is apparent that the canines are best suited to accept these forces. [WHY?] Cuspids are best suited to accept horizontal forces of Occlusion • Long, thick roots • Better crown/root ratio • Surrounded by dense bone • Extensive periodontal ligament • Most proprioceptively sensitive tooth in the mouth Posterior disocclusion Guidance Canine Canines disocclude the posterior teeth in lateral excursions. When this condition exists, it is called canine guidance. Scheme of Occlusion: Canine Guidance Scheme of Occlusion: Canine Guidance To restart movie, click on image! IF canines not positioned well (or absent) • When restoring this occlusal scheme the best alternative is group function – Group function is when several posterior teeth on the working side contact during excursions – No contact on non-working side during excursions – No posterior contact during protrusive movements – Most desirable is canine plus premolars and the MB cusp of the first molar – More posterior than the MB cusp of first molar not desirable because of increased force that can be generated closer to the fulcrum (TMJ) and force vectors (muscles). Group function • Laterotrusive (working) contacts must provide adequate guidance to disocclude teeth on the opposite side of the arch immediately… BECAUSE • Mediotrusive (non-working) contacts can be destructive due to the amount and direction of forces applied to the joint and dental structures (horizontal = bad) Group Function: Working Side Note: Shift of midline laterally and slightly anteriorly Group Function: Balancing Side (No Contacts) Scheme of Occlusion: Group Function To restart movie, click on image! Anterior Group Function • A form of articulation in which the canines and incisors (usually just the lateral incisors) function together to disocclude the posterior teeth during lateral and lateral protrusive excursions of the mandible. In this scenario the premolar would probably work in conjunction with the lateral incisor to support the lateral and lateral protrusive excursions. Anterior and posterior teeth function differently • Posterior teeth accept forces well during closure of mouth. Because of their position in the arch, forces can be directed along the long axis of the teeth and dissipated • Posterior teeth function effectively in stopping the mandible during closure ANTERIOR GUIDANCE Posterior Disocclusion Anterior guiding contacts Anterior and posterior teeth function differently • Anterior teeth are not positioned to accept heavy forces. Their labial angle makes it impossible to achieve axial loading. • They CAN direct eccentric forces Illustrations Reprinted and modified from: Okeson, J.P. (2003). Management of Temporomandibular Disorders and Occlusion, 5th Ed. , St. Louis, MO: Mosby., with permission from Elsevier. Pg. 124 • Malocclusion! – This patient has an anterior open bite and will not have the normal wear pattern of a young adult. – Note: This patient has no anterior guidance! Anterior and posterior teeth function differently • Posterior teeth should contact slightly more heavily than anterior teeth in centric occlusion. This is called mutually protected occlusion. Interferences • Three Types: • Interference to the desired Occlusal scheme (Canine Guidance/Group function): excursive interference – eg. Mediotrusive/Non-working side interference • Prematurity (usually a high restoration) • Deflective Occlusal Contact (centric interference-usually natural) Contacts on inclines (eccentric forces) • When forces are NOT effectively dissipated to the bone, a pathologic response may be elicited – Neuromuscular reflex activity • Avoidance • Protection Figures reprinted from: Evaluation, Diagnosis, and Treatment of Occlusal Problems, 2nd ed., Peter Dawson, Mosby,1989. pg.438-439, with permission from Elsevier. Deflective Occlusal Contacts Centric Interferences In these slides, the “red” areas indicate interferences. The indicated treatment is an occlusal adjustment to remove the interference. Arc of closure interferences Line of closure interferences Figures reprinted from: Evaluation, Diagnosis, and Treatment of Occlusal Problems, 2nd ed., Peter Dawson, Mosby,1989. pg.438439, with permission from Elsevier. Summary • When the mouth closes, the condyles should be in the most supero-anterior (musculoskeletally stable) position, resting on the posterior slopes of the articular eminences with articular discs properly interposed. In this position, there should be even and simultaneous contact of all posterior teeth. Anterior teeth contact, but more lightly than posterior teeth Summary • All tooth contacts should provide axial loading of occlusal forces when possible. • When the mandible moves into laterotrusive position, there should be adequate tooth-guided contacts on the laterotrusive side (working) to disocclude the mediotrusive (nonworking) side immediately. The most desirable guidance is provided by the canines (canine guidance) Summary • When the mandible moves in protrusive position, there should be adequate tooth-guided contacts on the anterior teeth to disocclude all posterior teeth immediately= Christensen’s effect • In the alert feeding position, posterior tooth contacts should be heavier than anterior tooth contacts.