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OCCLUSION. Dental Anatomy & Occlusion Dent 202. Occlusion. Definition The act of closure or being closed A static morphological tooth contact relationship Includes all factors concerned with the development and stability of the masticatory system and the use of teeth in oral motor behavior
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OCCLUSION Dental Anatomy & Occlusion Dent 202
Occlusion • Definition • The act of closure or being closed • A static morphological tooth contact relationship • Includes all factors concerned with the development and stability of the masticatory system and the use of teeth in oral motor behavior • Includes the integrated system of functional units involving teeth, joints and muscles of the head and neck
Concepts of occlusion • Balanced occlusion • Bilateral contacts in all functional excursions • Prevent tipping of the denture bases • Not necessarily existing in natural dentition because each tooth is a separate unit • Intercuspal position • Centric occlusion Concepts developed in relation to orthodontics, complete dentures and full mouth rehabilitation • None are completely applicable to natural dentition
Overview of primary occlusion • Each tooth occludes with 2 teeth of the opposing jaw • Exceptions • Mandibular central incisor • Maxillary second molar • Occlusion is supported and made more efficient after eruption of first permanent molars • Interdental spacing is important for future sufficiency of space in permanent teeth • Probability of crowding in permanent teeth is related to the amount of interdental spacing in primary dentition
Primary molar relationship • Terminal plane relationship • Flush • 56% - Class I Angle’s molar relationship • 44% - Class II Angle’s molar relationship • Distal step • Class II Angle’s molar relationship • Mesial step • A greater probability for Class I Angle’s molar relationship • A lesser probability for Class III Angle’s molar relationship
Primary molar relationship • Factors influencing the effect of terminal plane relationship on Angle’s molar relationship • Differential growth of the jaw • Forward growth of the mandible • Sufficient Leeway space to accommodate a mesial shift of the permanent molars • Leeway space is the amount of space gained by the difference in the mesiodistal diameter between deciduous molars and premolars
Permanent occlusion • Anteroposterior relationship • Incisors: Class I, II, III • Canine: Class I, II, III • Molars: Angle’s Class I, II, III • Faciolingual relationship • Premolars • Molars
Incisal relationship • Class I • Class II • Class III • Overjet • Reverse overjet • Overbite
Canine relationship • Class I • Class II • Class III
Molar Occlusal relationship • Angle’s Class I • Angle’s Class II • Angle’s Class III
Curves of occlusion • Curve of Spee • Curve of Wilson • Sphere of Monson
Inclination & angulation of the roots of the teeth • Mandibular arch is wider than maxillary arch • Each tooth must be placed at the angle that best withstands the line of forces brought against it during function • If the tooth is placed at a disadvantage, its longevity may be at risk • Anterior teeth are placed at a disadvantage
Antagonists • With the exception of mandibular incisors and maxillary third molars, each tooth contacts two antagonist teeth in the opposing arch • Loss of one tooth keeps the adjacent tooth in contact with opposing antagonist • Mesial or distal drifting into the space disturbs occlusal contact with antagonist teeth
Centric stops • Lingual cusp tips of maxillary posterior make contact with opposing fossae and marginal ridges of mandibular posterior teeth • Buccal cusp tips of mandibular posterior make contact with opposing fossae and marginal ridges of maxillary posterior teeth • Lingual cusps of maxillary posterior teeth and buccal cusps of mandibular posterior teeth are called “supporting cusps” • Areas of occlusal contact that a supporting cusp make with opposing teeth in centric occlusion are “centric stops” • The tip of that cusp is also a centric stop • Knowledge of centric stops are important in restorative dentistry
Movements away from centric occlusion • Lateral • Working side • Non-working side • In complete dentures • Balancing side • Non-balancing side • Movement in TMJ • Tooth guidance • Group function • Canine guidance • Protrusive • Incisal guidance • Retrusive • The most retrusive position is the centric occlusion in complete dentures