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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 unitIntercuspal positionCentric 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 jawExceptions Mandibular central incisor Maxillary second molar
Occlusion is supported and made more efficient after eruption of first permanent molarsInterdental spacing is important for future sufficiency of space in permanent teethProbability 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
Arch Occlusal
relationship
Curves of occlusion
Curve of SpeeCurve of WilsonSphere 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 archLoss of one tooth keeps the adjacent tooth in contact with opposing antagonistMesial 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 teethBuccal cusp tips of mandibular posterior make contact with opposing fossae and marginal ridges of maxillary posterior teethLingual 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 stopKnowledge 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