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