Complete denture occlusion
Unlike natural teeth, the artificial teeth act as a single unit. Hence, there should be a minimum of three contact points (usually one anterior and two posterior) between the upper and lower teeth at any position of the mandible for even force distribution and stabilization of the denture.
Complete denture occlusion varies with the type of teeth selected. Anatomic teeth should be arranged using balanced occlusion and non-anatomic teeth are usually arranged using monoplane occlusion. All occlusal forms should at least have a tripod contact in centric relation. Balanced occlusion should have tripod contact even in eccentric relation.
Different concepts of occlusion
Spherical Concept of Occlusion (Monson)
According to this concept, the anteroposterior and mesiodistal inclines of the artificial teeth should be arranged in harmony with a spherical surface.
Organic Concept of Occlusion
Here, the shapes of the teeth are altered to have cusps suitable for the patient. The movement of the condyle determines the direction of the ridges and grooves of the teeth and the mandibular movements determine other factors like cusp height, fossa, depth of the fissure, and concavity of the lingual surfaces.
In organic or organized occlusion, the aim is to relate the occlusal surfaces of the teeth so that the teeth are in harmony with the muscles and joints during function. The muscles and joints determine the mandibular position of occlusion without any tooth guidance. In function, the teeth are supposed to have a passive role and do not influence or determine the path of mandibular movement. (In normal occlusion, tooth factors determine mandibular movements e.g. incisal guidance).
Neutrocentric Concept of Occlusion
According to this concept, the plane of occlusion should be flat and parallel to the residual alveolar ridge. This concept is similar to the monoplane occlusion used to set non-anatomic teeth. The term neutrocentric denotes an occlusion that eliminates the anteroposterior and buccolingual inclines in order to direct the forces to the posterior teeth.
Sears Axioms of Complete Denture Occlusion
Sears published the following factors to be considered that helps to plan a complete denture occlusion.
- Smaller the area of the occlusal surface, the lesser is the amount of occlusal load transmitted to the supporting structures.
- Vertical force on a tilted occlusal surface will produce a non-vertical force on the denture.
- Vertical force-acting on a tilted tissue support will produce a non-vertical force on the denture base.
- Vertical force on the denture base lying over the resilient tissues will produce lever forces on the denture.
- Vertical forces acting outside the ridge crest will produce tipping of the denture.
Ideal Requirements of Complete Denture Occlusion
- Stability of the denture and its occlusion when the mandible is in both centric and eccentric relations.
- Balanced occlusal contacts (tripod contact) during all eccentric movements.
- Unlocking (removing interferences) the cusps mesiodistally so that the denture can settle when there is ridge resorption.
- The cuspal height should be reduced to control the horizontal forces.
- Functional lever balance should be obtained by vertical tooth to ridge crest relationship. (Lever balance is the balance against leverage foces acting on the denture. Presence of positive contact on the opposing side provides lever balance. It differs from bilateral balance in that it does not necessarily require three-point contact).
- Cutting, penetrating and shearing efficiency of the occlusal surface equivalent to that of natural dentition.
- Incisal clearance during posterior functions like chewing.
- Minimal area of contact to reduce pressure while crushing food (Lingualized occlusion).
- Sharp ridges, cusps and sluiceways to increase masticating efficiency.
Occlusal Scheme Requisites to Fulfil the Requirements
Each occlusal scheme has three characteristics, namely, the incisal, working and balancing units. The incisal unit includes all the four incisors. The working unit includes the canine and the posterior teeth of the side towards which the mandible moves. The balancing unit includes the canine and the posteriors opposite to the working side.
The ideal requirement of a complete denture occlusion can be fulfilled by creating or providing the following characteristics for each unit.
- Sharp units for improved incising efficiency.
- The units should not contact during mastication. The units should contact only during protrusion.
- Shallow incisal guidance.
- Increased horizontal overlap to avoid interference during settling (the mandibular denture may slide anteriorly as it settles).
- Cusps for good cutting and grinding efficiency.
- Smaller buccolingual width to decrease the occlusal load transferred to the tissues.
- Group function at the end of the chewing cycle in eccentric positions. (During lateral movement if there is simultaneous contact of the posterior teeth of the working side, it is called group function. In the same situation if the canine alone contacts then its called canine guided occlusion. Canine guided occlusion and group function are usually described in relation to the natural teeth).
- The occlusal load should be directed to the anteroposterior centre of the denture.
- The plane of occlusion should be parallel to the mean foundation plane of the ridge.
- The second molars should be in contact during protrusive action (Protrusive balance).
- They should have contact along with the working side at the end of the chewing cycle.
- Smooth gliding contacts should be available for uninterfered lateral and protrusive movements.
Types of Complete Denture Occlusion
Complete denture occlusion can be of three types namely:
Each type has its own indications and contraindications, advantages and disadvantages. The most important type of occlusion employed in complete dentures is the balanced occlusion.
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