Centric relation

Definition

The maxillomandibular relationship in which the condyles articulate with the thinnest avascular portion of their respective disks with the complex in the anterior-superior position against the shapes of the articular eminencies. This position is independent of tooth contact. This position is clinically discernible when the mandible is directed superior and anteriorly. It is restricted to a purely rotary movement about the transverse horizontal axis (GPT-5).

Importance of Centric Relation

Proprioceptive impulses (impulses of three-dimensional spatial orientation) guide the mandibular movements. In dentulous patients the proprioceptive impulses are obtained from the periodontal ligament.

Edentulous patients do not have any proprioceptive guidance from their teeth to guide their mandibular movements. The source of the proprioceptive impulses for an edentulous patient is transferred to the temporomandibular joint. The centric relation position acts as a proprioceptive centre to guide the mandibular movements.

The centric relation has the following salient features:

• It is learnable, repeatable and recordable position which remains constant throughout life.
• It is a definite learned position from which the mandible can move to any eccentric position and return back involuntarily. It acts as a centre from which all movements can be made.
• If the mandible has to move from one eccentric position to another it should go to the centric relation before advancing to the target eccentric position.

Functional movements like chewing and swallowing are performed in this position, because it is the most unstrained position.

• The muscles that act on the temporomandibular joint are arranged in such a way that it is easy to move the mandible to the centric position from where all movements can be made.
• The casts should be mounted in centric relation because it is the point from which all the movements can be made or simulated in the articulator.
• It is helpful in adjusting condylar guidance in an articulator to produce balanced occlusion.
• It is a definite entity, so it is used as a reference point in establishing centric occlusion.

Centric relation is a learned position (not a default position) and the dentist should teach the patient with patience to move his mandible from the centric relation position.

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