Centric relation (not centric occlusion)is the relation of the mandible to the maxilla when the mandibular condyles are in the most superior and retruded position in their glenoid fossa with the articular disc properly interposed.
Centric relation is also called ligamentous position or terminal hinge position. At centric relation both the condyles are simultaneously seated most superiority in their glenoid fossa.
In trying to obtain centric relation the mandible may be forced too far back, thus the term unstrained appears in some definitions.
Centric occlusion is that position of the mandibular condyle when the teeth are in maximum intercuspation. Centric occlusion is also called inter-cuspal position or convenience occlusion.
Centric relation and centric occlusion should coincide in order to have perfect harmony between the teeth, the temperomandibular joint and the neuromuscular system. Some studies have shown that majority of the population have a maximum inter-cuspation 1 —2 mm forward of centric.
Maximum cuspation can also occur without being in centric. This is called maximum intecuspation, habitual occlusion or acquired occlusion.
They are areas of the teeth that contact the opposing teeth. Centric contacts have been classified into posterior centric contacts and anterior centric contacts.
Posterior centric contacts
The posterior centric contacts consist of the facial range of contacts and the lingual range of contacts. Facial range of posterior centric contacts involve the mandibular Facial cusp tips contacting the central fossae and mesial marginal ridges of the opposing maxillary teeth.
Lingual range of posterior centric occlusion involve the maxillary lingual cusp tips contacting the central fossae and distal marginal ridges of the opposing mandibular teeth.
Anterior centric contacts
Anterior teeth have one range of centric contacts and are in line with facial range of posterior centric contacts.
Posterior centric contacts result in axially directed forces as convex cusp tips occlude on an opposing tooth area that is perpendicular to the force.
However centric contacts often occur in inclines of posterior teeth. These contacts that occur on inclines are called poded centric contacts.
The contacts occurring on inclines should be balanced by an equal contact on an opposing incline to resolve the forces in an axial direction. If the contacts occur on two inclines, the contact is termed bi-poded contact.
Contacts (not centric occlusion) that occur on three inclines are called triopoded contacts. Contacts that occur on four inclines are called quadra-poded contacts.