Nature of contacts in centric occlusion in 32 adults.

Understanding the nature of the intercuspation of the teeth in centric occlusion is necessary for the practice of restorative dentistry. Intercuspation of the teeth is one of the factors responsible for maintaining the correct position of the teeth. Changes in occlusal anatomy at the time restorations are made may result in movement of the involved teeth to new positions of equilibrium. The ideal patterns of tooth intercuspation have been described by Friell,2 for deciduous, mixed, and adult dentitions. Friel described the location of the various contacts between the maxillary and mandibular teeth and divided the contacts into four categories: (1) cusp point contact with a fossa, a groove, or the occlusal embrasure between teeth, (2) ridge contact with an embrasure, (3) ridge contact with a groove, and (4) surface contacts. Friel's illustrations have become classics in this field (Fig 1). More recently, Ramfjord and Ash3 have published drawings of ideal tooth contacts in centric occlusion. In general, these ideal occlusal relations are of such a nature that the posterior mandibular and maxillary teeth are locked when in centric occlusion and mutually support each other against other forces acting on them. Hellman,4 in a discussion of the factors that influence occlusion, classified contacts into the same four groups as Friel. Stuart5