CLASSIC ARTICLE Group function or canine protection

In the diversified literature on occlusion and its role for functional patterns of the masticatory system, two conflicting concepts stand out: (1) canine protection as described by D’Amico and others is said to favor a vertical chewing pattern and to prevent wear of teeth, as in lateral occlusion where the canine guides the mandibular movement directly through contact or indirectly through periodontal receptors; and (2) group function as discussed by Beyron following his observations on Australian Aborigines implies contact and stress on several teeth in lateral occlusion and indicates abrasion as a positive and inevitable adjustment. Telemetric studies have proved tooth contacts to occur during chewing, contacts initiating periodontal receptor signals. These guiding contacts are considered to be irregular without sliding into occlusion. The cranial part of the chewing cycle motion is analyzed with different methods, and various opinions prevail. Thus, Jankelson et al report lack of uniformity of the cranial part of the cycle, while Suit et al report contradictory observations. The effect of the type of occlusion on the general chewing pattern has been the object of many investigations. Ahlgren reports more regular mandibular movements in test subjects with ‘‘normal’’occlusion. Shepherd as well as Koivumaafound a relationship between the pattern of mandibular movements and the type of occlusion. However, only occasional studies deal with the effect of changes in the occlusal pattern on the masticatory motion. Beyron reported observations of the change to the bilateral chewing pattern after alteration of the occlusion. Butler and Zander found a difference in the tooth contact pattern in two test subjects rehabilitated with two types of fixed partial dentures. Such observations indicate adaptability in the masticatory system to changes in the occlusal pattern. However, there are rarely any detailed reports on the shape and pattern of the masticatory cycle following a change in the occlusal pattern in the individual.