[Measurement of supra-eruption of the human first upper molar in the absence of an opposing tooth].

The situation and configuration of the occlusal plane can be modified by the process of supra-eruption, which can be split up into: active eruption (the tooth leaves its socket) and periodontal growth. In order to dissociate and better by understand them, supra eruption of the first upper molar was observed in the absence of the first lower molar. Three groups of subjects were selected, the first group, our reference group (n = 50), consisted of subjects with complete healthy dental arches for which we could determine the extent of the gingival margin and the crown height. The second group of subjects (n = 50) differed from the former by the presence of a supra-erupted first upper molar. This allowed us to evaluate the migration of the gingival margin and the crown height increase in terms of the length of time the antagonist tooth was missing. The analysis of these 2 values shows that in the early years after the tooth loss, supra-eruption is due mainly to periodontal growth. It is only later that tooth movement beyond the occlusal plane is due principally to active eruption. The third group was made up of subjects showing pathological conditions of the periodontium. We observed an apical migration of the gingival margin and in increase in crown height, resulting from a periodontal regression (passive eruption) and a rapid active eruption.