The relationship between Carabelli's trait and the size, number and morphology of the maxillary molars.

AJXHOUGH the importance of Carabelli's cusp in phylogenetic studies and for primary racial classification is generally acknowledged, the exact significance of this variable trait remains obscure.and controversial (MOORREES, 1957; KORENHOF, 1960). In this report we examine the " progressive " versus " regressive " aspect of the controversy on which opinions have remained sharply divided for almost a century. argued that the presence of Carabelli's cusp on the first molar tends to enlarge the occlusal surface, compensating to some extent for the loss of tooth structure associated with reduction of the second and third maxillary molars. DAHLBERG (1963) has suggested that such compensatory addition of tooth material may have been of adaptive signiJicance in natural selection. MOORREES (1957) pointed out that the frequent absence of maxillary third molars in Aleuts (and Mongoloids in general) together with the occurrence of a small percentage of faintly developed Carabelli cusps tends to contradict the " functional adaptation " theory. For compensation to appear in upper molars at the same time with their reduction seemed to KORENHOF (1960) a contradiction also. K~TZSCHKE (1953) and more recently DE JONGE (1960) suggested that reduction and elimination of Carabelli's cusp is related to the simplification of the occlusal surface as exemplified by hypocone reduction. MOOFLREE~ (1957) rendered an opposite opinion with the statement, ". .. the incidence and degree of development of Carabelli's cusp is independent of the number of cusps in the maxillary molars. " The latter view is opposed somewhat by the data of BOLK (1915) which indicate a higher frequency of Carabelli's cusp in the quadricuspal (12.3 per cent) than in the tricuspal second molar (1.7 per cent) and also the data of KEEN@ (1965) which demonstrate a reduction in size and frequency of Carabelli's cusp on first molars that are associated with maxillary third molar agenesis or tricuspal second molars. GARN et al. (1966) found Carabelli's cusp to be " genetically independent " of cusp number and groove morphology of the mandibular first molar and mesiodistal diameter of the maxillary first molar. KORENHOF'S (1960) Malayan material, on the other hand, indicates an increase in crown length associated with larger Carabelli cusps. A 1023