Cusp pattern, tooth size and third molar agenesis in the human mandibular dentition

Abstract

A total of 301 casts, made from white British subjects, aged 18–25 years, were analyzed: ( a) to give further information about mandibular molar cusp morphology, and ( b) to enquire into the extent to which overall tooth size, and the presence or absence of the hypoconulid on the lower first molar, is correlated with agenesis of the third molar. The frequencies with which the variations in cusp and groove patterns occur were, in each lower molar tooth, similar to those reported for other caucasoid populations, although different from, for instance, those typical of negroid and mongoloid groups. In both males and females, the third molar was lacking in 11 per cent and the hypoconulid in 8 per cent. These two features appeared to be un-correlated. The jaw anterior to the lower third molar was smaller where the third molar was congenitally absent than in those with complete dentitions. This contrast affected the mesiodistal diameters of the teeth, to an even greater extent. Elimination of the hypoconulid and congenital absence of the lower third molar are common dental polymorphisms in man. Their high frequency might result from the hypoconulid being the final cusp to appear during development, and from the lower third molar being the last to bud from the dental lamina.