Mandibular molar tooth configurations in different racial groups.

Abstract

The basic human molar configuration-five cusps, a longitudinal groove, and a Y shaped transverse groove-has changed during evolution. The most deviant type (+4) possesses four main cusps separated by a cruciform groove system; the hypoconulid is eliminated. A further deviant is the X pattern. Although the four main cusps meet at a point, the pairs of grooves surrounding the protoconid and entoconid form an acute angle. Other modifications are the Y4 and +5. Studies have tended to ba confined to single population samples. Categorization of occlusal configurations tends to be subjective. Thus it is difficult to compare data from different investigators. This study was undertaken to compare occlusal configurations of permanent mandibular molars of four major racial groups. One hundred thirty sets of permanent first, second, and third molars from the left side of the mandible were examined. Three hundred eighty-one teeth were from caucasians, 319 from mongoloids, 286 from negroids, and 44 from australoids. The australoid teeth were examined from dried skulls only, whereas the negroid and mongoloid samples were based on dried skulls and hydrocolloid casts. Thus, this study was confined to casts or skulls with a full complement of mandibular molars, which were all assessed to bear a definitely recognizable groove and cusp configuration. Each molar was scored according to groove configuration and cusp number. The resulting categories were Y and + groove configurations and 4 and 5 cusps. The category of + groove configuration included the X category, since preliminary trials revealed various gradations between the X and + configurations, which made discrimination difficult and arbitary. The frequencies of occurrence of these categories were compared between the various racial groups by means of the chi-square test. The frequencies of both groove configurations and cusp numbers showed significant differences between the various racial groups (P < 0.001). No significant differences were detected, however, within either the caucasoid or negroid racial groups. There was a significant difference for the groove configuration within the negroid sample (P < 0.001), but no such variation was apparent for the cusp frequency. The data showed considerable molar occlusal variation both between and within the major racial groups, so it is difficult to distinguish with certainty the racial grouping of single, isolated permanent mandibular molars. CO