Sex Discriminatory Effectiveness Using Combinations of Root Lengths and Crown Diameters

Using optical-scanner (OPTOCOM) and radiogrammetric mea- surements on mandibular permanent teeth, root length alone affords sex-dis- criminatory effectiveness equal to or exceeding conventional crown diameters. Combinations of root lengths and crown dimensions yield up to 80% accuracy in sexing with as few as two teeth, and discriminatory effectiveness of 87% with mandibular teeth alone. Root lengths of the permanent teeth are systematically characterized by a degree of sexual dimorphism greater than that for the corresponding crown dimensions of the same teeth (Garn et al., '78a). The root lengths of the permanent teeth moreover, prove to be largely independent of the conventional mesiodistal and buccolingual crown diameters (Garn et al., '78b). Under these circumstances, it might be expected that root lengths, alone, would show sex discriminatory effectiveness at least equal to the corresponding mesiodistal and buccolingual crown dimensions (cf. Garn et al., '77; Black, '78) and that combinations involving root lengths and crown diameters should further improve odontometric sex dis- crimination beyond levels previously attained (cf. Ditch and Rose, '72). To test these various possibilities we have explored the value of radiogrammetrically- determined mandibular root lengths mea- sured from the cemento-enamel junction to the apex of C-M2. This was done on 45" oblique-jaw radiographs of 83 16- to 17-year- old participants in the University of Michigan Longitudinal Study (Garn et al., '78a,b). De- scriptions of the measuring technique, rep- licability and considerations of radiographic enlargement are given in our previous pub- lications. In addition to the dial-reading caliper measurements of root lengths, made directly on the radiographs, we also employed mesiodistal and buccolingual crown diameters of C-M2. These were measured with an X-Y AM. J. PHYS. ANTHROP. (1979) 50: 115.118. coordinate optical-scanner (OPTOCOM) as de- scribed by Van der Linden, Boersma, Zelders, Peters and Raaben in 1972 (Van der Linden et al., '72). Sex-discriminatory effectiveness using all 15 measures (3 for each tooth con- sidered) was tested with a stepwise discrimi- nant function program that allowed the incor- poration of N variables, one at a time (Fox and Guire, '76). In this way, it was possible both to ascertain the discriminatory effectiveness of different combinations of crown size and root length and to determine those crown and root dimensions that contribute most to sex dis- crimination. In the first of the analytic steps, we ex- plored the proportion of individuals correctly sexed, using both individual measurements for each tooth (mesiodistal, buccolingual and root length) as well as combinations of crown measurements and root lengths. As shown in the first table (table l), root length by itself attains discriminatory effectiveness generally equal to or greater than individual mesiodis- tal or buccolingual crown diameters alone. De- spite unequal samples for the different teeth considered-a function of the age and erup- tion status-single root lengths slightly ex- ceed single crown diameters in the proportion correctly sexed for most of the measurements paired. Moreover, the combination of root and crown measurements (MD + BL + RL) gen- erally achieve superior discriminatory effec- tiveness over single crown or root dimensions, tooth by tooth.