Relationship between root lengths and crown diameters of corresponding teeth.

The, fact that root-length measurements may be made on 450 oblique-jaw radiographs of older adolescents with reasonable replicability even on a year-to-year basis (GARN, VAN ALSTINE & COLE, J Dent Res 57:A114, 1978) opens the possibility of exploring root-length crown-size correspondences in the mandibular dentition. Taking, then, root-length measurements for C through M2 on 122 subjects aged 16 to 17 (69 boys and 53 girls), the cemento-enamel junction-to-apex length measurements were correlated with mesiodistal and buccolingual crownsize measurements of the corresponding teeth. The crown-size measurements were obtained from casts using a tape-punching optical-readout measuring device (OPTOCOM) as previously described (VAN DER LINDEN ET AL, J Dent Res 51:1100, 1972). Correlations were then computer-calculated on a sex-specific basis. Finally, the sex-specific values of r were pooled, using the z transforms of r as described by FISHER (Statistical Method for Research Workers, 1970). As shown in the pooled-sex table, root length and crown size are systematically and positively correlated for both mesiodistal and buccolingual diameters, though to a low order of magnitude. Overall, the root-length crownsize correlations approximate 0.12 and the highest crown-root correlations are on the order of 0.2 to 0.3. Moreover, mesiodistal crown-size measurements apparently show higher correlations with the root lengths (r = 0.13) than do the analogous buccolingual crown-size values (r _ 0.1 1 ) in this pilot study.