Correlations between root length and face size.

Mandibular tooth root lengths, as measured on oblique-jaw radiographs, are systematically intercorrelated, with a declining "distance" gradient from adjacent teeth to those more remote in the dental arch (Garn etal., JDentRes 57:270, 1978). They also exhibit low-order positive correlations with the corresponding crown diameters, despite temporal differences in crown completion and completion of root elongation (Garn et al., J Dent Res 57:636, 1978). The question, therefore, arises as to the relationship between root lengths and facial diameters, and the existence of a general "size" factor linking crowns, roots and the bony face. Accordingly, we have made use of root lengths of C-M2, measured as previously described, and 3 facial perimeter measurements on 122 Michigan adolescents, 16-17 years of age. Landmarks included Nasion, Articulare and Gnathion, as located on lateral-skull radiographs of each subject. Derived diameters included face length (N-Gn), face depth (N-Ar) and jaw length (Ar-Gn). Correlations were first sex-specific and then pooled, using the z transform of r, thereby reducing the total number of rs from 30 to 15. As shown in the table, correlations between root length and face size were systematically positive, though of a low order of magnitude averaging close to 0.15 overall. The highest correlations generally involved jaw lengths (Ar-Gn), most of which were individually significant at p< 0.05. The overall trends were highly significant by the sign test (15:0), ignoring questions of independence. In a separate approach, individuals in the upper and lower deciles for root length were compared for facial dimensions. Those with the longest roots generally exceeded those with short roots in all three facial dimensions by a maximum