Size and shape analysis of human molars: comparing traditional and geometric morphometric techniques

Dental size and shape have been widely used to study biological relationships among human populations. Although several techniques have been proposed to quantify dental form, few attempts have been made to compare results obtained by application of different techniques. This work aims at comparing the information about size and shape of molar contours obtained from linear measurements, landmarks and semi-landmarks as well as evaluating the variation patterns among populations obtained by each method. The crowns of 35 permanent upper second molars belonging to archaeological samples from three regions of Argentina were analyzed. Buccolingual and mesiodistal crown diameters were measured and centroid size and crown index were used as size and shape descriptors, respectively. Likewise, four landmarks and 79 semi-landmarks were collected from the molar outline and relative warps (RW) analysis was performed on partial warps and uniform vectors; centroid size was estimated to summarize tooth size. The results indicate that size was consistently estimated by the three variable types. On the contrary, noticeable differences were found when the results of molar shape described by linear measurements were compared with those obtained using either landmarks or semi-landmarks. This study shows that considerable information about molar contour is added by using landmarks instead of crown diameters and that some morphological features, such as degree of cusp development, can only be captured by means of semi-landmark analysis. Finally, the interpretation of similarities among samples differs according to the selected description system.