Quantitative assessment of interproximal wear facet outlines for the association of isolated molars

The determination of the minimum number of individuals can be very challenging, especially in an assemblage of fragmentary bones and isolated teeth. Similarities in tooth morphology, degree of wear, and interproximal wear facets (IPWF) are generally used to associate isolated teeth qualitatively. However, no quantitative method has yet been established for an objective identification and matching of isolated tooth crowns. In this study, we analyze the IPWF morphology of adjacent mandibular molars (17 M(1)/M(2) pairs), applying both qualitative and quantitative methods to test a reproducible approach for crown association. The surfaces of distal (for M(1)) and mesial (for M(2)) IPWF were surface-scanned and digitally selected. Three-dimensional (3D) and two-dimensional (2D) outlines of IPWF were analyzed using elliptic Fourier analysis (EFA) and geometric morphometrics methods (GMM). Additionally, teeth were qualitatively associated by visual evaluation of the IPWF outline and by physical matching. Unsatisfactory results with less than 50% of tooth pairs correctly associated were obtained by using both methods, shape analysis (digital approach) and the visual evaluation (qualitative assessment) of the IPWF outline. The physical matching of the crowns showed highly variable accuracy ranging between 53% and 77%. The quantitative form-space analysis of 2D IPWF outlines provided the best results (82% of correctly associated teeth), but no statistically significant differences were recorded when compared with the manual matching. Since three tooth pairs out of 17 could not be quantitatively associated, we suggest that the quantitative analysis of IPWF should be used only in addition with other approaches.