[A study on tooth marks--morphological differences between dentitions and tooth marks thereof and selection of...

Tooth marks in human skin assume so various aspects depending upon such factors as the forms and properties of the bitten regions that they do not necessarily represent the dentition of a suspect as it is. In the present study a cylindrical dummy with skin-like elasticity was used as a recording medium on which to make experimental tooth marks. Morphological comparisons were made of the tooth marks with the oral models by the use of measurements of 28 items. Furthermore, the selection of the effective items for identification was also considered by applying the discriminant analysis to the rate of morphological change on the base of the measurements. The results obtained were as follows: 1) In respect of the tooth marks and the oral models derived from the same subject, the values of their difference (i.e., the measured value of the former minus that of the latter) were calculated for each item so that the directional changes of the tooth marks should be investigated. It was found that the values for the lengths of the dental arch showed a tendency to be positive and that those for the widths negative, and that the values for the angles of lateral incisors and canines tended to be positive. 2) Among the mean values of the rates of morphological change for each item on the same subject, those for the lengths of the dental arch were larger, whereas those for the widths were smaller. Regarding the widths of tooth edge, large were those values for the mandibular canines in particular. 3) The identifying indices were calculated from the rate of morphological change on the basis of the measured values for 28 items in 400 combinations of the oral models with the tooth marks. They indicated that, out of the combinations derived from different subjects, 11.3% for maxillary overlapped those from the same subject and so did 8.7% for mandible in the distribution of their indices. 4) A discriminant analysis was carried out for identification. The range of coefficients thereby obtained rendered it possible to consider how much each item contributed to identification. As a result, the range of the inter-canine distance was largest. It could be considered that these items are effective in identification for tooth marks by using measurements.