Sexual dimorphism of the human permanent mandibular canine tissue proportions

Accurate sex estimation is one of the most important steps for the reconstruction of the biological profile of an individual both in a forensic and a paleoanthopologycal context. Previous works have highlighted that elements of the human permanent dentition are sexually dimorphic. Traditional studies of enamel thickness based on two-dimensional measurements from buccolingual sections of teeth showed that the amount of enamel and dentine can differ significantly between males and females. Among the different dental classes, canines show the highest degree of sexual dimorphism. However, the available data on enamel thickness in anterior teeth is very scarce. Thus, the mechanisms underlying the variability are currently not well understood. Indeed, the same pattern of dental tissue distribution that is used for distinguishing modern humans from Neanderthals (relatively smaller amount of dentine and thicker enamel) is used to distinguish males and females in a forensic context. Thus, to better understand the biological meaning of these histological patterns, it is necessary to go into detail about how sex influences the dental tissue proportions in modern human populations. The purpose of the present study is to identify the sexual variability of the dental tissues proportions of modern human permanent mandibular canines, using two-dimensional and volumetric measurements of the enamel, dentine and pulp. We also aim to estimate the accuracy of these features for the sex estimation of isolated remains in a forensic context. The analytical sample consisted of a total of 22 mandibular permanent canines of known sex and age at death from the exhumation of two Spanish cemeteries from the Anthropological Collection of Escuela de Medicina Legal de Madrid. The teeth were scanned by X-ray microtomography (microCT). Following reconstruction, each virtual record was reoriented to obtain crown buccolingual sections and 3D reconstructions were generated after the segmentation process. Then, 2D and 3D variables and ratios described by Olejniczak and Bayle et al. were measured and statistically compared. Our results support previous studies that suggest that males have larger mandibular canines than females . We show that sexual dimorphism is principally due to the presence of larger dentine proportions and enamel-dentine (EDJ) surface in males, whereas the amount of enamel does not differ significantly between sexes. Our study also reveals that 3D variables are more discriminative than 2D variables. Future studies will explore the full potential of these variables for sex estimation of isolated dental remains in modern and fossil human populations.