Sexual Dimorphism in Modern Human Permanent Teeth Gary T. Schwartz, 1 * and M. Christopher Dean 2 1 Department of Anthropology, Institute of Human Origins, Arizona State University, Tempe, Arizona 85287 2 Evolutionary Anatomy Unit, Department of Anatomy and Developmental Biology, University College London, London WC1E 6JJ, UK KEY WORDS enamel thickness; dentine; dimorphism; tooth weight; growth and development ABSTRACT On average, males possess larger tooth crowns than females in contemporary human popula- tions, although the degree of dimorphism varies within different populations. In previous studies, different amounts of either enamel or dentine were implicated as the cause of this dimorphism. In this study, we attempt to determine the nature of sexual dimorphism in the crowns of permanent modern human teeth and to deter- mine if two contrasting tooth types (permanent third molars and canines) show identical patterns of dimorph- ism in enamel and dentine distribution. We estimated the relative contributions of both enamel and dentine to total crown size, from buccolingual sections of teeth. Our sample consisted of a total of 144 mandibular permanent third molars and 25 permanent mandibular canines of known sex. We show that sexual dimorphism is likely due, in part, to the presence of relatively more dentine in the crowns of male teeth. However, whatever the underlying cause, dimorphism in both tooth root and tooth crown size should produce measurable dimorphism in tooth weight, though this has not been previously explored. Therefore, we provide some preliminary data that indicate the usefulness of wet tooth weight as a measure of sexual dimorphism. Both male permanent third molars and canines are significantly heavier than those of females. The weight dimorphism reported here for both classes of teeth may prove a useful finding for future forensic studies. In particular, weights of canines may be more useful as a means of sexing modern human skeletal material than linear or area measurements of teeth. Am J Phys Anthropol 128:312–317, 2005. ' 2005 Wiley-Liss, Inc. In most contemporary human populations, males pos- sess larger permanent molar crowns than females (e.g., Garn et al., 1964, 1967; Alvesalo, 1971; Townsend, 1979; Harris and Bailit, 1987; Harris and Hicks, 1998; May- hall and Kanazawa, 1989; Kieser, 1990). Historically, this dimorphism has been viewed as being primarily due to larger amounts of either enamel or dentine. Some authors suggested that it is enamel (Moss and Moss- Salentijn, 1977; Moss, 1978; Alvesalo et al., 1987), while others found significant differences in the amounts of dentine (Harris and Hicks, 1998; Stroud et al., 1994, 1998). These and other studies relied on linear measure- ments of tissue thickness derived from either intraoral periapical or bitewing radiographs. In these studies, enamel thickness measurements were confined to the mesial and distal interproximal regions (the so-called ‘‘marginal enamel thickness’’), while dentine thickness was usually represented by a measure of maximum lin- ear distance of the dentine cap between the enamel-den- tine junctions in the mesiodistal plane (Alvesalo and Tammisalo, 1981; Alvesalo et al., 1987; Zilberman and Smith, 1992; Zilberman et al., 1992; Stroud et al., 1994; Harris and Hicks, 1998; Harris et al., 2001). For the most part, these measures were chosen because they are the most accessible and reliable that can be made from radiographs that were taken for clinical reasons. Linear measurements of this sort might, however, be limited for a number of reasons, and one aim of this study was to confirm previous findings using different measurements (tissue areas) made from buccolingual (not mesiodistal) longitudinal sections of teeth and not from radiographs. Larger dentine crown caps in males might also arise, for example, from greater crown heights, and occlusal enamel thickness might similarly influence the pattern of enamel dimorphism in a different way from that recorded interproximally from radiographs that image teeth in the mesiodistal plane. Moreover, given differ- ences (ca. 6.5%) in overall crown size both between males and females and between tooth types (Kieser, 1990), the pattern of similarities/differences in enamel and dentine distribution may or may not differ between anterior and posterior tooth types. There is then a possi- bility that measurements of sexual dimorphism made in different ways might give different results. One suggestion of an optimal measure for comparative purposes is volume of enamel over the entire tooth (Mar- tin, 1983), which necessitates either the use of destruc- tive procedures such as separating the enamel cap from the underlying dentine surface (e.g., Kraus, 1952; Koren- hof, 1960; Nager, 1960; Achermann, 1970; Sakai, 1967; Corruccini, 1987a,b), or noninvasive imaging modalities such as computed tomography (e.g., Conroy, 1991; Schwartz, 1997; Schwartz et al., 1998; Hlusko and Suwa, 2002; Kono, 2004). Linear measurements of tissue thick- ness (e.g., Macho and Berner, 1993; Schwartz, 2000a,b) Grant sponsor: Leverhulme Trust; Grant sponsor: Royal Society. *Correspondence to: Gary T. Schwartz, Department of Anthropol- ogy, Institute of Human Origins, Arizona State University, Tempe, AZ 85287. E-mail: garys.iho@asu.edu Received 14 April 2003; accepted 14 September 2004. DOI 10.1002/ajpa.20211 Published online 28 April 2005 in Wiley InterScience (www.interscience.wiley.com). # 2005 WILEY-LISS, INC. AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 128:312–317 (2005)