在基于计算机断层扫描技术（CT）和虚拟图像处理技术的灵长类牙齿测量学研究中,经常需要分离三维虚拟模型的齿冠和齿根,再进行后续测量工作,如计算机辅助的生物力学分析、釉质厚度测量等。而分离齿冠和齿根这一步骤,目前有多种方法,如,1)根据齿颈线切分齿冠,或2)人工建立基底平面切分齿冠。为了评估这两种不同的处理方式对后续的牙齿测量学上的影响,本文使用三维方法测量了82例化石和现代人类下颌后部牙齿的釉质厚度,包括南方古猿、早期人属、尼安德特人和现代人。使用配对t检验对比发现,两种方法得到的釉质厚度数值上没有显著差别,但随后进行的种间比较发现,使用基底平面切分齿冠的方法比较费时,更依赖于测量者的人工操作,并且可能弱化了物种间前臼齿绝对釉质厚度的差异,造成系统误差。其原因是对于前臼齿和前部牙齿等齿颈线形状不规则的标本,基底平面难以建立或误差较大。在未来对釉质厚度的种间差异的研究中,特别对齿颈线形状不规则的标本（如人类前部牙齿及猩猩、黑猩猩的牙齿等）,本文推荐使用齿颈线分离齿冠和齿根,测量和计算齿颈线之上的釉质厚度。釉质厚度有一定的分类学、功能形态学和系统发育学意义。本文积累了一批可供未来对比研究的原始数据,并且发现尼安德特人前臼齿的相对釉质厚度显著小于现代人,这与前人利用臼齿、犬齿所做的对比研究结果相同,支持了尼安德特人拥有较薄的相对釉质厚度这一观点。

In computer-aided dental anthropology it is sometimes a regular process to separate the crown from the roots. In order to assess the methodological impact of sectioning crown and roots for the computation of enamel thickness, we compared two digital approaches(separating the crown from the root using the cervical line or a basal plane) for the 3D analysis of enamel thickness on a total number of 82 hominin lower postcanine teeth, including South African fossil hominins(n=26), Neanderthals(n=22), and modern humans(n=34). According to paired t-test, no significant difference is observed in the enamel thickness values between two methods, but subsequent inter-taxa comparisons reveal different results in average enamel thickness(AET) in premolars. Separation based on a basal plane is more operator-dependent, not practical to sinuous cervical margin and might mask between-group distinctions. Besides providing a set of raw data for further investigation, this study reports thinner premolar RET in Neanderthals compared with modern H. sapiens and therefore support the notion that Neanderthal has generally thinner relative enamel. Our results show that, for studies aimed at discriminating among different species, using the cervical margin to isolate the crown from the root is a practical option as it considers the anatomical nature of tooth, especially for those specimens(such as anterior dentition, or molars of Pan and Gorilla) with steep cervical line.