Smith T M, Reid D J, Dean M C, Olejniczak A J, Martin L B
Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, D-04103 Leipzig, Germany.
J Hum Evol. 2007 Feb;52(2):201-16. doi: 10.1016/j.jhevol.2006.09.004. Epub 2006 Sep 23.
Numerous studies have reported on enamel and dentine development in hominoid molars, although little is known about intraspecific incremental feature variation. Furthermore, a recent histological study suggested that there is little or no time between age at chimpanzee crown completion and age at molar eruption, which is unlikely given that root growth is necessary for tooth eruption. The study presented here redefines growth standards for chimpanzee molar teeth and examines variation in incremental features. The periodicity of Retzius lines in a relatively large sample was found to be 6 or 7 days. The number of Retzius lines and cuspal enamel thickness both vary within a cusp type, among cusps, and among molars, resulting in marked variation in formation time. Daily secretion rate is consistent within analogous cuspal zones (inner, middle, and outer enamel) within and among cusp types and among molar types. Significantly increasing trends are found from inner to outer cuspal enamel (3 to 5 microns/day). Cuspal initiation and completion sequences also vary, although sequences for mandibular molar cusps are more consistent. Cusp-specific formation time ranges from approximately 2 to 3 years, increasing from M1 to M2, and often decreasing from M2 to M3. These times are intermediate between radiographic studies and a previous histological study, although both formation time within cusps and overlap between molars vary considerably. Cusp-specific (coronal) extension rates range from approximately 4 to 9 microns/day, and root extension rates in the first 5 mm of roots range from 3 to 9 microns/day. These rates are greater in M1 than in M2 or M3, and they are greater in mandibular molars than in respective maxillary molars. This significant enlargement of comparative data on nonhuman primate incremental development demonstrates that developmental variation among cusp and molar types should be considered during interpretations and comparisons of small samples of fossil hominins and hominoids.
许多研究报告了类人猿臼齿的釉质和牙本质发育情况，尽管对于种内增量特征变异了解甚少。此外，最近一项组织学研究表明，黑猩猩牙冠完成年龄与臼齿萌出年龄之间几乎没有时间间隔，鉴于牙齿萌出需要牙根生长，这是不太可能的。本文所呈现的研究重新定义了黑猩猩臼齿的生长标准，并研究了增量特征的变异情况。在一个相对较大的样本中发现芮氏线的周期为6或7天。芮氏线的数量和牙尖釉质厚度在牙尖类型内、牙尖之间以及臼齿之间均有变化，导致形成时间存在显著差异。在牙尖类型内和之间以及臼齿类型之间，类似牙尖区域（内层、中层和外层釉质）的每日分泌速率是一致的。从牙尖内层釉质到外层釉质有显著增加的趋势（3至5微米/天）。牙尖起始和完成顺序也有所不同，尽管下颌臼齿牙尖的顺序更为一致。特定牙尖的形成时间范围约为2至3年，从M1到M2增加，且通常从M2到M3减少。这些时间介于放射学研究和先前的组织学研究之间，尽管牙尖内的形成时间以及臼齿之间的重叠都有很大差异。特定牙尖（冠部）的延伸速率范围约为4至9微米/天，牙根前5毫米的牙根延伸速率范围为3至9微米/天。这些速率在M1中比在M2或M3中更大，在下颌臼齿中比在上颌相应臼齿中更大。关于非人类灵长类动物增量发育的比较数据大幅扩充，这表明在解释和比较少量化石人族和类人猿样本时，应考虑牙尖和臼齿类型之间的发育变异。
