Doctoral Dissertation: A Three-Dimensional Analysis of Age-Related Change in the Adult Craniofacial Skeleton

大多数骨骼研究假设，人类头骨的形状或大小在20岁之后不会改变。事实上，大多数研究都是在这样的假设下进行的：年龄对成人颅骨变异的影响很小，或者没有影响，任何年龄的成年人都可以平等地用于研究人类的颅骨形态。与这一假设相反，许多科学家发现成人头盖骨在性成熟后很长一段时间内发生了显著变化。这给数以百计的临床、古人类学和法医学研究带来了潜在的问题，这些研究在选择人类比较样本时没有考虑颅骨形状与年龄相关的变异性。一个来自医学领域的假设例子最清楚地证明了这一点，尽管这本身并不是医学研究。一些临床研究比较了正常和异常成人头骨的形状，以更好地了解影响头骨发育的遗传病的性质。如果成人头骨随年龄变化，则将60岁正常和异常标本进行比较。老年人在头骨形状和大小上可能表现出很大的差异。使用正常和异常20年的样本进行同样的比较。另一方面，老年人可能表现出很少的差异或没有差异。根据对比样本的年龄组成，医生可能会避免治疗实际上是病理性的头骨区域，或者尝试纠正个人的头骨，只是看起来不正常。研究人员永远不会想到比较年龄不匹配的青少年，但这是成年人的常见做法。如果存在成人颅骨改变，任何不考虑样本中年龄差异的颅骨研究都不能确定其结果的有效性或不偏不倚的性质。这项拟议的研究将使用三维方法严格测试成人颅骨稳定性的假设。多个已知年龄和性别、不同阶段的牙齿脱落和来自不同地理区域的骨骼样本将被检查，以寻找与年龄相关的颅骨变化的系统模式。三维坐标数据将从头骨和下颌骨上的115个地标中收集。这些数据将使用欧几里德距离矩阵分析进行分析。使用这种方法的一项初步研究支持成人头骨存在系统性变化，并记录了这种变化模式的性别差异，这些差异在以前的研究中没有被检测到。这些先导数据表明，在分析人类头骨形状时，迫切需要考虑成人年龄相关的变化，以及拟议的研究在重组和重新解释以前的工作中具有重要作用。

Most skeletal research assumes that the human skull does not change in shape or size after age 20. Indeed, most studies work under the assumption that aging plays little or no role in adult cranial variation, and adults of any age can be used equally in a study of human cranial form. Contrary to this assumption, many scientists have found significant change in the adult skull long after sexual maturation. This poses potential problemsfor hundreds of clinical, paleoanthropological, and forensic studies that donot consider age-related variability in skull form in their choice of humancomparative samples. A hypothetical example from the medical realm demonstrates this most clearly, though this is not itself medical research. Some clinical studies compare the shape of normal and abnormal adult skulls to better understand the nature of genetic diseases affecting skull development. If the adult skull changes with age, a comparison between a normal and abnormal sample of 60 yr. olds might display extensive differences in skull shape and size. The same comparison using samples of normal and abnormal 20 yr. olds, on the other hand, might show few or no differences. Depending on the age-composition of comparative samples, doctors may refrain from treating skull regions that are actually pathological, or alternatively, attempt to correct an individual's skull that only appears to be abnormal. Researchers would never think of comparing non-age-matched juveniles, yet this is common practice with adults. If adult cranial change exists, any study of the skull that does not consider variation due to age in their samples cannot be sure of the validity or unbiased character of their results. The proposed study will rigorously test assumptions of adult cranial stability using three-dimensional methods. Multiple skeletal samples of known age and sex, differing stages of tooth-loss, and from different geographic regions will be examined for systematic patterns of age-related change in the skull. Three-dimensional coordinate data will be collected from 115 landmarks on the skull and mandible. These data will be analyzed using Euclidean Distance Matrix Analysis. A pilot study using this method supports the presence of systematic change in the adult skull and documents sex differences in the patterns of this change that were not detected in previous studies. These pilot data demonstrate the critical need to consider adult age-related change in analyses of human skull form, and the essential role the proposed study has in the restructuring and reinterpretation of previous works.