Andrews A H
Res Vet Sci. 1981 Jul;31(1):65-8.
The intra-oral development of the second molar in cattle was examined using a system of molar codes based on degree of eruption. Observations on eight Friesian heifers seen more than once were compared with those from 320 cattle studied by the cross-sectional method. The average ages of the Friesians for a given degree of eruption tended to be higher than those in the larger survey. There were too few data to provide a statistical comparison but, by using the age range for each stage of second upper molar development, it was found that in absolute terms an animal showing no emergence of the tooth was younger than one exhibiting complete eruption of the rostral and caudal units. In addition, in most cases an animal at molar code 1 (rostral unit emerging, caudal unit not visible) was younger than one at molar code 8 (rostral and caudal units both fully up). Although the method of second molar development had limitations in age estimation it did provide an indication at a time before eruption of the first permanent incisor tooth pair and the age range at each stage of molar development tended to be lower than for the permanent rostral teeth.
利用基于萌出程度的磨牙编码系统，对牛第二磨牙的口腔内发育情况进行了检查。对8头多次观察的弗里斯兰小母牛的观察结果，与通过横断面法研究的320头牛的观察结果进行了比较。对于给定的萌出程度，弗里斯兰牛的平均年龄往往高于较大规模调查中的牛。数据太少，无法进行统计比较，但通过使用上颌第二磨牙发育各阶段的年龄范围发现，从绝对意义上讲，一颗牙齿未萌出的动物比一颗上颌和下颌单位均完全萌出的动物年轻。此外，在大多数情况下，处于磨牙编码1（上颌单位萌出，下颌单位不可见）的动物比处于磨牙编码8（上颌和下颌单位均完全长出）的动物年轻。虽然第二磨牙发育方法在年龄估计方面存在局限性，但它确实在第一对恒切牙萌出之前提供了一个指示，并且磨牙发育各阶段的年龄范围往往低于恒上前牙。
