Navsa N
School of Dentistry, University of Witwatersrand, Johannesburg.
J Dent Assoc S Afr. 1992 Jun;47(6):257-60.
The present study examined the cusp reduction pattern of molars in two San-Hybrid groups, namely, the Vassekela and Barakwena. Cusp and crownbase area measurements were undertaken on enlarged photographs of maxillary molars and on camera lucida drawings of mandibular molars. The protocone values for the Barakwena were significantly larger than those of the Vassekela and were also the largest of the four maxillary molar cusps (especially in M2). The metacone was the second largest cusp in M1, the paracone the second largest cusp in M2 and M3, while the hypocone was the smallest cusp in all maxillary molars. Maxillary crownbase areas were larger in the Barakwena than in the Vassekela but these differences were not statistically significant. The protoconid, entoconid and metaconid were the largest of the mandibular molar cusps. Generally, the cusp area values in first and third molars were larger in the taller Barakwena than in the shorter Vassekela. These differences were not statistically significant. In second molars, however, an unexpected finding was that crownbase and cusp areas (except the metaconulid) were significantly larger in the Vassekela than in the Barakwena. This study indicates that second molars show more cusp size differences in the two groups than do the other two molars. This may be regarded as a conservative tendency (Korenhof, 1960) in which case it would indicate that some second molar cusps are in a less active phase of evolutionary reduction than the same cusps in first and third molars.
本研究考察了两个桑杂交群体（即瓦塞凯拉群体和巴拉克韦纳群体）中磨牙的牙尖缩减模式。对上颌磨牙的放大照片和下颌磨牙的明视绘图进行了牙尖和冠基部面积测量。巴拉克韦纳群体的原尖值显著大于瓦塞凯拉群体，并且也是上颌四颗磨牙牙尖中最大的（尤其是在M2中）。在M1中，次尖是第二大牙尖；在M2和M3中，副尖是第二大牙尖；而在所有上颌磨牙中，低尖是最小的牙尖。巴拉克韦纳群体的上颌冠基部面积大于瓦塞凯拉群体，但这些差异无统计学意义。下颌磨牙牙尖中，原尖、内尖和次尖最大。一般来说，较高的巴拉克韦纳群体第一和第三磨牙的牙尖面积值大于较矮的瓦塞凯拉群体。这些差异无统计学意义。然而，在第二磨牙中，一个意外发现是，瓦塞凯拉群体的冠基部和牙尖面积（除了后尖小突）显著大于巴拉克韦纳群体。本研究表明，与其他两颗磨牙相比，这两个群体的第二磨牙显示出更多的牙尖大小差异。这可能被视为一种保守趋势（科伦霍夫，1960年），在这种情况下，这将表明一些第二磨牙牙尖处于进化缩减的较不活跃阶段，比第一和第三磨牙中的相同牙尖更为不活跃。
