Loh H S
Department of Oral and Maxillofacial Surgery, Faculty of Dentistry, National University of Singapore.
Aust Dent J. 1991 Dec;36(6):442-4. doi: 10.1111/j.1834-7819.1991.tb04723.x.
The permanent mandibular second molar is usually described as four-cusped, two placed buccally and two lingually. It has been reported that five-cusp forms were more commonly present in dentitions of mongoloid origin. The prevalence and features of this tooth form were examined in a Singaporean sample of 380 subjects with bilateral presence of the mandibular second molars. One-hundred and sixty four cases (43.1 per cent) were found to have bilateral occurrence of five-cusp forms and thirty-four cases (8.9 per cent) with unilateral occurrence. Six-cusp forms were detected in three cases. There was almost equal prevalence in both sexes and both sides were equally involved in unilateral cases. The extra cusp was smallest, placed disto-buccally and sometimes midway at the distal border. The occlusal outline of five-cusp second molars was rectangular with a somewhat similar groove pattern to the first molar. There was an increase in the mesio-distal width of the crown. The high incidence was comparable with other studies of mongoloid dentitions and it could be considered as an important morphological and racial characteristic of the Singaporean Chinese.
恒下颌第二磨牙通常被描述为四尖型，两个颊尖和两个舌尖。据报道，五尖型在蒙古人种起源的牙列中更为常见。在一个有380名双侧存在下颌第二磨牙的新加坡样本中，研究了这种牙型的患病率和特征。发现164例（43.1%）双侧出现五尖型，34例（8.9%）单侧出现。在3例中检测到六尖型。在性别上患病率几乎相等，在单侧病例中两侧受累程度相同。额外的尖最小，位于远中颊侧，有时在远中边缘的中间位置。五尖型第二磨牙的咬合面轮廓呈长方形，沟纹模式与第一磨牙有些相似。牙冠的近远中宽度增加。高发病率与其他蒙古人种牙列研究相当，可以被认为是新加坡华人的一个重要形态学和种族特征。
