Incidence and features of three-rooted permanent mandibular molars.

Seven hundred and eighty-six patients of Singaporean Chinese origin requiring extractions of permanent mandibular molars were screened. Personal details, identification of the tooth and the presence or absence of an extra root were recorded. Thirty-two cases (4.1 per cent) exhibited an extra disto-lingual root. None was found in the second molar. The first molar was affected (7.9 per cent) slightly more than twice as often as the third molar (3.7 per cent). The extra root was present almost equally in both sexes with a higher presentation on the left side. Six cases had a fracture of the extra root. A comparison was made with a study done by Tratman' on the same population and with other studies involving those of Chinese and Mongoloid origin in other countries.