Aim: To determine the prevalence of distolingual roots in mandibular first molar teeth in Taiwanese Han Chinese, and its impact on root morphology. Methodology: The presence of distolingual roots in 375 subjects (521 molars) were assessed from 624 patients attending the dental clinics of medical centres around Taiwan island from August 2004 to April 2007 using computed tomography. The following observations were made: (i) numbers of roots and canals, (ii) mesial and distal root types and (iii) levels of furca in the molars presence or absence of distolingual root. Results: The mean age of the subject was 45; 43% were women. Among all the examined molars, 56%, 27% and 18% were two-, three- and four-rooted, respectively. Two per cent, 72% and 26% of molars had two, three and four canals, respectively. All of the four-rooted molars had four canals, but all of the molars with four canals varied in the number of roots. All molars with distolingual roots had two mesial canals. Bilateral consistency in terms of distolingual root, root canal number, root number and root type was observed in subjects with bilateral molars. In molars with distolingual roots, a higher prevalence of two mesial roots and a shorter mesial root trunk were observed than in teeth without distolingual roots. Conclusions: A distolingual root was found in 22% of molars and in 24% of the subjects examined. Most subjects with a distolingual root had them bilaterally. The presence of a distolingual root was associated with variation in the root morphology, including the furcation level, the root type and the number of roots and canals.
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