Fluctuating asymmetry of the permanent mandibular molars in a Japanese population

The purpose of the present study is to investigate the pattern of fluctuating odontometric asymmetry of permanent mandibular first and second molars in a Japanese population. Dental plaster casts of 112 (57 males and 55 females) Japanese undergraduate dental students were used. The mesiodistal and buccolingual diameters of the whole crown and trigonid and talonid crown components were taken on the left and right sides of the mandibular permanent first and second molars. Crown areas were also calculated. The fluctuating asymmetry (FA) value was obtained by dividing the absolute side difference by the absolute mean size of the left and right teeth: FA = abs (R-L)/((R + L)/2). Fluctuating asymmetry between mandibular first and second molars was significantly different with the mandibular second molar showing higher asymmetry in both males and females. Meanwhile, fluctuating asymmetry between males and females in the first and second molars was not significantly different in all measured dimensions. With regard to trigonid and talonid components, fluctuating asymmetry of the distal talonid area was significantly larger than the mesial trigonid area in the mandibular permanent first molar of males (P < 0.01), and asymmetry of buccolingual diameter of the talonid was also larger than that of the trigonid in the mandibular permanent second molar of males (P < 0.05). In conclusion, these findings suggest that the crown dimensions of later developing teeth in the mandibular molar tooth class and crown component in the same molar tooth show more asymmetry and, therefore, are more affected by external factors.