Asymmetrical Eruption of Permanent Teeth in Australian Aborigines

Objectives: A better understanding of the factors influencing tooth eruption is important given the association between altered eruption patterns and crowded or decayed teeth. Hence, the aims of this study were to quantify the extent of asymmetry in tooth eruption and to determine whether eruption asymmetry was significantly influenced by sex, tooth position or timing of emergence. Additionally, directionality of asymmetry and variation between ethnic groups were also explored. Methods: Data collection was based on the examination of serial dental casts from a sample of 90 Aborigines (50 male, 40 female) aged 6-18 years from the Yuendumu settlement in the Northern Territory. These casts were obtained at yearly intervals from the 1950s to the early 1970s. Tooth antimeres on each cast were compared using a 4-graded eruption score (Heikkinen et al., 1999: Dental Morphology 1998, pp 473-482). Casts that were damaged or had missing teeth were excluded. Asymmetry frequencies were calculated and associations between variables assessed using SPPS software with statistical significance set at p<0.05. Results: High (>70%) inter- and intra-observer concordances confirmed reliability of the recording system. Significantly higher asymmetry was found for more distally-positioned teeth (I2-31%, P2-70%, M2-45%, M3-59%) and among males. Correlation coefficients between symmetry level and mean emergence time ranged from -0.64 to -0.72 indicating that later-erupting teeth tended to show more asymmetry. Significant directional asymmetry was found for the Mx I1, I2 and Md I2, C, P1, P2 (right earlier) and the Mx M2, M3 and Md M1 (left earlier). No clear differences in patterns of eruption asymmetry were noted between ethnic groups, possibly due to methodological differences between studies. Conclusion: Patterned asymmetry for permanent tooth eruption was noted in a sample of Australian Aborigines, with the distally positioned, later-forming teeth showing the highest levels of asymmetry.