Aim: To determine whether there is sexual dimorphism regarding Bolton ratios within four ethnic groups and to compare them against Bolton standards. Methods: The sample consisted of 140 dental study casts of untreated normal occlusion subjects, derived from four racial groups: black, white, Afro-Mediterranean, and Japanese. Anterior and overall Bolton ratios were calculated for each cast. The Kolmogorov-Smirnov test, t test, and one-way ANOVA were used. Results: No statistically significant sexual dimorphism in anterior or total tooth-size ratios were found within any group. Only the Japanese anterior ratio (75.09) was statistically less than the Bolton standard (77.2; P < .001). Conclusion: The Bolton ratio can be applied to the investigated ethnic groups except for the anterior ratio in Japanese patients. World J Orthod 2010;11:e57–e62.

Key words: anterior ratio, overall ratio, tooth-size discrepancy