Abstract: Objective: To establish an equation between mesiodistal crown diameters of different types of malocclusion teeth and other teeth, and to use just one equation to describe the situation of the teeth with same position and same gender. Methods: Pre-treatment casts of malocclusion patients' diagnosed as classⅠ, Ⅱ, Ⅲ were screened out. 100 for each type, and 50 males 50 females respectively. Among these, 45 were designed as analog samples and the other 5 casts were set as test samples. An equation for these three classes of malocclusion was established between the mesiodistal teeth diameter measured by a vernier caliper and that of the other teeth, and then compared with linear regression analysis. Results: The equation between mesiodistal crown diameters of different types of malocclusion teeth and that of other teeth was established. Comparing the predictive value with measured value, there existed no statistical significance neither GAS nor linear regression analysis but the absolute mean error of test samples by GAS was less than by linear regression analysis. Conclusion: The prediction accuracy by GAS is better than by linear regression analysis method.The established equation is of value to do full dentition gap analysis for different types of malocclusion.

Key words: Different types of malocclusion, Mesiodistal crown diameters, Genetic algorithms