Abstract:

Objective　The purpose of this studywas to evaluate the role of Angle′s class, overall ratio and anterior ratio in the creation of tooth size discrepancies, and to determine whether any tooth extraction combinations create more severe discrep- ancies.Methods　166 dental casts of orthodontic patients were selected randomly. These models were classified according to an- gle′s criterion. Mesio-distal dimensions of mandibular and maxillary teeth were measured before treatment, and subjected to Bolt- on′s analysis. Hypothetical tooth extraction by the following combinations: all the first premolars, all the second premolars, upper first and lower second premolars, and upper second and lower first premolars, was performed on each patient. The measurement results were again subjected to Bolton′s analysis to seewhether anytooth-size discrepancy had been created. The resultswere eval- uated statistically by means of Logistic regression model.Results　Overall ratio, anterior ratio and extraction models affected me- sio-distal tooth size ratio of both maxillary and mandibular teeth in the final stage of orthodontic treatment, Whereas, the results showed no significant difference among these groups of malocclusion.Conclusion　The results suggested that dentists should al- ways keep in mind that each patient should be treated individually and should be aware of that other factors also played important roles in determiningwhat teeth, if any, should be removed and the Bolton analyses of all kinds of extraction models should be car- ried out, as well as the general Bolton analysis.

Key words: Logistic regression model, extraction model, Bolton ratio