The effect of premolar extractions on tooth-size discrepancy.

The purpose of this study is to investigate whether the extraction of four premolars as a requirement of orthodontic therapy is a factor in the creation of tooth size discrepancies, and to determine whether any tooth extraction combinations create more severe discrepancies. The study is carried out on the pretreatment dental casts of 50 patients with malocclusions. The dental casts were selected according to the main criteria. No tooth-size discrepancy between the mandibular and maxillary dental arches should exist before treatment. Pretreatment mesiodistal dimensions of mandibular and maxillary teeth were measured, recorded on a computer program, and subjected to Bolton's analysis. Hypothetical tooth extractions were performed on each patient by the following combinations: all first premolars, all second premolars, upper first and lower second premolars, and upper second and lower first premolars. The resultant measurements were again subjected to Bolton's analysis to see whether a tooth-size discrepancy had been created. The results were evaluated statistically by the use of paired samples t test. The difference between the pretreatment and postextraction Bolton values was found statistically significant for the first premolar extraction and insignificant for the others. The removal of the four first premolars created the most severe tooth-size discrepancy, whereas the extraction of all four second premolars created fewer discrepancies and the smallest range in the size of discrepancies. The results of this study indicate a new point of view to the question of which teeth to extract when evaluated for tooth size aspect only.