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 (TSD) (Bolton value (BV)), and to determine whether any tooth extraction combinations create more severe discrepancies comparing our result with the results from analogical studies. Hypothetical tooth extractions were performed in all cases by the following combinations: all first premolars, all second premolars, upper first and lower second premolars, and upper second and lower first premolars, estimating extraction influence on TSD frequency and size. 148 pretreatment dental casts were examined. It has been determined that in normal TBI group the smallest discrepancies were created after the second (1.087 mm) and fourth types of combinations have been chosen (1.174 mm). In a low TBI group, the smallest discrepancies occur after first (1.544 mm) and third (1.568 mm) types of removal. In high TBI group the smallest discrepancies appear after type two (3.379 mm) and type four (3.586 mm) have been chosen.