Introduction: In orthodontic treatment, tooth extraction is common to achieve the most acceptable esthetic and functional results for the patients, and the 4 premolars extraction is most common. The Bolton's overall ratio and tooth-size discrepancies are directly affected by premolar extraction. The aim of this study was to investigate the effects of extractions of various combinations of premolars on the Bolton overall ratios and tooth-size discrepancies in different malocclusion groups of a sample of Egyptian orthodontic population.
Materials and methods: This study was conducted on study models of 220 patients with varying malocclusions, their age ranged between 15 and 23 years of age, with a mean age of 17.24 years. The subjects were classified into Class I (80 subjects, 25 males and 55 females); Class II (88 subjects 26 males and 62 females) and Class III (52 subjects 20 males and 32 females). In each malocclusion group, the Bolton's overall ratios were measured and according to the Bolton overall ratio1 standard deviation (91.3 + 1.91%) subjects were divided into three groups:1) Bolton small (BS) group: small overall ratios (smaller than 89.39%, 2), Bolton normal (BN) group: normal overall ratios (between 89.39% and 93.21%, 3), Bolton big (BB) group: big overall ratios (larger than 93.21%). In each malocclusion group, hypothetical tooth extractions were performed on each subject in the following 4 combinations: (1) all first premolars, (2) all second premolars, (3) maxillary first and mandibular second premolars, and (4) maxillary second and mandibular first premolars.
Results: The number of small overall ratios was significantly increased after different categories of premolars extraction. The mean values of normal Bolton's over all ratios group was least affected after extractions of all first or maxillary first and mandibular second premolars (the mean differences were -0.13 and 0.01 respectively).
Conclusions: The Bolton overall ratios were significantly decreased after all categories of extraction combination of the premolarsespecially after extraction of all second premolars or maxillary secondand mandibular first premolars. In Patients with normal Bolton overall ratios who need extraction, it is preferred to extract all first or maxillary first and mandibular second premolars to decrease the effect of various premolar extractions on Bolton's overall ratios.