The Effect of Premolar Extraction on Bolton Overall Ratio in Class I Malocclusion at RSGMP FKG USU

Abstract

Abstract-In orthodontics treatment, to obtain a good and stable occlusion, harmony between the combined mesiodistal width of maxillary teeth and that of mandibular teeth must be attempted. Extraction of premolar is routinely carried out as part of orthodontic treatment, but it can lead to the changes of the overall Bolton ratio and the changes are influenced by different extraction combinations. The purpose of this study is to investigate the effects of premolar extraction on the overall Bolton ratio in Class I malocclusion patients. Mesiodistal tooth width of 40 pretreatment dental casts of subjects with Class I malocclusions was measured with 0.01 mm accuracy digital caliper. The overall ratios and tooth-size discrepancies were determined before and after hypothetical premolar extractions. Before and after extractions, the subjects were divided into small, normal, and large overall ratio groups categorized by the Bolton ± standard deviation definition. Extractions were performed in the following combinations: (1) all first premolars, (2) all second premolars, (3) maxillary first and mandibular second premolars, and (4) maxillary second and mandibular first premolars. Statistical evaluations were performed using One-way ANOVA analysis, Wilcoxon Signed Rank test. Results showed that the overall ratios decreased after extraction in any combinations of premolars. The subjects in Bolton small group were still in small group after extractions. Some subjects of the Bolton normal group were then categorized as Bolton normal and Bolton small after extractions. Most subjects of the Bolton large were classified as the Bolton normal group after extractions. It is concluded that the four premolar extraction combinations had significant impact on the overall Bolton ratio; the overall Bolton ratio is decreased after extraction of premolar in any combinations of extraction.