THE EFFECT OF EXTRACTION OF FOUR PREMOLARS ON INTERMAXILLARY TOOTH-SIZE DISCREPANCY IN DIFFERENT ANGLE'S CLASSES OF MALOCCLUSION (A LABORATORY STUDY

Abstract

This study was attempted to evaluate the effect of premolars extraction on the inter-maxillary tooth size discrepancy and to identify the premolars extraction combination that would alleviate the tooth size discrepancy (if present) for different malocclusion Classes.

The sample consisted of two groups. The experimental group (120 pretreatment dental casts), divided into 30 casts for each malocclusion group: Class I, Class II div.l, Class II div.2 and Class III. The control group consisted of 30 post-treatment dental models of ideally finished orthodontic cases after treatment with four premolars extraction. For each cast enrolled in this study, specific selection criteria were fulfilled. An optimum extraction ratio, which yielded a satisfactory relation between the upper and lower dental arches, was obtained from the control group.

Bolton's tooth size ratio(9.41

was calculated for each set of

models for each Class of the experimental group, these measurements were compared with Bolton's mean ratio using student t-test. Then hypothetical extraction of different premolars combinations was applied on the mean overall ratio for each malocclusion group, the extraction ratio obtained was further compared with the optimum extraction ratio of the control group. Moreover, comparison between the ratios before and after extraction was undertaken.