Occlusal Characteristics for Selecting the Extraction Pattern in Orthodontic Cases

Malocclusions commonly are due to arch-size tooth-size discrepancies, and inadequate arch size may have to be resolved by premolar extractions. Treatment planning in such cases usually involves the decision to remove first or second premolars. Objective: This study contrasts occlusal characteristics between first (P1) and second (P2) premolar extraction cases to understand the decision-making process of which teeth to extract in a given malocclusion. Methods: Dental casts of 100 orthodontic cases with Class I malocclusions from American white adolescents were digitized (70 landmarks) at the start and end of treatment to capture the in-treatment movements of all teeth in all three planes of space. Half the cases were P1 extractions; half were P2. A battery of 20 pretreatment occlusal variables (overjet, overbite, arch length, etc.) was used as predictor variables, and the in-treatment changes in each tooth's position were the outcomes. Multivariate linear regression was used to find pretreatment characteristics that predicted which premolars had been extracted. Results: Cases treated with first-premolar extractions exhibited (1) greater incisor irregularity, (2) greater overjet, (3) more frequent interdental spacing, (4) longer arch lengths (1-3 and 1-6), (5) greater overbite, and (6) broader arch widths (3-3 and 6-6). Predictably, the occlusal variables in combination were more predictive than when studied univariately. Only about half the extraction space was used to resolve anterior problems in the average P1 case, and little (ca. 1 mm) was used in the average P2 case. Conclusions: Choosing an extraction pattern appropriate to a malocclusion is a learned skill. This study quantifies some of those diagnostic characteristics that specialists use to choose a premolar extraction pattern suited to a particular malocclusion.