Objective: This study compared treatment-associated changes in hard-tissue morphology of
borderline cases treated by extraction versus non-extraction orthodontic methods.
Methods: Seventy-one
borderline cases were identified by 5 associate professors from Peking University, orthodontic clinic. Forty-five finished cases were collected as a study sample. Among them 21 cases had extraction treatment, 24 had non-extraction treatment. Among extraction cases, 13 cases had four first premolars (4PM1) extracted, and 8 had four second premolars (4PM2) extracted. Twenty conventional cephalometric measurements of hard-tissue morphology were examined. Differences between the non-extraction and the pooled extraction groups were studied by t-test. Differences between the non-extraction group and the two extraction groups considered separately were studied using analysis of variance.
Results: Between non-extraction group and pooled extraction groups, the post-treatment changes of MP/PP, L1/MP were statistical significantly different (p<0.05 and p<0.001 respectively). Among the non-extraction, 4PM1 extraction and 4PM2 extraction groups, analysis of variance showed statistical significant differences in change for U1/PP and L1/MP. For U1/PP, the changes were: -0.87±10.78 in non-extraction group, -11.84±8.42 in 4PM1 extraction group
and 3.10±13.87 in 4PM2 extraction group. Statistically significant differences were found between the non-extraction group and the 4PM1 extraction group (p<0.01) and also between the two extraction groups (p<0.01). For L1/MP, the changes were: 8.75±10.61 in non-extraction group, -5.41±8.34 in 4PM1 extraction group, and 2.83±6.39 in 4PM2 extraction group. Statistical significant differences were found between non-extraction group and 4PM1 extraction group (p<0.001), and also between the two extraction groups (p<0.05).
Conclusions: The main difference detected between extraction and non-extraction changes in borderline cases was incisor inclination. The changes for second premolar extraction were closer to non-extraction than those for first premolar extraction. There were significant differences between first premolar extraction and non-extraction, and between first premolar extraction and second premolar extraction.
Supported by Ministry of Health PR China