Determination of pretreatment and patient cooperation factors affecting treatment outcome in orthodontic treatment with premolar extraction: a retrospective cohort study

The objective was to evaluate the outcomes of orthodontic treatment following two or four first premolar extractions using the ABO-OGS and potential influencing factors. This study included 100 patients treated with upper two-premolar extractions (TPE) (mean age: 14.7 ± 2.3) and 85 patients treated with four-premolar extractions (FPE) (mean age: 14.5 ± 3.0). Pretreatment parameters, cephalometric radiographs, and dental casts were evaluated. Patient cooperation was assessed based on regular appointment attendance, elastic use, recurrent bracket failures, and oral hygiene. There were no significant differences between TPE and FPE groups in pretreatment age, case complexity according to ABO-DI, or treatment duration. Total OGS scores were comparable between the two groups; however, marginal ridges were better aligned in the TPE group (p = 0.005). In both groups, pretreatment lip properties and additional mechanical requirement were associated with the total OGS score (p < 0.05). Additionally, in the TPE group, inadequate lip-closure and curve of Spee depth affected the total OGS score, whereas U1-PP angle had an impact in the FPE group (p < 0.05). In the TPE group, patients who didn’t attend appointments regularly had higher interproximal contact scores, and those who didn’t use elastics regularly had higher total OGS and occlusal relationship scores (p < 0.05). In the FPE group, patients with recurrent bracket failures had higher total OGS, tooth alignment, and occlusal relationship scores (p < 0.05). Poor oral hygiene was associated with higher occlusal contact scores (p < 0.05). Pretreatment factors, including incisor proclination, lip properties, additional mechanical requirement, and patient cooperation during treatment, influenced treatment outcomes in patients treated with TPE and FPE. D-KA24/28.