Comparison of En Masse Retraction and Two-Step Retraction Mechanics in Class I Bimaxillary Protrusion: A Retrospective Comparative Study.

INTRODUCTION: Bimaxillary protrusion is commonly treated using extraction-based orthodontic therapy, followed by anterior tooth retraction. En masse retraction and two-step retraction are widely used space-closure mechanics; however, differences in treatment efficiency, anchorage preservation, and arch dimensional changes remain. This study aimed to compare the outcomes of en masse retraction and two-step retraction mechanics in patients with Class I bimaxillary protrusion undergoing extraction-based orthodontic treatment. MATERIALS AND METHODS: This retrospective comparative study evaluated the completed orthodontic records of 100 patients with Class I bimaxillary protrusion who were treated between 2016 and 2021. The patients were classified into two groups: en masse retraction (n = 50) and two-step retraction (n = 50). Measurements were obtained from the pretreatment and post-treatment study models and treatment records. The variables assessed were maxillary incisor retraction, anchorage loss, treatment duration, retraction rate, extraction space closure efficiency, residual extraction space, and transverse arch dimensional changes. Data were analyzed using an independent samples t-test, a chi-square test, and a Mann-Whitney U test. Statistical significance was set at p < 0.05. RESULTS: Both treatment modalities achieved comparable maxillary incisor (6.84 ± 1.12 mm vs. 6.52 ± 1.08 mm; p = 0.129). The en masse retraction group demonstrated significantly greater anchorage loss, with a first molar mesial drift of 2.18 ± 0.76 mm compared with 1.43 ± 0.61 mm in the two-step retraction group (p < 0.001). Space closure duration was significantly shorter in the en masse group (8.6 ± 1.8 months) than in the two-step group (11.4 ± 2.3 months) (p < 0.001). Extraction space closure efficiency was higher in the en masse group (96.90 ± 2.80%) than in the two-step group (95.40 ± 3.20%) (p = 0.011). Significant reductions in intercanine, intermolar, and interpremolar widths were observed in the en masse group compared with the two-step group (p < 0.001). CONCLUSION: Both retraction mechanics were effective in achieving anterior tooth movement. En masse retraction provided faster space closure and greater treatment efficiency but was associated with increased anchorage loss and greater transverse arch constriction. Two-step retraction demonstrated superior anchorage preservation and transverse dimension stability.