Evaluating the Effect of Canine Retraction with Poul Gjessing Spring and Sliding Mechanics Using Cone Beam Computed Tomography: A Split-Mouth Study

Background: Canine retraction is an important phase of orthodontic treatment following extraction of maxillary first premolars. The choice of retraction mechanics may influence the rate of tooth movement and undesirable effects such as tipping, rotation, and root resorption. This study compared frictional sliding mechanics and frictionless Poul Gjessing (PG) spring mechanics using three-dimensional cone beam computed tomography (CBCT).Aim: To compare the efficacy of maxillary canine retraction using Poul Gjessing spring and sliding mechanics using CBCT in a split-mouth study design. Materials and Methods: Fifteen adult patients requiring bilateral extraction of maxillary first premolars and subsequent canine retraction were initially enrolled. Three patients were lost to follow-up, leaving 12 patients and 24 maxillary canines for analysis. Each patient served as their own control. One canine was retracted using sliding mechanics with a 9-mm nickel-titanium closed-coil spring delivering 150 g of force, while the contralateral canine was retracted using a frictionless PG spring. Retraction continued for four months. CBCT scans were obtained before and after retraction. Rate of canine movement, tipping, rotation, and root resorption were evaluated. Data were analyzed using SPSS version 23 and paired t-tests, with p<0.05 considered statistically significant.Results: The mean rate of canine retraction was 1.20±0.50 mm/month with sliding mechanics and 0.88±0.30 mm/month with PG spring mechanics (p<0.01). Mean tipping was 0.60±0.31° and 4.55±2.80° in the sliding and PG spring groups, respectively (p=0.03). Mean rotation was 2.05±1.39° and 3.79±1.90°, respectively (p=0.02). Mean root resorption was 0.45±0.21 mm with sliding mechanics and 0.58±0.13 mm with PG spring mechanics (p=0.02).Conclusion: Both mechanics were effective for maxillary canine retraction. Sliding mechanics demonstrated a higher rate of tooth movement and comparatively less tipping and rotation, whereas PG spring mechanics showed greater angular changes. The observed root-resorption values were small in magnitude despite the statistically significant between-group difference.