Effect of gradually increasing force magnitude on the rate of canine retraction: a split mouth randomized controlled trial

Abstract Objective To evaluate the effect of gradually increasing orthodontic force magnitude compared with a constant force magnitude on the rate of tooth movement during maxillary canine retraction. Methods This split-mouth randomized controlled clinical trial included 15 patients (30 sides). Each patient received both interventions. On the intervention side, canine retraction was performed using nickel–titanium closed-coil springs delivering progressively increased forces of 50 g, 100 g, and 150 g over three consecutive monthly intervals. On the control side, a constant force of 150 g was applied throughout the study period. Maxillary arch impressions were obtained at baseline (T0) and at 4-week intervals for three months (T1, T2, and T3). Digital model analysis was used to assess the rate and total amount of canine movement. Results No statistically significant difference was observed between the two sides in the monthly rate of canine retraction at any time point (P > 0.05). The total distance of canine movement was 2.58 ± 0.70 mm in the control side and 2.24 ± 0.82 mm in the intervention side, with no significant intergroup difference (mean difference = 0.34 ± 1.08 mm, P > 0.05). Conclusion Gradually increasing orthodontic force magnitude did not enhance the rate of maxillary canine retraction compared with a conventional constant force protocol. Clinical relevance Progressive force escalation during canine retraction does not provide a clinical advantage over constant force application, supporting the use of simpler, continuous force mechanics in routine orthodontic practice. Trial registration The trial was registered in ClinicalTrials.gov Identifier: NCT05643443. https://clinicaltrials.gov/study/NCT05643443 . Registered December 18, 2022.