A Comparison of Movement Rate in Two Canine Retraction Strategies

Objectives: Although two treatment strategies, translation, or controlled tipping followed by root correction, are commonly used by clinicians in canine retraction cases, there is no clinical consensus on which strategy is more efficient.  We hypothesize that one strategy is significantly faster than the other.

Methods: We selected for a split-mouth trial 5 patients who needed bilateral canine retraction to close extraction space as part of their treatment plan. Two segmental T-loops designed for controlled tipping and for translation were applied randomly to each side. Cone beam computed tomograms (CBCT) were taken immediately pre-and post-space closure to check root alignment.  Initial M: F ratios were determined based on patient-specific finite element models. The canines ended in their upright positions. Maxillary dental casts (taken pre- and post-treatment) were digitized with an OPTIX 400S^® 3D laser scanner. Casts were aligned at the palatal rugae regions using the iterative closest point method, and displacement was calculated. Six displacement components were expressed in the coordinate system (CS) defined in the initial model. Movement rate was calculated by dividing the resultant displacement by the corresponding treatment time. CS origin was at the junction of the incisive papilla and median palatine raphe. Three axes were defined as: x-axis, antero-posterior direction; z-axis, vertical direction; and y-axis, transverse direction.

Results: Controlled tipping T-loops moved canines slightly faster (mean difference = 0.008 mm/day) than translation T-loops. The difference is not statistically significant (p = 0.12) due to a small sample size. The rate for both controlled tipping and translation ranged between 0.01 and 0.03 mm/day.  CBCT data confirmed root position.

Conclusion: With the same force magnitude, controlled tipping strategy is faster than translation although this difference is not statistically significant.  More patients will be needed to statistically prove this.