Experimental evaluation of tooth movement in the beagle dog with the mini-screw implant for orthodontic anchorage

Introduction: The purposes of this study were to evaluate the stability of mini-screw implants (MSIs) and tooth movements in relation to the timing, amount, and location of force application. Additionally, clinical measurements of peri-implant health were recorded to determine predictors for MSI failure. Methods: A randomized split-mouth design was used in 7 skeletally mature male beagle dogs. All third premolars were extracted to facilitate retraction of the second premolars via sectional orthodontic appliances. In the maxilla, the effect of delayed vs immediate loading was tested under constant force (25 g). In the mandible, the effect of force level (25 vs 50 g) was tested on immediately loaded MSIs. All experimental MSIs had a corresponding unloaded control. Clinical records and measurements of tooth movement were taken at specified intervals. Results: The overall success rate of the implants was 93% with no significant effects of timing, amount, or location of force applied. Peri-implant tissue health was not predictive of MSI failure. The maxillary and the mandibular second premolars were moved 3.3 ± 1.0 and 3.8 ± 1.3 mm, respectively. No significant differences in tooth movement were observed between immediate and delayed loading, at either 25 or 50 g or force, or between the maxilla and the mandible. Conclusions: These results support the notion that immediate MSI loading with light forces (25 and 50 g) can be accomplished with high rates of success, producing clinically relevant amounts of tooth movement that are not influenced by the amount of force or the location at which they are applied.