Slow and fast orthodontic tooth movement: an experimental study on humans.

INTRODUCTION: The aim of this study was to investigate the variation in the amount of the orthodontically induced tooth movement in humans and potential associations between the amount of tooth movement with age and location in the mandible or maxilla. SUBJECTS AND METHODS: This study included 11 participants (7 females, 4 males) with an age range of 11.3-28.6 years. In a standardized experimental orthodontic tooth movement protocol, two premolars of each participant were moved buccally during 8 weeks with the use of 1 N force. No functional or localized obstacles were affecting the displacement. Plaster models before and after the experimental tooth movement were constructed, digitized, and superimposed, to evaluate the amount of tooth movement of each tooth. Random effects linear regression analysis was performed to examine associations between tooth displacement, age, and tooth location. RESULTS: The mean displacement of the teeth was 2.7+/-1.4mm. The range of tooth movement varied substantially between individuals (0.6-5.8mm). The displacement of the teeth within the same individual was highly correlated (R (2) = 0.78, P < 0.001). The tooth displacement decreased with age; however, this finding did not reach statistical significance (beta = -0.11, 95% CI: -0.28, 0.05, P = 0.172). The tooth movement was higher in the maxilla than in the mandible (beta = 0.47, 95% CI: 0.81, 0.86, P = 0.018). CONCLUSION: Wide range of tooth displacement revealed slow and fast movers in this sample. Larger displacements were recorded in the maxilla compared to the mandible and in younger individuals.