Rate of orthodontic tooth movement after changing the force magnitude: an experimental study in beagle dogs.

OBJECTIVES

To study a possible dose-response relation between force magnitude and rate of orthodontic tooth movement by altering forces during bodily orthodontic tooth movement.

SETTING AND SAMPLE POPULATION

Eight young adult beagle dogs were used. The experiments were carried out in the Central Animal Facility, and all analyses were conducted in the Department of Orthodontics and Oral Biology, Radboud University Nijmegen Medical Centre.

MATERIALS AND METHODS

Orthodontic appliances were placed exerting a reciprocal force on the mandibular second premolars and first molars. A force of 10 or 300 cN was randomly assigned to each side of the dogs. After 22 weeks, all forces were changed to 600 cN. Based on intra-oral measurements, tooth movement rates were calculated.

RESULTS

The premolars showed no difference in the rates of tooth movement with 10 or 300 cN. Replacing 10 for 600 cN increased the rate, but replacing 300 for 600 cN did not. Molars moved faster with 300 than with 10 cN, and changing both forces to 600 cN increased the rate of tooth movement. Data from all teeth were pooled considering their relative root surfaces, and a logarithmic relation was found between force and rate of tooth movement.

CONCLUSIONS

Only in the very low force range, a positive dose-response relation exists, while in higher force ranges, no such relation could be established.