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Comparison of self-tapping and self-drilling orthodontic mini-implants: an animal study of insertion torque and displacement under lateral loading.

PURPOSE
The aim of this study was to compare two types of orthodontic mini-implants, self-tapping and self-drilling, by measurement of the insertion torques and the displacements under lateral loading in an animal model.


MATERIALS AND METHODS
After predrilling of host sites, 27 self-tapping and 27 self-drilling mini-implants were inserted in vitro in the ilia of country pigs. The axial drilling forces at each host site and the insertion torques during placement were recorded, and the displacements applied by variable lateral force (1 to 9 N) were measured. Analyses of covariance with insertion torques or displacements under lateral loading as the main effect and average drilling forces as the covariate (at the alpha=5% level) were performed to determine statistical significance.


RESULTS
There was a significant difference in peak insertion torque between the self-tapping and self-drilling group (P<.05), except when the average drilling force at host sites was less than 1.2 N (P>.05). In addition, this experiment demonstrated that the lateral displacement of the self-tapping group was comparable to that of the self-drilling group (P>.05).


CONCLUSIONS
During implantation, the self-tapping implants typically had a lower insertion torque than the self-drilling implants. Based on the displacements under lateral loading, however, both the self-tapping and self-drilling implants showed similar resistance to lateral forces.