Factors associated with initial stability of miniscrews for orthodontic treatment.

INTRODUCTION: The purpose of this study was to investigate various factors associated with initial miniscrew stability for the prediction of the success rate.

METHODS: A total of 378 miniscrews in 154 patients were examined by reviewing their charts. Potential confounding variables examined were age, sex, jaw (maxilla or mandible), placement site, tissue mobility (firm or movable tissue), type, length, and diameter of the miniscrew, and the number of previous operations. The outcome variable of this study was initial stability, defined as the stability of the miniscrew from placement to orthodontic force application. We used the generalized estimating equations method to estimate the influence of each factor on stability for the correlated outcomes of each patient.

RESULTS: The overall success rate was 83.6% for all miniscrews (316 of 378). After adjusting for the type of miniscrew, the relative success rate in the mandible was 0.48 times that in the maxilla but without statistical significance (crude odds ratio = 0.52, P = 0.13; adjusted odds ratio = 0.48, P = 0.09). There was no statistically significant association of any factors in this model with respect to initial stability.

CONCLUSIONS: These results suggest that initial stability cannot be guaranteed or predicted. For this reason, any treatment plan should consider the possibility of failure.