Evaluation of orthodontic mini-implant anchorage in premolar extraction therapy in adolescents

Introduction: The purpose of this study was to determine the success rate, positional stability, and patient evaluation of orthodontic mini-implants (OMIs). Methods: Thirteen patients (8 girls, 5 boys; average age, 14 years 10 months) were treated with 82 OMIs measuring 1.6 mm in diameter and 6 mm in length placed in the buccal alveoli (1 unloaded OMI and 1 loaded OMI per quadrant). The right or left side of each arch was randomly selected for immediate loading with up to 250 g of direct force; the contralateral side was loaded 3 to 5 weeks later. Serial impressions, clinical observations, and orthodontic maintenance were performed until adequate space closure was achieved. Results: The overall OMI success rate was 70.73%. As calculated with a mixed-model analysis, there was no statistically significant difference between the success rates of immediately loaded OMIs (80.0%) and delayed loaded OMIs (80.95%). The combined success rate for loaded OMIs (80.49%) was significantly higher than that of unloaded OMIs (60.98%). Patients' motivation for OMI treatment was primarily the desire to avoid headgear. Using a 100-mm visual analog scale, the patients indicated average scores of 54.77 for the amount of pain during OMI placement and 27.10 for the amount of pain during OMI removal. Conclusions: OMIs are a predictable, effective, and well-tolerated anchorage source for adolescents. Neither the timing of force application nor the force itself precipitated failure of the OMIs. Orthodontic forces can be applied immediately to OMIs. Various anatomic and behavioral conditions unique to adolescents and a clinical learning curve can affect the success rate of OMIs.