Aim: Mini-implant failure rates of approximately 10%–30% as described in the literature are still not satisfactory. This clinical study investigated the effect of insertion torque and the insertion site on failure rates of orthodontic mini-implants.
Material and Methods: The study was conducted on a total of 493 orthodontic mini-implants placed in 284 patients (128 male, 156 female; age 19.3±9.6 years). The relationship between insertion torques, insertion sites, mini-implant-coupling (tandem implant) and failure of the mini-implants was analysed.
Results: The overall failure rate was 14.6 % (n=72). There was a significant difference of mean insertion torques between the failed (8.0±4.8 Ncm) and the successful group (11.4±5.7 Ncm) (P=0.0013). Below an insertion torque of 7 Ncm the risk of implant failure increased significantly. The lowest failure rates were found in the anterior palate (5.6%). Coupling of two mini-implants in the line of force increased the mini-implant stability significantly.
Conclusions: Failure rates of mini-implants depend on the insertion torque, site of insertion and usage of coupled implants. Below a value of less then 7 Ncm the risk of failure increases. The anterior palate compares very favorably with the alveolar ridges of the maxilla and the mandible in terms of failure rates.