Removal torque of osseointegrated mini-implants: an in vivo evaluation

The possibility of using osseointegrated implants for orthodontic anchorage is well known. When absolute orthodontic anchorage is needed, mini-implants can be inserted in the non-alveolar bone area (e.g. palatal process or retromolar areas of the mandible). However, what happens to these implants at the end of treatment can be a problem as neither trephine explantation nor simply leaving the subgingival part of the implant in the bone permanently are acceptable solutions. In this investigation, 16 Exacta small screw titanium implants (Exacta MS series conical profile, with a diameter of 3.3 mm and a length of 7.0 mm) were used as indirect orthodontic anchorage in 16 adult patients. The site of implant placement was established based on radiological investigations. There were eight palatal and eight retromolar implants inserted in seven males and nine females (mean age 30.3 years). On completion of treatment, the implants were unscrewed to the maximum limits of their removal torque values (RTVs) and the obtained data were analysed using a t-test. An in vitro study before the clinical trial was also undertaken to determine the maximum mechanical resistance of the unscrewing system. The clinical procedure and average RTV (67.91 +/- 12.47 N/cm) were considered compatible with safe, non-invasive removal of the implant followed by rapid anatomical reconstruction of the area involved.