Mini-implants in Orthodontics: a Systematic Review of the Literature

Introduction: In this article, we systematically reviewed the literature to quantify success and complications encountered with the use of mini-implants for orthodontic anchorage, and to analyze factors associated with success or failure.

Methods: Computerized and manual searches were conducted up to March 31, 2008, for clinical studies that addressed these objectives. The selection criteria required that these studies (1) reported the success rates of mini-implants on samples sizes of 10 implants or more, (2) gave a definition of success, (3) used implants with a diameter smaller than 2.5 mm, and (4) applied forces for a minimum duration of 3 months. Factors associated with implant success were accepted only if potentially influencing variables were controlled. The Cochrane Handbook for Systematic Reviews of Interventions was used as the guideline for this article.

Results: Nineteen reports met the inclusion criteria, but definitions of success, duration of force application, and quality of the methodology of these studies varied widely. Rates of primary outcomes ranged from 0% to 100%, but most articles reported success rates greater than 80% if mobile and displaced implants were included as successful. Adverse effects of miniscrews included biologic damage, inflammation, and pain and discomfort. Only a few articles reported negative outcomes. All proposed correlations between clinical success and specific variables such as implant, patient, location, surgery, orthodontic, and implant-maintenance factors were rejected because they did not meet the selection criteria for controlling those variables.

Conclusions: Mini-implants can be used as temporary anchorage devices, but research in this field is still in its infancy. Interpretation of findings was conditioned by lack of clarity and poor methodology of most studies. Questions concerning patient acceptability, rate and severity of adverse effects of miniscrews, and variables that influenced success remain unanswered. This article includes a guideline for future studies of these issues, based on specific definitions of primary and secondary outcomes correlated with specific operational variables.