Temporary anchorage devices (TADs) in orthodontics: Review of the factors that influence the clinical success rate of the mini-implants

The mini-implant, temporary anchorage devices (TADS), are now a common method of treatment in Orthodontics with versatility, minimal invasiveness and the relationship between costs and benefits that they offer even today. Skeletal anchorage has, to a large degree, replaced conventional anchorage in situations where anchorage is considered either critical, insufficient, or likely to result in undesirable side effects such as vertical displacements generated by inter-maxillary force systems. Objective. The objective of this study is to carry out a review about the factors that seem affect the success or failure rate of orthodontic mini-implants. A computerized literature review was performed by searching the MEDLINE database (Entrez PubMed, www.ncbi.nlm.nih.gov), Google Scholar, Scopus, Cochrane Central Register of Controlled Trials, Isi Web of Knowledge until March 2016 . The main subject heading "orthodontics" was combined with these keywords mini-implant, mini-screw, micro-implants, mini-implant success rate, mini-implant failure rate, skeletal anchorage, temporary anchorage device (TADS). In the selection process, abstracts were initially read independently by two researchers to identify potentially eligible full text papers which were then retrieved and assessed in order to decide on the final inclusion. Conclusions. The clinical success of orthodontic anchorage by mini-implants depends on the stability of the miniscrews used for fixation. For good stability, the application site must provide bone of good quantity and quality. We can reasonably assume that the stability of the anchorage of the mini-implants could be optimized by selecting a position with particular characteristics of quality and quantity of bone, in relation to cortical and total mandibular and jaw bone thickness. These expected informations are important because they indicates that the bone quality and quantity are significant when considering an implant placement site, but also that there are other confounding factors influencing the success rate.