# A Brief Review on Micro-Implants and Their Use in Orthodontics and Dentofacial Orthopaedics
## 1 Introduction  
Anchorage is one of the most important elements for successful orthodontic treatment. Traditionally, orthodontics employed teeth and extraoral or intraoral appliances for anchorage, often relying on the patient compliance for its effectiveness. Micro-implants (OMIs), also known in orthodontics as temporary anchorage devices (TAD) or mini-implants or mini-screws have been used to realize difficult orthodontic movements. Orthodontic mini-implants can be a powerful aid in resolving challenging malocclusions that require increased anchorage potential. Their use is versatile, minimally invasive, and proves a good ratio between costs and benefits of orthodontic treatments. They can help orthopedic dentofacial treatments by supporting distraction procedures, maxillary protractions, cleft segment expansion, stabilization, and tooth movements into narrow alveolar sites. Anchorage control is essential for an orthodontic treatment's success. The anchorage on micro-implants prevents undesirable movements of tooth elements that were used in classic orthodontic procedures, offers an alternative to orthognathic surgery. As temporary anchorage devices, the use of micro-implants solves difficult problems such as guiding osteo-distractions, fixing maxillary cants after the vertical distraction of a ramus, stabilizing an edentulous premaxilla, moving teeth into atrophic alveolar sites [1]. The skeletalanchorage on micro-implants is a solution to treat adult orthodontic patients with a lack of quantity or quality of dental elements when conventional dental or mobile anchorage is not possible or cases with poor patients' compliance where the wear of mobile devices or elastics is compromised [2]. Their use is the ideal solution in cases where dental anchorage may result in undesirable side effects such as vertical dimension changes produced by the use of conventional inter-maximillary forces [1]. Micro-implants as skeletal anchorage lead to a more effective orthopedic growth modification, and their use helps camouflage orthodontic treatment for those patients who were not eligible for orthognathic surgery [3; 4].  
Surgical atraumatic techniques, regeneration and osseointegration, an environment favorable for the primary healing, and biocompatible materials are necessary for micro-implants success. Other important issues in using micro-implants as anchorage elements are patients' cooperation and the perception of the pain and trauma produced by surgical insertion and retraction procedures [4].  
Many orthodontists avoid using micro-implants as anchorage elements because they are unfamiliar with the surgical procedures required for their insertion or because of fear of failure. Another cause could be a lack of interest in approaching new techniques compared to treatments that are already routine. These limitations should disappear, and orthodontists should also acquire the surgical skills necessary to use micro-implants, The present paper is intended to be a small guide in the practical activity of orthodontists and not only, which can help them in terms of the use of micro-implants by showing the existing types, how to apply them, the clinical situations in which they can be used, and the difficulties that may occur during treatments that use this type of anchorage.  
The aim of this study was to review the literature and evaluate the failure rates and factors that affect the stability and success of temporary anchorage devices used as orthodontic anchorage.