This chapter reviews the current knowledge of the biological reactions to temporary anchorage devices (TADs) and the factors that affect a successful application of TADs. In addition to clinical investigations, finite element analysis (FEA) is also extensively used to analyze the factors on the mechanical stress surrounding TADs. The tissue reactions to TADs should also contain two phases: the primary stability (mechanical) that is derived from a mechanical engraving of the titanium screw implant in the bone tissue; and the secondary stability (biological) that results from the ongoing process of Osseointegration. In clinical investigations, the failure of TADs was partially attributed to a local infection and inflammation. Therefore, the assessment of factors involved in such inflammation has become crucial to increase TAD stability in orthodontics. The TADs are widely used in orthodontics for the correction of various orofacial deformities and malocclusions.