Skeletal Anchorage in Orthodontics-A Review of Various Systems in Animal and Human Studies

Purpose: The aim of the present investigation was to review and evaluate the current literature on skeletal bone anchorage in orthodontics with regard to success rates of the various systems. Materials and Methods: MEDLINE, PubMed, and Cochrane searches (period January 1966 to January 2006, English language) of animal and human studies using skeletal anchorage during orthodontic treatment were scrutinized. A total of 50 relevant articles were identified which investigated various types of implants. Results: Two types of anchorage systems are used in orthodontics: (1) osseointegrated dental implants, including temporary mid-palatal implants. These systems were associated with a wide variety of success rates in animal studies. In human studies, the systems were shown to be reliable, with success rates between 85% and 100% (ie, systems still functioning at the end of the orthodontic treatment). (2) Nonosseointegrated mini-plates and mini-screw anchorage systems. Titanium mini-plates were associated with 100% success in animals, and hardly any loss of these mini-plates (bone anchors) were lost due to infection in human studies, with success rates between 91% and 100%. Few long-term studies on nonosseointegrated mini-screws were found, but in animal studies, success rates ranged from 90% to 100%. A success rate of more than 75% in human studies is considered favorable for these orthodontic implants, which confirms the clinical applicability of this type of immediate loading anchor support in orthodontics. Conclusions: Both animal and human studies revealed that mesiodistal and intrusion movements can be reliably carried out by means of skeletal anchorage devices. A drawback is that animal studies do not reflect the real orthodontic clinical situation; thus, the outcome of these studies should be interpreted with caution. Human studies, however, show that orthodontic forces between 100 and 400 grams can be applied successfully to skeletal anchorage devices. Appropriate treatment strategies need to be confirmed by randomized prospective clinical trials. (More than 50 references.) Keywords: bone anchors, micro-screws, mid-palatal implants, mini-screws, skeletal anchorage