Systematic review of mini-implant displacement under orthodontic loading

A growing number of studies have reported that mini-implants do not remain in exactly the same position during treatment, although they remain stable. The aim of this review was to collect data regarding primary displacement immediately straight after loading and secondary displacement over time. A systematic review was performed to investigate primary and secondary displacement. The amount and type of displacement were recorded. A total of 27 studies were included. Sixteen in vitro studies or studies using finite element analysis addressed primary displacement, and nine clinical studies and two animal studies addressed secondary displacement. Significant primary displacement was detected (6.4–24.4 µm) for relevant orthodontic forces (0.5–2.5 N). The mean secondary displacement ranged from 0 to 2.7 mm for entire mini-implants. The maximum values for each clinical study ranged from 1.0 to 4.1 mm for the head, 1.0 to 1.5 for the body and 1.0 to 1.92 mm for the tail part. The most frequent type of movement was controlled tipping or bodily movement. Primary displacement did not reach a clinically significant level. However, clinicians can expect relevant secondary displacement in the direction of force. Consequently, decentralized insertion within the inter-radicular space, away from force direction, might be favourable. More evidence is needed to provide quantitative recommendations. Mini-implants provide stable anchorage for orthodontics, despite secondary movement over time, report dental researchers in Germany. When teeth are damaged due to misalignment, they must be rebuilt and carefully anchored to the jaw. Recently, developed mini-implants are useful for such anchorage, but they may move over time with use. Manuel Nienkemper and colleagues at Heinrich-Heine University in Düsseldorf reviewed 27 recent research studies about the displacement of mini-implants. They found that movement during the initial placement was insignificant, but secondary movement caused by dental forces over time could cause problems for the patient. The team emphasizes that mini-implants require a suitable bone site with a thin mucosal covering. They also suggest that implant failure could be avoided by inserting the implant slightly off-centre, leaving space in the opposite direction from the main orthodontic forces.