The present systematic review was conducted to address the following focused question: “In patients with a need for en masse retraction of the upper front teeth, what is the efficacy of orthodontic mini implants for anchorage control compared with conventional anchorage devices?”

The literature search revealed that efficacy of anchorage control of orthodontic mini implants in comparison to conventional devices was evaluated in nine randomized clinical trials (RCTs) [1, 4, 5, 9, 11, 28, 48,49,50, 52]. Seven of these studies employed direct anchorage in the alveolar ridge, whereas one study employed indirect anchorage together with a buccal implant [9], and one study used a mid-palatal implant and indirect anchorage [5]. Each of these studies reported on anchorage loss in the horizontal dimension, whereas vertical and transversal anchorage loss was only addressed in six and one of these studies, respectively. One cohort study also evaluated vertical anchorage loss associated with mini implants [48], whereas transversal changes have also been addressed in one controlled clinical trial and in one cohort study [54, 57].

Data syntheses of respective RCTs revealed a gain of anchorage for direct anchorage in the horizontal and vertical dimension, whereas indirect anchorage was associated with minor amounts of anchorage loss. Conventional treatments were commonly associated with a mesial migration and extrusion of the first upper molars.

Even though all studies favored orthodontic mini implants over conventional devices, distal migration and slight molar intrusion were only observed in groups employing direct anchorage through mini implants in the alveolar ridge. It has been suggested that the distal and intrusive forces result from the direction of the retraction forces causing some binding (or increase in friction) of the archwire to the brackets or tubes. Friction may have prevented sliding thus causing the force to be transmitted through the archwire to the dentition [11, 48, 50]. Whether this effect will be more pronounced if a coil spring is left in place for a couple of months after completion of front retraction as suggested by Upadhyay et al. [48] has not been analyzed so far. Notably, the observed effects varied from absolute anchorage with no tooth migration [4] to varying amounts of distal migration up to − 0.88 mm ± 1.13 mm. Hence, the underlying biomechanical causes need to be further analyzed.