Mini-implant insertion can be performed in various sites, depending on the desired biomechanical movement and on anatomical limitations of the selected areas.
Specifically for maxillary molar intrusion, palatal mini-implant sites seem to be much more effective than the buccal sites. At least 3 advantages can be mentioned:
1.greater range for vertical traction, because of the limited height of attached gingiva at the buccal side.
2.greater cortical bone thickness, which increases the primary cortical bone-to-implant contact, enhancing the mini-implant stability.
3.greater availability of interproximal space, which reduces the risks of root/periodontal damage during mini-implant installation.
Attention should be taken to one potential disadvantage: considering that the distance from the outer alveolar cortical bone to the maxillary sinus is usually shorter in the patatal than in the buccal side (Figure 1), the mini-implant should be inserted as occlusally/marginally as possible, still with an apical direction.
Figure 1. The distances from the outer cortical bone to the maxillary sinus cavity were measured at mid-root level simulating mini-implant insertion angles of 45 and 90 degrees to the long axis of the teeth. Note the shorter distances in the patatal than in the buccal side for both angles of insertion. (Ref. Morten GL, Melsen B and Cattaneo P et al. 2013).
Moreover, mini-implants can also be safely inserted into the midpalatal suture or lateral to it. Mini-implants placed in the hard palate can be useful in supporting a great number of movements, such as posterior intrusion, en masse protraction or retraction, space closures and molar distalization.
The images used to illustrate this post are from the article of Dr Morten G. Laursen, published at The Angle Orthodontist: Laursen MG, Melsen B, Cattaneo PM. An evaluation of insertion sites for mini-implants: a micro-CT study of human autopsy material. Angle Orthod. 2013;83:222-9.