Root proximity and inclination of orthodontic mini-implants after placement: cone-beam computed tomography evaluation

Root contact by mini-implants should be avoided. Prolonged contact can damage the root and might cause external root resorption. To reduce the proximity of a mini-implant to the root, information about positioning of the implants and the variability of inclination is useful. The purpose of this study was to investigate root proximity and variability of the placement inclination of a mini-implant according to placement position.

Fifty patients with 147 implants (diameter, 1.6 mm; length, 8 mm) were included. Cone-beam computed tomography images were taken of the area around the implant-placement site. The distances between the root and the mini-implant, and the vertical and horizontal inclinations of the placed implants, were measured.

Of 147 implants, approximately 20% were in contact with a root. The vertical inclinations of the mini-implants were 48.3° to 50.4° in the maxilla and 57.5° to 63.3° in the mandible. In the right maxilla, the incidence of root contact with the distal adjacent tooth was significantly greater than that with the mesial tooth.

One fifth of the mini-implants in this study contacted adjacent roots. During placement of mini-implants in the buccal maxillary right alveolar bone, contact with the root of the distal adjacent tooth should be avoided.