Tomographic mapping of mandibular interradicular spaces for placement of orthodontic mini-implants.

INTRODUCTION The purposes of this study were to determine the ideal sites for placement of orthodontic mini-implants in mandibular interradicular spaces by using computed tomography (CT) and to suggest length, diameter, and angulation of the mini-implants. METHODS CT scans were performed on 15 dry human mandibles with 1-mm tomography slices. Measurements were made at 3, 5, 7, 9, and 11 mm heights from the bone crest. Bone thickness was obtained for the buccolingual, lingual cortex, and buccal cortex areas. The mesiodistal interradicular distance and the distance from the bone crest to the mental foramen were also measured. Simulated placement of 1.5 x 9 mm mini-implants was performed in the tomographic images at angulations 10 degrees , 20 degrees , and 30 degrees . Twenty-four 1.5 x 9 mm mini-implants were then placed in the mandibles, and a new set of CT scans was obtained. Mandibles with implants were sectioned, enabling direct observation. RESULTS Based on 3000 measurements, means and standard deviations were obtained. The thickness of the mandibular alveolar bone in the cortical buccal and lingual areas, and the interradicular distances increased from the cervical toward the apical aspects. In descending order, the widest spaces were found between the first and second molars, the second premolars and the first molars, and the first and second premolars. Between the premolars, caution should be exercised starting at 9 mm from the bone crest because of the mental foramen. Between the incisors, the placement of interradicular mini-implants is not feasible. Between the first premolars and the canines, no appropriate region was found. Between the lateral incisor and the canine, at a height of 11 mm, a device can be placed but only with utmost care. CONCLUSIONS The most convenient site for implant placement in a mandible was between the first and second molars, with a 10 degrees to 20 degrees inclination, but orthodontic mini-implants should not exceed 1.5 mm in diameter and 6 mm in length.