Tomographic analysis of the interalveolar space and thickness of the vestibular cortical bone in the parasymphyseal region of adult human mandibles.

Purpose: The aim of this study was to determine by computed tomography (CT) the interalveolar distance on mandible relative to the canine, first and second pre-molar, and the thickness of the cortical bone in the same region.

Methods: A hundred adult cadaveric dentate human hemi-mandibles were examined. A point (P) above the upper margin of the mental foramen was determined, the height at which monocortical screws are inserted to place miniplate according to the technique to treat mandibular fracture. Then, points A, B and C at the same height as point P, referring to the dental units namely canine, first and second pre-molars were marked to determine the CT cut level to measure cortical bone thickness and the interalveolar distance.

Results: The figures showed no statistically significant difference between the sides. The thickness of the vestibular cortical bone was less than 3.0 mm in 96% of the samples. In 91% of the samples the interalveolar distance between canine, first and second pre-molars was greater than 2 mm, a potentially safe condition to insert 2.0-mm diameter monocortical screws at the study points.

Conclusions: The individual actual anatomy of the region where screws are to be inserted above the mental foramen is important to perform the technique safely. We believe that the minimal cortical thickness to obtain sufficient screw anchorage should be studied in order to determine the actually safe shortest screw length. It is important to minimize the risk of tooth root damage or nerve injury and the amount of titanium in the human tissues.