Lateral Cortical Bone Thickness of Human Mandibles in Region of Mental Foramen

Is There a Safe Zone for Lateral Border Fixation of Mandibular Angle Fractures?

Study Design

Cross-sectional study design.

Objective

There are multiple accepted treatment options for internal fixation of mandibular angle fractures. The purpose of this study was to determine if there is a safe zone for lateral border fixation of mandibular angle fractures.

Methods

One hundred coronal images of facial computed tomography (CT) scans were reviewed on patients between the ages of 18 to 48. Measurements were taken in the area of the second and third molar region related to the inferior border to the superior extent of the inferior alveolar canal and apex of the second molar root, along with buccal cortical measurements to the inferior alveolar canal and apical third of the second molar root.

Results

The average measurement of the inferior border in the second molar area to the inferior alveolar canal and apex of the root was 1.12 cm (0.70-1.77) and 1.39 cm (0.91-2.30), respectively. The average measurement of the inferior border of the third molar to the inferior alveolar canal was 1.26 cm (0.78-1.83). The average measurement of the buccal cortex of the second molar to the inferior alveolar canal and apical one-third of the root was 0.64 cm (0.34-1.25) and 0.59 cm (0.33-0.98), respectively. The average measurement of the third molar buccal cortex to the inferior alveolar canal was 0.45 cm (0.18-0.98).

Conclusion

In the area of the second molar region, there is no ubiquitous safe zone for screw placement, cortical bone thickness is more critical than vertical placement of the fixation plate and screws. In the third molar region, cortical bone thickness and vertical orientation may provide a safe zone for screw placement.

Direct and tomographic dimensional analysis of the inter-radicular distance and thickness of the vestibular cortical bone in the parasymphyseal region of adult human mandibles

We calculated the inter-radicular distances between the canine, and first and second premolars, of human mandibles and the thickness of the cortical bone at adjacent sites using computed tomographic (CT) imaging, and assessed the precision of the dimensional assessment made by CT compared with the same measurement made directly with calipers. We examined 100 adult cadaveric dentate human hemimandibles. At the level at which monocortical screws are inserted to place miniplates according to the current technique used to treat mandibular fractures, points A, B, and C referred to the canine, and first and second premolars, and were marked to calculate the level of the CT slice and as the reference for sectioning of the hemimandible. Our findings showed that there was no significant difference in the inter-radicular distance or in the thickness of cortical bone between the sides of the mandible. The vestibular cortical bone was less than 3.0mm thick in 91 of the samples. In 98 of the samples the inter-radicular distance between the canine and the first and second premolars was more than 2mm. There was no significant difference in micrometric precision between the dimensional assessment on CT and direct measurement using a caliper. In the region of the mental foramen the screws have cortical bone less than 3mm thick in which to be anchored. The inter-radicular distance suggests that there is a minimal risk of radicular injury when miniscrews are inserted between the alveolar structures. CT is a reliable tool for measuring the inter-radicular distance and the thickness of mandibular cortical bone.