The mental nerve constitutes one of the terminal branches of the inferior alveolar nerve. It is made up of sensory fibers that convey sensitivity to parts of the gingiva, lower lip, and of the skin of the chin.
The “anterior loop” is defined as that intraosseous section that passes the mental foramen. The nerve will then curve backward before emerging, in fact, at the foramen.
The position of the foramen, together with the possible presence of the anterior loop, exposes the nerve to potential trauma, which tends to occur mainly during implant surgery.
Panoramic radiography, whose images show distortions and inconsistent magnifications, is widely used in the planning of implant treatment but can lead to errors in hypothesising the course of the structure under examination.
In order to evaluate realistic parameters, the collection of a three-dimensional test consisting of a cone beam CT can, therefore, be indicated.
Recently, Gupta and colleagues published a retrospective study in the Journal of Maxillofacial and Oral Surgery to evaluate the distance between the anterior loop and the mental foramen.
Mental nerve anatomy: a cone beam evaluation
The work considered a sample of 149 patients undergoing cone beam CT.
The results of the study reveal the absence of the anterior loop in 56.4% of patients on the left side, and in 61.7% on the right side.
Twenty-nine patients, corresponding to 19.5% of the sample, had a loop of up to 4 mm in length, on both the right and left sides. Another 16.8% on the left side, and 14.1% on the right side, reported a loop of longer length, between 4.1 and 8 mm. Finally, the remaining 7.4% (left), and 4.7% (right) had an even more developed front loop (over 8 mm).
The results of the study show, overall, the lack of the anterior loop in more than half of the sample analyzed.
Wanting to suggest a minimum safety margin, the authors recommend a 4 mm threshold, within which most of the detected loops fall. The data has also been weighed against the results of a few other anatomical studies previously available.
A relevant share of cases of the present research, however, falls within the range immediately below, which reaches up to 8 mm. In conclusion, the authors state that, at the current state of the art, cone beam CT is an irreplaceable method in evaluating the presence and extension of the anterior loop. This test is, therefore, always indicated in the study of implant surgery involving the region immediately anterior to the mental foramen.