Assessment of the Anterior Loop of the Mental Nerve Using Cone Beam Computerized Tomography Scan
The purpose of this study is to use cone-beam computerized tomography (CBCT) scans with oblique-transverse reconstruction modality to measure and compare the anterior loop length (AnLL) of the mental nerve between gender and age groups and to compare the difference between the right and left sides. Sixty-one female and 61 male CBCT scans were randomly selected for each age group: 21–40, 41–60, and 61–80 years. Both right- and left-side AnLLs were measured in each subject using i-CATVision software to measure AnLLs on the oblique transverse plane using multiplanar reconstruction. The anterior loop was identified in 85.2% of cases, with the mean AnLL of the 366 subjects (732 hemimandibles) being 1.46 ± 1.25 mm with no statistically significant difference between right and left sides or between different gender groups. However, the mean AnLL in the 21–40 year group (1.89 ± 1.35 mm) was larger than the AnLL in the 41–60 year group (1.35 ± 1.19 mm) and the 61–80 year group (1.13 ± 1.08 mm). In conclusion, when placing implants in close proximity to mental foramina, caution is recommended to avoid injury to the inferior alveolar nerve. No fixed distance anteriorly from the mental foramen should be considered safe. Using CBCT scans with the oblique-transverse method to accurately identify and measure the AnLL is of utmost importance in avoiding and protecting its integrity.
How to move the axial cut (red bar) in the sagittal plane until the best view of mental foramen (yellow circle) is attained in the axial plane.
Axial plane that is rotated until the sagittal cut (green bar) is parallel to the buccal plate in the area of the mental foramen, and the coronal cut (blue bar) in the axial plane that is adjusted until the best view of the mental foramen (yellow square) is attained in the coronal plane.
Figure 3. How to make an oblique cut using the function “line” to gain an ideal oblique view (Figure 4). (The cut is adjusted to pass through the center of the mental foramen in the coronal plane and meanwhile to obtain the best view of the anterior loop in the oblique plane.). Figure 4. Mental foramen, anterior loop of the mental nerve, and bifurcation at the same view. Line 1 is parallel to the buccal plate. Line 2 is perpendicular to line 1 and passes through the most anterior point of the anterior loop. (In this case, it is the part of the mental nerve, not the origin of the incisive canal.) Line 3 (yellow) shows the measurement of the anterior loop length. Figure 5. Example of the measurement (line 3: 6.8 mm) of the maximal anterior loop length. The average of all measurements (6.8, 6.8, 6, 6.4, 6.8, 7.2 mm) was 6.67 mm. Figure 6. Example of the measurement (line 3: −3.2 mm) of the minimal anterior loop length. The average of all measurements (−3.2, −3.2, −3.2, −2.8, −2.4, −2.4 mm) was −2.87 mm.
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