Cone-Beam Computed Tomography Analysis of the Prevalence, Length, and Passage of the Anterior Loop of the Mandibular Canal
When placing implants in the anterior mandible, it is important to avoid damaging the mandibular nerve and its terminal extensions. The objective of this study was to determine the prevalence, length, and passage of the anterior loop of the mandibular canal, as well as the quantity of alveolar bone that is coronal to the canal, to help with implant placement in the anterior mandible. Cone-beam computerized tomography (CBCT) scans of 124 patients with 248 hemi-sections were evaluated. Anterior loop prevalence was determined using reconstructed panoramic and cross-sectional views; length was measured as the distance between the most mesial aspect of the mental foramen to the most mesial aspect of the anterior loop on cross-sectional views. The bucco-lingual position of the anterior loop inside the mandible and the apico-coronal dimensions of the alveolar bone above it were measured on cross-sectional views to determine the passage of the anterior loop and the bone available coronally, respectively. The effects of sex, age, side, and dentate status on the prevalence and length of the anterior loop were analyzed statistically. Prevalence of the anterior loop at the patient and hemi-section levels was 25% and 24%, respectively, and its median length was 1.63 mm (range, 0.52–3.92 mm). The anterior loop was apical to the mental foramen and mostly located within the buccal or middle one-third of the alveolar ridge, with an average height of coronal alveolar bone of 17.12 mm. Sex, age, side, and dentate status did not affect anterior loop prevalence and length. In conclusion, because of great variation, a case-by-case CBCT evaluation of the anterior loop is necessary before placing implants in the anterior mandible.
Identification and measurements for the mental foramen. (a) Identification of the most mesial aspect of the mental foramen on the panoramic view. (b) Measurements on the cross-sectional view corresponding to the most mesial aspect of the mental foramen. The distance from the coronal aspect of the mental foramen to the crest of the alveolar ridge was 5.76 mm (alveolar bone available coronally to the mental foramen), and the total ridge height from the inferior border of the mandible to the alveolar crest was 22.56 mm.
Identification and measurements for the anterior loop. (a) Identification of the most mesial aspect of the anterior loop on the panoramic view. (b) Measurements on the cross-sectional view corresponding to the most mesial aspect of the anterior loop. The distance from the coronal aspect of the anterior loop to the alveolar crest (bone available coronally to the anterior loop) was 8.22 mm, and the total ridge height from the inferior border of the mandible to the alveolar crest was 22.56 mm. In terms of the passage of the anterior loop in the mandible, the distance from the buccal cortical plate of the mandible to the buccal wall of the anterior loop was 3.86 mm, from the buccal plate to the lingual wall of the anterior loop it was 6.44 mm, and from the buccal to the lingual cortical plate of the mandible it was 11.94 mm. The distance from the lingual wall of the anterior loop to the lingual plate of the mandible was calculated as 11.94 − 6.44 = 5.50 mm. MIN, mandibular incisive nerve.
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