Tracking of the inferior alveolar nerve: its implication in surgical planning.

OBJECTIVES: The objective of the study is to assess the correlation between the mandibular canal tracing done on cone beam CT (CBCT) data, with the size, shape, and position of the neurovascular bundle (NB) obtained by magnetic resonance imaging (MRI). MATERIAL AND METHODS: Six human cadaver mandibles were scanned with a CBCT Promax® scanner (Planmeca, Helsinki, Finland) and with an Ingenia® 3.0 T MR system (Philips, Amsterdam, The Netherlands). The NB was segmented from the MRI dataset, while the mandibular canal (MC) tracing was done on the CBCT images. Quantitative 3D analysis was made for the full-segmented nerves and for three defined regions of specific clinical interest, namely angle, body, and mental region. RESULTS: From the 3D MRI analysis, the nerve thickness (for the angle, body, and mental region) ranges from 0.8 to 5.2 mm, while the thickness of the mandibular canal tracing is approximately 2.00 mm on both sides as chosen in the tracing software. The mean volume of the NB on the left is 828.49 ± 215.54 mm3 and on the right 792.98 ± 264.57 mm3. For the nerve tracing, the mean value is 351.92 ± 16.42 and 339.69 ± 16.12 mm3 on the left and right sides, respectively. Wilcoxon signed-rank test showed significant differences between NB and MC volume measurements (p = 0.0005). The Bland-Altman plots show an increasing slope for thickness and volume, indicating that the absolute differences between neurovascular bundle, estimated by MRI, and the mandibular canal, drawn on the CBCT images, increase with larger mean values. CONCLUSIONS: Surgeons should be aware of the shortcomings of nerve tracing in the different regions of the mandible. CLINICAL RELEVANCE: Tracing of the inferior alveolar nerve (IAN) underestimates shape and volume. Whenever nerve tracing instead of well-recognizable anatomical bony landmarks is used for surgical planning that need precision, a wider safe margin is recommended.

A CBCT Based Three-Dimensional Assessment of Mandibular Posterior Region for Evaluating the Possibility of Bypassing the Inferior Alveolar Nerve While Placing Dental Implants.

A high rate of nerve injury and related consequences are seen during implant placement in the posterior mandibular arch. An approach has been proposed to avoid nerve injury by dodging the inferior alveolar nerve (IAN) while placing an implant. A prospective study with a total of 240 CBCT (cone beam computed tomography) images of patients with three dentate statuses, namely, edentulous (group I), partially edentulous (group II) and dentate (group III) were included in the study. The nerve path tracing was done on CBCT images with On-demand 3D software. The three dimensions, i.e., the linear distance from the outer buccal cortical plate to the inferior alveolar nerve (BCPN), linear distance from the outer lingual cortical plate to the inferior alveolar nerve (LCPN) and linear distance from the midpoint of the alveolar crest to the inferior alveolar nerve (ACN) were assessed. The data were presented and analyzed between variables using one-way ANOVA and independent t-test in SPSS version 21.LCPN of the right 1st premolar region (p < 0.05) was significantly different among the groups with edentulous subjects recorded with the minimum value (6.50 ± 1.20 mm). Females were found to have significantly (p < 0.05) less available bone (6.03 ± 1.46 mm) on the right side of the mandibular jaw compared to males in edentulous group of patients. On comparing age groups for partially edentulous subjects, LCPN of the right 1st premolar region had significantly (p < 0.05) less available bone (6.03 ± 0.38 mm) in subjects with age ≥54 years. The IAN follows a lingual course in the molar region and later flips to the buccal side in the premolar region. The LCPN dimension in the 1st and 2nd premolar region was found to be more than 6 mm irrespective of age, gender and side of the jaw. Thus, it can be considered as a suitable site for placing implants while bypassing the IAN with CBCT assessment remaining as the mainstay in the pre-surgical phase.