Intramandibular course of the mandibular nerve; clinical significance for distraction and implantology

Evaluation of the Linear Relationship of the Inferior Alveolar Nerve Canal to the Lateral Cortex and the Alveolar Crest in the Posterior Mandible: A Computed Tomographic Study

Background and Objective

A cross-sectional study was conducted to evaluate a clinically relevant position of the inferior alveolar nerve and canal with respect to the lateral cortex, alveolar crest, and first and second molar root apices in adult dentate patients.

Methods

The study was conducted in the patients who reported various oral and maxillofacial surgical procedures at the Department of Oral and Maxillofacial Surgery for whom preoperative computed tomography (CT) scan was taken for the required surgical procedures. CTs were selected based on the selection criteria, and a total of 50 CTs were evaluated. Predictor variables were gender and side. Outcome variables were the average linear buccal measurements from the lateral cortex to the outer cortical margin of the inferior alveolar canal from below the mandibular foramen till the mental foramen, linear vertical measurements from the alveolar crest to the superior crest of the inferior alveolar canal in the third, second and first molar regions, and linear vertical distance from the superior aspect of inferior alveolar canal till the apices of second and third molars. Descriptive statistics were analysed with t test and paired t test. P value < 0.05 was taken as significant.

Results

The study sample was composed of 27 male and 23 female patients with a mean age of 29 ± 4.6 years. The mean value of linear measurements of IAN to the right lateral cortex at the mandibular foramen was 4.96 ± 1.13, and for the left side, it was 4.79 ± 1.33. The mean values of linear measurements from the superior aspect of IAN canal to the alveolar crest at third, second and first molar regions obtained in this study were 18.5 ± 3.79, 19 + 3.83 and 19.5 + 3.48 for the right side and 17.8 + 3.86, 18.8 + 3.54 and 19.143.31 for the left side, respectively. The average linear measurements of IAN to the root apex of first molar were 10.8 3.89 for the right side and 10.868 + 3.85 for the left side; for second molars, they were 10.5 + 3.62 for the right side and 10.52 + 3.62 for the left side. Gender and side influenced the outcome with varying statistical significance.

Conclusion

The study has identified the average linear measurements of the buccal cortical bone along the path of IAN in the mandible, average height of alveolar bone above the IAN and average distance between the IAN with the first and second molar root apices. This will be useful guide while planning and performing various mandibular surgical procedures close to the IAN nerve and procedures that can disturb the IAN. The implications of these findings will influence the course of surgery.

Single geometry abutment for narrow and extra-narrow implant systems: Survival and failure modes

The use of identical prosthetic components for all implant diameters could reduce the production costs by companies and the complexity of component selection for the clinician and his team. However, it would imply in reduction of thickness of the cervical walls of tapered internal connection implants, which could compromise the reliability of narrow and extra-narrow implants. Therefore, this study aims to evaluate the probability of survival and failure modes of extra-narrow implant systems with the same internal diameter as standard-diameter implants using the same prosthetic components. It was used eigth different implant system configurations, including narrow (Ø 3.3 mm) (N) extra-narrow (Ø 2.9 mm) (EN) and extra-narrow-scalloped (Ø 2.9 mm) (ENS) implants, both with cementable abutments (Ce) or titanium bases (Tib) and one-piece implants (Ø 2.5 mm and Ø 3.0 mm) (OP) (Medens, Itu, SP, Brazil), comprising the following groups: OP 3.0; OP 2.5; N Ce; N Tib; EN Ce, EN Tib, ENS-Ce and ENS-Tib. The implants were embedded using polymethylmethacrylate acrylic resin in a 15 mm matrix. Standardized maxillary central incisor crowns were virtually designed and milled to fit on the different studied abutments and cemented using a dual self-adhesive resin cement. The specimens were submitted to SSALT (Step Stress Accelerated Life Testing) at 15 Hz in water until failure or suspension of the test, until a maximum load of 500 N. Fractographic analysis of the failed specimens were realized in scanning electron microscopy. All implant systems demonstrated high probability of survival (90-100%) for missions at 50 and 100 N and values of characteristic strength superior to 139 N. Failure modes were restricted to the abutment in all the implant configurations tested. Therefore, the use extra-narrow implants with standardized prosthetic components for different implant diameters is a viable option for the replacement of anterior teeth.

In vitro correlation of the level of inferior alveolar canal with CBCT imaging

PURPOSE

The aim was to correlate the level of the inferior alveolar canal on cadaver specimens and as evaluated with three-dimensional radiographic cone-beam computed tomography (CBCT) imaging.

METHODS

Twenty-one skulls with intact mandibles (42 inferior alveolar canals) were imaged with an I-CAT Cone-Beam 3D Imaging System and multi-planar reformatted images obtained were scored to assess the level of the canal (Level I, Level II, and Level III). The mandibles were later dissected and level of the canal was directly visualized, scored, and further correlated with results from CBCT imaging.

RESULTS

There was no difference in the level of the inferior alveolar canal between the dissected cadaver specimen and CBCT images. Also, there was no statistically significant difference in the level of the canal among the gender assigned to the specimens and corresponding CBCT images. There were no statistical differences in the level of the canal (cadaver specimen vs. CBCT) between the left and right sides of the specimens, as studied individually.

CONCLUSION

Our study indicates that there is close correlation of the level of the inferior alveolar canal between cadaver specimens and CBCT images. Well-designed studies would be required to further validate the findings in this study.