The variable position of the inferior alveolar nerve (IAN) in the mandibular ramus: a computed tomography (CT) study

Positioning of the Inferior Alveolar Nerve and Surgical Implications: A Study on Thai Mandibles

BACKGROUND

The inferior alveolar nerve (IAN), a crucial branch of the trigeminal nerve, innervates the mandible. Precise knowledge of IAN positioning ensures surgical safety.

METHODS

This cross-sectional study analyzed head and neck computed tomography scans from Maharaj Nakorn Chiang Mai Hospital. Inclusion criteria comprised dentate adults. Exclusion criteria included mandibular trauma/pathology or prior surgery. The study aimed to determine IAN positioning relative to key surgical landmarks: the first molar, lingula, and mental foramen.

RESULTS

A total of 450 Thai mandibles (900 hemimandibles) with a mean age of 36 years (58.2% male) were included. No significant differences were observed in IAN positioning relative to the first molar between the left and right sides in superior and inferior landmarks. However, the buccal distance was significantly closer on the left. The lingula distance was higher on the left, whereas that to the mental foramen was lower.

CONCLUSION

Surgical implications suggest maintaining a 15-mm distance from the lower mandibular border during osteotomy and upper plate placement, restricting horizontal cuts within this 15-mm range from the lingula, and ensuring screws do not extend more than 7 mm from the buccal surface. This study provides valuable guidance for minimizing the risk of iatrogenic injury to the IAN.

Risk factors for inferior alveolar nerve injury associated with implant surgery: An observational study

Background/purpose

Inferior alveolar nerve (IAN) injury is the most serious complication associated with dental implant surgery, posing difficulties in treatment and potential for permanent disabilities. This study aimed to identify patient-related risk factors for IAN injury during implant placement and to investigate sensory disturbances depending on whether the implant was removed.

Materials and methods

Twenty-eight patients with implant-related IAN injury were included. To determine risk factors, patient demographics and radiographic images were analyzed. Sensory functions were evaluated and compared based on whether the implant was removed.

Results

IAN injury occurred more frequently in women (60.7%), with a mean age of 62.9 years. The distance from the alveolar crest to the IAN was 9.8 ± 3.0 mm, with 40.9% patients having a residual alveolar bone of 10 mm or more. The mean bone density was measured at 586.2 ± 392.5 HU, which is below the normal range for the mandible. Notably, 31.8% of the patients were found to have D4 bone. Compared to patients who did not have implants removed, those who did showed better sensory function, except pressure perception, although these differences were not statistically significant.

Conclusion

Older women with lower bone density were at an increased risk of IAN injury, and IAN injury occurred even in cases with sufficient alveolar ridge. The removal of implants related to the injury alone does not markedly influence the extent of sensory disturbances during follow-up period, suggesting that other aspects such as the timing of removal and severity of injury could be crucial.

Parallel Osteotome Technique: New Approach to Reduce Neurosensory Disturbances following Bilateral Sagittal Split Osteotomy

BACKGROUND

The purpose of this study was to determine clinically whether the parallel osteotome technique (POST) reduces the incidence of neurosensory disturbances (NSDs) following bilateral sagittal split osteotomy (BSSO), and to corroborate the findings with finite element analysis.

METHODS

The authors conducted a quasiexperimental study of 30 patients requiring BSSO. The sample was divided into two groups: a control group who underwent the conventional osteotomy technique and an experimental group who underwent POST osteotomy. A finite element analysis simulation of the two techniques was also generated for computational analysis. The primary outcome was clinical comparison of subjective and objective measures for NSDs; the secondary outcome was a comparison of stress, strain, and deformation. The osteotomy technique was the exposure studied. Data were analyzed for differences in proportions and means.

RESULTS

Thirty patients (12 female and 18 male patients; age range, 18 to 28 years; mean age, 21.6 years) were recruited for the study, providing 60 sides as a sample. The experimental group had significantly lower subjective scores for NSD at the 3-month ( P = 0.03) and 6-month follow-ups ( P = 0.025). Objective testing revealed a lower incidence of NSDs for the experimental group during postoperative months 3 ( P = 0.07), 6 ( P = 0.007), and 12 ( P = 0.17). The computational analysis also revealed significantly lower stress ( P = 0.007), strain ( P = 0.009), and deformation ( P = 0.04) on the inferior alveolar nerve with the POST osteotomy.

CONCLUSIONS

The incidence of NSDs following BSSO is lower with the POST osteotomy. This technique also induced significantly lower deformational forces on the inferior alveolar nerve when compared with the conventional osteotomy.

Three-dimensional evaluation of mandibular lingula: Comparisons of skeletal angle classifications and growth patterns

OBJECTIVES

This study aimed to evaluate the position of the mandibular lingula (ML) in adult patients (aged between 18 and 35 years old) with different skeletal and growth patterns using cone-beam computed tomography (CBCT).

DESIGN

Cross-sectional.

SETTING

Dentistry department of University.

SUBJECTS

Subjects comprised CBCT images of 150 adult patients, including 300 rami.

METHODS AND MATERIALS

In total, 150 CBCT aged between 18 and 35 were selected and divided into three main groups of 50 samples based on their skeletal relationships (classes I, II and III). Patients were subdivided based on their growth pattern (vertical vs. horizontal), resulting in 25 samples per subgroup. Distances between the mandibular lingula and occlusal plane (ML-OP), sigmoid notch (ML-SN), external oblique ridge (ML-EOR), internal oblique ridge (ML-IOR), posterior border of the ramus (ML-PBR), inferior border of the ramus (ML-IBR), and horizontal and vertical distances to the mandibular foramen (ML-hMF and ML-vMF). One-way ANOVA variance analysis was employed to compare different angle classifications, and Bonferroni analysis was used for multiple comparisons. The Student's t-test was also used to compare growth patterns within each main group and genders within the subgroup.

RESULTS

The study revealed statistically significant differences in the position of the mandibular lingula between different angle classifications, growth patterns, and genders. Class II samples showed a more anterior position of the ML, whereas Class III samples displayed a more posterior position of the ML. Patients with horizontal growth patterns and Angle Class III had a more posteriorly positioned ML. Gender differences were observed, particularly in Class I and Class III classifications, suggesting that gender may influence the variability of ML position in these specific classifications.

CONCLUSION

The position of the mandibular lingula showed high variability among individuals with different angle classifications, growth patterns and genders.

Identification of the inferior alveolar canal using cone-beam computed tomography vs. panoramic radiography: a retrospective comparative study

BACKGROUND

This study aims at evaluating the visibility levels of the inferior alveolar canal (IAC) at different mandibular sites using panoramic (conventional & CBCT reformatted) and CBCT coronal views in a sample of a Palestinian population.

METHODS

The panoramic (conventional [CP] & CBCT reformatted [CRP]) and CBCT coronal views (CCV) of 103 patients (206 records, right and left sides) were analyzed. The visibility of IAC at five sites extending from the first premolar to the third mandibular molar region was evaluated visually (and compared among the radiographic views) as clearly visible, probably visible, invisible/poorly visible, or not present at the examined site. On CCV, the maximum dimension of the IAC (MD), the vertical distance (VD) between the mandibular cortex and IAC, and the horizontal position (HP) of the IAC were noted. Statistical significance in the differences and relationships of the variables was tested using several statistical tests.

RESULTS

There was a statistically significant relationship between the radiography modality (CP, CRP, CCV) and the visibility level of IAC (assessed in scores) at the five mandibular sites. When assessed on CP, CRP, and CCV, the IAC was clearly visible at all sites in 40.4%, 30.9%, and 39.6%, respectively, while being invisible/poorly visible in 27.5%, 38.9%, and 7.2% for the same views, respectively. The mean values of MD and VD were 3.61 mm and 8.48 mm, respectively.

CONCLUSION

Different radiographic modalities would characterize the IAC's structure in different qualities. Superior visibility levels were obtained interchangeably using CBCT cross-sectional views and conventional panorama at different sites compared to CBCT reformatted panorama. The IACs visibility was noted to improve at their distal aspects irrespective of the radiographic modality used. Gender -but not age- was a significant factor in the visibility level of IAC at only two mandibular sites.

Locating the Mandibular Lingula Using Cone-Beam Computed Tomography: A Literature Review

This study aimed to review the literature on adult mandibular lingula (ML) locations and related distances determined using cone-beam computed tomography (CBCT). A search was conducted for studies on CBCT using the following databases: PubMed, Web of Science, and Embase. The search results were limited to studies published between 1970 and 2021. The inclusion criteria were the investigation of ML location, CBCT, and participants aged ≥18 years. Eligible studies were examined for the distances from the lingual tip to the anterior ramus border, posterior ramus border, sigmoid notch, inferior ramus border, and occlusal plane. Eight studies on CBCT qualified for inclusion in the study. The mean distances from the ML to the anterior ramus border were 15.57 to 20 mm. In most of these, the ML was located above the occlusal plane. No significant differences were observed in the location and related distances for the ML among patients of different sexes, ethnicities, or skeletal patterns.

Positional Differences of the Mandibular Canal in Relation to Permanent Mandibular First Molars with Eruption Disturbances in Children

Eruption disturbances in permanent mandibular first molars (PM1s) are uncommon. This retrospective study aimed to investigate differences in the position of the mandibular canal in relation to PM1s, with or without, eruption disturbances. Panoramic and cross-sectional views were reconstructed from cone-beam computed tomography imaging of children with PM1 eruption disturbances. Distances from the most inferior margin of the mandible to the center of the mandibular canal (M-C) and from the outer margin of the lingual cortex to the center of the mandibular canal (L-C) were measured for normally erupted PM1s (normal group) and for PM1s with eruption disturbances (ED group) and compared using independent t-tests. The mean M-C was significantly shorter in the ED group (4.86 ± 1.07 mm) than in the normal group (6.56 ± 1.06 mm) (p < 0.05). The mean L-C was also significantly shorter in the ED group (2.74 ± 0.74 mm) than in the normal group (3.09 ± 0.71 mm) (p < 0.05). This study demonstrated that the mandibular canal tended to be positioned more inferiorly in relation to PM1s with eruption disturbances than normally erupted PM1s in children. Clinicians should be aware of this positional deviation when managing children with PM1 eruption disturbances.

Dimension and Location of the Mandibular Lingula: Comparisons of Gender and Skeletal Patterns Using Cone-Beam Computed Tomography

Objective

The study aimed to investigate and measure the anatomical relationship between the mandibular lingula (Li) and skeletal patterns using cone-beam computed tomography (CBCT). Materials and Methods. In total, 72 participants (23 men and 49 women) were categorized into three groups according to their skeletal patterns (specifically, the A point–nasion–B point (ANB]) angle) as follows: Class I (0° < ANB < 4°), Class II (ANB ≥ 4°), and Class III (ANB ≤ 0°). The CBCT images of 144 rami were collected, and the distance from the Li to the external oblique ridge (Li-EOR), internal oblique ridge (Li-IOR), posterior border of the ramus (Li-PBR), inferior border of the ramus (Li-IBR), sigmoid notch (Li-Sm), and mandibular foramen (Li-MF) was examined. The Li-hMF (horizontal distance from the Li to the MF) and Li-vMF (vertical distance from the Li to the MF) were measured. The comparisons of gender, side (right and left), and skeletal patterns were then evaluated by statistical analysis.

Results

The values of the Li-EOR and Li-PBR (19.99 mm and 15.93 mm, respectively) were significantly higher in men than in women (18.85 mm and 14.89 mm, respectively). Moreover, the Li-IBR was higher in men (32.91 mm) than in women (30.40 mm). Both sides (right and left) and skeletal patterns demonstrated that the Li-EOR, Li-IOR, and Li-PBR were not significantly different. Pearson's correlation test reported a strong correlation between the Li-EOR and Li-IOR (r=0.610).

Conclusion

The distances from mandibula lingula to the external oblique ridge, posterior border of ramus, and inferior border of ramus were significantly longer in men than in women. Similarly, both horizontal and vertical distances from the lingula to the mandibular foramen were significantly longer in men than in women. Therefore, the results demonstrated that the Li was longer and more protruding in men than in women. With respect to the horizontal distance from the mandibular lingula to the mandibular foramen, of the three types of the skeletal system (Class I, Class II, and Class III), Class III was the significantly largest.

Surgical implications of the anatomic situation of the mandibular canal for mandibular osteotomies: a cone beam computed tomographic study

PURPOSE

In bilateral sagittal split osteotomy (BSSO), the risk of lesion of the inferior alveolar nerve (IAN) is important. The aim of this study was to investigate the situation of the IAN in the area of the BSSO in preoperative 158 CBCT.

METHODS

The situation of the mandibular canal (MC) has been studied in six coronal sections (one section each 4 mm) from the proximal root of the second mandibular molar. The height of the MC related to the height of the mandible, and the horizontal distance between the MC and the lateral cortical plate related to the mandibular width have been determined in each section. The cancellous bone width has been measured allowing to determine a cancellous bone ratio.

RESULTS

The variability of the MC was high, depending mainly on the cancellous bone ratio which was higher when the IAN was deep. When a third molar was present, the MC was lower in the area of the third molar.

CONCLUSIONS

To decrease the risk of injuring the IAN in BSSO, the evaluation of the cancellous bone ratio by a preoperative CBCT may be proposed to adapt the surgical technique to the anatomy.

A mandibular bone defect of uncertain significance: report of a paleopathological case

Anatomical variations of the mandibular canal as well as the presence of accessory canals and foramina are common findings in the human mandible. Here, we present a previously unreported type of anatomical variation, consisting of a large full-thickness bone defect of the right mandibular ramus, observed in a young male unearthed from a mediaeval cemetery located in North-Eastern Italy. The defect was located very close to, yet not directly connected with, the mandibular canal. Awareness of the existence of deviations from the anatomical norm such as that we describe here is strategic to avoid diagnostic misinterpretations, minimise technical hitches, and prevent clinical complications during invasive procedures in the region of the mandible.