The course and distribution of the inferior alveolar nerve in the edentulous mandible

Prevalence and topography of bifid and trifid mandibular canal in Turkish Western Anatolia Population: evaluation of the inferior alveolar canal with CBCT

PURPOSE

Various anatomical variations of the inferior alveolar canal increase the incidence of surgical complications; Therefore, this study aimed to evaluate the frequency and configuration of bifid and trifid mandibular canals using cone beam computed tomography (CBCT) in the Turkish subpopulation.

METHODS

The inferior alveolar canal was evaluated on 1014 hemi-mandibles in the CBCT (I-CAT 3D Imaging System) images of 513 patients. The frequency and configuration of the bifid and trifid mandibular canal (MC) were examined. The relationship between bifid MC configuration and dental status and age groups was analyzed. The distance of the accessory canal to the buccal and lingual walls and the alveolar crest was measured. The diameter of the main canal and accessory canal was measured and its relationship with dental status and age groups was evaluated.

RESULTS

Bifid MC was found in 266 hemi-mandibles (24.7%) and 212 (41.3%) of 513 patients. The most common type of bifid MC was the retromolar canal (87 sides), followed by the forward canal without confluence (41; 4%) and the dental canal (34; 3.4%). 10 of the dental canals were opening to the 1st molar, 14 of the 2nd molars, and 10 of the 3rd molars. The number of retromolar foramina was 1 on 56 sides, 2 on 15 sides, and 3 on 4 sides. Forward canal without confluence was more common in edentulous patients than in dentulous patients, while the dental canal was more common in dentulous patients. The main canal diameter was 3.53 ± 0.97 mm and the bifid MC diameter was 1.82 ± 0.70 mm. Distance of the bifid MC to the lingual wall was higher in the > 64 years group than in the 18-39 years group (p = 0.022). Distance of the bifid MC to the alveolar crest was lower in the > 64 years group compared to the 18-39 years group and 40-64 years group (p = 0.015). The main canal diameter was higher in the 40-64 years group than in the 18-39 years group (p = 0.012).

CONCLUSION

Bifid MC has a high prevalence, occurring in almost one in two patients. Dental and retromolar types, which are close to the teeth, are more common, and this increases the possibility of complications. CBCT is the most accurate imaging technique used to detect and define these variations.

Mandibular canal assessment in dentate and edentulous ridges of 400 Iraqi Arab and Kurdish populations using cone beam computed tomography

Objectives

This study aims to compare differences in mandibular canal (MC) location between dentate and edentulous ridges, in the second premolar region as well as the first, second, and third molar regions using cone beam computed tomography (CBCT) of Arabic and Kurdish Iraqi populations.

Materials and Methods

CBCT images of 400 subjects (200 Arabs, 200 Kurds) were collected from radiological archives. RadiAnt DICOM software (Medixant, Poland) was used for image analyses. Measurements were performed from MC to buccal and lingual alveolar crests and to buccal, lingual, and inferior aspect of the mandible for both dentate and edentulous ridges. Additionally, distance to the most superior aspect of residual edentulous ridge were performed. Independent t-test and Mann-Whitney U Test were performed utilising SPSS v.26.

Results

Distances from MC to buccal and lingual alveolar crests were consistently lower in edentulous ridge compared to dentate ridge across all teeth regions. Distances to lingual and inferior border of the mandible were higher in edentulous ridge compared to dentate ridge of all teeth regions. Distances to buccal surface of the mandible varies with fluctuations of dentate and edentulous ridges displaying higher measurements. Distance to superior aspect of residual edentulous ridge revealed mean values in the range of 13.45 to 15.69 mm in Arabs and 13.96 to 16.37 mm in Kurds.

Conclusions

Discrepancy in vertical position of MC was observed between dentate and edentulous ridges within Arab and Kurd populations. Horizontal position of MC was unaffected by tooth loss and found to be closer to lingual surface of all molars. The residual alveolar ridge was sufficient to accommodate the common length and width of dental implants.

Clinical significance

The findings could play a crucial role in planning surgical interventions of the mandible, helping to prevent complications that might arise due to inadequate preoperative assessments.

Identifying the Anatomical Variations of the Inferior Alveolar Nerve with Magnetic Resonance Imaging

BACKGROUND

The inferior alveolar nerve (IAN) is located in the mandibular canal (MC). It is critical to evaluate the position of the MC during treatment planning to prevent intra or postoperative complications.

AIMS

This retrospective study aimed to identify the anatomy and anatomical variations of the IAN using soft tissue imaging (pulse sequence magnetic resonance imaging [MRI]).

MATERIALS AND METHODS

This study was designed as a retrospective Consolidated Standards of Reporting Trials (CONSORT) study. In total, 220 MR images were obtained. Nutrient canals (NCs) were classified as intraosseous and dental NCs, while bifid MCs (BMCs) were classified as forward, retromolar, and buccolingual canals. IBM SPSS Statistics 22 was used. Kolmogorov-Smirnov and Shapiro-Wilk tests, descriptive statistical methods (means, standard deviations, and frequencies), and the Chi-square test were used. Statistical significance was set at P < 0.05.

RESULTS

In total, 220 patients (172 females and 48 males) were evaluated. NCs were present in 92.3% of all MCs and were significantly higher in patients aged <25 years. BMCs were observed in 106 patients (24.1%). The most common BMC of MC/IAN was in the forward canal (14.4%), followed by the retromolar canal (7.5%).

CONCLUSION

Although previously, the dental canal was considered as an anatomical variation, this study revisited the classification and suggested that dental canals are anatomical structures.

Evaluation of Cortical Thicknesses and Bone Density Values of Mandibular Canal Borders and Coronal Site of Alveolar Crest

Objectives

The objectives of this retrospective study are to measure the amount of the alveolar crest cortication and cortication around the mandibular canal, and to evaluate bone density values of alveolar crest, cortication around mandibular canal, and possible implant placement area for edentulous sites.

Material and Methods

Six hundred forty-two cone-beam computed tomography scans from 642 subjects were evaluated in four centers. Cortical thicknesses of alveolar crest and mandibular canal cortical borders (buccal, lingual, apical, and coronal) in each mandibular posterior teeth region were measured. Bone density of alveolar crest and mandibular canal cortical borders (buccal, lingual, apical, and coronal) in each mandibular posterior teeth region were recorded. The correlations between numeric variables were investigated using Pearson's correlation test.

Results

The largest cortical border of the canal was measured 1.1 (SD 0.71) mm at the left second molar area and in coronal side of the mandibular canal (MC). Left and right first premolar regions showed higher bone density values compared to the other sites in all bone density values evaluations. The buccal side of the canal at the right first premolar region showed the highest bone density values (832.32 [SD 350.01]) while the coronal side of the canal at the left second molar region showed the lowest (508.75 [SD 225.47]). The bone density of possible implant placement area at the both left (692.25 [SD 238.25]) and right (604.43 [SD 240.92]) edentulous first premolar showed the highest values. Positive correlations between the bone density values of alveolar crest and the coronal side of MC were found in molar and left second premolar regions (P < 0.05).

Conclusions

Results may provide information about the amount of cortication and bone densities tooth by tooth for posterior mandible to surgeons for planning the treatment precisely.

Bifid Mandibular Canal: A Proportional Meta-Analysis of Computed Tomography Studies

Introduction

Growing body of evidences showed different grades in prevalence of bifid mandibular canals. Because the previous reviews focused solely on patient-level occurrence, hemi-mandible-level prevalence, bilateral symmetry, length, and diameter of bifid mandibular canals were required to be estimated collectively. The research question of this meta-analysis was "What is the prevalence of bifid mandibular canal among patients seeking computed tomography examinations"?

Materials and Methods

In vivo, computed tomography, and cross-sectional studies were eligible. Studies, with less than 100 subjects or anatomic site restriction or controlled class of bifid mandibular canal, were excluded. Joanna Briggs Institute (JBI) critical appraisal tool for prevalence studies was used to assess methodological quality of all included studies. Random effect meta-analyses for proportion of bifid mandibular canal were done.

Results

40 studies met the inclusion criteria. All studies were selected for both systematic review and meta-analyses. Totally, 17714 patients and 31973 hemi-mandibles were included. All eligible studies showed moderate risk of bias on average. Resulting from the random effect model, more than 20% of patients seeking computed tomographic examinations had bifid mandibular canals (BMCs) which penetrated into slightly more than 14% of hemi-mandibles. Of the patients having bifid mandibular canals (BMCs), nearly 23% exhibited such anatomy on both sides of their mandibles. Estimated mean length and diameter of the accessory canals of bifid mandibular canals were 12.17 mm and 1.54 mm, respectively.

Conclusion

The geographical locations, classifications, reliability test, and voxel size of computed tomography were all implicated in the prevalence of bifid mandibular canals along with gender and laterality, although considerable heterogeneity and bias were detected.

Variation of Mandibular Canal Branching Related to Anatomical Regions in Mandible: A Radiographic Study Without Contrast

PURPOSE

Screening mandibular canal branches and awareness of these possible canal branches is vital for patient safety and surgical success. The aim of this study was to evaluate the prevalence and localization of mandibular canal branching (MCB).

METHODS

This is an institutional and retrospective cohort study of patients who presented for evaluation of cone beam computed tomography (CBCT) between 2019 and 2020. The prevalence of MCB and the related foramina was estimated according to anatomical regions. Predictor variables were gender, age, anatomical region, and side of branches. Outcome variable of the study was MCB. Thus, multiple correspondence analysis was performed to determine the relationships between the categories of the variables, as well as between variables.

RESULTS

CBCT images were obtained from 180 patients (n = 360 hemimandible; 90 males, 90 females). MCB was observed in 130 (72.2%) of 180 patients (mean age = 38.2 ± 11.8 years). MCB was observed in 63 (48.5%) males and 67 (51.5%) females, and the prevalence of MCB did not differ significantly according to gender (P = .618). MCB was mostly observed in the molar region (69 branches, 34.3%). Foramina were detected in 60 of 248 branches (24.19%) and were mostly observed in the retromolar region (28 foramina, 46.7%). "Quadrafid" branching was detected in 2 females (1.11%). Female patients aged 19-38 years were more prone to have MCB in molar and retromolar regions. MCB was more likely to occur bilaterally. There was also a high positive correlation among the MCB, side, and anatomical regions.

CONCLUSIONS

MCB is not a rare anatomical variation, and even quadrafid branching can be observed in the hemimandible. CBCT images should be examined carefully for possible MCB to minimize postoperative complications during dental surgery.

What are the retromolar and bifid/trifid mandibular canals as seen on cone-beam computed tomography? Revisiting classic gross anatomy of the inferior alveolar nerve and correcting terminology

PURPOSE

Since cone-beam computed tomography was developed, a number of radiological studies on the bifid mandibular canals (BMCs) and trifid mandibular canals (TMCs) have been reported. However, many of the suggested subtypes of the BMC described in the literature seem to be normal branches of the inferior alveolar nerve. This might be due to a lack of revisiting classic anatomical studies in the field of radiology. Therefore, such studies are revisited here.

METHODS

A database search using PubMed and Google Scholar was conducted on BMC and TMC. Eighty-nine articles underwent full-text assessment. The reported three classifications of BMC and the six modified classifications were reviewed and compared to the intramandibular inferior alveolar nerve branches.

RESULTS

Some subtypes of BMC and TMC simply represent normal inferior alveolar nerve branches, i.e., retromolar branch, molar branch (alveolar branch/dental branch), large mental branch, or communicating branch. Others such as Naitoh's type III BMC and forward canal might be a true BMC.

CONCLUSION

We found that the bifid mandibular canal is an additional intramandibular canal running parallel to the mandibular canal with/without confluence with the main canal through comparison of classifications of BMC/TMC between the radiology and anatomy fields.

Anatomical Variations of the Bifid Mandibular Canal on Panoramic Radiographs in Citizens from Zagreb, Croatia

Background

The bifid mandibular canal (BMC) is an anatomical variation with reported prevalence ranging from 0.08 to 65%. Identifying anatomical variations of mandibular canal is very important in order to prevent possible complications during oral surgical and other dental procedures.

Objectives

The aim of this study was to determine the prevalence and to classify the morphology of BMCs using digital panoramic radiographs.

Material and methods

A retrospective study was conducted that included 1008 digital panoramic radiographs (412 female and 596 male) used to identify the type of BMC. Panoramic radiographs were analyzed by three oral surgeons and one dentist, and BMCs were classified into six different types, 4 types according to Langlais et al. (types 1-4), and two new types (types 5 and 6) described by authors.

Results

The prevalence of BMC was 4.66% (n=47), with no significant differences in gender between BMC types (P=0.947; χ²=0.74). The prevalence of type 1 BMC was 0.79% (n=8), type 2 2.08% (n=21), type 3 0.30% (n=3), type 4 0% (n=0), type 5 0.89% (n=9) and type 6 0.60% (n=6).

Conclusion

This study revealed a relatively high prevalence of BMCs among Zagreb citizens. Furthermore, two new types of BMCs were described. These results stress the importance of a careful and thorough radiographic analysis prior to each invasive procedure in the mandible.

Mandibular Third Molar Surgery: Intraosseous Localization of the Inferior Alveolar Nerve Using 3D Double-Echo Steady-State MRI (3D-DESS)

The aim of this study was to evaluate the inferior alveolar nerve's (IAN) intraosseous position within the inferior alveolar canal (IAC) using a 3D double-echo steady-state MRI sequence (3D-DESS). The IAN position was prospectively evaluated in 19 patients undergoing mandibular third molar (MTM) surgery. In the coronal reference layer, the IAC was divided into six segments. These segments were checked for the presence of hyperintense tubular MRI signals representing the IAN's nervous tissue and assessed as visible/non-visible. Furthermore, the IAN in MRI and the IAC in MRI and CBCT were segmented at the third and second molar, determining the maximum diameter in all planes and a conversion factor between the imaging modalities. Regardless of the positional relationship at the third and second molar, the IAN showed the highest localization probability in the central segments (segment 2: 97.4% vs. 94.4%, segment 5: 100% vs. 91.6%). The conversion factors from IAC in CBCT and MRI to IAN in MRI, respectively, were the following: axial (2.04 ± 1.95, 2.37 ± 2.41), sagittal (1.86 ± 0.96, 1.76 ± 0.74), and coronal (1.26 ± 0.39, 1.37 ± 0.25). This radiation-free imaging modality, demonstrating good feasibility of accurate visualization of nervous tissue within the nerve canal's osseous boundaries, may benefit preoperative assessment before complex surgical procedures are performed near the IAC.

Anatomy of the mandibular canal and surrounding structures: Part I: Morphology of the superior wall of the mandibular canal

INTRODUCTION

Previous studies of the mandibular canal (MC) have raised questions about the structure of its superior wall that have not been answered. The goal of this anatomical and radiological study was to investigate how CBCT imaging could predict the structure of the superior wall of the MC.

METHODS

Twenty sides from ten dry mandibles derived from six females and four males were used for this study. The mandibles were examined with CBCT. The specimens were then prepared by the methods of our previous study and observed inferiorly. The inferior views were classified into four groups by gross observation of the surface of the superior wall of the MC: class I (trabecular pattern), class II (osteoporotic pattern), class III (dense/irregular pattern), and class IV (smooth pattern). Coronal section CBCT images were classed according to whether the superior wall of the MC was visible.

RESULTS

Class I was most common in dentulous sections in both genders, and class IV was most common class in edentulous sections in both genders. The superior wall was visible in 59.1% in dentulous and 84.9% in edentulous sections, and non-visible in the remainder.

CONCLUSION

Tooth presence and sex are important factors influencing the superior wall of the MC. When the superior wall cannot be seen on CBCT, it is more likely to belong to class II (osteoporotic) than other classes.

The clinical significance of the retromolar canal and foramen in dentistry

The mandibular canal is nowadays acknowledged as a major trunk with multiple smaller branches running roughly parallel to it. Most of these accessory canals contain branches of the inferior alveolar neurovascular bundle that supplies the dentition, jawbone, and soft tissue around the gingiva and lower lip. This article reviews the prevalence, classification and morphometric measurements of the retromolar canal and its aperture. A retromolar canal is a bifid variation of the mandibular canal that divides from above this main canal, and travels anterosuperiorly within the bone to exit via a single foramen or multiple foramina into the retromolar fossa. This foramen, termed the retromolar foramen, allows accessory branches of the inferior alveolar neurovascular bundles to supply tissues at the retromolar trigone. Clinically, it is of the utmost importance to determine the exact location of the mandibular canal and to identify its retromolar accessory branches when surgery in the posterior mandible is to be performed.

Evolutionary Tinkering of the Mandibular Canal Linked to Convergent Regression of Teeth in Placental Mammals

Loss or reduction of teeth has occurred independently in all major clades of mammals [1]. This process is associated with specialized diets, such as myrmecophagy and filter feeding [2, 3], and led to an extensive rearrangement of the mandibular anatomy. The mandibular canal enables lower jaw innervation through the passage of the inferior alveolar nerve (IAN) [4, 5]. In order to innervate teeth, the IAN projects ascending branches directly through tooth roots [5, 6], bone trabeculae [6], or bone canaliculi (i.e., dorsal canaliculi) [7]. Here, we used micro-computed tomography (μ-CT) scans of mandibles, from eight myrmecophagous species with reduced dentition and 21 non-myrmecophages, to investigate the evolutionary fate of dental innervation structures following convergent tooth regression in mammals. Our observations provide strong evidence for a link between the presence of tooth loci and the development of dorsal canaliculi. Interestingly, toothless anteaters present dorsal canaliculi and preserve intact tooth innervation, while equally toothless pangolins do not. We show that the internal mandibular morphology of anteaters has a closer resemblance to that of baleen whales [7] than to pangolins. This is despite masticatory apparatus resemblances that have made anteaters and pangolins a textbook example of convergent evolution. Our results suggest that early tooth loci innervation [8] is required for maintaining the dorsal innervation of the mandible and underlines the dorsal canaliculi sensorial role in the context of mediolateral mandibular movements. This study presents a unique example of convergent redeployment of the tooth developmental pathway to a strictly sensorial function following tooth regression in anteaters and baleen whales.

Case-control study of mandibular canal branching and tooth-related inflammatory lesions

OBJECTIVES

Morphological variations of mandibular canals increase the risk of neurovascular damage and bleeding during surgical procedures by decreasing the predictability of the inferior alveolar neurovascular bundle location. To improve the predictability with such variations, the present study aimed to verify the possibility of a relationship between mandibular canal branches (MCBs) and tooth-related inflammatory lesions, using trough cone-beam computed tomography (CBCT) examinations.

METHODS

The sample comprised 150 age and sex-matched examinations (50 cases and 100 controls) from two databases. The CBCT examinations were grouped by the presence of MCBs starting in the mandibular body regions as the outcome variable. Tooth-related inflammatory lesions and measurements of gray levels in the posterior region of the alveolar ridge were assessed in both groups. A multiple logistic regression analysis was applied to verify the relationships between MCBs and independent variables (p < 0.05).

RESULTS

Occurrence of tooth-related inflammatory lesions increased the risk of MCBs in the mandibular body regions (p < 0.001; OR 11.640; 95% CI 4.327-31.311). High-contrast images had a weaker association with MCBs (p = 0.002; OR 1.002; 95% CI 1.002-1.003). The most frequent tooth-related inflammatory lesions in both groups were endodontic (34 lesions; 45.94% of the total lesions). Most of the tooth-related inflammatory lesions related to MCBs were endodontic (20 cases) and combined endodontic and periodontal inflammation (20 cases).

CONCLUSIONS

An association was observed between MCBs in the mandibular body regions and tooth-related inflammatory lesions. Inflammatory lesions of endodontic origin are most often associated with MCBs.

A randomized controlled trial comparing nerve block and mandibular infiltration techniques in posterior mandible implant surgeries

Background

To compare global surgical pain under nerve block and mandibular infiltration anesthesia techniques, and to evaluate pain during drilling and the distance to the mandibular canal in posterior mandible implant surgeries.

Material and Methods

A prospective, randomized, controlled, double-blind, clinical trial was conducted to compare nerve block (Group A) to mandibular infiltration (Group B) techniques for dental implant placement. Global surgical pain (VAS = visual analogue scale), pain during drilling or implant placement (MPQ = McGill pain questionnaire) and distance to the mandibular canal (Image J) were statically analyzed. Age, gender, anxiety levels, tooth to be replaced, implant size, adjacent teeth and duration of surgery were also analyzed.

Results

172 patients were included and 283 dental implants were analyzed. VAS values were significantly higher in Group B (p<0.05). In Group A, 99% of the surgeries were performed painlessly during drilling and implant placement, but in Group B, 11.6% of implant placements (17 implants) felt pain during these surgical steps. Mean distance to mandibular canal (3.8 mm, range: 0.0 to 7.0) in those 17 implants placed under mandibular infiltration was clinically and statistically similar to the mean distance (3.0 mm, range: 0.0 to 9.0) of 130 implants placed painless (p=0.10). Pain during drilling under mandibular infiltration was significantly associated with the duration of surgery (p<0.05) and to both adjacent teeth being present (p<0.05).

Conclusions

Although both techniques are safe and effective for placing implants in the posterior mandible, nerve block provides a more profound analgesia than mandibular infiltration. When placing implants under mandibular infiltration, as getting closer to the canal does not increase the feeling of pain, it is not recommended to use the presence of pain as a preventive resource to avoid inferior alveolar nerve injuries. Key words:Dental implant, mandibular infiltration anesthesia, nerve block, pain, nerve injury.

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

INTRODUCTION

This study was designed to quantify the important anatomical landmarks and the path of the inferior alveolar nerve (IAN) within the human mandibular body and ramus, in particular with reference to the bilateral sagittal split osteotomy (BSSO).

MATERIALS AND METHODS

Four hundred and eleven CT scans were studied, 299 of these were involved in determining the position of lingula; and 230 were involved in determining the course of IAN in the mandibular molar region, namely from the mesial of the mandibular first molar to the distal of the mandibular second molar; 118 were involved with both measurements.

RESULTS

On average, the lingula was located 17.0 ± 2.2 mm from the external oblique ridge; 11.6 ± 2.0 mm from the internal oblique ridge; 17.2 ± 2.7 mm from the sigmoid notch; and 15.6 ± 1.9 mm from the posterior border of the mandible. The course of the IAN in the mandibular molar region was found to descend vertically from the distal of the mandibular second molar (7) to reach its lowest point between the first and second molars (6 and 7), and then ascend towards the mesial of the first molar (6). Horizontally, the IAN was found to traverse medially between the distal of the 7 and the middle of the 7, and then changes its path laterally towards the mesial of the 6.

CONCLUSION

Precise knowledge of the individual's position of the IAN will help surgical planning.

Predictive factors of the dimensions and location of mental foramen using cone beam computed tomography

Objective

The mental foramen (MF) hosts main neurovascular structures, making it of crucial importance for surgical procedures. This study aimed to analyze the factors influencing the dimensions and location of the MF.

Materials and methods

Cone beam computed tomography (CBCT) scans of 344 patients were examined for MF dimensions, as well as for the distances from the MF to the alveolar crest (MF-MSB), and to the inferior mandibular border (MF-MIB).

Results

Gender, mandibular side and presence of accessory mental foramina (AMF) significantly influence MF area. Males, left hemimandibles, and hemimandibles with no AMF had a higher rate of large MF areas (B = − 0.60; p = 0.003, females; B = 0.55; p = 0.005; B = 0.85; p = 0.038). Age, gender and dental status significantly influence MF-MSB distance. The distance decreased as age increased (B = −0.054; p = 0.001), females showed a lower rate of long MF-MSB distances (B = −0.94, p = 0.001), and dentate patients showed a higher rate of long MF-MSB distances (B = 2.27; p = 0.001). Age, gender and emerging angle significantly influenced MF-MIB distance. The distance decreased as age and emerging angle increased (B = −0.01; p = 0.001; B = −0.03; p = 0.001), and females had a lower rate of long MF-MIB distances (B = −1.94, p = 0.001).

Conclusions

General and local factors influence the dimensions and location of MF. MF dimensions are influenced by gender, mandibular side, anteroposterior position, and the presence of AMF. Distance from MF to alveolar crest is influenced by gender, age and dental status, while the relative MF position is influenced by age and dental status. CBCT images make it possible to analyze the MF in order to avoid complications during surgical procedures.

Alveoli, teeth, and tooth loss: Understanding the homology of internal mandibular structures in mysticete cetaceans

The evolution of filter feeding in baleen whales (Mysticeti) facilitated a wide range of ecological diversity and extreme gigantism. The innovation of filter feeding evolved in a shift from a mineralized upper and lower dentition in stem mysticetes to keratinous baleen plates that hang only from the roof of the mouth in extant species, which are all edentulous as adults. While all extant mysticetes are born with a mandible lacking a specialized feeding structure (i.e., baleen), the bony surface retains small foramina with elongated sulci that often merge together in what has been termed the alveolar gutter. Because mysticete embryos develop tooth buds that resorb in utero, these foramina have been interpreted as homologous to tooth alveoli in other mammals. Here, we test this homology by creating 3D models of the internal mandibular morphology from terrestrial artiodactyls and fossil and extant cetaceans, including stem cetaceans, odontocetes and mysticetes. We demonstrate that dorsal foramina on the mandible communicate with the mandibular canal via smaller canals, which we explain within the context of known mechanical models of bone resorption. We suggest that these dorsal foramina represent distinct branches of the inferior alveolar nerve (or artery), rather than alveoli homologous with those of other mammals. As a functional explanation, we propose that these branches provide sensation to the dorsal margin of the mandible to facilitate placement and occlusion of the baleen plates during filer feeding.

The Management of Persistent Pain From a Branch of the Trifid Mandibular Canal due to Implant Impingement

The mandibular canal is a conduit that allows the inferior alveolar neurovascular bundle to transverse the mandible to supply the dentition, jawbone, and soft tissue around the lower lip. It is now acknowledged that the mandibular canal is not a single canal but an anatomical structure with multiple branches and variations. Iatrogenic injury to branches of the mandibular canal that carry a neurovascular bundle has been reported to cause injury to the main canal as severe as if the main canal itself is traumatized. These injuries include bleeding, neurosensory disturbance, or the formation of traumatic neuroma, and so far, they have involved cases with the bifid mandibular canal. This current report presents a case of neurosensory disturbance that resulted from the impingement of a branch of a trifid mandibular canal during implant insertion. Its management included analgesics, reexamination, and reinserting a shorter implant.

Classifications of mandibular canal branching: A review of literature

AIM

To gather existing radiographic classifications of mandibular canals branching, considering the criteria on which these were based.

METHODS

The search for studies on mandibular canals based on imaging exams included literature reviews, epidemiological studies of prevalence, descriptive studies, or case reports. An electronic search in the MEDLINE (OvidSP), PubMed, EMBASE (OvidSP), Web of Science (Thompson Reuters), and Scopus (Elsevier) databases was performed, as well as a manual evaluation of the references of the selected articles. Combinations of key words were placed in each database. No restrictions were imposed regarding the year of publication or language. References collected in duplicate were removed by the authors. A table was drawn up, containing the included studies and respective interest data.

RESULTS

Six classifications of mandibular canals branching were selected for the present literature review. Four were based on two-dimensional radiographic exams, and two were performed based on three-dimensional tomographic exams. Three-dimensional classifications were determined based on the analysis found in the least number of exams, comparatively to two-dimensional studies. The prevalence of mandibular canal branching varied from 0% to 38.75% in the works based on two-dimensional exams, while those found in three-dimensional exams ranged from 15.6% to 65%. The studies were mostly referred to branches that began in the mandibular ramus. Just one classification considered the branches that began in the mandibular body region.

CONCLUSION

Three-dimensional exams appear to be the best method to view mandibular canal branching. Further studies are warranted to determine its true prevalence and questions concerning to associations.

Three-dimensional anatomic analysis of the lingula and mandibular foramen: a cone beam computed tomography study

PURPOSE

The authors analyzed the anatomic location differences of the mandibular foramen (MF) and lingula in a cone beam computed tomography study, aiming to obtain information that could be used when performing mandibular osteotomies and the inferior alveolar nerve block (IANB).

METHODS

Three-dimensional mandibular computed tomography images were reconstructed from data for 139 patients (278 sides) aged between 9 and 18 years (growth group, 27 patients) and aged 19 to 71 years (adult group, 112 patients).

RESULTS

In the adult group, positive correlations were seen between right and left measurements. In the growth group, there are significant differences in lingula-anterior and MF-posterior ramus measurements. In the adult group, there are significant differences between man and woman MF-gonion distance measurements. Differences were seen in edentulous and asymmetry patients.

CONCLUSIONS

The MF is an important anatomic landmark for ramus surgery and IANB. When applied to ramus operations and IANB, the anatomic data provided by this study may help surgeons gain more understanding of nerve position during surgery.

Anatomy of mandibular vital structures. Part I: mandibular canal and inferior alveolar neurovascular bundle in relation with dental implantology

Objectives

It is critical to determine the location and configuration of the mandibular canal and related vital structures during the implant treatment. The purpose of the present study was to review the literature concerning the mandibular canal and inferior alveolar neurovascular bundle anatomical variations related to the implant surgery.

Material and Methods

Literature was selected through the search of PubMed, Embase and Cochrane electronic databases. The keywords used for search were mandibular canal, inferior alveolar nerve, and inferior alveolar neurovascular bundle. The search was restricted to English language articles, published from 1973 to November 2009. Additionally, a manual search in the major anatomy, dental implant, prosthetic and periodontal journals and books were performed.

Results

In total, 46 literature sources were obtained and morphological aspects and variations of the anatomy related to implant treatment in posterior mandible were presented as two entities: intraosseous mandibular canal and associated inferior alveolar neurovascular bundle.

Conclusions

A review of morphological aspects and variations of the anatomy related to mandibular canal and mandibular vital structures are very important especially in implant therapy since inferior alveolar neurovascular bundle exists in different locations and possesses many variations. Individual, gender, age, race, assessing technique used and degree of edentulous alveolar bone atrophy largely influence these variations. It suggests that osteotomies in implant dentistry should not be developed in the posterior mandible until the position of the mandibular canal is established.

The position of the mandibular canal and histologic feature of the inferior alveolar nerve

The inferior alveolar nerve is the one of the large branches of the mandibular division of the trigeminal nerve. It is vulnerable during surgical procedures of the mandible. Despite its importance, no anatomical and histological examination has been conducted to provide a detailed cross-sectional morphology of the mandibular canal according to dental status. Therefore, the present study aimed to identify the position of the mandibular canal through direct measurement and to determine the branches of the inferior alveolar nerve through histologic examination. The area between the anterior margin of the third molar and the anterior margin of the second premolar of dentulous, partially dentulous, and edentulous hemimandible specimens (n = 49) from 26 human cadavers was serially sectioned into seven segments, and specific distances were measured using digital calipers. Following this, 5-microm cross-sections were prepared along the mandibular canal and mental foramen, and examined by fluorescence microscopy. The mandibular canal was located at a mean distance of 10.52 mm above the inferior margin of the mandible. The mean maximum diameters of the mandibular canal, inferior alveolar nerve, inferior alveolar artery, and inferior alveolar vein were 2.52, 1.84, 0.42, and 0.58 mm, respectively. This study found that the inferior alveolar nerve often gives rise to several branches at each level (range 0-3). To minimize the risk of injury, knowledge of the small branches of the nerve and of the detailed findings regarding the position of the mandibular canal reported here should be considered when planning mandibular surgery, especially during implant placement.

Reproducibility of 3 different tracing methods based on cone beam computed tomography in determining the anatomical position of the mandibular canal

PURPOSE

To investigate the reproducibility of 3 different tracing methods to determine a reliable method to define the proper anatomical position of the mandibular canal based on cone beam computed tomography (CBCT) data.

MATERIALS AND METHODS

Five dentate and 5 edentate patients were selected at random from the CBCT database. Two independent observers traced both the left and the right mandibular canal using 3-dimensional image-based planning software (Procera System NobelGuide; Nobel Biocare, Göteborg, Sweden). All mandibular canals were traced using 3 different methods. Method I was based on coronal views, also known as cross-sections. Panorama-like reconstructions were the starting point for method II. The third method combined methods I and II.

RESULTS

With respect to interobserver reliability, no significant difference (P = .34) for the various methods was observed. The reproducibility was better in edentate than in dentate jaws (P = .0015). The difference between 2 tracings was the lowest for the combined method: within a range of 1.3 mm in 95% of the course of the canal. The most obvious deviations were mainly seen in the anterior part of the canal.

CONCLUSIONS

The best reproducible method for mandibular canal tracing is the combined method III. Between observers, still a mean 95th percentile deviation threshold of 1.3 mm (SD 0.384) is noted, indicating that a safety zone of 1.7 mm should be respected. When planning surgery on CBCT-based data, surgeons should be aware of the obvious deviations located in the region of the anterior loop of the canal.

Inferior alveolar canal course: a radiographic study

OBJECTIVES

To describe the morphology and course of the inferior alveolar canal (IAC) as it appears in digital panoramic radiographs.

MATERIALS AND METHODS

Three hundred and eighty-six digital rotational panoramic radiographs (OPG) were studied using the Clinview Software (6.1.3.7 version, Instrumentarium). Among the 386 radiographs, 86 radiographs with 5-mm steel balls were used to calculate the magnification.

RESULTS

The average magnification of radiographs in this study was 7.24+/-7.55%. The course of IAC as seen in the panoramic radiograph may be classified into four types: (1) linear curve, 12.75%, (2) spoon-shaped curve, 29.25%, (3) elliptic-arc curve, 48.5%, and (4) turning curve, 9.5%. On panoramic radiographs, the IAC appeared closest to the inferior border of the mandible in the region of the first molar. In relation to the teeth, on panoramic radiographs, the IAC appeared closest to the distal root tip of the third molar and furthest from the mesial root tip of the first molar.

CONCLUSION

In the OPG, there are four types of IAC: linear, spoon shape, elliptic-arc, and turning curve. The data found in the study may be useful for dental implant, mandibule surgery, and dental anesthesia. The limitations of the panoramic radiograph in depicting the true three-dimensional (3D) morphology of the IAC are recognized, computed tomography (CT) and cone beam (CB)3D imaging being more precise.

Inferior Alveolar Nerve Canal Position: A Clinical and Radiographic Study

PURPOSE

To document a clinically relevant position of the inferior alveolar nerve (IAN) in dentate patients and identify patient factors associated with IAN position.

MATERIALS AND METHODS

The investigators used a cross-sectional study design and a study sample of subjects who had a radiographically identifiable IAN canal and at least 1 mandibular first molar was enrolled. Predictor variables were age, gender, and race. Outcome variables were the linear distances between the buccal aspect of the IAN canal and the outer buccal cortical margin of the mandible, and the superior aspect of the IAN canal and the alveolar crest. Appropriate uni-, bi-, and multivariate statistics were computed.

RESULTS

The study sample was composed of 50 patients with a mean age of 42 years, 42.0% were male, and 73.2% were white. On average, the buccal aspect of the canal was 4.9 mm from the buccal cortical margin of the mandible. The superior aspect of the IAN canal was 17.4 mm inferior from the alveolar crest. Age and race were statistically associated with IAN position relative to the buccal cortical mandibular margin (P<.05). None of the demographic variables were associated with vertical position.

CONCLUSIONS

The IAN canal was 4.9 mm and 17.4 mm from the buccal and superior cortical surfaces of the mandible, respectively. The bucco-lingual IAN canal position was associated with age and race. Older patients and white patients, on average, have less distance between the buccal aspect of the canal and the buccal mandibular border. To minimize the risk of IAN injury, these variables should be considered when planning mandibular osteotomies or using monocortical plates.