Detection and characterization of the mandibular accessory buccal foramen using CT

Clinical anatomy of coronoid foramina of mandible and review of its implications in maxillofacial surgery

INTRODUCTION

A foramen in the coronoid process of the human mandible is a recently identified anatomic variant. The authors in this script aim at presenting a detailed assessment of the coronoid foramen terming it as '''foramen of Nyer' (FN) based on the person first identifying it.

METHODS

Mandibular cone beam computed tomography scans from a total of 2168 patients were evaluated on a prospective and retrospective scale for confirmation of the coronoid foramen after first identification over a panoramic radiograph.

RESULTS

The coronoid foramen was found and confirmed in 96 (4.4%) patients. This script identifying the coronoid foramina of mandible becomes requisite research as a foundation for further analysis due to the scarcity of literature on this recent find.

DISCUSSION

This anatomical-radiological study aims to explore the variant foramina using cone beam computed tomography while determining its prevalence and evaluating its variability in terms of unilateral, bilateral, or gender predilection and propose the significance of this unique anatomic finding.

CLINICAL CONSEQUENCES

The lack of information about the presence of such variant foramina may lead to emergence of clinical morbidities such as increased risk of intra osseous hemorrhage and tumor spread due to presence of accessory blood vessels.

A Rare Anatomical Finding: Bilateral Accessory Mental Foramen

Aim

Accessory mental foramen (AMF) is a not common anatomical variation. During the surgical procedures involving the mandible such as implant surgery, periapical surgery, jaw surgeries, and periapical surgery and enucleation of pathologies at the mental region, obvious attention should be given to prevent postoperative sequelae. Case Report. Orthopantomograph (OPG) is routinely taken to visualize the maxillofacial region at a dental clinic. OPG shows exactly upper and lower jaw and teeth but superficially reveals some pathology or anatomic variation. It misses sometimes an anatomic landmark such as AMF. As the surgery is planned to a maxillofacial region, a detailed knowledge should be known before going into surgery to not interfere with anatomic landmarks. A 52-year-old male patient was referred to Kütahya Health Science University Dental Hospital, Turkey, to rehabilitate his bilateral partial edentulous lower jaw region. Implant surgery was planned in our patient. OPG was taken to evaluate the maxillofacial region but was unremarkable. Before the implant surgery, CBCT was obtained from our patient. CBCT and a three-dimensional reconstructed model of the male patient showed bilateral accessory mental foramen (AMF).

Conclusion

Accessory mental foramen (AMF) carries additional innervation to the chin, mandibular anterior gingiva, and mental region. Reflection and protection of the AMF during the surgery can prevent hemorrhage and neurosensory disturbance at the mental region and can improve quality of life for the patient. CBCT has higher precision but also a higher price and radiation dose. Although anatomical variations are uncommon, they can be found on digital panoramic radiographs but in limited percentage.

Evaluation of the Distance between the Mental Foramen and the Mandibular Edge: Cone Beam Computed Tomography Analysis in Turkish Population

Background/Aim: The aim of this study was to evaluate the distance between the mental foramen and the upper and lower edges of the mandible in the Turkish population according to different gender and age groups.

Material and Methods: A total of 1756 samples of 878 patients who presented at the Dentomaxillofacial Radiology Department of the Dentistry Faculty of Dicle University were included in the study for evaluation of the distance between the mental foramen and the upper and lower edges of the mandible. The cone beam computed tomography (CBCT) images were taken using an I-CAT Vision device (Imaging Science International, Hatfield, USA). Multiple variance analysis was used in the statistical analyses of the data.

Results: A statistically significant difference was identified between the genders in respect of the distance of the external edge of the mental foramen from the upper edge of the mandible (p=0,000). In the evaluations of the different age groups, no statistically significant difference was determined. A statistically significant difference was determined between the gender and age groups in respect of the distance of the mental foramen from the lower edge of the mandible (p=0,000).

Conclusions: The distance of the mental foramen from the upper and lower edges of the mandible can show variations according to age and gender. Therefore, the use of CBCT as a 3-dimensional imaging method with a low radiation dose is recommended.

Evaluation of Mental Foramen with Cone Beam Computed Tomography: A Systematic Review of Literature

Purpose

The aim of this systematic review is to assess whether the anatomy of mental foramen is precisely evaluable with cone beam computed tomography (CBCT) before implantation in humans.

Methods

A systematic review was carried out to evaluate the anatomy of mental foramen (size, position, symmetry, anterior loop, and accessory mental foramen or multiple mental foramina). According to Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines, an electronic search of three databases (Medline, Web of Science, and Cochrane Library) was undertaken until June 2020 and was supplemented by manual searching. Two reviewers will independently perform the processes of study inclusion, data extraction, and quality assessment. Systematic reviews, studies about children, and case reports were excluded. Only studies using CBCT to do preoperative evaluation were selected.

Results

From 728 potentially eligible articles, 72 were included in the qualitative analysis and quantitative synthesis. This systematic review provided an assessment of the anatomy of the mental foramen. The mental foramen was located mostly between the two premolars (between 50.4% and 61.95%) or apically to the second premolar (from 50.3% to 57.9%). The mean diameter of the mental foramen was bigger in males than in females; the difference between them could reach 0.62 mm. The anterior loop seemed to be longer in males (between 0.87 ± 1.81 and 7.25 ± 2.02 mm) than in females (between 0.81 ± 1.18 and 6.52 ± 1.63 mm) and with the presence of teeth (from 0.91 ± 1.18 to 2.55 ± 1.28 for dentate people and from 0.25 ± 0.61 to 2.40 ± 0.88 mm for edentate population). The anterior loop and the accessory mental foramina were detected more frequently with CBCT than panoramic X-ray: only between 0.0 and 48.6% AMFs detected with CBCT were also seen with panoramic images. Clinical Significance. The mental foramen (MF) is an important landmark for local anesthesia and surgical and implantology procedures. Its location, morphology, and anatomical variations need to be considered to avoid mental nerve injury. The aim of this review is to evaluate the mental foramen using CBCT through a systematic literature review to improve knowledge of this complex area for the clinician.

Cone beam CT-based measurement of the accessory mental foramina in the Chinese Han population

Anatomical data of accessory mental foramina (AMFs) were investigated in a Chinese Han population using cone beam CT (CBCT). A retrospective analysis was performed on 527 selected sets of CBCT images. The average frequency and diameter of AMFs, the diameter of the ipsilateral mental foramen (MF), and the center distance and relative position between the AMFs and MF were measured and calculated by three professional dentists. Among the 527 patients, AMFs were identified in 36 cases (frequency 6.83%), of which 68.75% of AMFs were larger than 1 mm. The mean diameters of the AMFs and the ipsilateral MF were 1.32±0.61 mm and 3.26±0.90 mm, respectively. The average distance from the AMFs to the alveolar ridge crest (ARC) was 15.05±3.50 mm, and the average distance to the mandibular plane was 15.87±3.64 mm. The positions of the AMFs relative to the MF varied widely. The AMFs were mostly positioned distal-inferior to the ipsilateral MF and under the mandibular second premolars. Nutrient foramina around the MFs were distinguished from AMFs. The reference plane for measuring AMFs was suggested to be the mandibular plane to increase the repeatability and accuracy of the experiment. Standard planes were proposed to determine the relative position between AMFs and the MFs. Based on our results, we propose that for implant surgeries, the safety region of 2 mm above the MFs should be reevaluated. CBCT examination is recommended before the operation to identify important anatomical structures around the MF region and their variations and set the safety distance on an individual basis.

The Sutton's Foramen of the Oblique Line of Mandible

Although the foramina of the adult mandible are well known and extensively studied, still additional foramina and canals could persist from the fetal stage and be detected occasionally in adult. At a routine anatomical evaluation of the Cone Beam Computed Tomography (CBCT) scan of a female patient of 47 years old, a rare anatomical variant of the mandible was found, and is presented here. It was termed foramen lineae obliquae and it was found in the right hemimandible at the level of the second molar, on the oblique line. From that foramen a canal continued within the mandible to join the mandibular canal. On orthogonal slices was accurately detected that the content of that foramen and canal was connected to an intramasseteric network, which was strongly suggestive for that content being vascular. Although a contribution from the buccal nerve could not be withdrawn, the most reasonable content to speculate is the aberrant anastomotic artery of the facial and inferior alveolar arteries. Vascular foramina of the mandible are relevant during various surgical procedures. Surgeons should be aware that if an artery is commonly regarded as a supplier of a muscle inserted on the mandible, it should not be rejected a priori the possibility for that artery being also an extrinsic supplier of the mandible, through an unexpected foramen in the vicinity of that muscle.

Variability in the number of mental foramina in the African green monkey (Grivet) (Chlorocebus aethiops)

This study aimed to determine the number of mental foramina (MFs) in vervet monkeys of the Cercopithecini tribe and perform a µCT analysis of mental foramina and mandibular canal morphology. A total of 19 simian skulls belonging to Chlorocebus aethiops species were used in the analyses. An average of three mental foramina was present in most individuals from the analyzed group. The Mann–Whitney test revealed no statistically significant difference between the number of foramina on the right- and left-hand side. Likewise, no statistically significant differences between the number of MFs across sexes were observed. Correlation coefficient values between mandibular length and the ipsilateral number of MF indicate a weak and statistically non-significant (p > 0.05) linear relationship. Volumetric reconstructions revealed the presence of a single periosteal sheathed mandibular canal terminated with four small mental foramina.

Variation in accessory mental foramen frequency and number in extant hominoids

Nerves providing sensation to the lower face and jaw exit the mandibular canal via the mental foramen. In humans, there are many documented occurrences of additional foramina (accessory mental foramina, AMFs) on the lateral mandibular surface that may also contain nervous structures. There are large discrepancies in the literature regarding how often AMFs occur in humans, and investigations of non-human hominoid AMFs are rare. Consequently, the causes of interspecific diversity in this variable have not been explored. This project seeks to compare the frequency and number of AMFs between males and females, and among human regional groups and hominoid subspecies and species, and to investigate possible causal factors for any differences identified. No significant differences were found between males and females in any group. Gorillas and orangutans had the highest percentages of individuals with AMFs and the highest mean number of foramina, while modern humans and siamangs had the lowest figures for these variables. Significant differences (p < .05) were found for the mean number of foramina between most pairs of species. The results also showed that species with mandibles that are larger overall, have a larger area anterior to mental foramen, and a longer mandibular canal typically present more AMFs. The strongest correlation was found between the mean number of mental foramina and mandibular canal length. We suggest that these results provide preliminary support for the hypothesis that increasing mandibular canal length increases the likelihood that that nerves will ramify, leading to greater frequencies of accessory mental foramina.

A rare anatomic variation: Triple mental foramina

Multiple mental foramina (MF) are rarely found in the human mandible. We report on the case, as documented using cone beam computed tomography (CBCT), of the triple MF that were identified on the right hemimandible of a 28-year-old female patient. The distal foramen was located on the mandible between the apices of the second premolar root and the first molar mesiovestibular root, being reached by a thin canal that left the mandibular canal. A pair of mesial foramina were identified between the apices of the premolar teeth. Thus, the three foramina corresponded to a surface area of 23.49mm² of the mandible. On the opposite side, a single mental foramen had a surface area of just 13.25mm². On each side, retromolar canals that opened into the retromolar fossae were also found. The anatomic possibility of multiple MF increases the surface area at risk during surgical procedures, increases the risk of neurovascular damage and obscures the common tooth-related location of the mental foramen. Practitioners should, therefore, consider a personalised and imaging-documented approach so as to avoid treatment failure.

Morphometric Analysis of the Mental Foramen Using Cone-Beam Computed Tomography

This study evaluated the effects of age and sex on the location and size of the mental foramen (MF). A total of 104 cone-beam computed tomography (CBCT) scans from patients' aged 18–80 years were selected. Images were evaluated using the following parameters: position and size of the MF, and Distances A (distance from the upper limit of the MF to the apex of the first lower premolar), B (distance from the upper cortical border of the MF to the alveolar crest), and C (distance from the border of the MF to the base of the mandible). Results revealed that the location of the MF was predominantly apical (44.4%), between the long axes of the premolars, at an average distance of 4.92 mm from the root of the first lower premolar. The height of the MF was significantly different between both sexes (3.41 and 2.99 mm, resp.; mean height: 3.11 mm; P=0.003). The MF was located on average at 11.21 mm from the alveolar crest and 12.31 mm from the base of the mandible; the former measurement was significantly different between both sexes (13.13 and 11.98 mm, resp.; P ≤ 0.001). In conclusion, the location of the MF was predominantly apical between the long axes of the premolars, and the mean size and distance of the MF were greater in men.

Inferior alveolar nerve trajectory, mental foramen location and incidence of mental nerve anterior loop

OBJECTIVES

Injury of the inferior alveolar nerve (IAN) is a serious intraoperative complication that may occur during routine surgical procedures, such as dental implant placement or extraction of impacted teeth. Thus, the purpose of this study was to analyze the trajectory of the mandibular canal (MC), the location of the mental foramen (MF) and the presence and extension of an anterior loop of the mental nerve (AL).

STUDY DESIGN

In this cross-sectional study, a total of 348 CBCTs were analyzed. Distances from MC to the surface of the basal, medial and lateral cortical of the mandible were measured at the level of the second molar, first molar and second premolar. Location of the MF relative to the apices of the premolars, as well as incidence and anterior extent of the AL were also determined.

RESULTS

Significant and clinically relevant correlations were found between the position of the MC in women, which was located more caudal (r=-0.219, p=0.007; r=-0.276, p<0.001; right and left, respectively) and lateral (r=-0.274, p=0.001; r=-0.285, p<0.001; right and left, respectively), particularly at the level of the premolars. Additionally, the presence (r=-0.181, p=0.001; r=-0.163, p=0.002; right and left, respectively) and anterior extension (r=-0.180, p=0.009; r=-0.285, p=0.05; right and left, respectively) of the AL was found to be inversely correlated with the age of the patient.

CONCLUSIONS

This analysis of a Caucasian population has found that the older the patient, the lower the incidence of the loop and the shorter its anterior extension.

Undetected Small Accessory Mental Foramina Using Cone-Beam Computed Tomography

INTRODUCTION

The accessory foramina could not be identified on some imaging modalities such as surface-rendered images. The purpose of this study was to investigate the ability of surface-rendered images in detecting these foramina.

MATERIALS AND METHODS

We analyzed 20 accessory mental foramina (AMF) in nine mandibles removed from cadavers with cone-beam computed tomography (CBCT) and assessed in surface-rendered images. All AMF were divided into three groups depending on their visibility.

RESULTS

Group 1 included AMF that were clearly visible as foramina, Group 2 were not clearly visible but could be recognized with concave parts, and Group 3 were not visible and the smooth surface of the bone was observed. Group 1 ranged from 1.3 to 5.1 mm², Group 2 from 0.3 to 3.8 mm², and Group 3 from 0.2 to 1.1 mm². A statistically significant difference in the mean size between Groups 1 and 3 was observed. Even if the AMF are smaller (e.g., 1 mm in diameter), they should still be avoided to prevent injury.

CONCLUSIONS

The clinician should be aware that smaller foramina might not be detected on these images.

Accessory mandibular foramen during dental implant placement: case report and review of literature

Accurate knowledge of vital anatomical structures, such as the inferior alveolar nerve, mental nerve, and mental foramen, is critical to achieve favorable results during oral surgical procedures and dental implant placement. Although uncommon, variations in mandibular foramina have been reported and if unnoticed and, as a result, injured, may lead to patient morbidity, neurosensory disturbances, and other undesired complications. We present a case report of identification of an accessory mandibular foramen (AMF) encountered during placement of 2 dental implants for a mandibular implant-retained overdenture and demonstrate appropriate management. In addition, we propose a more reasonable terminology for such accessory foramina so as to facilitate communication through common terminology among health care providers. As conventional radiography (periapical and panoramic films) may not allow for proper identification of such anatomical variations, cone-beam computed tomography may be useful in the diagnosis of AMF during treatment planning of dental implants in the mandible.

Anatomical characteristics and visibility of mental foramen and accessory mental foramen: Panoramic radiography vs. cone beam CT

Background

The mental foramen (MF) is a small foramen located in the anterolateral region of the mandible through which the mental nerve and vessels emerge. The knowledge on the anatomic characteristics and variations of MF is very important in surgical procedures involving that area. The aim of this study was two-fold: firstly, to analyze the anatomic characteristics of MF and the presence of accessory mental foramen (AMF) using CBCT and, secondly, to compare the capability of CBCT and PAN in terms of MF and AMF visualization, as well as influencing factors.

Material and Methods

A sample of 344 CBCT scans was analyzed for presence and characteristics (i.e. diameter, area, shape, exit angle) of MF and AMF. Subsequently, corresponding PANs were analyzed to ascertain whether MF and AMF were visible.

Results

Out of the 344 patients, 344 (100%) MFs and 45 (13%) AMFs were observed on CBCT. Regarding gender, MF diameter and area, MF-MIB and MF-MSB distances, and exit angle were all significantly higher in males. Also, statistically significant differences were found in terms of age and dental status. Statistically significant differences in MF long and short diameters and MF area were found with respect to AMF presence (p=.021, p=.008, p=.021). Only 83.87% of the MFs and 45.83% of the AMFs identified on CBCT were also visible on PANs. MF diameter, shape, exit angle, and age had a significant influence on MF visualization on PAN (B=.43, p=.005; B=-.55, p=.020; B=.20, p=.008; B=.61, p=.005).

Conclusions

PAN is not an adequate technique to properly identify MF and AMF. Diameter, shape, exit angle, and age are all factors influencing MF visualization on PAN images. For surgery involving the MF anatomical region, a preoperative radiological study with CBCT is of crucial importance to avoid complications.

Key words:Mental foramen, accessory mental foramen, mandibular anatomy, cone beam computed tomography, panoramic radiography.

Location of Mental Foramen in a Selected Iranian Population: A CBCT Assessment

INTRODUCTION

Mental foramen (MF) is an important anatomic landmark in dentistry and knowledge about its variable locations (L) and type of emergence (TE), has an effect on the sufficiency of local anesthesia and safety of surgical procedures. The aim of this study was to evaluate the L and TE of this radiographic landmark as well as the presence of accessory MF, by means of cone-beam computed tomography (CBCT).

METHODS AND MATERIALS

In this cross sectional study, a total of 156 CBCT images were retrieved from the archive of a private radiology clinic and were then evaluated for the position of MF and its TE and the existence of accessory foramina in the body of mandible. The extracted information was compared in both genders, in both sides of mandible and among three different age groups (20-29, 30-44 and 45-59 years). The Pearson chi-square and Fisher's Exact tests were used for statistical analysis. The level of significance was set at 0.05.

RESULTS

Second premolar was the most common anterolateral L of MF; in general, 48.7% of right and 51.9% of left MFs were located at the apex of second premolar. Anterior and straight ET were more common in right and left side, respectively. Accessory MF was present in only 8 (5.1%) of cases.

CONCLUSION

The possible presence of accessory MF should not be overlooked for avoiding the occurrence of a neurosensory disturbance during surgery and implant insertion.

Determination of the location of the mental foramen: a critical review

INTRODUCTION

The mental foramen (MF) is an important landmark to consider during surgical endodontic procedures. The purpose of this review article was to discuss the variety of techniques that have been developed to determine the location of the MF, to make recommendations for the current best technique available, and to discuss upcoming technologies.

METHODS

Articles that have addressed the location of the MF were evaluated for information pertinent to include in this review.

RESULTS

Different technologies have been used to help operators determine the clinical location of the MF. Most of the techniques have shortcomings such as magnification, radiation, and cost. Cone-beam computed tomographic imaging is the best current available imaging technology to determine the accurate location of the MF, but it has shortcomings such as radiation, cost, and not being real time, which means the data must be interpreted at a later time than when the information was computed.

CONCLUSIONS

In the future, magnetic resonance imaging and ultrasound technologies seem to provide promising noninvasive imaging techniques.

Number of accessory or nutrient canals in the human mandible

OBJECTIVES

The aim of the study was to assess the presence, location and the number of accessory or nutrient canals in the body of the mandible by means of cone beam CT images, obtained with the Planmeca ProMax® 3D Max device.

MATERIAL AND METHODS

Seventy-four cone beam images of the mandible from adult patients (37 males and 37 females) who were imaged for dental implantology planning or third molar extraction were used to assess the number and location of accessory or nutrient canals. All images were taken with the same machine (Planmeca® ProMax 3D Max) at 200-, 400- or 600-μm resolution. Distinction was made between canals entering or exiting the mandible superior or inferior of the inferior alveolar canal and between similar canals superior or inferior of the genial tubercula.

RESULTS

The number of accessory canals varied between nil to 11. No statistical significant difference between males and females was found with regard to the number or location of accessory canals in the mandible. Only 5.4% of patients had no accessory canals. One to five accessory canals were found in 71.6%, and 23% of patients had more than five accessory canals. The majority (81%) of patients had between two and six accessory canals.

CONCLUSION

It seems that subjects showing no accessory canals whatsoever should be considered exceptional as more subjects with than without accessory canals in the body of the mandible were found.

CLINICAL RELEVANCE

These results are clinically relevant for mandibular surgery and mandibular local anaesthesia.