Assessment of the prevalence and length of the anterior and caudal loops of the mental nerve as anatomical variants of exiting the mandible at the mental foramen using cone-beam computed tomography: a systematic review and meta-analysis

OBJECTIVES

This systematic review aimed to identify the studies that performed cone-beam computed tomography analysis of the prevalence and length of the anterior loop (AL) and caudal loop (CL) of the mental nerve.

MATERIALS AND METHODS

An electronic database search was performed across PubMed, EMBASE, Web of Science, Scopus, the Cochrane library, and Google Scholar. Original studies reporting the frequency and length of the AL and CL were selected. Qualitative synthesis and meta-analysis were then conducted to assess the prevalence and length of the AL and CL and their associations with age, gender, sides, and dentition status.

RESULTS

A total of 21 studies were included in this review. The pooled prevalence of the AL (95% confidence interval) of the mental nerve at the patient and side level was 51% (31-71%) and 53% (37-69%) while the mean anterior loop length was 2.08 (1.46-2.70) mm. The pooled prevalence of the CL and mean caudal loop length were 100% and 4.73 (3.44-6.01) mm. No significant associations were found between the prevalence and length of the AL and CL and age, gender, sides, and dentition status.

CONCLUSIONS

Overall, the pooled prevalence and mean length of AL of the mental nerve varied among different populations while CL seems to be a constant anatomical landmark with a longer CL than AL.

CLINICAL RELEVANCE

Surgeons performing inter-foraminal oral surgeries like dental implant placement and genioplasty should be aware of the possible distance of the AL and CL to avoid iatrogenic mental nerve injury.

Mental Foramen and Anterior Loop Anatomic Characteristics: A Systematic Review and Meta-analysis of Cross-sectional Imaging Studies

INTRODUCTION

The present study aimed to review the epidemiologic, topographic, and morphometric aspects of the mental foramen (MF) and anterior loop (AL) on cone-beam computed tomographic imaging studies.

METHODS

An International Prospective Register of Systematic Reviews (PROSPERO)-registered systematic review (CRD42018112991) was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Two reviewers independently performed data extraction from observational studies that evaluated MF and AL on 7 electronic databases. MedCalc (MedCalc Software bv, Ostend, Belgium) software was used to perform a meta-analysis with a 95% confidence level.

RESULTS

Of 1545 articles, 66 met the inclusion criteria, totaling 14,233 patients from 5 continents, with a total of 6655 females and 5884 males (some studies did not report sex), with an age range between 8 and 89 years. The most prevalent shapes of MF were oval (48.72%) and circular (44.36%), and the most frequent horizontal positions were between premolars (43.66%) and in line with the long axis of the second premolar (43.12%).

CONCLUSIONS

Based on the articles that assessed AL, the mean prevalence was 43.18%, with most studies reporting bilateral localization as the most prevalent.

Evaluation of the Dimensions of Anterior Loop of Mental Nerve in CBCT: A Radiographic Analysis

Background

Information on the dimensions of the anterior loop of mental nerve is important for dental implant placement.

Aims

The purpose of this study was to determine the total length of anterior loop of mental nerve from the mental foramen.

Materials and Methods

CBCT data of 150 patients were evaluated.

Results

We found that the anterior loop was absent in 56.4% of patients on the left side and 61.7% patients on the right side. 19.5% of the total patients (29 patients) had up to 4 mm length of the loop which was exactly same on both right and left sides. The remaining 16.8% on the left side (25 patients) and 14.1% on the right side (21 patients) had the length of the loop ranging between 4.1 and 8 mm. The rest 7.4% of patients on the left side and 4.7% patients on the right side had more than 8 mm of the loop length.

Conclusions

Based on this study, the dimensions of the anterior loop are variable and hold great significance in dental implant planning in the mandibular premolar region.

A cone beam computerized tomography study

Background

The portion of inferior alveolar nerve (IAN) existent anterior to the mental foramen, before parting the canal, is referred to as the anterior loop (AL) of the IAN. The presence of AL is important when placing the implant interforaminal area of the mandible. These anatomical discrepancies can be assessed by cone-beam CT (CBCT), for evaluating its position and exact location. The AL is classified into Types I, II and III. In Type I, Y-shaped anatomy; in Type II, anatomy is T-shaped; and in Type III, Y-shaped anatomy is seen, and the incisive branch is thicker as compared to the main branch.

Aim

In this study, we aim to analyse the prevalence of different types of AL of the IAN in Saudi sample population.

Materials and Methods

The present study is a retrospective analysis of 149 (86 female & 63 male) CBCT images of patients records from 2018 June to 2018 September in the department of implant dentistry, KSMC, Riyadh. The age range of the patients who participated in the study was 30–60 years. The mean age of female participants is 42.5 ± 5.8, for the male participants is 48.6 ± 11.4 years respectively.

Results

The most frequent type of AL of mental nerve noticed on the right side was of type I (59.1%), followed by type II (27.5%) and type III (13.4%). The most frequent type of AL of mental nerve noticed on the left side was type I (61.7%), followed by type II (26.8%) and type III (11.4%).

Conclusion

The results of the study encourage the usage of CBCT for planning implant treatment. We also suggest that it is obligatory for professionals to categorise the presence of AL and to measure them appropriately when planning for the procedures in the interforaminal region.

Momentousness of the Mental Loop: A Comparative Study

Background and Purpose

To assess the anterior (aAL) and caudal (cAL) extensions of Anterior loop (AL) of Inferior alveolar nerve (IAN) using Digital Panoramic (DP) and Cone Beam Computed Tomography (CBCT) for its presence and dimensions in various age groups, genders, right and left sides of the mandible and between dentulous and edentulous patients.

Methods

A 1-year retrospective comparative study between DP and CBCT to assess the extensions of AL of IAN was conducted on individuals referred to a private imaging center located in Bengaluru, South India. 360 mandibular sites were examined using DP and CBCT to assess the presence and dimensions of AL.

Results

Results showed higher frequency of AL in CBCT compared to DP. Also there was a decreasing frequency of AL with increasing age and an insignificant difference in frequency between males and females. Bilateral looping was most common, aAL was more frequent on the left side and cAL on the right of the mandible. Statistically higher frequency in dentate group compared to edentulous. A decreasing mean value with increasing age and higher mean values in CBCT than DP. No significant difference in mean values among males and females or between the dentulous and edentulous groups. Higher mean values in CBCT compared to DP on the left side of the mandible compared to the right.

Conclusion

Choosing mental foramen as reference for termination of IAN could result in injury to AL; low sensitivity and specificity of DP compared to CBCT in assessing frequency and extent of AL underlines its inadequacy, while CBCT can be performed with comparable resolution, to accurately analyze AL.

Assessment of the Anterior Loop of the Mandibular Canal Using Cone-Beam Computed Tomography in Eastern India: A Record-Based Study

Objective:

The aim of this study was to assess the presence and course of the anterior loop (AL) in an Odisha sample population using cone-beam computed tomography (CBCT) and to accurately identify and analyze the length, height, and diameter of AL in male and females.

Materials and Methods:

CBCT images from 1000 patients obtained for various clinical indications were randomly selected and evaluated to determine the presence, length, height, and diameter of the AL. The various parameters were then compared based on gender, age, and the side of the mandible. The data were analyzed using the Chi-square test, independent t-test, multiple post hoc procedure, and one-way ANOVA test.

Results:

An AL was identified in 9.7% of the cases, and its mean length ranged from 1.8 to 4.8 mm. The loop had a greater mean length and was significantly more prevalent in males. The diameter ranged from 1 to 4 mm and height ranged from 7.8 to 15.1 mm. The AL was most commonly found in the middle-aged patients (39–48 years) which attributed to around 27.83%.

Conclusion:

In this study, a lower prevalence of the AL of the mandibular canal was found. Being an anatomical variation, an exact evaluation of the AL must be established using the imaging techniques prior to any surgical procedure.

Cone-beam CT assessment of implant-related anatomy landmarks of the anterior mandible in a Chinese population

PURPOSE

To investigate the prevalence, location, and morphology of the mandibular lingual foramen (MLF), mandibular incisive canal (MIC), and anterior loop of the inferior alveolar canal (ALC) in a Chinese population using cone-beam CT (CBCT).

MATERIALS AND METHODS

From 2014 to 2016, CBCT images from patients with various scanning purposes were obtained from the database of the Affiliated Stomatology Hospital of Kunming Medical University, China. Imaging analyses of the MLF, MIC, and ALC were performed via the NNT viewer software. The prevalence, location, length, classification of MLF, and its distances to the alveolar crest and the lower border of mandible were investigated, and the prevalence and length of MIC and the prevalence of ALC were also studied.

RESULTS

This study examined 1008 subjects, 521 (51.7%) males, and 487 (48.3%) females. 916 (90.9%) subjects showed the medial lingual foramina (LF), a single medial LF with the supraspinous-type predominating. Lateral LF were observed in 547 (54.3%) subjects mostly located in the premolar areas. 876 (86.9%) subjects had the MIC on the left side, whereas 877 (87.0%) had the MIC on the right side. The ALC was present in 147 (14.6%) subjects.

CONCLUSIONS

This study showed a high prevalence of LF and MIC in the Southwest Chinese population. Therefore, caution should be taken during the implant treatment at the anterior mandible region.

Available bone morphology and status of neural structures in the mandibular interforaminal region: three-dimensional analysis of anatomical structures

PURPOSE

This study aimed to clarify the size and morphology of the mandible and to determine state of neural structures for the planning of the dental implantation using cone-beam computerized tomography (CBCT).

METHODS

Of the 252 patients, CBCT images of 48 selected patients were evaluated. The bone height and width were measured and the type of the mental portion of the inferior alveolar canal, the anterior loop length (ALL), the location of the incisive canal and lingual foramen were identified with cross-sectional and multiplane reformatted CBCT images. According to buccal and lingual concavities, the shape of the mandible is classified as type A, B and C.

RESULTS

Bone widths of males were significantly higher than female (p < 0.05). The thickest part of the alveolar bone was measured in the middle triple zone (d line) and the thinnest part was measured in the area near the alveolar crest (b line). The most seen type of mandible was type B (45.8%) that mandible was concave on the buccal side. Bone heights had a tendency to increase towards to the anterior mandible, and bone height in male patients was slightly but not significantly greater than that in female patients. ALL was 4.2 ± 1.2 mm and visible incisive canal length on CBCT was 9.7 ± 3.8 mm.

CONCLUSION

CBCT assessment of morphological features of the alveolar bone and locations of nerve canals and foramina in the anterior-premolar region of mandible represent useful practical anatomical information about the interforaminal region. This information is the guide to the dentist before implant surgery.

Radiographic Evaluation of Anterior Loop of Inferior Alveolar Nerve: A Cone-Beam Computer Tomography Study

Background:

A well awareness of the variation of inferior alveolar canal is mandatory to avoid iatrogenic complication. This study was conducted among 90 patients to determine variation in inferior alveolar nerve (IAN) loop through cone-beam computed tomography (CBCT) images.

Materials and Methods:

CBCT images of 90 patients were involved in this study. All images were studied by the expert radiologist to see Type I, Type II, and Type III pattern of IAN canal (IANC). Results were subjected to statistical analysis for correct inferences.

Results:

Forty males and 50 females were included in the study. The difference was statistically nonsignificant (P = 0.5). Type I pattern was seen in 26 patients, Type II in 19, and Type III in 45 patients. The difference was statistically significant (P < 0.05). The most prevalent pattern was Type III (males - 15 and females - 30), followed by Type I (males - 14 and females - 12) and Type II (males - 11 and females - 8). There was statistical significance difference between males and females in Type II (P < 0.05).

Conclusion:

The anterior loop of IAC is quite common and IANC may show variation in structure. The most common pattern recorded was Type III. CBCT is very useful in the detection of IANC.

A retrospective CBCT study

Objectives

To determine the position of mental foramen (MF) and frequency of anterior loop (AL) using dental cone beam computed tomography (CBCT).

Materials and methods

The study involved the evaluation of 302 CBCT scans (196 males, 106 females). The position of MF was determined with respect to adjacent teeth, nearest root apex of adjacent teeth and mandibular borders. MF position was also assessed based on gender and age. In addition, prevalence of anterior loop was evaluated by categorizing the inferior alveolar canal (IAC) patterns into linear, perpendicular and anterior looping.

Results

The study revealed that the most common position of MF was below the apex of 2nd premolar accounting for a total of 52.8% of scans whereas, only 29.6% observed MF between 1st and 2nd premolar (p > 0.05). 38.7% of MF were located at a distance of 1–3 mm from the nearest root apex (2nd premolar), followed by a distance of less than 1 mm in 17.05 of cases. 63.2% of foramen on left side of the mandible were observed below the apex of 2nd premolar in females (p = 0.023). Statistically significant findings were observed with regards to position of MF in different age groups (p < 0.05). The most common IAC pattern observed was linear in nature which accounted for 46.2% of cases followed by perpendicular pattern (38.6%). AL was found only in 15.2% of cases.

Conclusions

Our sample population most commonly exhibited MF below the apex of 2nd premolar with linear IAC pattern. AL was regarded as the least common pattern in Saudi population.

Morphological assessment of the anterior loop of the mandibular canal in Koreans

The mandibular canal divides into the mental and incisive canals at the premolar region, forms the anterior loop which crosses anterior to the mental foramen, and turns back to reach the mental foramen. The aim of this study was to elucidate the general anatomical structure of the anterior loop of the mandibular canal using morphometry. Twenty-six hemimandibles from 19 cadavers (16 males, 3 females; mean age at death, 54.4 years) were studied by meticulous dissection with the aid of a surgical microscope. The location of the anterior loop, the diameters of the mandibular, mental, and incisive canals, and their distances from bony landmarks were measured using digital calipers. The anterior loop of the mandibular canal was located 3.05±1.15 mm (mean±SD) anterior to the anterior margin of the mental foramen and 2.72±1.41 mm inferior to the superior margin of the mental foramen, and was 4.34±1.46 mm long. The diameters of the mandibular, mental, and incisive canals were 2.8±0.49, 2.63±0.64, and 2.22±0.59 mm, respectively. The distances between the inferior border of the mandible and each of these canals were 7.82±1.52, 10.11±1.27, and 9.08±1.66 mm, respectively. The anterior loop of the mandibular canal was located a mean of 3.1 mm anterior and 2.7 mm inferior to the mental foramen, and continued upward and backward into the mental canal, and forward into the incisive canal. These detailed morphological features of the anterior loop of the mandibular canal represent useful practical anatomical knowledge regarding the interforaminal region.

Configuration of the inferior alveolar canal as detected by cone beam computed tomography

AIMS

The aim of this study is to evaluate the course of the inferior alveolar canal (IAC) including its frequently seen variations in relation to root apices and the cortices of the mandible at fixed pre-determined anatomic reference points using cone beam volumetric computed tomography (CBVCT).

MATERIAL AND METHODS

This retrospective study utilized CBVCT images from 44 patients to obtain quantifiable data to localize the IAC. Measurements to the IAC were made from the buccal and lingual cortical plates (BCP/LCP), inferior border of the mandible and the root apices of the mandibular posterior teeth and canine. Descriptive analysis was used to map out the course of the IAC.

RESULTS

IACs were noted to course superiorly toward the root apices from the second molar to the first premolar and closer to the buccal cortical plate anteriorly. The canal was closest to the LCP at the level of the second molar. In 32.95% of the cases, the canal was seen at the level of the canine.

CONCLUSIONS

This study indicates that caution needs to be exercised during endodontic surgical procedures in the mandible even at the level of the canine. CBVCT seems to provide an optimal, low-dose, 3D imaging modality to help address the complexities in canal configuration.