Branching Patterns and Intraosseous Course of the Mental Nerve

Proprioceptive innervation of the human lips

The objective of this study was to analyze the proprioceptive innervation of human lips, especially of the orbicularis oris muscle, since it is classically accepted that facial muscles lack typical proprioceptors, that is, muscle spindles, but recently this has been doubted. Upper and lower human lips (n = 5) from non-embalmed frozen cadavers were immunostained for detection of S100 protein (to identify nerves and sensory nerve formations), myosin heavy chain (to label muscle fibers within muscle spindles), and the mechano-gated ion channel PIEZO2. No muscle spindles were found, but there was a high density of sensory nerve formations, which were morphologically heterogeneous, and in some cases resemble Ruffini-like and Pacinian sensory corpuscles. The axons of these sensory formations displayed immunoreactivity for PIEZO2. Human lip muscles lack typical proprioceptors but possess a dense sensory innervation which can serve the lip proprioception.

Exploring somatosensory innervation of the human lip: A focus on the vermilion

BACKGROUND

The lips are a vital component of the face and are densely innervated to perform various functions. The lip edges are covered with mucocutaneous tissue called vermilion which is particularly receptive to touch and temperature. The aim of this study was to investigate the somatosensory innervation of human lips, focusing on sensory corpuscles and the presence of mechano-gated (ASIC2, PIEZO2, and TRPV4) and thermosensing (TRPV1, TRPM2, and RPM8) ion channels within them.

METHODS

Twelve intact lips (6 upper and 6 lower) were obtained from non-embalmed frozen cadavers (five females and seven males) with an age range of 60-80 years. The specimens were divided into three zones (medial, lateral, and median). The morphotypes of sensory corpuscles and their immunohistochemical profile was analysed. The occurrence of ion channels involved in mechanosensation and temperature detection was examined using various antibodies. Sensory corpuscle density was quantified in vermilion sections, and statistical analyses were conducted to assess differences between the upper and lower lips, as well as between females and males (p < 0.05).

RESULTS

Different morphotypes of sensory corpuscles were identified: Ruffini-like associated with hair follicles, Meissner and glomerular corpuscles in the vermilion, and less classifiable sensory corpuscles within the mucosa. The density of sensory corpuscles in the vermilion was higher in the upper lip than in the lower lip; glomerular corpuscles predominated in the medial and median segments, whereas Meissner corpuscles were more abundant in the lateral segment. No sex-related differences were observed in the density or distribution of the two main corpuscular morphotypes. In contrast, the axons of both the glomeruli and Meissner corpuscles regularly displayed ASIC2 and PIEZO2 immunoreactivity, whereas immunoreactivity for TRPV1, TRPV4, TRPM2, and TRPV8 was absent.

CONCLUSIONS

These results demonstrate that the sensory corpuscles of the vermilion are a mixture of those typical of glabrous skin mucocutaneous tissues. The presence of PIEZO2 and ASIC2 in their axons suggests that these sensory corpuscles function as mechanosensors.

The Temporary Mental Nerve Paresthesia as an Outcome of Dentigerous Cyst Removal during Preparation for Dental Implant Placement: A Case Report

The usage of xenograft material is widely used in almost all oral cavity bone defects for regenerative and reconstructive purposes. The presented xenograft usage in the following care report enabled good bone defect healing and enabled the preservation of affected premolars. It is quite common to use any possible variations of bone materials to ensure bone defect improved healing. In some cases, the scope of surgeries requires the removal of each cyst within close proximity to various nerves and vessels. The inferior alveolar, infraorbital, lingual, and mental nerves are those most commonly adjacent to most operating sites in jaw bones. The usage of some additional materials such as collagen sponges, bone substitutes, resorbable membranes, or other additional materials are useful in each bone defect reconstruction but should be handled with care, as described in the following case. Before planning their usage, it is important to perform each surgery with close cone beam computed tomography imaging, which is very helpful to establish the scope of each lesion and the proximity of vital structures. There are a lot of factors that might influence any possible nerve damage, especially the different nerve anatomical variations. Even factors including the subperiosteal preparation and compression of adjacent tissues might influence later nerve function. When the lesion is expanding through the buccal cortical plate and when soft tissue fluctuation is present, some special care is needed. Similar to the presented case, a limitation in crushing, blowing, or any irritation of nerve fibers improves later postoperative outcomes. When the wound and surrounding tissues are handled with care, a limited possibility of any damage or paresthesia can occur. When the nerve itself is damaged or cut, loss of function can be permanent. Immediately after or even prophylactic prescription 1–2 days before the surgery of Vitamin B with NSAIDs (Non-steroidal anti-inflammatory drugs) (or other additional supplementary medicaments can improve nerve function in time. Possible nerve damage can be divided into many etiological factors. A quite different situation arises when the nerve is pulled in by the cyst growth into the cyst wall. The presented case report describes the outcomes of a cyst removal from the mandibular basis and treatment modalities.

Working Space Creation in Transoral Thyroidectomy: Pearls and Pitfalls

Simple Summary

Transoral thyroidectomy accesses the thyroid gland through three incisions in the oral vestibule. The cosmetic outcome was excellent since no scar was observed on the body surface. However, it is challenging to create a working space using this new approach. Unconventional but severe complications can also occur. Our review summarizes the tips regarding working space creation in transoral thyroidectomy and tricks for preventing complications.

Abstract

Transoral thyroidectomy is a novel technique that uses three small incisions hidden in the oral vestibule to remove the thyroid gland. It provides excellent cosmetic results and outcomes comparable to the open approach. One of the main obstacles for this technique is the creation of a working space from the lip and chin to the neck. The anatomy of the perioral region and the top-down surgical view are both unfamiliar to general surgeons. As a result, inadequate manipulation might easily occur and would lead to several unconventional complications, such as mental nerve injury, carbon dioxide embolism, and skin perforation, which are rarely observed in open surgery. Herein, we summarize the basic concepts, techniques, and rationales behind working space creation in transoral thyroidectomy to assist surgeons in obtaining an adequate surgical field while eliminating preventable complications.

Assessment of implant-related anatomical landmarks in the mandibular interforaminal region in an Iranian population using cone-beam computed tomography

Background:

This study was aimed to assess the implant-related anatomical landmarks in the mandibular interforaminal region in an Iranian population using cone-beam computed tomography (CBCT).

Methods:

In this retrospective cross-sectional study, 378 CBCT images of the mandible were evaluated for the presence of the incisive canal, anterior loop of the inferior alveolar nerve (IAN), mandibular canal, mental foramen, and incisive canal. The effect of age and gender of patients on the abovementioned variables was also evaluated. Data were analyzed using independent t-test, analysis of variance, and Chi-square test.

Results:

The anterior loop and the incisive canal were present in 36.24% and 97.62% of the cases, respectively. The mean length of the anterior loop and the incisive canal was 2.70 ± 1.20 mm and 12 ± 3.29 mm in the right, and 2.86 ± 1.24 mm and 12.21 ± 3.38 mm in the left side, respectively. The mean diameter of the mental foramen and incisive canal was 4.25 ± 1.08 mm and 1.89 ± 0.46 mm in the right, and 4.21 ± 1.02 mm and 1.94 ± 0.45 mm in the left side, respectively. The descending path was the most common path of the incisive canal. The distance from the incisive canal to the buccal plate and inferior border of the mandible was significantly shorter in females (P < 0.001).

Conclusion:

Considering the high variability and clinical significance of the incisive canal and anterior loop of the IAN, and their high prevalence, it is recommended to assess the presence/absence of these structures in the interforaminal region of the mandible on CBCT scans before surgical procedures in this region.

An anatomical and histological study of mental nerve branches to the inferior labial glands

PURPOSE

In this study, we aimed to reveal the detailed anatomy of mental nerve branches to the inferior labial glands.

METHODS

Embalmed cadaveric heads were used in this study and the mental nerve branches to the inferior labial glands were dissected. Branches to the glands were then excised for histological observation.

RESULTS

On all sides, the inferior labial glands were innervated by small branches arising from mental nerve branches that innervated the lower lip. No nerve branches to the inferior labial gland crossed the midline. Histological observation found that the tissue to the inferior labial gland were composed primarily of nerve fibers with a small number of surrounding vessels. Histological findings in examined specimens were consistent.

CONCLUSION

The inferior labial glands were innervated by small branches of the mental nerve to the lower lip.

Posterior superior alveolar nerves contribute to sensation in the anterior teeth

BACKGROUND

There is no available data on the occurrence rate of a converged alveolar canal, the detailed three-dimensional (3D) courses of alveolar canals/grooves (ACGs), or the contribution of each superior alveolar nerve to each area in the maxilla. This study aimed to clarify the 3D courses of ACGs, the relationship between ACGs and superior alveolar nerves, and the contribution of posterior superior alveolar nerves (PSANs) using computed tomography (CT) with histological analysis.

METHODS

During the gross anatomy course at Niigata University, we investigated nine human cadavers.

RESULTS

All anterior and posterior ACGs converged into the common alveolar canal, which contained blood vessels and several nerve bundles surrounded by perineurium, located at the nasal floor near the pyriform aperture. Histometrical analysis clarified that 16.3% of the nerve bundles in this canal were derived from PSANs, and 67% of the bundles were dispersed while they coursed down to the nasal floor. There seems to be no relationship between the density of nerve bundles in the canal and the number of remaining anterior teeth.

CONCLUSIONS

Data obtained from observing the detailed 3D courses of anterior and posterior ACGs, and their relationship with superior alveolar nerves, suggest that PSANs partially contribute to the nociception of the anterior teeth.

Management of Traumatic Trigeminal and Facial Nerve Injuries

In the area of craniomaxillofacial trauma, neurosensory disturbances are encountered commonly, especially with regard to the trigeminal and facial nerve systems. This article reviews the specific microanatomy of both cranial nerves V and VII, and evaluates contemporary neurosensory testing, current imaging modalities, and available nerve injury classification systems. In addition, the article proposes treatment paradigms for management of trigeminal and facial nerve injuries, specifically with regard to the craniomaxillofacial trauma setting.

Characteristics of Mandibular Canal Branches Related to Nociceptive Marker

It is difficult to correlate the direction of mandibular canal branches (MCBs) with altered sensation in dental treatments. In contrast, calcitonin gene-related peptide (CGRP) is related to vasodilation, bone formation, and the interaction with the peripheral nervous system. Therefore, we investigated the detailed morphological characteristics of MCBs using cone-beam computed tomography (CBCT) and observation of the CGRP distribution around the MCB. The MCB measurements were evaluated using principal component analysis (PCA) to identify morphological correlations. A total of 168 sides of mandibles from 84 cadavers were analyzed in this study. Most of the MCBs were primarily in the direction of the clock model from X to XI in sagittal sections and XII to I in coronal sections of the mandible. The structure of the MCB was divided into the fine canal branch (60.4%, 223/369), partial branch (24.4%, 90/369), and no canal branch (15.2%, 56/369). PCA indicated that the measurement element with the MCB and its structures were correlated in contrast to tooth factors. Positive CGRP reactions were clearly observed in the no-canal branch group compared to other groups. These data provide useful suggestions for MCB dynamics and information for clinical dental treatment.

Three-dimensional evaluation of the mandibular symphyseal region in block graft harvesting for dental implants using cone-beam computed tomography

Purpose

The purpose of this study was to analyze the quantity and quality of the mandibular anterior alveolar bone in terms of alveolar width, density, and total alveolar height (TAH) based on dental status, gender, and age. Additionally, this study aimed to quantitatively evaluate the available alveolar height for graft harvesting (AHGH) and examine its variability based on the aforementioned factors.

Materials and Methods

This retrospective cone-beam computed tomographic study included a total of 100 subjects. On the basis of gender, dental status, and age, the scans were divided into 3 primary groups and 8 subgroups. The mandibular alveolar width and density were measured 5 mm mesial to the mental foramen bilaterally and at the midline. The TAH was measured at the midline, and the AHGH was measured as the midline distance between 5 mm apical to the root of the canines and 5 mm superior to the lower border.

Results

The mandibular alveolar width was statistically similar between dentulous and edentulous patients (P>0.05). A significantly greater density was observed at the midline in edentulous patients (P<0.05). The TAH was significantly greater in edentulous male patients than in edentulous female patients (P<0.05). Dentulous and male patients had significantly greater AHGH than edentulous and female patients, respectively (P<0.05).

Conclusion

Based on the data evaluated in this study, it can be concluded that the mandibular symphyseal area has adequate bone quality and quantity for bone graft harvesting for dental implant therapy.

Branching Patterns of Mental Nerve in Newborns

In classical textbooks of Anatomy, the mental nerve is considered to be the terminal or main branch of the inferior alveolar nerve, especially trifurcate with no designated names as soon as it emerges from the mental foramen. The textbooks define the innervation area of the mental nerve regionally without naming its terminal branches. Nomina Anatomica designates 3 terminal branches of mental nerve as "labial, gingival, and mental branch" but offers no description about their distribution on the mandible. In the present study, bilateral dissections were performed on the lower lip specimens of 20 newborns for 40 mental nerves to determine the branching types of mental nerve. Although anatomy textbooks indicate that mental nerve divides into 3 branches, the authors noted that mental nerve branched into 1, 2, or 3 branches at or right after its exit from the mental foramen. Branching patterns were typed in 13 different subclasses under 3 main groups (Form I-II-III). Moreover, the branching patterns that could not be included in one of these 3 main groups were defined as "Complex Form." The most common type of branching that the authors observed was Form II, which had 2 terminal branches with an incidence of 41.9% (16 specimens). The next frequently encountered type was Form III, having 3 terminal branches, and it was detected in 32.0% of patients (12 specimens). The least common form was Form I, which had 1 terminal branch with a frequency of 15.8% (6 specimens). The unclassified group, Complex Form, was found 10.5% (4 specimens).

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.

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.

Location of the Mandibular Incisive Canal Related to the Placement of Dental Implants: A Case Report

Cone-beam computerized tomography (CBCT) can show an uncommon mandibular incisive canal that cannot be detected by panoramic radiography, which is used preoperatively to form the initial plan of the size and length of an implant fixture for surgical placement in the mandibular interforaminal area. Determination of the position and anatomical configuration of the mandibular incisive canal is challenging. The purpose of this case report is to discuss anatomical variations in the mandibular incisive canal and the mental canal by reviewing previous studies. Furthermore, we propose that the anterior loop length of the mental canal near the mental foramen, as well as the diameter of the mandibular incisive canal, should be verified by CBCT prior to performing implant surgery in the anterior mandibular area to prevent possible nerve damage.

Anatomical study of gasless transoral thyroidectomy and clinical application

BACKGROUND

Transoral thyroidectomy is becoming a preferred technique because it has the advantage of not leaving a scar after surgery. However, it is not yet standard because of the anatomic nerve complexity of this oral cavity and difficulty of approach. The aim of this study was to determine the safety zone of a gasless transoral thyroidectomy approach using an anatomical study and to evaluate the efficacy of this approach on clinical application.

METHODS

Phase 1, twenty unilateral specimens from fresh cadavers underwent staining by the modified Sihler's method to identify nerves around the oral vestibules. Then, the safety zone of the transoral thyroidectomy approach was proposed. Phase 2, a comparative analysis of the clinical outcomes of gasless transoral thyroidectomy through the safety zone versus transcutaneous thyroidectomy approach.

RESULTS

In phase 1, numerous inferior labial branches diverged from the mental nerve and were distributed across the lower lip. In most cases, the most lateral branch reached almost to the corner of the mouth, whereas a nerve-free area was present at the medial region of the lower lip. The suggested safety zone was presented as a trapezoid shape. In phase 2, there were no significant differences in age, mass size, or complications between the two groups. However, the operation time in the transoral thyroidectomy group was longer than in the transcutaneous group (p = 0.001).

CONCLUSIONS

Based on the anatomical study, we suggested a safety zone for the gasless transoral thyroidectomy. On application of this safety zone, gasless transoral thyroidectomy is a safe and feasible procedure.

Prevalence and Length of the Anterior Loop of the Inferior Alveolar Nerve in Iranians

The anterior loop of the inferior alveolar nerve is a sensitive anatomical feature that should be taken into account during installation of dental implants anterior to the mental foramen. This study was conducted to explore the controversy regarding prevalence and length. A total of 452 mandible quadrants of 234 patients (age: 50.1 ± 13.3 years, 113 males, 121 females) were studied using cone-beam computerized tomography. After reconstructing axial, frontal, and sagittal slices, the region between the most anterior point on the mental foramen and the most anterior part of the mandibular nerve was inspected for signs of anterior loop presence. If positive, the length of the anterior loop was measured in mm as the distance between the anterior border of mental foramen and the anterior border of the loop. Prevalence and length of the anterior loop were compared statistically between sexes and age groups. The anterior loop was observed in 106 quadrants (23.5% of 451 quadrants) of 95 patients (40.6% of 234 patients), of whom 11 had bilateral anterior loops. Prevalences were similar in males (41%) and females (39%, chi-square P =.791). The mean anterior loop length was 2.77 ± 1.56 mm (95% CI: 2.5–3.1 mm), without significant sex (regression beta = −0.159, P = .134) or age (beta = −0.059, P = .578) differences. The anterior loop might exist in about 40% of patients, regardless of their gender. The mean safe anterior distance from the anterior loop is about 3 mm + (2.5–3.1 mm) = 5.5–6.1 mm, regardless of age.

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.

Determination of the position of mental foramen and frequency of anterior loop in Saudi population. 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.

Study of the mandibular incisive canal anatomy using cone beam computed tomography

PURPOSE

The aim of this study was to identify the range of individual variability in dimensions and topography of the mandibular incisive canal (MIC) in vivo.

METHODS

One hundred cone beam computed tomography (CBCT) scans of patients from dental outpatient hospitals of Minsk, Belarus were performed on Galileos GAX5 using standard exposure and patient positioning protocol. Reformatted panoramic and sagittal CBCT images were analyzed.

RESULTS

The MIC was visualized in 92% of CBCT images. It was detected in the first premolar root region in 93% of cases, and only in 21% of cases it reached the central incisors root area. The MIC started prior to the mental foramen opening with formation of the anterior mental loop in 48% of cases. The MIC started at the level of the mental foramen or close to it in 52% of cases. The degree of MIC visibility and its internal vertical diameter decreases when it comes closer to the midline of the mandible. The distance from the roots of teeth to the upper wall of MIC increases in the mesial direction, while the position of MIC in relation to the base of the mandible remains virtually unchanged.

CONCLUSIONS

The MIC can appear in a different length and can reach the level of the root of the central mandibular incisor. Individual topography of MIC should be determined during the preoperative radiological examination and surgical procedures in the anterior region of the mandible.

Panoramic radiographs underestimate extensions of the anterior loop and mandibular incisive canal

Purpose

The purpose of this study was to detect the anterior loop of the mental nerve and the mandibular incisive canal in panoramic radiographs (PAN) and cone-beam computed tomography (CBCT) images, as well as to determine the anterior/mesial extension of these structures in panoramic and cross-sectional reconstructions using PAN and CBCT images.

Materials and Methods

Images (both PAN and CBCT) from 90 patients were evaluated by 2 independent observers. Detection of the anterior loop and the incisive canal were compared between PAN and CBCT. The anterior/mesial extension of these structures was compared between PAN and both cross-sectional and panoramic CBCT reconstructions.

Results

In CBCT, the anterior loop and the incisive canal were observed in 7.7% and 24.4% of the hemimandibles, respectively. In PAN, the anterior loop and the incisive canal were detected in 15% and 5.5% of cases, respectively. PAN presented more difficulties in the visualization of structures. The anterior/mesial extensions ranged from 0.0 mm to 19.0 mm on CBCT. PAN underestimated the measurements by approximately 2.0 mm.

Conclusion

CBCT appears to be a more reliable imaging modality than PAN for preoperative workups of the anterior mandible. Individual variations in the anterior/mesial extensions of the anterior loop of the mental nerve and the mandibular incisive canal mean that is not prudent to rely on a general safe zone for implant placement or bone surgery in the interforaminal region.

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.

Anterior Loop of the Inferior Alveolar Canal: A Cone-Beam Computerized Tomography Study of 494 Cases

The aim of this study was to use cone-beam computerized tomography (CBCT) images of patients to assess the prevalence of different types, especially anterior loop, of the mental portion of the inferior alveolar canal and to evaluate the anterior loop lengths. CBCT images of 494 patients providing inclusion criteria were examined by 2 oral radiologists. Sagittal, axial, and multiplanar reformatted images were used to detect the type of mental portion of the inferior alveolar canal. The anterior loop length was measured in the respective sections of each CBCT image. Statistical analysis was performed using SPSS v. 15, and t tests were used for statistical analysis. Of the 494 patients, 217 anterior loops were detected in 141 (28.5%) patients. The mean anterior loop lengths for the right side and the left side were 2.19 ± 1 mm and 2.08 ± 0.89 mm, respectively. The difference between males and females in the mean anterior loop length was statistically significant for both sides (Right: P < .05; Left: P < .05). A presurgical CBCT image examination is necessary prior to implant insertion to reveal the presence of anterior loop and to detect actual anterior loop length.

A Practical Surgical Technique to Expose the Mental Nerve in Narrowing Genioplasty

In this article, the authors present a practical surgical technique using the anatomical character of the inferior alveolar nerve to fully expose the mental nerve (MN) in narrowing genioplasty. During the procedure, a rectangular mandibular outer cortex adjacent to the mental foramen is removed before the osteotomy. The objective is to avoid the injury of the MN from the reciprocating saw or bur and offer abundant space for the surgical operation. The technique has a minimal learning curve and will be useful to plastic surgeons to minimize unintentional cutting or pulling injury to the MN in narrowing genioplasty.

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.

Anterior Loop of the Mandibular Canal-A Source of Possible Complications

INTRODUCTION

Recognizing the radiographic position of the mental foramina is not sufficient to avoid complications during dental implant surgery. In many cases, the inferior alveolar nerve extends mesially as an "anterior loop" (AL). The aim of this study was to investigate the prevalence and spatial extension of the AL on computed tomography (CT).

MATERIALS AND METHODS

Thirty-seven human mandibles from an anatomical collection underwent CT analysis. Cross-sectional views and panoramic reconstructions were obtained. Prevalence and length of the AL were investigated.

RESULTS

Recognition of the AL on CT was 100%. Prevalence of the AL was 97.3% (n = 36). AL mean length was 2.26 mm (maximum: 7.0 mm).

CONCLUSION

Recognition of the AL on CT scans (100%) is higher compared with data in literature for detection on panoramic radiographs (38.2%). To avoid complications, it is important to detect the AL presence and its mesial extension from the mental foramen. Safety distance of at least 2 mm from the mesial extend of the AL is recommended. Therefore, 3D imaging techniques are advised for loops which courses are not clearly identifiable on panoramic radiographs.

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.

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.

Nerve Damage Assessment Following Implant Placement in Human Cadaver Jaws: An Ex Vivo Comparative Study

The present study compared the use of cone beam computerized tomography (CBCT) images and intra-oral radiographs in the placement of final implant drills in terms of nerve damage to cadaver mandibles. Twelve cadaver hemimandibles obtained from 6 cadavers were used. Right hemimandibles were imaged using peri-apical radiography and left hemimandibles using CBCT, and the images obtained were used in treatment planning for the placement of implant drills (22 for each modality, for a total of 44 final drills). Specimens were dissected, and the distances between the apex of the final implant drill and the inferior alveolar neurovascular bundle and incisive nerve were measured using a digital calliper. Nerves were assessed as damaged or not damaged, and the Chi-square test was used to compare nerve damage between modalities (P &lt; 0.05). Nerve damage occurred with 7 final drills placed based on peri-apical radiography (31.8%) and 1 final drill placed using CBCT images (4.5%). The difference in nerve damage between imaging modalities was statistically significant (P = 0.023), with CBCT outperforming intraoral film in the placement of final implant drills ex vivo. In order to prevent nerve damage, CBCT is recommended as the principal imaging modality for pre-implant assessment.

Branching Pattern of the Extraosseous Mental Nerve in a Kenyan Population

Knowledge of the branching pattern of the mental nerve is an important consideration during placement of tooth implants and reconstructive plates. It is known to display population variations and data for the same is scarce form the sub-Saharan region. With the recent increase in surgical interventions in the mandibular region in Kenya, a detailed description of mental nerve is warranted. A total of 64 mental nerves were dissected and branching pattern was noted. Single mental nerve was present in 60 (93.7%) cadavers while double mental nerves occurred in 3 (4.7%) and accessory in 1(1.6%). Most common pattern was bifurcation (39%) followed by trifurcation (34%), single (19%), and quadrification (8%). The double and triple branches were seen to further divide into two to three subbranches with diverse patterns. Side symmetry in branching was seen in four (6.25%). These are important anatomical considerations during placement of reconstructive plates for mandibular trauma and administration of mental nerve blocks.

Sihler staining study of anastomosis between the facial and trigeminal nerves in the ocular area and its clinical implications

INTRODUCTION

The trigeminal nerve (CN V) supplies mostly sensory innervation to the face, and the facial nerve (CN VII) conveys primarily motor fibers. The aim of this study was to elucidate their distributions and anastomoses.

METHODS

Fourteen specimens of hemisectioned faces were gathered from human cadavers and stained with Sihler staining.

RESULTS

The temporal (Tbr), zygomatic (Zbr), and buccal (Bbr) branches of CN VII formed trigeminofacial anastomoses in the ocular area. Communications were observed between the supraorbital nerve and the Tbr (85.7%), the infraorbital nerve and the Bbr (100%) and Zbr (28.6%), and the zygomaticofacial nerve and the Zbr (41.7%). Anastomoses were formed between the supratrochlear nerve and the Tbr (57.1%) and Bbr (50%), and the infratrochlear nerve and the Bbr (85.7%).

CONCLUSIONS

Motor and sensory axons to the face contribute to trigeminofacial anastomoses, which may play key roles in subtle movements of muscles of facial expression.

Comparative analysis of mandibular anatomical variations between panoramic radiography and cone beam computed tomography

PURPOSE

The objective of this study is to compare the ability of panoramic radiography and cone beam computed tomography (CBCT) in detecting anatomical variations of the mandibular canal and mental foramen.

METHODS

One hundred twenty-seven preoperative panoramic and CBCT images were evaluated. Two oral and maxillofacial radiologists investigated the presence of bifid mandibular canals and/or additional mental foramina on the right, left, or both sides of the mandible. Intra- and interobserver reliability was determined using Cohen's kappa coefficient. McNemar's test compared the prevalence of mandibular anatomical variations between panoramic radiography and CBCT. The significance level was set at 0.05.

RESULTS

Additional mental foramen and bifid mandibular canal were detected in 1.2 and 7.4 % of the panoramic radiographs and 7.4 and 9.8 % of the CBCT images, respectively. The incidence of anatomical variations on the mandibular canal was not significantly different between both imaging modalities (P > 0.05).

CONCLUSIONS

Although CBCT provides better viewing of anatomical structures, including location, shape, and relationship with the surrounding area, panoramic radiography is a conventional imaging modality that can be used in the study of the bifid mandibular canals.

Identification of the mental neurovascular bundle: a comparative study of panoramic radiography and computer tomography

OBJECTIVES

To compare the images of the mental canal in panoramic radiography (PR) and computed tomography (CT) by analyzing the concordance with diagnostic tests and examiners.

MATERIAL AND METHODS

The position of the mental foramen (MF), distance to the lower mandibular border, anterior length of the mental loop (ML), agreement between examiners and diagnostic concordance were registered in 50PR and 50CT.

RESULTS

ML was identified (34.5/41%, PR/CT). PR magnification was 36.6% higher than in CT. The anterior extension and distance to the inferior border of the MF was higher for PR (2-6.2 mm). Inter-examiner agreement on CT was good (κ = 0.628) and very good on PR (κ = 0.845).

CONCLUSION

There is a magnification (36.6%) of the images in PR with respect to the CT. Identification of MF and ML is not related to the bone quality. Inter-examiner agreement is better on PR.