Anterior loop of the mental canal: an anatomical-radiologic study

Mental Nerve Anterior Loop Detection in Panoramic and Cone Beam Computed Tomography Radiograph for Safe Dental Implant Placement

Background and aim Different imaging modalities have been used as preoperative assessment tools since the emergence of dental implants. This study aimed to compare the detection and presence of mental nerve anterior loop in cone beam computed tomography (CBCT) radiograph and panoramic radiograph. Material and methods A descriptive, retrospective study was done. The optimal sample size was calculated using Epi Info software. According to the study population (795), the sample size was 259 cases which gave 95% power of the study. A previously taken CBCT and digital panoramic radiographs from the database of Taibah University Dental School and Hospital were observed by two trained and calibrated examiners to determine the presence of a mental nerve anterior loop and compare the two modalities. The mean length of the mental nerve anterior loop was also assessed.  Results Mental nerve anterior loops were detected bilaterally in 57.1% and 17.4% using CBCT and panoramic radiographs, respectively. In CBCT, the right side (20.8%) had a higher prevalence of mental nerve anterior loop than the left side (12%). The mental nerve anterior loop was not visible in 49.4% of the cases using a panoramic radiograph, while CBCT gave 10% of cases as not visible. The mental nerve anterior loop average length was 1.8 ± 0.35 mm and the width was 1.7 ± 0.28 mm. The average distance from the mental foramen to the inferior border of the mandible was 12.1 ± 0.87 mm and the average distance from the mental frogmen to the mandibular midline was 25.1 ± 0.68 mm. Conclusion As differences between CBCT and panoramic radiographs were statistically significant, CBCT is more accurate and reliable. CBCT is recommended to be used as a preoperative assessment tool to minimize nerve injury-related surgical complications during implant placement at the mandibular premolar area.

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.

Cone-beam computed tomography evaluation of prevalence and location of mandibular incisive canal in patients attending King Saud University Dental Hospital

OBJECTIVE:

This study aims to facilitate a surgeon's preoperative assessment by detecting the prevalence, location, and course of the mandibular incisive canal (MIC) in our population.

METHODOLOGY:

A retrospective study was conducted at King Saud University, Riyadh, Saudi Arabia. A total of 93 cone-beam computed tomography (CBCT) scans of patients aged 18–50 years were taken. The images were reformatted from the sagittal sections to para-sagittal sections at premolars, canines, lateral incisors, and central incisors measured to the distance of MIC to the tooth apex, to the inferior border of the mandible, to the buccal cortex, and to the lingual cortex.

RESULTS:

MIC among the patients was found to be present in 96.8% of the total subjects. Prevalence between genders showed that it was present in 97.9% of the male patients and 95.5% of the female patients. The average distance from the buccal cortex is 4.88, the lingual cortex is 5.54, inferior border is 9.94, and root apices is 7.67. The age-wise and gender-wise comparison of a mean distance of MIC to the different surfaces in the different cross-sections showed that there is no correlation, and there is a significant correlation, respectively.

CONCLUSION:

The detection of the MIC presence and location using CBCT should be earnestly considered for surgical procedures that are intended to be done in the interforaminal region.

Anatomical Variations of the Mandibular Symphysis in a Normal Occlusion Population Using Cone-Beam Computed Tomography

This study aimed to assess the anatomical variations of the mandibular symphysis in a normal occlusion population using cone-beam computed tomography (CBCT). This retrospective cross-sectional study evaluated 200 CBCT scans of patients aged ≥17 with class I occlusion, 1-3 mm overbite and overjet, and <3 mm crowding. The CBCT scans were obtained with NewTom 3G scanner with the exposure settings of 110 kVp, 1.2 mA, 5.4 s time, and six-inch field of view and saved in NNT Viewer. The anterior loop length, labial bone thickness, mandibular bone height at the symphysis, and cortical bone thickness at the right and left canine teeth and central and lateral incisors were measured and compared between males and females and different age groups using one-way ANOVA. The intra- and inter-observer agreements for all landmarks were ICC >0.9 (excellent). The mean length of the anterior loop in females was significantly greater than that in males (P=0.02). Different age groups had significant differences in cortical bone width at the site of the left canine (P=0.03) and vertical bone height at the site of the right central incisor (P=0.05). The majority of parameters related to the mandibular symphysis were greater in normal occlusion males than females. Preoperative CBCT assessment of the mandibular symphysis can greatly help in diagnosis and treatment planning as well as bone harvesting from this area.

A New Concept of Narrowing Genioplasty: Home Plate-Shaped Sliding Osteotomy

BACKGROUND

Narrowing genioplasty is commonly performed among East Asian populations, as a broad and/or square chin can be aesthetically unappealing. This study was aimed to introduce the home plate-shaped sliding osteotomy technique for narrowing genioplasty and to evaluate the results of this technique.

METHODS

A retrospective chart review of 117 patients who underwent home plate-shaped sliding osteotomy alone between 2011 and 2019 was performed. The angles of oblique osteotomy lines and measurements of caudal repositioning, which significantly affect the postoperative chin shape, were evaluated.

RESULTS

The home plate-shaped sliding osteotomy technique was successfully accomplished for narrowing genioplasty as an isolated procedure. The mean distance of caudal repositioning was 3.9 ± 0.8 mm, and the mean angles of oblique osteotomy lines were 23.3 ± 4.8 degrees on the right and 21.8 ± 3.5 degrees on the left. This produced an aesthetically pleasing rounded and proportionately narrow chin. The incidence of minor complications was 6.0 percent. There were no major complications. In particular, the risk of inferior alveolar nerve injury was obviated, as an additional mandibular border osteotomy was not typically used with this technique.

CONCLUSIONS

This new surgical procedure for narrowing genioplasty provides improved aesthetic results by altering the chin shape, rather than reducing the transverse width of the chin. The versatility of this procedure allows the chin shape to be adjusted with respect to narrowing, vertical lengthening, anterior advancement, and asymmetric or cleft chin correction. The present study suggests that home plate-shaped sliding genioplasty may be an excellent alternative for correcting broad and/or square chins and more complex chin deformities.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, IV.

Bone quality and quantity of the mandibular symphyseal region in autogenous bone grafting using cone-beam computed tomography: a cross-sectional study

BACKGROUND

Bone volume plays a pivotal role in the success of dental implant treatment. Autogenous bone grafts should be harvested from reliable sites in the maxillofacial region. This study sought to assess the quantity and quality of bone in the mandibular symphysis for autogenous bone graft harvesting using cone-beam computed tomography (CBCT).

METHODS

This cross-sectional study evaluated the CBCT scans of 78 adults presenting to three oral and maxillofacial radiology centers. The vertical (VD) and horizontal (HD) alveolar bone dimensions, cortical thickness (CT), and cancellous to cortical bone ratio (C/C) were measured in the interforaminal region of the mandible at the sites of central incisor to first premolar teeth. The interforaminal distance (ID) and the anterior loop length were also measured. Nonparametric statistical tests were used to analyze the data with respect to sex, age, and tooth position.

RESULTS

The median VD, HD, and CT of the symphysis were 20.21 (3.26), 4.13 (0.37), and 2.25 (0.23) mm, respectively. The median C/C was 1.51 (0.11). The median ID was 52.24 (8.24) mm, and the median anterior loop length was 1.82 (1.06) mm. Significant differences were observed in all parameters among different teeth. Most of the measured parameters were greater in males compared with females. There were significant differences in ID, VD, and CT between different age groups.

CONCLUSIONS

The quantity and quality of the available bone in the mandibular symphysis for bone graft harvesting vary by gender, age, and harvesting site, necessitating careful preoperative evaluation.

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.

Assessment of prevalence and position of mandibular incisive canal: A cone beam computed tomography study

Objectives:

To avoid anatomical and functional damage to mandibular interforaminal region during surgeries, it is necessary to detect the existence of mandibular incisive canal (MIC) and its proximity to adjacent structures. This study was aimed to evaluate the prevalence of MIC and its proximity to adjacent structures among Indian population.

Materials and Methods:

The images of 80 subjects with the age range of 20–60 years who had undergone cone beam computed tomography examination of the mandible were retrieved from the archival records. There was equal distribution of males and females.

Results:

The prevalence of MIC in the current study sample was found to be 43.89% with a slightly higher prevalence on left side as compared to right side, and higher prevalence among females as compared to males. Among different age groups, there was an increased incidence in the age group of >50 years. The distance of MIC from labial and lingual cortical plates and lower border of mandible were 4.338 ± 1.478 mm, 4.34 ± 1.53 mm and 9.417 ± 1.832 mm respectively.

Conclusions:

To conclude, the prevalence of MIC among Indian population was lower as compared to the prevalence among other populations. There were variations in prevalence in terms of age, gender and laterality, which could be used as a reference for further studies conducted on larger sample size. Mapping the incisive nerve canal will enable oral radiologists, to plan safely and negotiate the interforaminal region.

CBCT Evaluation of the Vital Mandibular Interforaminal Anatomical Structures

BACKGROUND

Oral implants are considered safe in the mandibular anterior region, but complications often occur if vital structures such as inferior alveolar nerve, mandibular incisive canal (MIC), anterior mental loop (AL), or mental foramen (MF) are not properly identified.

AIM

The aim was to evaluate vital anatomical structures in the mandibular interforaminal region and to investigate sexual dimorphism and differences with respect to left and right side regions using cone-beam computed tomography (CBCT).

MATERIALS AND METHODS

Eighty CBCT scans (forty male and forty female) were analyzed for MF position and shape, presence and measurement of AL and MIC (both in mm), emergence patterns of mandibular canal, and symmetry of MF and AL. A pilot study was conducted on five patients to determine interobserver reliability among two oral and maxillofacial radiologists, considered for interpretation of CBCT images. All the scans were taken by CS 9300, CBCT machine adjusted at 80 kVp, 15 mA, voxel size 0.3 × 0.3 × 0.3, and field of view of 10 × 5 (mandible only). The acquired images were reconstructed into multiplanar views (axial, panoramic, and cross-sectional) for evaluation.

RESULTS

The mean age of the study population was 42.64 ± 16.22 years, with males noted with slightly higher age. Position 4 of MF (below the apex of the second premolar) was noted the most on the right side, whereas position 3 (between the first and second premolars) was noted on the left side, with 75% of symmetrical MF position. The oval-shaped MF was most common among both genders and sides. The prevalence of MIC was noted in 93.75% of patients with a mean length of 12.09 ± 5.95 mm. The prevalence of AL was 53.13%, with a mean length of 1.07 ± 1.42 mm. No statistically significant sexual dimorphism (P > 0.05) was found between genders or sides for all the evaluated interforaminal parameters.

CONCLUSION

CBCT evaluation of vital anatomical structures needs to be elicited before planning an interforaminal placement of implants, and no sexual dimorphism was found regarding them.

Detection and characterization of the accessory mental foramen using cone-beam computed tomography

OBJECTIVE

This study aimed to investigate the frequency and characteristics of accessory mental foramina (AMFs) and their bony canals in a selected Chinese population using cone-beam computed tomography (CBCT).

MATERIALS AND METHODS

Reconstructed CBCT images of the mandible in 784 Chinese patients (305 males and 479 females) were retrospectively analysed to identify the AMF. The presence, dimension and location of the AMF as well as the origin and course of the associated bony canal were evaluated and classified. Variations in these characteristics were analysed according to gender, side and age.

RESULTS

A total of 66 AMFs were found in 57 (7.3%) of the 784 patients. The frequency of AMFs was significantly influenced by gender and side of the mandible (p < .05). Most AMFs were located apically between apices of the first and second premolars. The high-position AMFs (above the mental foramen) accounted for 54.5% of the total. The mean horizontal and vertical diameters of the AMF were 1.38 ± 0.47 and 1.23 ± 0.37 mm, respectively. Two typical types of the bony canal leading to the AMF were identified according to their bifurcation site from the mandibular canal. Most bony canals originated from the anterior loop of the mental canal (56.1%) and coursed posterosuperiorly (36.3%). The mean length of the bony canals was 5.78 ± 2.31 mm.

CONCLUSIONS

This study presents a considerable frequency of AMFs in a Chinese population. The high-position AMF and the associated bony canal coursing in the oblique upward direction appear frequently. Thus, clinicians should be alert to the presence of the AMF to avoid neurovascular complications especially when dental procedures require periosteum detachment and implant insertion in the mental region.

Assessment of the anterior loop of the inferior alveolar nerve via cone-beam computed tomography

Objectives

The aim of this study was to evaluate different anatomical variants of the anterior loop of the inferior alveolar nerve (IAN) via cone-beam computed tomography (CBCT).

Materials and Methods

CBCT images of 71 patients (36 males and 35 females) were evaluated. We used the classification described by Solar for IAN evaluation. In this classification, three different types of IAN loops were introduced prior to emerging from the mental foramen. We classified patients according to this system and introduced a new, fourth type.

Results

Type I was seen in 15 sites (10.6%), type II in 39 sites (27.5%), and type III in 50 sites (35.2%). We found a new type in 38 sites (26.8%) that constituted a fourth type.

Conclusion

We found that type III was the most common variant. In the fourth type, the IAN was not detectable because the main nerve was adjacent to the cortical plate and the incisive branch was thinner than the main branch and alongside it. In this type, more care is needed for surgeries including inferior alveolar and mental nerve transposition.

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.

The inferior alveolar nerve's loop at the mental foramen and its implications for surgery

BACKGROUND

In this study, the authors aimed to identify and measure the anterior extension of the alveolar loop (aAL) and the caudal extension of the alveolar loop (cAL) of the inferior alveolar nerve by using cone-beam computed tomography (CBCT). They also aimed to provide recommendations for surgery in the anterior mandible.

METHODS

In this retrospective case study of the frequency and extension of aAL and cAL, the authors evaluated 1,384 mandibular sites in 694 CBCT scans of dentate and partly edentulous patients, performed mainly for further diagnosis before removal of the mandibular third molars between January 2009 and February 2013, by using multiplanar reconstructions.

RESULTS

The frequency of aAL was 69.73 percent and of cAL was 100 percent. The mean value for aAL was 1.16 millimeters, with a range of 0.3 to 5.6 mm; the mean value for cAL was 4.11 mm, with a range of 0.25 to 8.87 mm. For aAL, 95.81 percent of the sites showed values of 0 to 3 mm; for cAL, 93.78 percent of the sites showed values of 0.25 to 6 mm. Dentate patients showed statistically significantly higher values for cAL than did partly edentulous patients (P = .043). CBCT resolution had a statistically significant impact on cAL measurements (P = .001), with higher values at higher resolution.

CONCLUSIONS

This study showed a high frequency of and large variations in aAL and cAL. In contrast to panoramic radiography, CBCT has been shown to be a reliable tool for identifying and measuring the AL. Therefore, preoperative diagnosis with CBCT is recommended for planning three-dimensional tasks such as implant placement in the vicinity of the mental foramen.

PRACTICAL IMPLICATIONS

Owing to the variability of aAL and cAL measurements, it is difficult to recommend reliable safety margins for surgical procedures such as implant placement, bone harvesting or genioplasty Depending on the indication, the clinician should consider preoperative diagnosis by means of CBCT.

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.

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.

Assessment of the Anterior Loop of the Mental Nerve Using Cone Beam Computerized Tomography Scan

The purpose of this study is to use cone-beam computerized tomography (CBCT) scans with oblique-transverse reconstruction modality to measure and compare the anterior loop length (AnLL) of the mental nerve between gender and age groups and to compare the difference between the right and left sides. Sixty-one female and 61 male CBCT scans were randomly selected for each age group: 21–40, 41–60, and 61–80 years. Both right- and left-side AnLLs were measured in each subject using i-CATVision software to measure AnLLs on the oblique transverse plane using multiplanar reconstruction. The anterior loop was identified in 85.2% of cases, with the mean AnLL of the 366 subjects (732 hemimandibles) being 1.46 ± 1.25 mm with no statistically significant difference between right and left sides or between different gender groups. However, the mean AnLL in the 21–40 year group (1.89 ± 1.35 mm) was larger than the AnLL in the 41–60 year group (1.35 ± 1.19 mm) and the 61–80 year group (1.13 ± 1.08 mm). In conclusion, when placing implants in close proximity to mental foramina, caution is recommended to avoid injury to the inferior alveolar nerve. No fixed distance anteriorly from the mental foramen should be considered safe. Using CBCT scans with the oblique-transverse method to accurately identify and measure the AnLL is of utmost importance in avoiding and protecting its integrity.

Topographic analysis of the mandibular symphysis in a normal occlusion population using cone-beam computed tomography

At present, the relationship between the morphological characteristics of the sympheseal region and occlusion has not been well documented. The aim of the present study was to investigate the following, using cone-beam computed tomography (CBCT): Interforaminal distance, the anterior loop, labial bone thickness at the tooth apex, cortical bone thickness, and the basal bone height from the apex of the tooth to the base of the mandible. Three-dimensional CBCT was performed on 20 normal occlusion subjects (9 males and 11 females; mean age=21.9±3.0 years); the mean interforaminal distance was 53.1±3.6 mm, with 85% of the participants demonstrating a mental foramen located below the second premolars on both sides. The mean anterior loop was 1.9±0.8 mm, the mean horizontal distance value was 4.5±1.3 mm, and the mean cortical bone thickness value was 2.3±0.5 mm. An increasing tendency for cortical bone thickness was seen from the central incisor to the second premolar. The mean vertical distance value was 20.3±3.1 mm. Decreasing tendency of vertical distance was seen from the central incisor to the second premolar. Furthermore, the width (mental foramina of both sides and their anterior loops), height (teeth apices and the inferior border of the mandible), depth (cortical bone thickness of the symphysis), and safety margins for vital anatomical structures (anterior loop, tooth apex, and inferior border of mandible) should be taken into account prior to symphyseal block-bone harvesting. The results of the present study suggested that a pre-operative evaluation with CBCT may be useful for diagnosis and treatment planning, and for minimizing complications during block-bone graft.

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.

Accuracy in the Diagnosis of the Mental Nerve Loop. A Comparative Study Between Panoramic Radiography and Cone Beam Computed Tomography

Dental implant and chin osteotomy are executed on the mandible body and the mental nerve is an important anatomical limit. The aim of this research was to know the position of the mental nerve loop comparing result in panoramic radiography and cone beam computed tomography. We analyzed 94 hemimandibles and the patient sample comprised female and male subjects of ages ranging from 18 to 52 years (mean age, 35 years) selected randomly from the database of patients at the Division of Oral Radiology at Piracicaba Dental School State University of Campinas; the anterior loop (AL) of the mental nerve was evaluated regarding the presence or absence, which was classified as rectilinear or curvilinear and measurement of its length was obtained. The observations were made in the digital panoramic radiography (PR) and the cone beam computed tomography (CBCT) according to a routine technique. The frequencies of the AL identified through PR and CBCT were different: in PR the loop was identified in 42.6% of cases, and only 12.8% were bilateral. In contrast, the AL was detected in 29.8% of the samples using CBCT, with 6.4% being bilateral; Statistical comparison between PR and CBCT showed that the PR led to false-positive diagnosis of the AL in this sample. According to the results of this study, the frequency of AL is low. Thus, it can be assumed that it is not a common condition in this population.

Computed tomographic analysis of the mental foramen and nerve in Japanese patients

PURPOSE

The aims of this study were to investigate the anatomical features of the mental foramen in Japanese patients through computed tomography (CT) imaging to reduce inadvertent damage to the mental nerve during implant placement.

MATERIALS AND METHODS

The mandibles of 100 patients were observed on CT imaging. The location, shape, number, and size of the mental foramen were evaluated. Furthermore, the vertical and horizontal dimensions of the anterior loops were measured.

RESULTS

The mental foramen was mainly located by the apex of the second mandibular premolar in male, whereas the mental foramen was mainly located by the apex of the second mandibular premolar and between the apex of the second premolar and the first mandibular molar in female. With exception of a few hemi-mandibles, its shape was oval and the number of the mental foramen was 1. There was no significant difference in the size of the mental foramen between male and female. There was a significant difference in the vertical dimension of the anterior loops between the males and females.

CONCLUSION

In general, altered lip sensations are preventable if the mental foramen is located, and this knowledge is employed when performing surgical procedures in the foraminal area.

Identification of the mandibular landmarks in a pediatric population

Objectives: The aim of this study was to determine and compare the reliability to accomplish of common mandibular landmarks and to determine the incidence of incisive canals, anterior looping, and lingual foramina in children from panoramic and CBCT images. Study Design: Panoramic and CBCT images from 100 children and adolescent patients were randomly selected. In order to grade the visibility of mandibular anatomical landmarks, a four-point rating scale was used. Results: In panoramic images, the mandibular canal could be observed in 92.5% of cases, with good visibility in 12.0%. The mental foramen could be observed in 44.5% of cases, while none had good visibility. Anterior looping of the mental nerve was present in 16.5% of the cases, and none had good visibility. An incisive canal could be identified in 22.5% of cases, with only 1.5% showing good visibility. The lingual foramen could be visualized in 61.0% of cases, with good visibility in 6%. In CBCT images, the mandibular canal, the mental foramen, and the lingual foramen could be observed in 100% of the cases, with good visibility in 51.0%, 98.5%, and 45.0% of cases, respectively. Anterior looping of the mental nerve was present in 26% of cases, with 2% having good visibility. An incisive canal could be identified in 49.5% of cases, with only 75% showing good visibility. Conclusions: This study confirms the applicability of CBCT images to visualize critical structures in children.

Key words:Panoramic radiography, cone beam computed tomography, anatomical landmark.

Accuracy of Cone Beam Computerized Tomography and a Three-Dimensional Stereolithographic Model in Identifying the Anterior Loop of the Mental Nerve: A Study on Cadavers

The objective of this ex vivo cadaver study was to determine the accuracy of cone beam computerized tomography (CBCT) and a 3-dimensional stereolithographic (STL) model in identifying and measuring the anterior loop length (ANLL) of the mental nerve. A total of 12 cadavers (24 mental nerve plexus) were used for this study. Standardized CBCT scans of each mandible were obtained both with and without radiographic contrast tracer injected into the mental nerve plexus, and STL models of the two acquired CBCT images were made. The ANLL were measured using CBCT, STL model, and anatomy. The measurements obtained from the CBCT images and STL models were then analyzed and compared with the direct anatomic measurements. A paired sample t test was used, and P values less than .05 were considered statistically significant. The mean difference between CBCT and anatomic measurement was 0.04 mm and was not statistically significant (P = .332), whereas the mean difference between STL models and anatomic measurement was 0.4 mm and was statistically significant (P = .042). There was also a statistical significant difference between CBCT and the STL model (P = .048) with the mean difference of 0.35 mm. Therefore, CBCT is an accurate and reliable method in determining and measuring the ANLL but the STL model over- or underestimated the ANLL by as much as 1.51 mm and 1.83 mm, respectively.

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.

Appearance of anatomical structures of mandible on panoramic radiographs in Iranian population

PURPOSE

Currently panoramic radiography is used for diagnosis of dental and bone lesions, but anatomical structures also can be seen and may be useful in dental managements. This study aimed to investigate the visibility of some important mandibular features relating to neurovascular structures in Iranian population.

MATERIALS AND METHODS

Panoramic radiographs were taken by Planmeca machine from 412 patients using standard exposure. The position of patient was in compliance with standard protocol. Then mandibular incisive canal was evaluated and data were analyzed statistically.

RESULTS

Mental foramen, anterior loop of mental nerve and incisive canal could be observed in 84.2, 66 and 51.7% of the cases. Respectively, lingual foramen was observed in only 6.1% of the radiographs. Gender doesn't affect on the visibility of these structures. There was a relationship between mandibular foramen and canal with age.

CONCLUSION

Mandibular incisive canal was considered in 51.7% of cases, it was observed that the result obtained was more than those of other researches.

The anterior loop of the inferior alveolar nerve: prevalence, measurement of its length and a recommendation for interforaminal implant installation based on cone beam CT imaging

OBJECTIVES

Interforaminal implant surgery requires anatomical knowledge of the area and adequate information on the location of the various landmarks of significance such as the mental foramen, the anterior loop of the inferior alveolar nerve and the mandibular incisive canal. Cone beam computed tomography (CBCT) is a relatively new imaging modality that provides a multi-dimensional view of the facial skeleton with, in most instances, lower radiation dose to the patient compared to medical CT. The present study aims to use CBCT to identify and measure variation in the presence and extent of the anterior loop of the inferior alveolar nerve. This information may be used to provide recommendations to the surgeon without access to a 3D scan of the dento-alveolar region.

MATERIAL AND METHODS

Ninety-three patients scanned with a Newtom VG device for a variety of clinical indications were included in this retrospective study. Using the multiplanar capabilities of the device's software the prevalence and length of the anterior loop was assessed.

RESULTS

The results show that an anterior loop could be identified in 48% of the cases with a mean length (range) of 0.89 mm (0-5.7).

CONCLUSIONS

In almost half of the surveyed cases an anterior loop was present. Even though in 95% of the study cases the loop was <3 mm, a 100% safety margin in the placement of anterior mandibular implants, in the absence of a CBCT scan, would only be achieved with a distance of 6 mm between the anterior border of the mental foramen and the most distal interforaminal implant fixture.

Direct and tomographic dimensional analysis of the inter-radicular distance and thickness of the vestibular cortical bone in the parasymphyseal region of adult human mandibles

We calculated the inter-radicular distances between the canine, and first and second premolars, of human mandibles and the thickness of the cortical bone at adjacent sites using computed tomographic (CT) imaging, and assessed the precision of the dimensional assessment made by CT compared with the same measurement made directly with calipers. We examined 100 adult cadaveric dentate human hemimandibles. At the level at which monocortical screws are inserted to place miniplates according to the current technique used to treat mandibular fractures, points A, B, and C referred to the canine, and first and second premolars, and were marked to calculate the level of the CT slice and as the reference for sectioning of the hemimandible. Our findings showed that there was no significant difference in the inter-radicular distance or in the thickness of cortical bone between the sides of the mandible. The vestibular cortical bone was less than 3.0mm thick in 91 of the samples. In 98 of the samples the inter-radicular distance between the canine and the first and second premolars was more than 2mm. There was no significant difference in micrometric precision between the dimensional assessment on CT and direct measurement using a caliper. In the region of the mental foramen the screws have cortical bone less than 3mm thick in which to be anchored. The inter-radicular distance suggests that there is a minimal risk of radicular injury when miniscrews are inserted between the alveolar structures. CT is a reliable tool for measuring the inter-radicular distance and the thickness of mandibular cortical bone.

Evaluation of bone thickness around the mental foramen for potential fixation of a bone-borne functional appliance: a computer tomography scan study

AIM

A mandible bone-borne Herbst appliance (MBBHA) would avoid the proclination of the lower incisors that occurs with any teeth-borne functional appliance. But mapping of the bone characteristics at potential fixation areas around the mental foramen has not been carried out so far. The aim of this computer tomographic (CT) study was to evaluate bone thickness at specific positions around the mental foramen.

MATERIAL AND METHODS

CT scans of 60 randomly chosen adult Hong Kong Chinese subjects (mean age 28 ± 6.3 years) were used to measure the bi-cortical bone thickness in the mandible in the mental foramen area. The thickness of buccal and lingual cortical and cancellous bone was assessed at the following locations: 10 mm (A10 mm) and 5 mm (A5 mm) anterior, 10 mm (P10 mm) and 5 mm (P5 mm) posterior, and 5 mm (Inf5 mm) below the mental foramen.

RESULTS

The amount of buccal cortical bone thickness ranged between 1.89 mm, 10 mm anterior of the mental foramen, and 2.16 mm, 10 mm posterior to its location. At the A10 mm level, cortical thickness showed a marginal statistically significant difference between A5 and A10 mm. The total amount of bone thickness ranged from 10.19 to 12.06 mm.

CONCLUSION

At the locations studied around the mental foramen, a mean bicortical bone thickness of 10-12 mm was measured. No large variation in the thickness was found between bicortical bone thicknesses in the measured locations around the mental foramen. Thorough evaluation on a case-by-case basis is advisable.

The role of cone-beam computed tomography in the planning and placement of implants

BACKGROUND

Three-dimensional imaging, particularly cone-beam computed tomography (CBCT), has made significant contributions to the planning and placement of implants to replace missing teeth. The accuracy of CBCT data can be used to fabricate a surgical guide that transfers the implant planning information to the surgical site to facilitate implant placement. The authors describe a method for applying CBCT data to aid in the planning and placement of implants.

METHODS

The authors outline clinical goals for implant planning and placement and describe the anatomical and prosthetic requirements for successful implant placement. They also present imaging solutions, including CBCT scanning and software analysis, to the clinical goals.

CONCLUSIONS

Virtual implant planning using CBCT data allows the clinicians to create and visualize the end result before initiating treatment. CBCT scans are accurate and cost effective and can be used to improve communication and coordination of a multidisciplinary team to achieve the desired clinical outcome. Virtual planning allows clinicians to investigate multiple treatment scenarios until the optimum treatment plan is attained. The optimized virtual plan may be converted through modeling to create a surgical guide for clinical implementation.

CLINICAL IMPLICATIONS

The precise planning and delivery of implants to replace missing teeth can avert recognized and concealed treatment problems. This process aids the clinician and benefits the patient.

Identification of the mandibular vital structures: practical clinical applications of anatomy and radiological examination methods

Objectives

The purpose of this article was to review the current available clinical techniques and to recommend the most appropriate imaging modalities for the identification of mandibular vital structures when planning for oral implants.

Material and Methods

The literature was selected through a search of PubMed, Embase and Cochrane electronic databases. The keywords used for search were mandibular canal, mandibular incisive canal, mental foramen, anterior loop of the mental nerve, radiography, dental implants. The search was restricted to English language articles, published from January 1976 to January 2010.

Results

In total 111 literature sources were obtained and reviewed. The peculiarities of the clinical anatomy of mandibular canal, mandibular incisive canal, mental foramen and anterior loop of mental nerve were discussed. Radiological diagnostic methods currently available for the identification of the mandibular vital structures when planning for oral implants were presented. Guidelines for the identification of the mandibular vital structures in dental implantology were made.

Conclusions

The proposed guideline provides clinicians a tool in proper identifying the important mandibular vital structures thus minimizing the potential complications during implant surgery.

Computerized tomographic evaluation of symphyseal donor sites used in the reconstruction of the posterior maxilla: a case report of 2 patients

Autogenous bone grafts are commonly used for reconstruction of the deficient maxillary alveolar ridge. Mandibular ramus, symphysis, extraction sites, and retromolar sites are the most common sources for harvesting autogenous bone grafts from intraoral regions. Several authors have used computerized tomography (CT) to evaluate the dimensional change of bone graft, but there are limited reports evaluating donor sites for autogenous bone. In this report, 2 patients were treated with autogenous bone graft from the mandibular symphysis. Postoperative CT scans were used to evaluate the radiographic change in the symphyseal area. The patients treated with autogenous bone showed uneventful healing at the donor and recipient sites and good acceptance of the procedure. At the final evaluation, CT analysis demonstrated a persisting radiolucency in the donor area, even though the defect size was reduced. Further evaluation may be needed to evaluate the progress of remineralization and long-term results.

Tomographic analysis of the interalveolar space and thickness of the vestibular cortical bone in the parasymphyseal region of adult human mandibles

PURPOSE

The aim of this study was to determine by computed tomography (CT) the interalveolar distance on mandible relative to the canine, first and second pre-molar, and the thickness of the cortical bone in the same region.

METHODS

A hundred adult cadaveric dentate human hemi-mandibles were examined. A point (P) above the upper margin of the mental foramen was determined, the height at which monocortical screws are inserted to place miniplate according to the technique to treat mandibular fracture. Then, points A, B and C at the same height as point P, referring to the dental units namely canine, first and second pre-molars were marked to determine the CT cut level to measure cortical bone thickness and the interalveolar distance.

RESULTS

The figures showed no statistically significant difference between the sides. The thickness of the vestibular cortical bone was less than 3.0 mm in 96% of the samples. In 91% of the samples the interalveolar distance between canine, first and second pre-molars was greater than 2 mm, a potentially safe condition to insert 2.0-mm diameter monocortical screws at the study points.

CONCLUSIONS

The individual actual anatomy of the region where screws are to be inserted above the mental foramen is important to perform the technique safely. We believe that the minimal cortical thickness to obtain sufficient screw anchorage should be studied in order to determine the actually safe shortest screw length. It is important to minimize the risk of tooth root damage or nerve injury and the amount of titanium in the human tissues.

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.

Anatomy of Mandibular Vital Structures. Part II: Mandibular Incisive Canal, Mental Foramen and Associated Neurovascular Bundles in Relation with Dental Implantology

Objectives

The purpose of the present study was to review the literature of how to identify the mental foramen, mandibular incisive canal and associated neurovascular bundles during implant surgery and how to detect and avoid the damage of these vital structures during implant therapy.

Material and Methods

Literature was selected through a search of PubMed, Embase and Cochrane electronic databases. The keywords used for search were mandibular incisive canal, mental foramen, mental nerve, anterior mental loop. The search was restricted to English language articles, published from 1979 to November 2009. Additionally, a manual search in the major anatomy, dental implant, and periodontal journals and books was performed.

Results

In total, 47 literature sources were obtained and reviewed. The morphology and variations of the mandibular incisive canal, mental foramen and associated neurovascular bundles were presented as two entities. It suggested that clinicians should carefully assess these vital structures to avoid nerve/artery damage.

Conclusions

The mandibular incisive canal, mental foramen and associated neurovascular bundles exist in different locations and possess many variations. Individual, gender, age, race, assessing technique used and degree of edentulous alveolar bone atrophy largely influence these variations. It suggests that the clinicians should carefully identify these anatomical landmarks, by analyzing all influencing factors, prior to their implant surgical operation.