|Year : 2020 | Volume
| Issue : 2 | Page : 91-96
Assessment of accessory mental foramen using cone-beam computed tomography and its clinical relevance
Milos Z Zivic1, Miroslav R Vasovic1, Aleksandar B Acovic1, Ana Z Lukovic2, Ivana K Zivanovic-Macuzic2, Milica M Velickovic2, Tatjana V Kanjevac1
1 Department of Dentistry, Faculty of Medical Sciences, University of Kragujevac, Kragujevac, Serbia
2 Department of Anatomy, Faculty of Medical Sciences, University of Kragujevac, Kragujevac, Serbia
|Date of Submission||23-Jul-2019|
|Date of Acceptance||22-May-2020|
|Date of Web Publication||30-Jun-2020|
Dr. Milos Z Zivic
Svetozara Markovica 69, 34000 Kragujevac
Source of Support: None, Conflict of Interest: None
Introduction: Accessory mental foramen (AMF) is defined as any additional opening on the anterior surface of the mandible body that is connected to the mandibular canal. The presence of AMF is an important anatomical parameter when planning the therapy to avoid neurovascular bundle injury and other complications. Cone-beam computed tomography (CBCT) provides an accurate, three-dimensional determining of the position, its dimensions and the relation of AMF to the mental foramen (MF), as well as the distinction from nutritive openings. Material and Methods: The research was carried out at the Department of Dentistry, Faculty of Medical Sciences, University of Kragujevac, as a retrospective study where 148 CBCT images were analyzed. The analysis of the position of AMF, the relation to and the distance from the MF were made on cross-sectional and axial images. Only those openings that have had a clear connection with the mandibular canal were counted as AMF. Results: AMF was present in 12 (8.11%) patients. In most cases, AMF was positioned superior to MF, in 27% of patients. There was no significant statistical difference between sex and the jaw side. The average distance of AMF from MF was 4.52 ± 2.21 mm. In most cases, AMF is round shaped (60%). The average value of the surface area is 1.62 ± 1.14 mm2. Discussion and Conclusion: Timely detection of AMF using CBCT contributes to the diagnosis and planning of appropriate dentures, surgical technique, preventing possible damage to adjacent anatomical structures, or some other therapy.
Keywords: Accessory mental foramen, anatomical variations, cone-beam computed tomography, mental foramen
|How to cite this article:|
Zivic MZ, Vasovic MR, Acovic AB, Lukovic AZ, Zivanovic-Macuzic IK, Velickovic MM, Kanjevac TV. Assessment of accessory mental foramen using cone-beam computed tomography and its clinical relevance. J Anat Soc India 2020;69:91-6
|How to cite this URL:|
Zivic MZ, Vasovic MR, Acovic AB, Lukovic AZ, Zivanovic-Macuzic IK, Velickovic MM, Kanjevac TV. Assessment of accessory mental foramen using cone-beam computed tomography and its clinical relevance. J Anat Soc India [serial online] 2020 [cited 2020 Jul 4];69:91-6. Available from: http://www.jasi.org.in/text.asp?2020/69/2/91/288678
| Introduction|| |
Knowing the anatomical characteristics of the orofacial region is a necessary factor for the adequate implementation of both preventive and therapeutic procedures in that region. Anatomical variations, which are often present, are an important role in the planning of these procedures, and they can easily be overlooked. Cone-beam computed tomography (CBCT) has a great clinical significance in the detection of anatomic variations. The most important use of CBCT in the orofacial region is the three-dimensional (3D) reconstruction of the anatomical characteristics of the region. This allows for the detection of all anatomical variations and pathological conditions, such as changes in soft and bone tissue, as well as variations in the number, shape, structure, and size of the teeth.
Mental foramen (MF) is a bilateral anatomical structure on the anterior surface of the mandible body through which exits mental nerve, terminal branch of the inferior alveolar nerve, and the corresponding artery and vein.,, Intraosseous part of the inferior alveolar nerve, after the variable separation of the lateral branches, is usually divided into two final branches (mental nerve and incisive nerve), which diverge in the form of letters Y or T. The mental nerve that passes through MF is, in most cases, posteriorly oriented, and it subdivides out into three branches, below depressor angulioris., Hu et al. describe four branches of the mental nerve: angular to the angle of the lip, the outer branch of the lower lip (often separated from the angular branch), the inner branch of the lower lip, and the branch of the chin.,, A variation marked as “anterior loop,” with a length range of 0.5–5 mm, approximately 1 mm, on average describes that mental nerve passes under MF, proceeding to the midline, after which it creates the arc to the top and returns to MF.,
MF is most commonly round or oval shaped and is usually located between the apices of mandibular first and second premolars. It is possible for MF to be positioned in the periapical projection of canine and extremely rarely, in the area of the first molar. In dental practice, the importance of MF refers to the use of this structure as a reference point in the implementation of local anesthesia, in the insertion of dental implants and in the implementation of prosthetic, endodontic, and other dental procedures in that region.,,,,,
Anatomical variations of MF can occur in a certain number of cases in the form of differences in shape, size, position, and number of openings. In some cases, there are one or more additional openings, which are called accessory mental foramen (AMF). It is stated in the literature that the frequency of AMF is 1.4%–20%.,, The presence of AMF is the consequence of the branching of mental nerve and the presence of its accessory branch, which passes through this opening. Other, mostly smaller openings, which may occur near MF and AMF and which are not in direct contact with the mandibular canal, are nutritive. An additional branch of the mental nerve that comes out of AMF mainly innervates the part of the mucous membrane of the cheek, the skin of the corner of the lips, and the mucous membrane of the lower lip on that side and can have anastomoses with buccal nerve and facial nerve. The persistence of pain after the mental nerve neurectomy is explained by the presence of an additional branch that passes through AMF, which is one of the trigger points of the trigeminal neuralgia emergence. There are also described the cases of the presence of two mental nerve openings, which are the same dimensions and are observed next to each other, on the same side of the mandible. An anterior location of AMF relative to MF can also be a re-entry point of mental nerve to the mandible, which goes to the incisors (crossed innervation).,
The presence of AMF is often overlooked during oral surgery interventions. The detection of AMF is especially important from the aspect of implant therapy planning to avoid neurovascular bundle injury during surgical, prosthetic, endodontic, and other dental procedures.,,
On the 2D orthopantomogram, it is not possible to diagnose the presence of AMF, as well as its distance and position relative to MF due to the distortion of the image, superposition of anatomical structures and an inadequate resolution. The method of choice is CBCT which provides a 3D reconstruction in the high resolution and without superposition of anatomical structures.,,,, Timely diagnosis of AMF enables avoiding complications during and after therapeutic procedures which can directly affect the outcome of the therapy.
The study aimed to determine the presence of AMF, the position and relation to MF, by using CBCT.
| Material and Methods|| |
This research was conducted as a retrospective study. Ethical approval was obtained from the Local Ethical Committee. The study included 200 CBCT images from the existing database. Scans that do not show mandibular canal completely or with deformity, pathological changes and previous surgical interventions in the region of the mental opening were excluded. All CBCT scans were made at the Department of Dentistry at the Faculty of Medical Sciences, University of Kragujevac, in the period from October 25, 2014, to September 20, 2018.
Scans were made on Orthophos XG 3D device (Sirona Dental Systems GmbH, Bensheim, Germany), with the field size 8 cm × 8 cm, and three-dimensionally reconstructed by the software GALAXIS version 1.9.4 (Sirona Dental Systems GmbH, Bensheim, Germany), with a high image definition (100 μm). The CBCT scans were made because of implantological, prosthetic, endodontic, surgical, or orthodontic indications. The images were viewed on a Philips light-emitting diode monitor of 23 inches with a resolution of 1920 × 1080 pixels. Brightness and contrast were customized by the software, and images were viewed in a room with a dimmed light.
The presence of AMF was proven by 3D image analysis. The positions of all AMFs were presented in eight groups depending on the relation to MF [Figure 1] and [Figure 2]. Software built-in meter was used to take all the measurements. The size of AMF, the distance and the ratio between AMF and MF in horizontal and vertical dimensions were performed. Vertical and horizontal dimensions were acquired measuring foramen's edge to edge distance in cross-sectional and axial section, respectively. The distance between MF and AMF was also measured in cross-sectional and axial section [Figure 3]. As reference points, AMF and MF centers were used in both sections. Furthermore, the distance of AMF from the inferior border of the mandible was measured., Any additional opening that did not come into contact with the mandibular canal was considered a nutritive opening and was excluded from the analysis. The shape was defined as an oval if the difference between the horizontal and vertical dimensions of the foramen was >0.5 mm and round if it was <0.5 mm. The surface of AMF was calculated by the following formula. The AMF location relative to MF at the sagittal section was recorded along with its shortest distance to MF., All the measurements were repeated twice in an interval of 7 days to ensure the objectivity of the measurement. The reproducibility value was k = 0.846.
|Figure 1: A three-dimensional view of the mandible with the presence of an accessory mental foramen|
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|Figure 2: Graphical display of accessory mental foramen position relative to mental foramen in eight fields: 1 – Superior; 2 – Anterosuperior; 3 – Anterior; 4 – Anteroinferior; 5 – Inferior; 6 –Posteroinferior; 7 – Posterior; 8 – Posterosuperior|
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|Figure 3: Display of distance measurement of accessory mental foramen in cross-sectional (a) and axial (b) view|
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Statistical data were analyzed by using the statistical software SPSS version 20.0 (SPSS Inc., Chicago, IL, USA). For the evaluation of the relation between sex and anatomical variations, Pearson Chi-square was used at a significance level P < 0.05.
| Results|| |
Within this study, 200 CBCT images were analyzed. Based on the inclusion criteria, 148 images were included in the study, 71 (48%) of male and 77 (52%) of female patients. A total of 15 AMFs were found in 12 (8.11%) cases, 2.70% of males and 5.40% of females [Table 1].
|Table 1: Accessory mental foramen presence in relation to gender and Chi-square value|
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The presence of one AMF was observed in 6.76%, two AMFs in 0.67% and three AMFs in 0.67% of cases. AMF was present on the right side of the mandible in 50% of cases, on the left side in 33% while, on both sides, AMF was present in 17% of cases [Figure 4].
|Figure 4: Graphical display of accessory mental foramen in relation to side of mandible and gender|
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The average values of the horizontal and vertical AMF diameters were 1.72 ± 1.02 mm and 1.18 ± 0.38 mm, respectively. The average surface area of AMF was 1.62 ± 1.14 mm 2. In most cases, AMF was round shaped (60%). The position relative to MF was analyzed as well [Figure 5]. There was no statistically significant difference in the position of AMF between genders (P = 0.186). The AMF's most prevalent position was superior to MF, accounting for 27%. Posterior and posteroinferiorly positioned AMFs were present in 20% of cases [Table 2].
|Figure 5: Display of each accessory mental foramen location and distance (accessory mental foramen) in relation to mental foramen shown in millimeter scale|
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|Table 2: Accessory mental foramen localization in relation to medial mental foramen and Chi-square value|
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The mean diagonal distance between AMF and MF was 4.52 ± 2.21 mm. Mean horizontal distance between AMF and MF was 3.38 ± 2.60 mm, whereas mean vertical distance was 2.15 ± 1.68 mm [Table 3]. Distance from the inferior border of the mandible and AMF was measured, and its mean value was 14.44 ± 1.14 mm.
|Table 3: Comparison of horizontal and vertical dimensions of accessory mental foramen and his distance from mental foramen by gender|
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| Discussion|| |
Diagnostic issue or a predisposition for the complications after dental procedures is often caused by the anatomical variations of the mandibular canal and its openings. Knowing the exact topography of the inferior alveolar nerve and the mandibular canal is important for preventing impairment of the neurovascular bundle.,
Because of the relatively small percentage of AMF presence (1.4%–20%), it is often overlooked in standard 2D radiographic images. Accessory openings of the mandibular canal can be observed at lingual position, at retromolar position, and near MF, when the opening is designated as AMF. The presence of AMF may indicate a variation of the mandibular canal, formed during embryonic development due to a branching of the inferior alveolar nerve prior 12th gestational week, before the complete formation of MF. Variations in MF position, as well as the presence of AMF, show significant ethnic differences, although they also depend on individual variations in the development of mandible. The position and direction of the inferior alveolar nerve can be altered in people with alveolar bone atrophy.
The direction of the accessory mental nerve canal was mainly posterosuperior or posteroinferior. The position of AMF depends on the separation site and length of the accessory mental nerve. Variation in the relative position of AMF to MF is greater in horizontal than in the vertical direction. Given the significance of this opening, Iwanaga et al. (2015) proposed the definition of AMF according to which it refers to each opening detected on the computed tomography image, which is in continuity with the mandibular canal and smaller than MF, regardless of whether blood vessels and/or nerves that pass through it are detected, which the authors of the current study agree with.
The frequency of AMF varies among ethnic groups ranging from 1.4% to over 20%. Caucasian race shows the lowest prevalence of AMF.,, The presence of bilateral AMF is rare and is observed in <1% of the population. Apart from the ethnic variations, a large difference in frequency may be due to the diversity of methodology and the definition of AMF.
The findings of the current study prove that AMF was represented in 8.11% of cases. This frequency is similar in the study of Han et al. where a frequency of 8.1% was shown. In the study of Li et al., the frequency of AMF was 7.3%, while in the study of Muinelo-Lorenzo et al. it was 13.08%. Zmysłowska-Polakowska et al. demonstrated in their study the presence of AMF on 7% of cases, and Kumari et al. on 10% of cases.,
The authors also determined that the difference in the frequency of AMF was present among the sexes. The frequency was higher in women (5.40%) than in men (2.70%). Muinelo-Lorenzo's et al. and Naitohet al.'s studies showed a higher prevalence of AMF in women,, which findings of the present study support. Opposite results were shown in the study of Zmysłowska-Polakowska et al., where the frequency of AMF was higher in male subjects, as well as in other studies. [3, 10, 20, 23, 28, 31]
In the current study, the presence of AMF on the right side of the mandible was in 50% of cases, on the left side of mandible in 33% of cases, while on both sides AMF was present in 17% of cases. Kumari et al. analyzed the frequency of AMF localization on both sides. AMF was more often localized on the right side of the mandible.
In most cases, these findings suggest that AMF was set superior (27%) to MF. Posterior and posteroinferior localizations are equally present both in 20% of cases. In the study of Naitoh et al., AMF is most often positioned posteroinferior. A study of Kumari et al. showed that in all cases when AMF was on the right side of the mandible, it was positioned anterior to MF. In cases where AMF was on the left side, there was an equal frequency in inferior, superior, posterior, and posteroinferior localization, 25% each localization. Katakami et al. showed posteriorly positioned AMF to MF as the most common in 41% of cases, and inferior position in 29% as the second according to the frequency. In the study by Gümüşok et al., it was shown that AMF was most often placed in a posteroinferior position to MF. Kalender et al. state that AMF is most frequently placed anteroinferior to MF. No statistically significant difference was found in the localization between the sexes.
The average diagonal distance between AMF and MF in the present study was 4.52 ± 2.21 mm. The mean value of horizontal distance between AMF and MF was 3.38 ± 2.60 mm, and vertical distance was 2.15 ± 1.68 mm. The values of horizontal and vertical AMF diameters were 1.72 ± 1.02 mm and 1.18 ± 0.38 mm, respectively. The mean AMF surface area was 1.62 ±1.14 mm 2. In 60% of cases, AMF was round shaped. Unlike our data, in the study of Iwanaga et al., the distance between MF and AMF was between 0.67 mm and 6.3 mm on average. The surface of AMF was on average 1.7 mm 2, which is similar to our results. Data can be found that the average value of MF surface area is greater in the absence of AMF., Mean AMF surface area in Muinelo-Lorenzo et al. and Saranaka study. was 1.5 mm 2, which is similar to other studies.,
The distance of AMF from the inferior border of the mandible was also analyzed. The mean distance from the inferior border of the mandible in our study was 14.44 ± 1.14 mm. In the study of Muinelo-Lorenzo et al., the mean distance of AMF from the inferior border of the mandible was 11.72 ± 4.14 mm. The results shown in the study by Li et al., where the mean distance of AMF from the inferior border of the mandible was 13.36 ± 1.77 mm, are similar to the values in this study.
| Conclusion|| |
The presence of anatomical variations in the upper and lower jaw is still often overlooked. Better examination of orofacial structures is accessible using CBCT imaging helping in the early and accurate diagnosis of lesions. Timely detection of AMF using CBCT contributes to diagnosis and planning appropriate dentures, surgical technique, preventing possible damage to adjacent anatomical structures or some other therapy. Using advanced software and hardware systems, CBCT can be improved to make more reliable images with better contrast resolution, improved bone density information and less or no artifacts, which will have better use in oral and maxillofacial surgery, implantology, endodontic, orthodontic, prosthetic, and forensic dentistry.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
[Table 1], [Table 2], [Table 3]