A retrospective radiographic evaluation of incisive canal and anterior loop of mental nerve using cone beam computed tomography

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1 Research Article A retrospective radiographic evaluation of incisive canal and anterior loop of mental nerve using cone beam computed tomography M. Sridhar 1, Dhanraj M 2, Thiyaneswaran N 3, Ashish R. Jain* 2 ABSTRACT Introduction: The pattern of entry of mental nerve into the mental foramen after its emergence from the inferior alveolar nerve bundle is an important presurgical landmark in the mandibular premolar region. The inferior alveolar nerve gives an anterior loop before entering soft tissues and ends as mental nerve in mental foramen. When traced anteriorly, mental nerve continues as incisive nerve inside mandibular incisive canal. The aim of this study is to identify the presence and location of mandibular incisive canal and anterior loop of mental nerve. Materials and Methods: A total of 146 cone beam computed tomographic (CBCT) images of 146 patients were evaluated for the presence of anterior loop of mental foramen and mandibular incisive canal. These CBCT images were analyzed using Galileos software for measuring the diameter of the incisive canal and anterior loop and also buccal proximity, lingual proximity, and distance between the incisive canal and inferior border of mandible. The readings were tabulated and statistical analysis was done with Chi-square test using SPSS software. The prevalence among gender and also in different age groups was also noted. Results: On examining 146 CBCTs, only 26 (17.80%) patients had anterior loop of mental foramen and only 8 (5.48%) patients had mandibular incisive canal. Anterior loop of mental foramen was present, unilaterally (left or right side) in 24 cases (16.43%) and bilaterally in remaining 2 (1.36%) cases. Mandibular incisive canal was found unilaterally (left or right) in 6 (4.10%) and bilaterally in 2 (1.37%) patients. These structures were more commonly found in patients around years of age. Conclusion: Care should be taken to avoid injury to mental nerve during implant placement in the interforaminal region. Hence, a safe fixed distance, anterior from mental foramen should not be taken into account for every patient. Alterations in the distance are present among different individuals. KEY WORDS: Incisive canal, Mental nerve, CBCT INTRODUCTION Inferior alveolar nerve enters the mandibular bone through the mandibular foramen and runs inside the mandibular bone in the mandibular canal which ends at mental foramen. From here, the nerve gives off smaller mandibular incisive branch after which the main nerve curves back to enter the foramen and emerges into soft tissues as mental nerve. A portion of inferior alveolar nerve presents anterior to mental foramen before the area of ramification into incisive nerve is called as anterior loop of mental foramen. Access this article online Website: jprsolutions.info ISSN: The anterior loop of mental nerve is defined as the mental canal which rises from the mandibular canal and runs outward, upward, and backward to open at the mental foramen as defined by Sicher. [1] The mandibular incisive canal is a bilateral canal which runs medial to mental foramen on either side. This canal contains neurovascular bundle which supplies the incisors, canines, and first premolar. During surgery, any nerve injury can lead to complications such as neurosensory disturbances and hemorrhage in that area. [2] Anterior region of mandible is considered as a safe zone for performing any surgeries in the interforaminal area. Any surgical interventions during placement of endosseous implant, orthognathic surgery, screw-retained plating in cases of trauma in 1 Department of Prosthodontics, Saveetha Dental College and Hospitals, Saveetha Institute of Medical and Technical Sciences, Chennai, Tamil Nadu, India, 2 Department of Prosthodontics, Saveetha Dental College and Hospitals, Saveetha Institute of Medical and Technical Sciences, Chennai, Tamil Nadu, India, 3 Department of Prosthodontics and Implantology, Saveetha Dental College and Hospitals, Saveetha Institute of Medical and Technical Sciences, Chennai, Tamil Nadu, India *Corresponding author: Dr. Ashish R. Jain, Department of Prosthodontics, Saveetha Dental College and Hospital, Saveetha University, Ponamalle High Road, Chennai , Tamil Nadu, India. Phone: dr.ashishjain_r@yahoo.com Received on: ; Revised on: ; Accepted on:

2 the anterior region, bone harvesting, etc., can direct or indirect trauma to the nerve. [3] This can be reversible or irreversible based on the duration of the symptoms which persists for longer time in case of latter. Hence, careful presurgical planning is necessary to avoid any complications during and postsurgical in interforaminal area to achieve success in the treatment. Panoramic radiographs come to play a role in diagnostic evaluation of proposed surgical site. They cannot be used as only reliable source as magnification of anatomical structures are shown small. [4] Cone beam computed tomographic (CBCT), a new imaging modality helps dentists to visualize small anatomical structures in high spatial resolution with same effective dose. CBCTs are widely being used to study anterior loop of mental foramen, its variation, course of mandibular canal, etc. [5] MATERIALS AND METHODS This is a retrospective study. Patients who were planned to get implant placed were sent for CBCT scan. The sample size was about 146 patients and their CBCTs were collected from a time period of January 2016 January These CBCTs were read with the help of Galileos software for identifying the location of anterior loop of mental foramen and to find the prevalence of mandibular incisive canal and its dimensions. The CBCTs were divided into two groups. One group containing 63 male patients and other groups contain 83 female patients. These patients were divided into five age groups: Group I years, Group II years, Group III years, Group IV years, and Group V years. Incidence of anterior loop of mental foramen and mandibular incisive canal among different age group was noted. Inclusion Criteria The following criteria are included in the study: 1. Image should be of high quality and geometric accuracy with good contrast of image. 2. Teeth should be present from molar on one side to molar on another side. 3. No deep carious lesions or tooth-associated periapical pathologies. 4. Absence of any unerupted or supernumerary tooth which obscures the mental foramen. 5. Absence of any radiolucent or radiopaque structure in lower jaw or previous trauma or accidents resulting in plate fixation. Exclusion Criteria The following criteria are excluded from the study: 1. Presence of mixed dentition. 2. Presence of any plate fixation done in cases of mandibular fracture or resection of mandible. 3. CBCTs which contain only upper arch. 4. CBCTs which have improper or distorted images of lower jaw. METHODS All CBCT images were taken by Sirona Orthophos, GALILEOS version 1.7 (Sirona, Germany) with a flat panel detector. The adjusted scan parameters were 85 kvp and ma, depending on the size of patients. The exposure time was 14 s, the effective exposure time was 2 6 s, and the voxel size was 0.3 mm 0.3 mm 0.3 mm. 146 CBCTs were evaluated after meeting the inclusion and exclusion criterion. These scans were analyzed for the location of anterior loop of mental foramen and mandibular incisive canal. Anterior Loop of Mental Foramen The presence of anterior loop of mental foramen was detected similar to a study conducted by Mardinger et al. [6] Anterior loop status was divided into four groups: Group I - present on the left side only, Group II - present on the right side only, Group III - present on either side, and Group IV - absent on either side [Figures 1-4]. To measure the length of anterior loop in tangential plane, two parallel lines from the anterior point of mental foramen and anterior point of anterior loop were drawn using length measuring option on Galileos software. The distance between these two lines was measured by drawing a perpendicular line on them and was considered as the length of anterior loop. Mandibular Incisive Canal Similar to that of anterior loop of mental foramen, incisive canal is traced by moving the cursor anteriorly and medially from the mental foramen region. In cases where there is the presence of incisive canal, dimensions and measurement of buccal proximity, lingual proximity, and distance between canal and the base of the mandible were noted. Mandibular incisive canal can either be present on one side (left or right) or on both sides. In some cases, there is the absence of canal. CBCT projections were analyzed in different sectional planes (tangential, cross-sectional, and axial) [Figures 5-6]. RESULTS From 146 CBCT images, 63 and 83 images belonged to men and women, respectively. The mean age of the patients was ± years. There were 97.26% partial edentulous and 2.74% completely edentulous patients. 1657

3 Figure 1: Anterior loop of mental foramen on the left side Figure 4: Reveals anterior loop of mental foramen on the left side Figure 2: Anterior loop of mental foramen on the right side Figure 5: Mandibular incisive canal on the left side Figure 3: Anterior loop of mental foramen on the right side On examining 146 CBCTs, only 26 (17.80%) patients had anterior loop of mental foramen which was present unilaterally (left or right side) in 24 cases (16.43%) and bilaterally in the remaining 2 (1.36%) cases. Anterior loop of mental foramen was seen in 11 of 63 males (17.46%). There was no bilateral presence of anterior loop of mental foramen. Of 11 males, six were present on the right side (9.52%) and five were present on the left side (7.94%) unilaterally. The average length of anterior loop was found to be 1.75 ± 0.79 mm and 1.46 ± 0.32 mm for the right and left sides, respectively. Figure 6: Mandibular incisive canal on the right side Anterior loop of mental foramen was seen in 15 of 83 females (18.07%). There were only 2 (2.41%) cases in which bilateral the presence of anterior loop of mental foramen was found. In remaining 13 cases, anterior loop was found in 5 (6.02%) of 83 cases on the right side and 8 of 83 (9.64%) cases on the left side. Average length of unilateral canal was 1.52 ± 0.33 on 1658

4 the right side and 1.54 ± 0.50 mm on the left side, respectively. Only 8 (5.48%) patients had mandibular incisive canal. Mandibular incisive canal was found unilaterally (left or right) in 5 (3.42%) and bilaterally in 3 (2.05%) patients. Of 6 unilaterally present canals, 2 (3.17%) were present in the right-sided mandible of males and one canal was present in the right mandible in female. 1 (1.59% and 1.20%) canal each was present on the left-sided mandible for males and females, respectively. 3 (4.76%) bilateral canals were present in males with no bilateral canal seen in any females. Average length of mandibular incisive canal on the right side is 1.46 ± 0.26 mm, whereas it is 1.58 ± 0.29 mm on the left side. The average distance between the buccal proximity of the canal was found to be 1.83 ± 0.25 mm. The average distance between the canal and lingual proximity was found to be 1.58 ± 0.29 mm. The distance between the incisive canal and base of the mandible was found to be ± 1.69 mm. DISCUSSION The successful placement of dental implants depends on proper diagnosis and pretreatment planning. Anterior loop of mental foramen is an important anatomical structure in the interforaminal area of mandible. Great care is required in surgeries of this area to prevent mental nerve injury and further complications. The anterior loop has been evaluated by different radiographic methods including panoramic radiography, CT, and CBCT. Panoramic radiography, which is a two-dimensional conventional method, has a disadvantage that it has limited potency to detect and trace the anterior loop. Studies have shown that panoramic radiography is not sufficient for presurgical implant planning in the mental region and may need to be supplemented with other advanced modalities such as CT or CBCT for better visualization of the interforaminal area. [7,8] Among the advanced imaging modalities, the CT and CBCT allow three-dimensional imaging without magnification and distortion. CBCT has the slighter advantage of providing high-quality images with less radiation dose than CT, and it is been widely used in implant planning. [4,9,10] Incidence of anterior loop of mental foramen was observed in 11 of 63 males (17.46%) and 15 of 83 females (18.07%) with a total of 26 of 146 (35.53%). This value is in correlation with studies previously conducted by Jacobs et al., [11] Yosue and Brooks, [12] and Kuzmanovic et al. [13] This may be due to visualization of anterior loop is different in two-dimensional panoramic radiograph and threedimensional CBCTs. The visibility of anterior loop decreases with increase in age. It is due to reduced calcification of cortex with age which makes the bone remodeling to be slower. At this age, the cortical porosity and Haversian canals increase markedly showing resorption of bone; [14] as a result, the bone marrow space enlarges and trabecular pattern arranged in much-disoriented manner affects the visibility of anterior loop of mental foramen. [12] Mandibular incisive canal was found in 8 of 146 patients (5.49%). However, in contrast to a study conducted by Alani et al., [15] the mandibular incisive canal was found in all the cases studied. Certain authors have also found a high prevalence of MIC using CBCT these with a variable visibility of %. In the study of Sokhn et al., [16] the incisive canal was identified in 97.5% of the images. Sahman et al. [17] reported that the MIC was visible in 459 (94.4%) CBCT images. Relationship of mandibular incisive canal with close proximity to buccal and lingual cortical plates and distance between mandibular incisive canal and the base of the mandible are noted. Average distance of canal to buccal proximity was found to be 1.83 ± 0.25 mm, whereas the distance of canal to lingual proximity was found to be 1.58 ± 0.29 mm. The distance between mandibular incisive canal and base of the mandible was found to be ± 1.69 mm. These results obtained are in contrary to the study conducted by Mardinger et al. [18] and Rose et al. [19] As regards gender, there was no significant difference when comparing the proximity of the MIC to the buccal and lingual walls and alveolar process. The average length of mandibular incisive canal was found to be 1.46 ± 0.26 mm on the right side and 1.58 ± 0.29 mm on the left side. Our study showed greater difference in the length of the anterior loop when compared to that of study conducted by Pires et al. [20] where the MIC lengths of 7.1 ± 4 mm and 6.6 ± 3.7 mm were seen for the right and left sides, respectively. Possible drawback of this study was the fact that the measurements were performed by the same observer, allowing some consistency, but this always includes the possibility for methodological bias. Hence, two observers for visualizing anterior loop of mental foramen and mandibular incisive canal reduce the methodological error and improve the reliability of the study. CONCLUSION Placing implants in proximity to mental foramen require great care to avoid anterior loop injury. Variations in length of anterior loop in each patient 1659

5 reveal that a fixed distance anterior to the mental foramen is not safe. Hence, the length of anterior loop should be determined for each individual. The use of CBCTs in treatment planning of implants helps in assessing the anterior loop and incisive canal before surgery to avoid post-extraction complications. REFERENCES 1. Arzouman MJ, Otis L, Kipnis V, Levine D. Observation of the anterior loop of the inferior alveolar canal. Int J Oral Maxillofac Implants 1993;8: Abarca MD, Steenberghe V, Malevez C, De Ridder J, Jacobs R. Neurosensory disturbances after immediate loading of implants in the anterior mandible. Clin Oral Invest 2006;10: Ellies LG, Hawker PB. The prevalence of altered sensation associated with implant surgery. Int J Oral Maxillofac Implants 1993;8: Gümüşok M, Kayadüǧün A, Üçok Ö. Anterior loop of the mental nerve and its radiologic imaging: A review. Marmara Dent J 2013;2: Makris N, Stamatakis H, Syriopoulos K, Tsiklakis K, Van der Stelt PF. Evaluation of the visibility and the course of the mandibular incisive canal and the lingual foramen using cone-beam computed tomography. Clin Oral Implants Res 2010;21: Mardinger O, Chaushu G, Arensburg B, Taicher S, Kaffe I. Anterior loop of mental canal; An anatomical and radiological study. Implant Dent 2000;9; Ngeow WC, Dionysius DD, Ishak H, Nambiar P. A radiographic study on the visualization of the anterior loop in dentate subjects of different age groups. J Oral Sci 2009;51: do Couto-Filho CE, de Moraes PH, Alonso MB, Haiter- Neto F, Olate S, de Albergaria-Barbosa JR, et al. Accuracy in the diagnosis of the mental nerve loop. A comparative study between panoramic radiography and cone beam computed tomography. Int J Morphol 2015;33: Scarfe WC, Farman AG, Sukovic P. Clinical applications of cone beam computed tomography in dental practice. J Can Dent Assoc 2006;72: Jacobs R, Mraiwa N, vansteenberghe D, Gijbels F, Quirynen M. Appearance, location, course, and morphology of the mandibular incisive canal: An assessment on spiral CT scan. Dentomaxillofac Radiol 2002;31: Jacob R, Mraiwa N, Van Steenberghe D, sanderlink G, Quirynen M. Appearance of mandibular incisive canal on panoramic radiographs. Surg Radiol Anat 2004;26: Yosue T, Brooks SL. The appearance of mental foramina on the panoramic radiographs. I. Evaluation of patients. Oral surg Oral Med Oral Pathol 1989;68: Kuzmanovic DV, Payne AG, Kisser JA, Dias GJ. Anterior loop of mental nerve: A morphological and radiographical study. Clin Oral Implants Res 2003;14: Kieser J, Kuzmanovic D, Payne A, Dennison J, Herbison P. Patterns of emergence of the human mental nerve. Arch Oral Biol 2002;47: Al-Ani O, Nambiar P, Ha KO, Ngeow WC. Safe zone for bone harvesting from the interforaminal region of the mandible. Clin Oral Implants Res 2013;24 Suppl A100: Sokhn S, Nasseh I, Noujeim M. Using cone beam computed tomography to determine safe regions for implant placement. Gen Dent 2011;59:e Sahman H, Sekerci AE, Sisman Y, Payveren M. Assessment of the visibility and characteristics of the mandibular incisive canal: Cone beam computed tomography versus panoramic radiography. Int J Oral Maxillofac Implants 2014;29: Mardinger O, Chaushu G, Arensburg B, Taicher S, Kaffe I. Anatomic and radiologic course of the mandibular incisive canal. Surg Radiol Anat 2000;22: Rosa MB, Sotto-Maior BS, Machado VC, Francischone CE. Study of the anterior loop of the inferior alveolar nerve and the incisive canal using cone beam computed tomography. Int J Oral Maxillofa Implants 2013;28: Pires CA, Bissada NF, Becker JJ, Kanawati A, Landers MA. Mandibular incisive canal: Cone beam computed tomography. Clin Implant Dent Relat Res 2012;14: Source of support: Nil; Conflict of interest: None Declared 1660