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Mandibular incisive canal in Han Chinese using cone beam computed tomography
YIJOM-3413; No of Pages 5
Int. J. Oral Maxillofac. Surg. 2016; xxx: xxx–xxx http://dx.doi.org/10.1016/j.ijom.2016.04.019, available online at http://www.sciencedirect.com
Clinical Paper Dental Implants
Mandibular incisive canal in Han Chinese using cone beam computed tomography
N. Kong1, M. Hui2, F. Miao3, H. Yuan2, Y. Du2,4, N. Chen2,4 1 Department of Stomatology, The Affiliated Children’s Hospital, School of Medicine, Zhejiang University, Hangzhou, Zhejiang, People’s Republic of China; 2Institute of Stomatology, Nanjing Medical University, Nanjing, Jiangsu, People’s Republic of China; 3 Department of Stomatology, The Affiliated Stomatology Hospital, School of Medicine, Zhejiang University, Hangzhou, Zhejiang, People’s Republic of China
N. Kong, M. Hui, F. Miao, H. Yuan, Y. Du, N. Chen: Mandibular incisive canal in Han Chinese using cone beam computed tomography. Int. J. Oral Maxillofac. Surg. 2016; xxx: xxx–xxx. # 2016 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Abstract. The aim of this study was to provide reference information for implantology and chin bone harvesting in people of Han Chinese ethnicity by studying the mandibular incisive canal (MIC) using cone beam computed tomography (CBCT). Fifty subjects were included in the study. CBCT scans were obtained for all subjects, and 22 also underwent panoramic radiography to evaluate the visibility of the MIC. The CBCT data of the 50 subjects were reconstructed to measure MIC diameter, length, and location within the mandible. A MIC was identified in 38.6% of panoramic radiographs, with good clarity in 13.6%, while a MIC was identified in 100% of CBCT images, with good clarity in 63.6%. The diameter of the MIC decreased from origin to end. The left and right average MIC lengths were 17.84 mm and 17.73 mm, respectively. The MIC was close to the buccal cortical border and lower margin of the mandible. In conclusion, the MIC is an anatomical structure in the mandible that can be identified reliably with CBCT. On insertion, implants should be inclined slightly towards the lingual aspect of the anterior mandible to protect the MIC. The chin bone harvesting depth should be limited to 4 mm; the harvesting site can be adjusted to the region above or below the MIC.
Surgery in the anterior mandibular bone region is assumed to be safe and without severe complications. Such surgeries include implant surgery, chin bone grafting, and genioplasty.1 However, there are reports of unexplained implant failure and bleeding on implant insertion and chin bone harvesting associated with the mandibular incisive canal (MIC). Patients may experience pain, discomfort, and sensory disturbances.2,3 The MIC was investigated 0901-5027/000001+05
as early as 1928.4 Since then, studies have shown the MIC to be a consistent finding in cadavers.5 Thus, it is essential to identify the MIC to prevent injury when performing implant surgery or harvesting chin bone in the anterior mandible. Conventional radiography often fails to display the MIC, since panoramic radiographs and peri-apical radiographs are two-dimensional images. Moreover, in comparison to the mandibular canal, the
Key words: mandibular incisive canal; anterior mandible; dental implant; bone graft; cone beam computed tomography. Accepted for publication 22 April 2016
MIC shows less bony corticalization and the diameter is smaller.5,6 Cone beam computed tomography (CBCT) is an excellent imaging system for oral and maxillofacial application. The advantages of CBCT include uniform magnification, the ability to produce three-dimensional (3D) 4
These authors contributed equally to this work and should be considered as co-correspondence authors.
# 2016 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: Kong N, et al. Mandibular incisive canal in Han Chinese using cone beam computed tomography, Int J Oral Maxillofac Surg (2016), http://dx.doi.org/10.1016/j.ijom.2016.04.019
YIJOM-3413; No of Pages 5
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reconstructions using software, and the high geometric accuracy, as well as low radiation doses and a relatively low cost. For the study of teeth, spongy bone, and lamina dura, the accuracy of CBCT has been judged to be equivalent to multi-slice computed tomography.7,8 This study was conducted to evaluate the visibility of the MIC on panoramic radiography and CBCT. The diameter, length, and location of the MIC were also assessed on CBCT to provide reference information on the anterior mandible for people of Han Chinese ethnicity. Materials and methods Subjects and materials
Fifty Han Chinese adults (25 men, 25 women; mean age 29.82 7.00 years, range 18–42 years) were recruited between January 2011 and January 2013 at the study hospital in Nanjing, China. Consent was obtained from all subjects. This study was granted ethical approval by the medical ethics committee. Inclusion criteria were the following: subjects with all teeth present in the interforaminal region, without crowding or spacing; no untreated caries, apical diseases, tooth trauma, or periodontal diseases. The subjects had no current or past history of trauma or pathology, surgical interventions in the mandible, neurogenic disorders, or systemic diseases. CBCT scans were obtained for all 50 of the subjects by the same professional dental technologist following a standardized protocol, with the same machine (NewTom VG 10048S; QR srl Inc., Verona, Italy), and with uniform parameter settings (110 kVp). Panoramic radiographs were also obtained for 22 of the subjects; these were taken by the same technologist following a standardized protocol, with the same panoramic radiograph unit (OP100 Orthopantomograph; Instrumentarium Imaging Corporation, Tuusula, Finland). The scanning region covered the entire skull for each subject. The reformatted CBCT images were clear and symmetrical, and were not distorted or blurred. The panoramic radiograph (OPG) images were analyzed using ClinView software version 10.0.1.8 (Instrumentarium Imaging Corporation).
Methods
CBCT data were imported into SimPlant 11.04 software (Materialise Dental, Leuven, Belgium). Axial images were reoriented to make the occlusal plane parallel
Fig. 1. Mandibular incisive canal on panoramic radiograph (left panel) and CBCT (right panel): a–b, mandibular incisive canal; b–c, mental foramen; c–d, mandibular canal.
to the base plane and to ensure symmetry prior to performing the second reconstruction for each subject.9 After creating panoramic curves, the cross-sectional views were perpendicular to the mandibular dental arch. The MIC was measured in the axial, cross-sectional, and panoramic views. A desktop personal computer was used, with an Intel-based processor and resolution of 1366 768 pixels (ProBook 4416s; Hewlett-Packard). All images were investigated by an observer who was trained in the interpretation of oral and maxillofacial images and were checked by an oral and maxillofacial radiologist. Following an interval of 1 month, the CBCT DICOM data of 10 randomly selected subjects were reconstructed and the MIC re-measured to assess intra-observer reliability and repeatability.10 A three-point rating scale was used to grade MIC visibility on the CBCT and OPG images of the 22 subjects: not visible, visible but unclear, and visible and clear (bony cortical borders were easily identified; good clarity)11 (Fig. 1). The positions of the origin (anterior region of the mental foramen) and end (where the MIC disappears) and the
distribution of the MIC were evaluated on the CBCT images of the 50 subjects. The following measurements of the MIC were taken below the origin, second premolar, first premolar, canine, lateral incisor, central incisor, and end in the cross-sectional view (Fig. 2): vertical and horizontal diameter of the MIC; horizontal distance from the MIC to the lingual and buccal cortical borders of the mandible; and the vertical distance from the MIC to the apex of the tooth, lower margin, and alveolar crest of the mandible. The lengths of the left and right MICs were measured from the origin to the end in the panoramic view. If the MIC disappeared, it was marked as ‘disappeared’. For example, if the MIC ended at the canine, measurements of the lateral incisor and central incisor were not performed and were marked as ‘disappeared’ instead (Fig. 2). Statistical analysis
The x2 test was used to analyze MIC visibility on OPG and CBCT. The paired t-test, the x2 test, and Fisher’s exact test were used to analyze intra-observer reliability and to determine the influence of
Fig. 2. Measurements of the mandibular incisive canal (MIC) in cross-sectional view and panoramic view on CBCT: A–C, vertical diameter; B–D, horizontal diameter; D1, distance from the MIC to the alveolar crest of the mandible; D2, distance from the MIC to the apex of the tooth; D3, distance from the MIC to the buccal cortical border of the mandible; D4, distance from the MIC to the lingual cortical border of the mandible; D5, distance from the MIC to the lower margin of mandible; ab, length of the MIC (length of curve).
Please cite this article in press as: Kong N, et al. Mandibular incisive canal in Han Chinese using cone beam computed tomography, Int J Oral Maxillofac Surg (2016), http://dx.doi.org/10.1016/j.ijom.2016.04.019
YIJOM-3413; No of Pages 5
Mandibular incisive canal in Han Chinese the relative side of the mandible (left and right). The intra-class correlation (ICC) test was also used to test the intra-observer validity and reliability of MIC measurements. The independent samples t-test, the x2 test, and Fisher’s exact test were used to determine the influence of sex. Values of significance were all set at the alpha level of 5% (P < 0.05). The mean values and standard deviations of each measurement were calculated using SPSS version 13.0 software (SPSS Inc., Chicago, IL, USA). Results MIC visibility on OPG and CBCT of 22 subjects (44 hemimandibles)
On comparison of the CBCT and OPG images of 22 subjects (44 sides), there was no statistical difference with regard to site or sex. A MIC was identified in 38.6% of OPG images, with good clarity in 13.6%, and in 100% of CBCT images, with good clarity in 63.6%. There were statistically significant differences in visibility and in clarity of the MIC between OPG and CBCT (P < 0.001).
MIC measurements on CBCT of 50 subjects (100 hemimandibles)
On assessment of the CBCT images of 50 subjects (100 sides), the vertical distances from the MIC to the lower margin of the mandible at the second premolar and first premolar differed significantly according to sex (independent samples t-test, P < 0.05). The mean distance from the MIC to the lower margin at the second premolar was 11.34 mm in males and 8.75 mm in females; the mean distance at the first premolar was 9.44 mm in males and 8.43 mm in females. The distances were longer in males. No statistically significant difference with regard to the relative side of the mandible (left and right) was found (P > 0.05). The MIC started at the mental foramen in 100% of cases and ended below the incisors in 76% of cases. The left and right MIC connected mutually in seven subjects. The left and right MIC of eight subjects (16%) finally ascended to the alveolar crest at or near the midline of the mandible. Connections of small ascending branches occurred in four subjects (8%). The mean length of the MIC was 17.84 mm (range 9.61–35.74 mm) in the left mandible and 17.73 mm (range 5.93–40.35 mm) in the right mandible. As shown in Table 1, the diameter of the MIC decreased gradually from origin to
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Table 1. Horizontal and vertical diameters of the mandibular incisive canal (mean SD, millimetres). Site
Number
Horizontal diameter
Vertical diameter
100 16 100 97 76 34 100
2.16 0.58 1.97 0.55 1.53 0.51 1.16 0.28 0.93 0.26 0.76 0.21 0.84 0.23
2.15 0.62 2.08 0.61 1.47 0.49 1.17 0.27 1.00 0.38 0.73 0.29 0.89 0.34
Origin Second premolar First premolar Canine Lateral incisor Central incisor End SD, standard deviation.
Table 2. Horizontal distances from the mandibular incisive canal to the buccal and lingual cortical borders (mean SD, millimetres). Site Origin Second premolar First premolar Canine Lateral incisor Central incisor End
Number
Buccal
Lingual
100 16 100 97 76 34 100
2.97 0.83 3.01 0.75 4.05 1.14 4.65 1.28 4.15 1.13 4.25 1.18 4.21 1.22
5.25 1.52 5.60 1.61 4.94 1.29 5.11 1.43 6.27 1.40 6.33 1.96 5.96 1.66
SD, standard deviation.
end. Only 8% of the subjects with large MIC diameters (>1 mm) reached the middle part of the mandible. The mean distances from the MIC to the buccal cortical border of the mandible at the second premolar, first premolar, canine, lateral incisor, and central incisor were shorter than those from the MIC to the lingual cortical border (Table 2). The mean distance from the MIC to the tooth apex was >7 mm for each tooth. The mean distance from the MIC to the alveolar crest was longer than that to the lower margin of the mandible for each tooth (Table 3). Thus, the MIC in the mandible was close to the buccal border and lower margin. There was no statistically significant difference in intra-observer reliability using the paired t-test, the x2 test, or Fisher’s exact test (P > 0.05). The ICC value was 0.849, indicating good intra-observer validity and reliability.
Discussion
The mandibular incisive nerve provides innervation to the lower anterior teeth and surrounding mucosa. However, the MIC is usually overlooked since its bony corticalization is poorer and its diameter smaller than those of the mandibular canal.5,6 The MIC can be identified well in cadavers.12 Mardinger et al. reported that a mandibular incisive bundle was anatomically found in all hemimandibles of cadavers.6 However, conventional two-dimensional images often fail to show the MIC. Jacobs et al. reported that the incisive canal was identified in 15% of panoramic radiographs, with good visibility in only 1%.13 Jalili et al. observed the MIC in 51.7% of panoramic radiographs, which may be the highest reported percentage.14 Some studies have indicated the usefulness of high-resolution magnetic resonance imaging for microanatomical
Table 3. Vertical distances from the mandibular incisive canal to the apex, alveolar crest, and lower margin of the mandible (mean SD, millimetres). Site Origin Second premolar First premolar Canine Lateral incisor Central incisor End
Number
Root apex
Alveolar crest
Lower margin
100 16 100 97 76 34 100
10.21 4.00a 11.92 4.20 8.81 3.43 7.74 3.22 9.51 3.70 8.02 4.03 8.04 4.02b
17.86 2.60 20.78 2.48 20.04 3.28 20.44 3.26 18.48 3.72 16.23 3.15 17.72 4.17
9.92 1.64 10.04 1.73 8.92 1.62 8.21 2.15 10.18 2.80 12.39 3.62 11.50 3.92
SD, standard deviation. a Number of distances from the MIC to the root apex was 12 at the origin. b Number of distances from the MIC to the root apex was 50 at the end.
Please cite this article in press as: Kong N, et al. Mandibular incisive canal in Han Chinese using cone beam computed tomography, Int J Oral Maxillofac Surg (2016), http://dx.doi.org/10.1016/j.ijom.2016.04.019
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studies of the mandibular incisive nerve. However, this technology is not in widespread use because of its limited scanning volume, long waiting time, high cost, and limited availability.15 CBCT is particularly suitable for the mandible since it enables the 3D reconstruction of high-resolution images of the entire mandible. Excellent imaging of the mandible and mandibular canal has been reported for CBCT, along with a high accuracy of linear measurements and a low radiation dose and lower cost compared to multi-slice computed tomography.7 Timock et al. found that CBCT could be used to quantitatively assess buccal bone height and thickness with high precision.16 Al-Ani et al. observed a MIC in the CBCT images of all 60 patients examined.17 In the present study, a MIC was identified in 38.6% of panoramic radiographs and 100% of CBCT images obtained from Han Chinese subjects; the Han Chinese comprise about one-sixth of the world’s population. Other studies by researchers from Greece, the USA, Belgium, Malaysia, Germany, and elsewhere have reported a high percentage of MIC detection in CBCT images.8,11,15,17,18 The MIC is an anatomical structure in the mandible. It has been suggested that CBCT should be a regular examination before any interventions in the anterior mandible. Mardinger et al. dissected hemimandibles to explore the MIC.6 They found that the diameter of the MIC decreased from its origin to end. Makris et al.8 in Greece and Pires et al.11 in the USA reported that the MIC was closer to the buccal border than the lingual border. The results of the present study showed that the MIC was closer to the buccal border in the Han Chinese subjects. In the vertical direction, the MIC was located in the lower segments of the mandible, a finding that is consistent with those of studies performed in the populations of Malaysia and Turkey.17,19 Little difference was noted in a comparison of MIC diameter and location between this study and previous studies involving subjects of other races. However, the length of the MIC in this study was longer than those reported in some other studies: 17.84 mm in the left mandible and 17.73 mm in the right mandible.17 This might be due to the subjects selected. For inclusion in the present study, the subjects had to be healthy adults with all teeth present and no obvious disease in the interforaminal region, while other studies have included dentate or edentulous patients with a wide range of ages. Bone resorption frequently occurs in edentulous patients.
Fig. 3. Preoperative and postoperative CBCT of incisor implants (white arrows, mental foramen; red arrows, mandibular incisive canal; blue arrows, implants).
Anterior mandibular teeth are often lost as a result of trauma or periodontal disease. Implant therapy has become a widely used treatment in this region. The anterior mandible has been considered an ideal implant site for decades. However, complications have been reported in the anterior lower jaw. Lee et al. described intraoperative complications resulting from injury to the structures within the MIC and the use of an active haemostatic matrix to manage these complications.20 Ku¨tu¨k et al.21 and Abarca et al.2 reported that patients complained of discomfort after implant surgery in the anterior mandible and attributed this complication to direct or indirect injury to the mandibular incisive nerve. In the present study, the MIC had a large diameter at the alveolar crest in 8% of subjects. In such cases, the implant may touch the MIC and cause complications. Figure 3 shows the CBCT images of a 56-year-old female patient who complained of pain for 7 months after incisor implants were inserted; she was treated at the study hospital in Nanjing on December 1, 2012. On imaging, it was found that the left implant was touching the MIC. The results of the present study showed that the mean distance from the MIC to the apex of each tooth was >7 mm and that the mean distance from the MIC to the alveolar crest was >16.23 mm. In such circumstances, the implant is not likely to touch the MIC.
However, vertical bone resorption often occurs, and in such cases the distance from the MIC to the alveolar crest may be greatly reduced. This serves as a reminder that implants should be inserted in a timely manner. Since the MIC is close to the buccal ridge, implant insertions should be inclined slightly towards the lingual border. The chin bone graft is a good choice for patients with insufficient bone volume due to its relatively low cost and osteoinductive, osteoconductive, and non-immunogenic properties. Neurosensory disturbances have been found to occur with defined safety margins of 5 mm anterior to the mental foramen, 5 mm below the tooth apex, and 5 mm above the lower border of the mandible.22 Joshi investigated the most likely reason for the paresthesia and reported it to be neurapraxia of the incisive nerve or the terminal branches of the mental nerve when the chin bone was harvested.23 Figure 4 shows the CBCT images of a 34year-old male patient who complained of pain and numbness of the surrounding tissue for more than 1 year after a bone graft was harvested from the right chin; this patient was treated at the study hospital in Nanjing on January 21, 2011. On CBCT imaging, injury to the right MIC was evident at the harvest site. Pommer et al. have suggested new safety margins to protect the MIC: at least 8 mm below the tooth apices and a maximum harvest depth of 4 mm.22
Fig. 4. Postoperative CBCT following bone harvesting from the right chin (green arrows, mandibular canal; white arrows, mental foramen; red arrows, mandibular incisive canal; blue arrows, chin bone harvest site; yellow arrows, harvest site touching the mandibular incisive canal). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of the article.)
Please cite this article in press as: Kong N, et al. Mandibular incisive canal in Han Chinese using cone beam computed tomography, Int J Oral Maxillofac Surg (2016), http://dx.doi.org/10.1016/j.ijom.2016.04.019
YIJOM-3413; No of Pages 5
Mandibular incisive canal in Han Chinese In this study, the mean distances from the MIC to the tooth apex at the first premolar, canine, lateral incisor, and central incisor were over 7.74 mm, and the mean distances from the MIC to the lower margin were over 8.21 mm, thus there could be sufficient space for a chin bone graft to be harvested above or below the MIC. The harvest site could be adjusted according to the position of the MIC on CBCT. In this study, the MIC was found to be close to the buccal cortical border, with the longest distance being 4.65 mm. Thus the depth should be limited to 4 mm during chin bone harvesting. Funding
This work was supported by the National Natural Science Foundation of China (81271109). Competing interests
None declared. Ethical approval
The study received ethical approval ([2011]10) from the Medical Ethics Committee of the Affiliated Stomatological Hospital of Nanjing Medical University. Patient consent
Informed consent was obtained from each subject. Acknowledgement. The authors thank Tao Chen for his contribution to the statistical analysis.
References 1. Parnia F, Moslehifard E, Hafezeqoran A, Mahboub F, Aer-Kahnamoui H. Characteristics of anatomical landmarks in the mandibular interforaminal region: a cone-beam computed tomography study. Med Oral Patol Oral Cir Bucal 2012;17:e420–5. 2. Abarca M, Van Steenberghe D, Malevez C, De Ridder J, Jacobs R. Neurosensory disturbances after immediate loading of implants in the anterior mandible: an initial questionnaire approach followed by a psychophysical assessment. Clin Oral Investig 2006;10:269–77.
3. Pogrel MA, Smith R, Ahani R. Innervation of the mandibular incisors by the mental nerve. J Oral Maxillofac Surg 1997;55: 961–3. 4. Olivier E. The inferior dental canal and its nerve in the adult. Br Dent J 1928;49:356–8. 5. Mraiwa N, Jacobs R, Moerman P, Lambrichts I, van Steenberghe D. Presence and course of the incisive canal in the human mandibular interforaminal region: two-dimensional imaging versus anatomical observations. Surg Radiol Anat 2003;25:416–23. 6. Mardinger O, Chaushu G, Arensburg B, Taicher S, Kaffe I. Anatomic and radiologic course of the mandibular incisive canal. Surg Radiol Anat 2000;22:157–61. 7. Carrafiello G, Dizonno M, Colli V, Strocchi S, Pozzi Taubert S, Leonardi A, et al. Comparative study of jaws with multislice computed tomography and cone-beam computed tomography. Radiol Med 2010;115:600–11. 8. 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;21:766–71. 9. Chen JC, Lin LM, Geist JR, Chen JY, Chen CH, Chen YK. A retrospective comparison of the location and diameter of the inferior alveolar canal at the mental foramen and length of the anterior loop between American and Taiwanese cohorts using CBCT. Surg Radiol Anat 2013;35:11–8. 10. Apostolakis D, Brown JE. 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. Clin Oral Implants Res 2012;23:1022–30. 11. Pires CA, Bissada NF, Becker JJ, Kanawati A, Landers MA. Mandibular incisive canal: cone beam computed tomography. Clin Implant Dent Relat Res 2012;14:67–73. 12. Uchida Y, Yamashita Y, Goto M, Hanihara T. Measurement of anterior loop length for the mandibular canal and diameter of the mandibular incisive canal to avoid nerve damage when installing endosseous implants in the interforaminal region. J Oral Maxillofac Surg 2007;65:1772–9. 13. Jacobs R, Mraiwa N, Van Steenberghe D, Sanderink G, Quirynen M. Appearance of the mandibular incisive canal on panoramic radiographs. Surg Radiol Anat 2004;26: 329–33. 14. Jalili MR, Esmaeelinejad M, Bayat M, Aghdasi MM. Appearance of anatomical structures of mandible on panoramic radiographs in Iranian population. Acta Odontol Scand 2012;70:384–9.
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15. Jacobs R, Lambrichts I, Lian X, Martens W, Mraiwa N, Adriaensens P, et al. Neurovascularization of the anterior jaw bones revisited using high-resolution magnetic resonance imaging. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2007;103: 683–93. 16. Timock AM, Cook V, McDonald T, Leo MC, Crowe J, Benninger BL, et al. Accuracy and reliability of buccal bone height and thickness measurements from cone-beam computed tomography imaging. Am J Orthod Dentofac Orthop 2011;140:734–44. 17. 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): 115–21. 18. Krasny A, Krasny N, Prescher A. Study of inferior dental canal and its contents using high-resolution magnetic resonance imaging. Surg Radiol Anat 2012;34:687–93. 19. Orhan K, Icen M, Aksoy S, Ozan O, Berberoglu A. Cone-beam CT evaluation of morphology, location, and course of mandibular incisive canal: considerations for implant treatment. Oral Radiol 2014;30:64–75. 20. Lee CY, Yanagihara LC, Suzuki JB. Brisk, pulsatile bleeding from the anterior mandibular incisive canal during implant surgery: a case report and use of an active hemostatic matrix to terminate acute bleeding. Implant Dent 2012;21:368–73. 21. Ku¨tu¨k N, Demirbas¸ AE, Go¨nen ZB, Topan C, Kilic¸ E, Eto¨z OA, et al. Anterior mandibular zone safe for implants. J Craniofac Surg 2013;22:e405–8. 22. Pommer B, Tepper GM, Gahleitner A, Zechner W, Watzek G. New safety margins for chin bone harvesting based on the course of the mandibular incisive canal in CT. Clin Oral Implants Res 2008;19:1312–6. 23. Joshi A. An investigation of post-operative morbidity following chin graft surgery. Br Dent J 2004;196:215–8.
Address: Ning Chen and Yi-fei Du Institute of Stomatology Nanjing Medical University No. 140 Han Zhong Road Nanjing 210029 Jiangsu People’s Republic of China Tel: +86 25 85031856 (N. Chen); Tel: +86 25 85031914 (Y. Du) E-mail: [email protected]
Please cite this article in press as: Kong N, et al. Mandibular incisive canal in Han Chinese using cone beam computed tomography, Int J Oral Maxillofac Surg (2016), http://dx.doi.org/10.1016/j.ijom.2016.04.019
Int. J. Oral Maxillofac. Surg. 2016; xxx: xxx–xxx http://dx.doi.org/10.1016/j.ijom.2016.04.019, available online at http://www.sciencedirect.com
Clinical Paper Dental Implants
Mandibular incisive canal in Han Chinese using cone beam computed tomography
N. Kong1, M. Hui2, F. Miao3, H. Yuan2, Y. Du2,4, N. Chen2,4 1 Department of Stomatology, The Affiliated Children’s Hospital, School of Medicine, Zhejiang University, Hangzhou, Zhejiang, People’s Republic of China; 2Institute of Stomatology, Nanjing Medical University, Nanjing, Jiangsu, People’s Republic of China; 3 Department of Stomatology, The Affiliated Stomatology Hospital, School of Medicine, Zhejiang University, Hangzhou, Zhejiang, People’s Republic of China
N. Kong, M. Hui, F. Miao, H. Yuan, Y. Du, N. Chen: Mandibular incisive canal in Han Chinese using cone beam computed tomography. Int. J. Oral Maxillofac. Surg. 2016; xxx: xxx–xxx. # 2016 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Abstract. The aim of this study was to provide reference information for implantology and chin bone harvesting in people of Han Chinese ethnicity by studying the mandibular incisive canal (MIC) using cone beam computed tomography (CBCT). Fifty subjects were included in the study. CBCT scans were obtained for all subjects, and 22 also underwent panoramic radiography to evaluate the visibility of the MIC. The CBCT data of the 50 subjects were reconstructed to measure MIC diameter, length, and location within the mandible. A MIC was identified in 38.6% of panoramic radiographs, with good clarity in 13.6%, while a MIC was identified in 100% of CBCT images, with good clarity in 63.6%. The diameter of the MIC decreased from origin to end. The left and right average MIC lengths were 17.84 mm and 17.73 mm, respectively. The MIC was close to the buccal cortical border and lower margin of the mandible. In conclusion, the MIC is an anatomical structure in the mandible that can be identified reliably with CBCT. On insertion, implants should be inclined slightly towards the lingual aspect of the anterior mandible to protect the MIC. The chin bone harvesting depth should be limited to 4 mm; the harvesting site can be adjusted to the region above or below the MIC.
Surgery in the anterior mandibular bone region is assumed to be safe and without severe complications. Such surgeries include implant surgery, chin bone grafting, and genioplasty.1 However, there are reports of unexplained implant failure and bleeding on implant insertion and chin bone harvesting associated with the mandibular incisive canal (MIC). Patients may experience pain, discomfort, and sensory disturbances.2,3 The MIC was investigated 0901-5027/000001+05
as early as 1928.4 Since then, studies have shown the MIC to be a consistent finding in cadavers.5 Thus, it is essential to identify the MIC to prevent injury when performing implant surgery or harvesting chin bone in the anterior mandible. Conventional radiography often fails to display the MIC, since panoramic radiographs and peri-apical radiographs are two-dimensional images. Moreover, in comparison to the mandibular canal, the
Key words: mandibular incisive canal; anterior mandible; dental implant; bone graft; cone beam computed tomography. Accepted for publication 22 April 2016
MIC shows less bony corticalization and the diameter is smaller.5,6 Cone beam computed tomography (CBCT) is an excellent imaging system for oral and maxillofacial application. The advantages of CBCT include uniform magnification, the ability to produce three-dimensional (3D) 4
These authors contributed equally to this work and should be considered as co-correspondence authors.
# 2016 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: Kong N, et al. Mandibular incisive canal in Han Chinese using cone beam computed tomography, Int J Oral Maxillofac Surg (2016), http://dx.doi.org/10.1016/j.ijom.2016.04.019
YIJOM-3413; No of Pages 5
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reconstructions using software, and the high geometric accuracy, as well as low radiation doses and a relatively low cost. For the study of teeth, spongy bone, and lamina dura, the accuracy of CBCT has been judged to be equivalent to multi-slice computed tomography.7,8 This study was conducted to evaluate the visibility of the MIC on panoramic radiography and CBCT. The diameter, length, and location of the MIC were also assessed on CBCT to provide reference information on the anterior mandible for people of Han Chinese ethnicity. Materials and methods Subjects and materials
Fifty Han Chinese adults (25 men, 25 women; mean age 29.82 7.00 years, range 18–42 years) were recruited between January 2011 and January 2013 at the study hospital in Nanjing, China. Consent was obtained from all subjects. This study was granted ethical approval by the medical ethics committee. Inclusion criteria were the following: subjects with all teeth present in the interforaminal region, without crowding or spacing; no untreated caries, apical diseases, tooth trauma, or periodontal diseases. The subjects had no current or past history of trauma or pathology, surgical interventions in the mandible, neurogenic disorders, or systemic diseases. CBCT scans were obtained for all 50 of the subjects by the same professional dental technologist following a standardized protocol, with the same machine (NewTom VG 10048S; QR srl Inc., Verona, Italy), and with uniform parameter settings (110 kVp). Panoramic radiographs were also obtained for 22 of the subjects; these were taken by the same technologist following a standardized protocol, with the same panoramic radiograph unit (OP100 Orthopantomograph; Instrumentarium Imaging Corporation, Tuusula, Finland). The scanning region covered the entire skull for each subject. The reformatted CBCT images were clear and symmetrical, and were not distorted or blurred. The panoramic radiograph (OPG) images were analyzed using ClinView software version 10.0.1.8 (Instrumentarium Imaging Corporation).
Methods
CBCT data were imported into SimPlant 11.04 software (Materialise Dental, Leuven, Belgium). Axial images were reoriented to make the occlusal plane parallel
Fig. 1. Mandibular incisive canal on panoramic radiograph (left panel) and CBCT (right panel): a–b, mandibular incisive canal; b–c, mental foramen; c–d, mandibular canal.
to the base plane and to ensure symmetry prior to performing the second reconstruction for each subject.9 After creating panoramic curves, the cross-sectional views were perpendicular to the mandibular dental arch. The MIC was measured in the axial, cross-sectional, and panoramic views. A desktop personal computer was used, with an Intel-based processor and resolution of 1366 768 pixels (ProBook 4416s; Hewlett-Packard). All images were investigated by an observer who was trained in the interpretation of oral and maxillofacial images and were checked by an oral and maxillofacial radiologist. Following an interval of 1 month, the CBCT DICOM data of 10 randomly selected subjects were reconstructed and the MIC re-measured to assess intra-observer reliability and repeatability.10 A three-point rating scale was used to grade MIC visibility on the CBCT and OPG images of the 22 subjects: not visible, visible but unclear, and visible and clear (bony cortical borders were easily identified; good clarity)11 (Fig. 1). The positions of the origin (anterior region of the mental foramen) and end (where the MIC disappears) and the
distribution of the MIC were evaluated on the CBCT images of the 50 subjects. The following measurements of the MIC were taken below the origin, second premolar, first premolar, canine, lateral incisor, central incisor, and end in the cross-sectional view (Fig. 2): vertical and horizontal diameter of the MIC; horizontal distance from the MIC to the lingual and buccal cortical borders of the mandible; and the vertical distance from the MIC to the apex of the tooth, lower margin, and alveolar crest of the mandible. The lengths of the left and right MICs were measured from the origin to the end in the panoramic view. If the MIC disappeared, it was marked as ‘disappeared’. For example, if the MIC ended at the canine, measurements of the lateral incisor and central incisor were not performed and were marked as ‘disappeared’ instead (Fig. 2). Statistical analysis
The x2 test was used to analyze MIC visibility on OPG and CBCT. The paired t-test, the x2 test, and Fisher’s exact test were used to analyze intra-observer reliability and to determine the influence of
Fig. 2. Measurements of the mandibular incisive canal (MIC) in cross-sectional view and panoramic view on CBCT: A–C, vertical diameter; B–D, horizontal diameter; D1, distance from the MIC to the alveolar crest of the mandible; D2, distance from the MIC to the apex of the tooth; D3, distance from the MIC to the buccal cortical border of the mandible; D4, distance from the MIC to the lingual cortical border of the mandible; D5, distance from the MIC to the lower margin of mandible; ab, length of the MIC (length of curve).
Please cite this article in press as: Kong N, et al. Mandibular incisive canal in Han Chinese using cone beam computed tomography, Int J Oral Maxillofac Surg (2016), http://dx.doi.org/10.1016/j.ijom.2016.04.019
YIJOM-3413; No of Pages 5
Mandibular incisive canal in Han Chinese the relative side of the mandible (left and right). The intra-class correlation (ICC) test was also used to test the intra-observer validity and reliability of MIC measurements. The independent samples t-test, the x2 test, and Fisher’s exact test were used to determine the influence of sex. Values of significance were all set at the alpha level of 5% (P < 0.05). The mean values and standard deviations of each measurement were calculated using SPSS version 13.0 software (SPSS Inc., Chicago, IL, USA). Results MIC visibility on OPG and CBCT of 22 subjects (44 hemimandibles)
On comparison of the CBCT and OPG images of 22 subjects (44 sides), there was no statistical difference with regard to site or sex. A MIC was identified in 38.6% of OPG images, with good clarity in 13.6%, and in 100% of CBCT images, with good clarity in 63.6%. There were statistically significant differences in visibility and in clarity of the MIC between OPG and CBCT (P < 0.001).
MIC measurements on CBCT of 50 subjects (100 hemimandibles)
On assessment of the CBCT images of 50 subjects (100 sides), the vertical distances from the MIC to the lower margin of the mandible at the second premolar and first premolar differed significantly according to sex (independent samples t-test, P < 0.05). The mean distance from the MIC to the lower margin at the second premolar was 11.34 mm in males and 8.75 mm in females; the mean distance at the first premolar was 9.44 mm in males and 8.43 mm in females. The distances were longer in males. No statistically significant difference with regard to the relative side of the mandible (left and right) was found (P > 0.05). The MIC started at the mental foramen in 100% of cases and ended below the incisors in 76% of cases. The left and right MIC connected mutually in seven subjects. The left and right MIC of eight subjects (16%) finally ascended to the alveolar crest at or near the midline of the mandible. Connections of small ascending branches occurred in four subjects (8%). The mean length of the MIC was 17.84 mm (range 9.61–35.74 mm) in the left mandible and 17.73 mm (range 5.93–40.35 mm) in the right mandible. As shown in Table 1, the diameter of the MIC decreased gradually from origin to
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Table 1. Horizontal and vertical diameters of the mandibular incisive canal (mean SD, millimetres). Site
Number
Horizontal diameter
Vertical diameter
100 16 100 97 76 34 100
2.16 0.58 1.97 0.55 1.53 0.51 1.16 0.28 0.93 0.26 0.76 0.21 0.84 0.23
2.15 0.62 2.08 0.61 1.47 0.49 1.17 0.27 1.00 0.38 0.73 0.29 0.89 0.34
Origin Second premolar First premolar Canine Lateral incisor Central incisor End SD, standard deviation.
Table 2. Horizontal distances from the mandibular incisive canal to the buccal and lingual cortical borders (mean SD, millimetres). Site Origin Second premolar First premolar Canine Lateral incisor Central incisor End
Number
Buccal
Lingual
100 16 100 97 76 34 100
2.97 0.83 3.01 0.75 4.05 1.14 4.65 1.28 4.15 1.13 4.25 1.18 4.21 1.22
5.25 1.52 5.60 1.61 4.94 1.29 5.11 1.43 6.27 1.40 6.33 1.96 5.96 1.66
SD, standard deviation.
end. Only 8% of the subjects with large MIC diameters (>1 mm) reached the middle part of the mandible. The mean distances from the MIC to the buccal cortical border of the mandible at the second premolar, first premolar, canine, lateral incisor, and central incisor were shorter than those from the MIC to the lingual cortical border (Table 2). The mean distance from the MIC to the tooth apex was >7 mm for each tooth. The mean distance from the MIC to the alveolar crest was longer than that to the lower margin of the mandible for each tooth (Table 3). Thus, the MIC in the mandible was close to the buccal border and lower margin. There was no statistically significant difference in intra-observer reliability using the paired t-test, the x2 test, or Fisher’s exact test (P > 0.05). The ICC value was 0.849, indicating good intra-observer validity and reliability.
Discussion
The mandibular incisive nerve provides innervation to the lower anterior teeth and surrounding mucosa. However, the MIC is usually overlooked since its bony corticalization is poorer and its diameter smaller than those of the mandibular canal.5,6 The MIC can be identified well in cadavers.12 Mardinger et al. reported that a mandibular incisive bundle was anatomically found in all hemimandibles of cadavers.6 However, conventional two-dimensional images often fail to show the MIC. Jacobs et al. reported that the incisive canal was identified in 15% of panoramic radiographs, with good visibility in only 1%.13 Jalili et al. observed the MIC in 51.7% of panoramic radiographs, which may be the highest reported percentage.14 Some studies have indicated the usefulness of high-resolution magnetic resonance imaging for microanatomical
Table 3. Vertical distances from the mandibular incisive canal to the apex, alveolar crest, and lower margin of the mandible (mean SD, millimetres). Site Origin Second premolar First premolar Canine Lateral incisor Central incisor End
Number
Root apex
Alveolar crest
Lower margin
100 16 100 97 76 34 100
10.21 4.00a 11.92 4.20 8.81 3.43 7.74 3.22 9.51 3.70 8.02 4.03 8.04 4.02b
17.86 2.60 20.78 2.48 20.04 3.28 20.44 3.26 18.48 3.72 16.23 3.15 17.72 4.17
9.92 1.64 10.04 1.73 8.92 1.62 8.21 2.15 10.18 2.80 12.39 3.62 11.50 3.92
SD, standard deviation. a Number of distances from the MIC to the root apex was 12 at the origin. b Number of distances from the MIC to the root apex was 50 at the end.
Please cite this article in press as: Kong N, et al. Mandibular incisive canal in Han Chinese using cone beam computed tomography, Int J Oral Maxillofac Surg (2016), http://dx.doi.org/10.1016/j.ijom.2016.04.019
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studies of the mandibular incisive nerve. However, this technology is not in widespread use because of its limited scanning volume, long waiting time, high cost, and limited availability.15 CBCT is particularly suitable for the mandible since it enables the 3D reconstruction of high-resolution images of the entire mandible. Excellent imaging of the mandible and mandibular canal has been reported for CBCT, along with a high accuracy of linear measurements and a low radiation dose and lower cost compared to multi-slice computed tomography.7 Timock et al. found that CBCT could be used to quantitatively assess buccal bone height and thickness with high precision.16 Al-Ani et al. observed a MIC in the CBCT images of all 60 patients examined.17 In the present study, a MIC was identified in 38.6% of panoramic radiographs and 100% of CBCT images obtained from Han Chinese subjects; the Han Chinese comprise about one-sixth of the world’s population. Other studies by researchers from Greece, the USA, Belgium, Malaysia, Germany, and elsewhere have reported a high percentage of MIC detection in CBCT images.8,11,15,17,18 The MIC is an anatomical structure in the mandible. It has been suggested that CBCT should be a regular examination before any interventions in the anterior mandible. Mardinger et al. dissected hemimandibles to explore the MIC.6 They found that the diameter of the MIC decreased from its origin to end. Makris et al.8 in Greece and Pires et al.11 in the USA reported that the MIC was closer to the buccal border than the lingual border. The results of the present study showed that the MIC was closer to the buccal border in the Han Chinese subjects. In the vertical direction, the MIC was located in the lower segments of the mandible, a finding that is consistent with those of studies performed in the populations of Malaysia and Turkey.17,19 Little difference was noted in a comparison of MIC diameter and location between this study and previous studies involving subjects of other races. However, the length of the MIC in this study was longer than those reported in some other studies: 17.84 mm in the left mandible and 17.73 mm in the right mandible.17 This might be due to the subjects selected. For inclusion in the present study, the subjects had to be healthy adults with all teeth present and no obvious disease in the interforaminal region, while other studies have included dentate or edentulous patients with a wide range of ages. Bone resorption frequently occurs in edentulous patients.
Fig. 3. Preoperative and postoperative CBCT of incisor implants (white arrows, mental foramen; red arrows, mandibular incisive canal; blue arrows, implants).
Anterior mandibular teeth are often lost as a result of trauma or periodontal disease. Implant therapy has become a widely used treatment in this region. The anterior mandible has been considered an ideal implant site for decades. However, complications have been reported in the anterior lower jaw. Lee et al. described intraoperative complications resulting from injury to the structures within the MIC and the use of an active haemostatic matrix to manage these complications.20 Ku¨tu¨k et al.21 and Abarca et al.2 reported that patients complained of discomfort after implant surgery in the anterior mandible and attributed this complication to direct or indirect injury to the mandibular incisive nerve. In the present study, the MIC had a large diameter at the alveolar crest in 8% of subjects. In such cases, the implant may touch the MIC and cause complications. Figure 3 shows the CBCT images of a 56-year-old female patient who complained of pain for 7 months after incisor implants were inserted; she was treated at the study hospital in Nanjing on December 1, 2012. On imaging, it was found that the left implant was touching the MIC. The results of the present study showed that the mean distance from the MIC to the apex of each tooth was >7 mm and that the mean distance from the MIC to the alveolar crest was >16.23 mm. In such circumstances, the implant is not likely to touch the MIC.
However, vertical bone resorption often occurs, and in such cases the distance from the MIC to the alveolar crest may be greatly reduced. This serves as a reminder that implants should be inserted in a timely manner. Since the MIC is close to the buccal ridge, implant insertions should be inclined slightly towards the lingual border. The chin bone graft is a good choice for patients with insufficient bone volume due to its relatively low cost and osteoinductive, osteoconductive, and non-immunogenic properties. Neurosensory disturbances have been found to occur with defined safety margins of 5 mm anterior to the mental foramen, 5 mm below the tooth apex, and 5 mm above the lower border of the mandible.22 Joshi investigated the most likely reason for the paresthesia and reported it to be neurapraxia of the incisive nerve or the terminal branches of the mental nerve when the chin bone was harvested.23 Figure 4 shows the CBCT images of a 34year-old male patient who complained of pain and numbness of the surrounding tissue for more than 1 year after a bone graft was harvested from the right chin; this patient was treated at the study hospital in Nanjing on January 21, 2011. On CBCT imaging, injury to the right MIC was evident at the harvest site. Pommer et al. have suggested new safety margins to protect the MIC: at least 8 mm below the tooth apices and a maximum harvest depth of 4 mm.22
Fig. 4. Postoperative CBCT following bone harvesting from the right chin (green arrows, mandibular canal; white arrows, mental foramen; red arrows, mandibular incisive canal; blue arrows, chin bone harvest site; yellow arrows, harvest site touching the mandibular incisive canal). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of the article.)
Please cite this article in press as: Kong N, et al. Mandibular incisive canal in Han Chinese using cone beam computed tomography, Int J Oral Maxillofac Surg (2016), http://dx.doi.org/10.1016/j.ijom.2016.04.019
YIJOM-3413; No of Pages 5
Mandibular incisive canal in Han Chinese In this study, the mean distances from the MIC to the tooth apex at the first premolar, canine, lateral incisor, and central incisor were over 7.74 mm, and the mean distances from the MIC to the lower margin were over 8.21 mm, thus there could be sufficient space for a chin bone graft to be harvested above or below the MIC. The harvest site could be adjusted according to the position of the MIC on CBCT. In this study, the MIC was found to be close to the buccal cortical border, with the longest distance being 4.65 mm. Thus the depth should be limited to 4 mm during chin bone harvesting. Funding
This work was supported by the National Natural Science Foundation of China (81271109). Competing interests
None declared. Ethical approval
The study received ethical approval ([2011]10) from the Medical Ethics Committee of the Affiliated Stomatological Hospital of Nanjing Medical University. Patient consent
Informed consent was obtained from each subject. Acknowledgement. The authors thank Tao Chen for his contribution to the statistical analysis.
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Address: Ning Chen and Yi-fei Du Institute of Stomatology Nanjing Medical University No. 140 Han Zhong Road Nanjing 210029 Jiangsu People’s Republic of China Tel: +86 25 85031856 (N. Chen); Tel: +86 25 85031914 (Y. Du) E-mail: [email protected]
Please cite this article in press as: Kong N, et al. Mandibular incisive canal in Han Chinese using cone beam computed tomography, Int J Oral Maxillofac Surg (2016), http://dx.doi.org/10.1016/j.ijom.2016.04.019