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British Journal of Oral and Maxillofacial Surgery 53 (2015) 347–351
Multivariate assessment of site of lingual nerve G.J. Dias a,∗ , R.K. de Silva b , T. Shah c , E. Sim c , N. Song c , S. Colombage c , J. Cornwall a a b c
Department of Anatomy, University of Otago, Dunedin, New Zealand Department of Oral Diagnostic and Surgical Sciences, Faculty of Dentistry, University of Otago, Dunedin, New Zealand Department of Health Services, Ministry of Health, Sri Lanka
Accepted 15 January 2015 Available online 7 February 2015
Abstract Injury to the lingual nerve can cause debilitating symptoms. The nerve lies in the retromolar region and its anatomical site can vary within patients and according to sex, age, and dentate status. To our knowledge, no previous studies have recorded its course from multiple bony landmarks and examined the association between age, dentate status, and sex, in the same sample. We dissected 30 white cadavers and took primary and secondary reference points from the internal oblique ridge. We measured the distance to the lingual nerve in sagittal, vertical, and horizontal planes, and recorded the position where the nerve was closest to the lingual plate. We dissected 46 hemimandibles (23 male, mean age 79 years, range 52–100) of which 26 were from the left side. Mean (SD) sagittal, vertical, and horizontal distances from the primary reference point were 9.29 (3.41) mm, 9.15 (3.87) mm, and 0.57 (0.56) mm, respectively. Mean (SD) vertical and horizontal distances from the secondary point were 7.79 (5.45) mm and 0.59 (0.64) mm, respectively. The proximity of the nerve to the lingual plate varied widely (range −13.00 to 15.17 mm from the primary reference point). Dentate status was significant for the sagittal measurement from the primary point, and the vertical measurement from the secondary point. Differences in age, sex, or site of the contralateral nerve were not significant (n = 16 pairs). Our findings suggest that the site of the nerve is consistent between and within subjects for sex and age, but not for dentate status. The association between the nerve and the lingual plate varied, which suggests that care must be taken when operating in the area. © 2015 The British Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Keywords: Lingual nerve; Cadaver; Anatomy; Morphology; Oral surgery
Introduction The lingual nerve can be injured when wisdom teeth are extracted, the jaw resected, when grafting the alveolar crest, operating on the salivary glands, inserting implants, and excising tumours.1–6 Injury can occur when a lingual flap is raised,7 when a nerve is retracted, and during intubation. It can also result from physical trauma or neurotoxicity of local anaesthesia,8,9 and when a burr is used to remove ∗ Corresponding author at: Department of Anatomy, University of Otago, PO Box 56, Dunedin, New Zealand. E-mail addresses: [email protected] (G.J. Dias), [email protected] (J. Cornwall).
bone because of the increased likelihood of perforating the lingual plate.1 The incidence of such complications varies from 0.04% to 22%.3,4,6 Nerves that lie on or above the alveolar ridge and those with variable branches can also be damaged,1–5,9–11 but this can be prevented if lingually extended incisions are avoided. Incisions made in the superior-lateral direction along the external oblique ridge are said to be among the safest.2,9 Severed nerves have little chance of healing.12 Damage can result in hypoaesthesia, hyperaesthesia, anaesthesia, and dysaesthesia of the anterior two-thirds of the tongue,4,13 and taste can be affected because the chorda tympani nerve runs within the sheath of the lingual nerve.1,3–5 In most cases the effects are temporary (the risk of permanent damage is
http://dx.doi.org/10.1016/j.bjoms.2015.01.011 0266-4356/© 2015 The British Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
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around 1:2 million).3 An extensive knowledge of the position of the nerve in the mandibular third molar region is therefore essential to avoid iatrogenic injury. Studies suggest that the actual distance from the lingual nerve to the mandible varies widely:10,14 mean horizontal distances of the nerve from the lingual plate range from 0.59 mm to 4.19 mm, and mean vertical distances to the lingual crest range from 0.52 mm to 15.5 mm below.1–3,5,14 The nerve is also described variously as having symmetry or not having symmetry within people,1,2 and it is suggested that sex has no effect on its site.2 However, it is difficult to interpret and compare previous studies. Bony landmarks used for measurements are inconsistent and uncontrolled. Measurements are taken in many different directions, and to our knowledge, ethnicity is mentioned in few but assessed in none,9,10 In others, radiographic divergence is not given,5 and some studies have very small sample sizes.14 Dentate status is mentioned in few and analysed, to our knowledge, in only 2 despite the many studies that use cadavers of elderly people.1,3 We know of only one that examined the effect of sex on the site of the nerve,2 and none that have recorded its course from multiple bony landmarks and examined the association between age, dentate status, and sex in the same sample. Our study aims to provide comprehensive details of the anatomical site of the nerve and to provide information that may minimise the potential for iatrogenic damage during oral operations.
Method We divided 30 heads from elderly white cadavers (embalmed with a commercially available embalming mix) in the sagittal plane. The study followed the Declaration of Helsinki on medical protocol and ethics, and met the requirements of the University of Otago. Cadavers were donated in accordance with the New Zealand Human Tissue Act (2008). We excluded those with disease or damage to the area or the surrounding structures (particularly the submandibular gland), those that had lost genioglossal attachment to the superior mental spine, and those that had had resection or reconstructive operations in the area. A total of 46 hemimandibles remained. The deep primary incision began at the lingual aspect of the body of the mandible (in the region of the lower canine) along the mucogingival junction posteriorly and superiorly to the inferior part of the coronoid process. We made a superficial secondary incision in the mucosa that continued from the primary incision medially to meet the palatoglossal arch then made an incision inferiorly to the lateral border of the tongue that extended to the lower canine. This created a mucosal flap attached at the lingual sulcus in the lower canine region. We carefully removed the flap using blunt dissection so as not to displace any tissues. The nerve was exposed but not dissected to maintain its anatomical association with adjacent
Fig. 1. Medial view (A) and occusal view (B) of a left hemimandible showing landmarks and measurement details (1◦ = primary reference point; 2◦ = secondary reference point; LN = lingual nerve; X = emergence of lingual nerve below the lateral pterygoid muscle).
Fig. 2. Coronal section through the mandible at primary (A) and secondary (B) reference points showing measurement points (1◦ = primary reference point; 2◦ = secondary reference point; LN = lingual nerve).
structures. We then raised the periosteum over the mandibular alveolar ridge. Measurements from 2 hard-tissue reference points were taken with digital callipers. The primary reference point (1◦ ) (Fig. 1A) was the position of transition from the horizontal to the vertical on the internal oblique line (deepest point of the internal oblique line). Horizontal measurements were based on the occlusal plane; vertical measurements were perpendicular to the horizontal. Sagittal measurements were based on the plane of the mandibular ramus. The secondary reference point (2◦ ) (Fig. 1A) was 1 cm anterior to 1◦ in the sagittal plane on the alveolar ridge. The 6 measurements are shown in Table 1. All measurements were taken by all 3 operators and final values were agreed by consensus. Data were recorded on a spreadsheet. Pearson’s correlation coefficient was used to assess association with age, and multiple and paired t tests were done to assess for symmetry. Statistical analyses were done using STATA statistical software (StataCorp LP, College Station, USA). Probabilities of less than 0.05 were considered significant.
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349
Table 2 Summary of measurements (mm).
Results
No. of samples
Descriptive data
Mean (SD)
Range
There were 46 hemisectioned mandibles, 23 each from male and female cadavers. A total of 32 mandibles were edentulous in the molar and premolar area, 14 had either the second or the third molar present and they had minimal residual resorption of the ridge. There were 26 nerves from the left and 20 from the right. The mean age at death was 79 years (range 52–100). The mean (SD) and range for each variable are shown in Table 2. In all cases, the lingual nerve emerged below the lower border of lateral pterygoid muscle posterior to the primary reference point in the sagittal direction from the point S1◦ a. None were found above or at the level of the ridge at the primary reference point in the vertical direction. In the horizontal direction (H1◦ ), 9 of the 46 nerves (20%) were in direct contact with the lingual plate at the primary reference point. At the secondary reference point, 3 (7%) were above or level with the lingual crest, and the nerve was in contact with the lingual plate in 12 cases (26%). The closest point from the nerve to the lingual plate in relation to point 1◦ in the anteroposterior direction varied widely in the sagittal plane (−13.00 mm posterior to point 1◦ to 15.17 mm anterior to point 1◦ ) (Table 2).
Vertical (V1◦ ) Horizontal (H1◦ ) Sagittal (S1◦ a): Edentulous Dentulous Closest point (S1◦ b) Vertical from 2◦ (V2◦ ): Edentulous Dentulous Horizontal from 2◦ (H2◦ )
Dentate status
Descriptive data
To assess how resorption of the residual ridge affected the site of the nerve, we compared dentulous (n = 14) with edentulous (n = 32) samples. Differences in the sagittal measurement from the primary reference point (S1◦ a) (p < 0.001) and in the vertical measurement from the secondary reference point (V2◦ ) (p < 0.001) were significant. Where there were significant differences within the sample population these subpopulations are presented separately (Table 2). From the primary reference point in the sagittal direction in an edentulous mandible, the nerve often emerged 3.56 mm further back than in a dentulous mandible (t(31) = −4.05, p = 0.0003). Vertically from the secondary reference point, it was about
We found that the mean (SD) vertical distance of the lingual nerve from the alveolar ridge at the retromolar region was 9.1 mm (3.87), similar to observations by Pogrel et al.1 Of the 46 nerves, 9 were in contact with the lingual plate at the primary reference point, and 12 at the secondary reference point. For white people in New Zealand, the nerve therefore has some protection in the vertical dimension as it is usually suspended under the trigone area. In agreement with many other studies,2,3,9,15 it is very close to the lingual plate in the horizontal direction, and can lie in this position over a large anterior-posterior distance (28.17 mm). This suggests that great care is needed when operating in the lingual aspect
46 46
9.15 (3.87) 0.57 (0.56)
2.33–17.50 0–2.50
32 14 46
10.37 (3.20) 6.81 (2.51) 1.88 (6.42)
2.67–17.50
32 14 46
6.34 (5.6) 11.1 (3.31) 0.59 (0.64)
−13.00–15.17 –5.33–17.67 0–2.50
4.75 mm closer to the lingual crest in an edentulous than a dentulous mandible (t(40) = 3.58, p = 0.0009). Symmetry, age, and sex Differences in the site of the nerve between the left and right sides of the same cadaver (n = 16, 8 male) were not significant. Age or sex did not correlate significantly for any variable.
Discussion
Table 1 Measurements taken, abbreviation, and figure where illustrated.
1 2 3 4 5 6
Measurement
Abbreviation
Figures
Vertical distance from the alveolar crest to the superior-most part of the lingual nerve at 1◦ Vertical distance from the alveolar crest to the superior-most part of the lingual nerve at 2◦ Horizontal distance from the most medial part of the lingual plate of the mandible to the lateral-most part of the lingual nerve at 1◦ Horizontal distance from the most medial part of the lingual plate of the mandible to the lateral-most part of the lingual nerve at 2◦ Distance between the lingual nerve (where it emerges below the lower border of the lateral pterygoid muscle) and 1◦ in the sagittal plane Distance in the sagittal plane between 1◦ and the point in the sagittal plane that coincides with the closest horizontal distance between the lingual nerve and the lingual plate of the mandible
V1◦
2A
V2◦
2B
H1◦
2A
H2◦
2B
S1◦ a
1A
S1◦ b
1B
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of retromolar and molar areas in elderly white people, and surgeons should assume that the nerve is in contact with the lingual plate somewhere in this region. Other comparisons with existing data are not possible because of differences in measuring techniques. Our choice of primary reference point on the internal oblique ridge where it changes from a vertical to a horizontal course was based on easy identification. The landmark is also important to clinicians who may be operating in the retromolar area as it generally corresponds to the retromolar pad. Measurements at the secondary reference point provided us with further information on the spatial relation between the nerve and the mandible along the mandibular body (which is particularly important given the common nature of oral procedures in this region), and our results should help clinicians identify the nerve more easily in this area. Dentate status There were significant differences in the site of the nerve in relation to dentate status. We know of few studies that have previously reported on this variable, Pogrel et al.1 indicated no difference, but Hölzle and Wolff found the nerve closer to the lingual mandibular crest. Our findings support those of Hölzle and Wolff because the lingual crest is likely to approximate the position of the nerve as the alveolar bone becomes resorbed in edentulous mandibles. Surprisingly, in edentulous mandibles there was also a significant difference in the position between the primary reference point and the point at which the nerve emerged (below the lateral pterygoid) into the retromolar region. It is not clear why such a difference exists, but it is thought that the resorption of bone contributes to the reshaping of the mandible in such a way as to affect the measurement. Clinicians should be aware of potential differences in the site of the nerve between dentate and edentulous populations. Symmetry, age, and sex We found no significant differences for any variables measured between sides. This corroborates the findings of one study,2 and contradicts those of Pogrel et al.1 We found no significant differences between age or sex for the site of the nerve, although increased age was a risk factor for damage.6 This suggests that variables other than anatomical site may contribute to the association between injury and age. Limitations Donated cadavers were from an elderly population, so it is not clear how well the results will transfer to younger groups. Some anatomical variation may be attributed to racial or genetic factors,5 but as donated cadavers in New Zealand are consistently white,16 it gives some validity to our findings being representative of a single ethnic population. However, it is not clear whether the results are transferable to other ethnic
groups, and surgeons should be mindful of the potential for variation.17 Conclusion To provide additional information on the anatomical site of the lingual nerve, further research is required to investigate the variables studied across different ethnic groups. Conflict of interest The authors declare they have no conflict of interest. Ethics statement The study uses cadavers and complies with local University ethics requirements. Acknowledgements Prof. Peter Herbison (biostatistician) for assistance with statistical analyses, and Mr David Stiles for co-ordinating the dissections. References 1. Pogrel MA, Renaut A, Schimdt B, et al. The relationship of the lingual nerve to the mandibular third molar region: an anatomic study. J Oral Maxillofac Surg 1995;53:1178–81. 2. Behnia H, Kheradvar A, Shahrokhi M. An anatomic study of the lingual nerve in the third molar region. J Oral Maxillofac Surg 2000;58:649–53. 3. Hölzle FW, Wolff KD. Anatomic position of the lingual nerve in the mandibular third molar region with special consideration of an atrophied mandibular crest: an anatomical study. Int J Oral Maxillofac Surg 2001;30:333–8. 4. Gomes AC, Vasconcelos BC, de Oliveira e Silva ED, et al. Lingual nerve damage after mandibular third molar surgery: a randomized control trial. J Oral Maxillofac Surg 2005;63:1443–6. 5. Karakas P, Uzel M, Koebke J. The relationship of the lingual nerve to the third molar region using radiographic imaging. Br Dent J 2007;203:29–31. 6. Leung YY, Cheung LK. Risk factors of neurosensory deficits in lower third molar surgery: a literature review of prospective studies. Int J Oral Maxillofac Surg 2011;40:1–10. 7. Berini-Aytes L, Valmaseda-Castellon E, Gay-Escoda C. Lingual Nerve Damage After Third Lower Molar Surgical Extraction. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2000;90(5):567–73. 8. Renton T, McGurk M. Evaluation of factors predictive of lingual nerve injury in third molar surgery. Br J Oral Maxillofac Surg 2001;39:423–8. 9. Erdogmus S, Govsa F, Celik S. Anatomic position of the lingual nerve in the mandibular third molar region as potential risk factors for nerve palsy. J Craniofac Surg 2008;19:264–70. 10. Kim SY, Hu KS, Chung IH, et al. Topographic anatomy of the lingual nerve and variations in communication pattern of the mandibular nerve branches. Surg Radiol Anat 2004;26:128–35. 11. Benninger B, Kloenne J, Horn JL. Clinical anatomy of the lingual nerve and identification with ultrasonography. Br J Oral Maxillofac Surg 2013;51:541–4.
G.J. Dias et al. / British Journal of Oral and Maxillofacial Surgery 53 (2015) 347–351 12. Loescher AR, Smith KG, Robinson P. Nerve damage and third molar removal. Dent Update 2003;30:375–82. 13. Smith KG, Robinson PP. The re-innervation of the tongue and salivary glands after lingual nerve repair by stretch, sural nerve graft or frozen muscle graft. J Dent Res 1995;74:1850–60. 14. Trost O, Kazemi A, Cheynel N, et al. Spatial relationships between lingual nerve and mandibular ramus: original study method, clinical and educational applications. Surg Radiol Anat 2009;31:447–52.
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15. Kiesselbach JE, Chamberlain JG. Clinical and anatomic observations on the relationship of the lingual nerve to the mandibular third molar region. J Oral Maxillofac Surg 1984;42:565–7. 16. Cornwall J, Perry GF, Louw G, et al. Who donates their body to science? An international, multicenter, prospective study. Anat Sci Educ 2012;5:208–16. 17. Dennison J. Polynesian dentition. Athropol Anz 2007;65:353–63.
British Journal of Oral and Maxillofacial Surgery 53 (2015) 347–351
Multivariate assessment of site of lingual nerve G.J. Dias a,∗ , R.K. de Silva b , T. Shah c , E. Sim c , N. Song c , S. Colombage c , J. Cornwall a a b c
Department of Anatomy, University of Otago, Dunedin, New Zealand Department of Oral Diagnostic and Surgical Sciences, Faculty of Dentistry, University of Otago, Dunedin, New Zealand Department of Health Services, Ministry of Health, Sri Lanka
Accepted 15 January 2015 Available online 7 February 2015
Abstract Injury to the lingual nerve can cause debilitating symptoms. The nerve lies in the retromolar region and its anatomical site can vary within patients and according to sex, age, and dentate status. To our knowledge, no previous studies have recorded its course from multiple bony landmarks and examined the association between age, dentate status, and sex, in the same sample. We dissected 30 white cadavers and took primary and secondary reference points from the internal oblique ridge. We measured the distance to the lingual nerve in sagittal, vertical, and horizontal planes, and recorded the position where the nerve was closest to the lingual plate. We dissected 46 hemimandibles (23 male, mean age 79 years, range 52–100) of which 26 were from the left side. Mean (SD) sagittal, vertical, and horizontal distances from the primary reference point were 9.29 (3.41) mm, 9.15 (3.87) mm, and 0.57 (0.56) mm, respectively. Mean (SD) vertical and horizontal distances from the secondary point were 7.79 (5.45) mm and 0.59 (0.64) mm, respectively. The proximity of the nerve to the lingual plate varied widely (range −13.00 to 15.17 mm from the primary reference point). Dentate status was significant for the sagittal measurement from the primary point, and the vertical measurement from the secondary point. Differences in age, sex, or site of the contralateral nerve were not significant (n = 16 pairs). Our findings suggest that the site of the nerve is consistent between and within subjects for sex and age, but not for dentate status. The association between the nerve and the lingual plate varied, which suggests that care must be taken when operating in the area. © 2015 The British Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Keywords: Lingual nerve; Cadaver; Anatomy; Morphology; Oral surgery
Introduction The lingual nerve can be injured when wisdom teeth are extracted, the jaw resected, when grafting the alveolar crest, operating on the salivary glands, inserting implants, and excising tumours.1–6 Injury can occur when a lingual flap is raised,7 when a nerve is retracted, and during intubation. It can also result from physical trauma or neurotoxicity of local anaesthesia,8,9 and when a burr is used to remove ∗ Corresponding author at: Department of Anatomy, University of Otago, PO Box 56, Dunedin, New Zealand. E-mail addresses: [email protected] (G.J. Dias), [email protected] (J. Cornwall).
bone because of the increased likelihood of perforating the lingual plate.1 The incidence of such complications varies from 0.04% to 22%.3,4,6 Nerves that lie on or above the alveolar ridge and those with variable branches can also be damaged,1–5,9–11 but this can be prevented if lingually extended incisions are avoided. Incisions made in the superior-lateral direction along the external oblique ridge are said to be among the safest.2,9 Severed nerves have little chance of healing.12 Damage can result in hypoaesthesia, hyperaesthesia, anaesthesia, and dysaesthesia of the anterior two-thirds of the tongue,4,13 and taste can be affected because the chorda tympani nerve runs within the sheath of the lingual nerve.1,3–5 In most cases the effects are temporary (the risk of permanent damage is
http://dx.doi.org/10.1016/j.bjoms.2015.01.011 0266-4356/© 2015 The British Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
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G.J. Dias et al. / British Journal of Oral and Maxillofacial Surgery 53 (2015) 347–351
around 1:2 million).3 An extensive knowledge of the position of the nerve in the mandibular third molar region is therefore essential to avoid iatrogenic injury. Studies suggest that the actual distance from the lingual nerve to the mandible varies widely:10,14 mean horizontal distances of the nerve from the lingual plate range from 0.59 mm to 4.19 mm, and mean vertical distances to the lingual crest range from 0.52 mm to 15.5 mm below.1–3,5,14 The nerve is also described variously as having symmetry or not having symmetry within people,1,2 and it is suggested that sex has no effect on its site.2 However, it is difficult to interpret and compare previous studies. Bony landmarks used for measurements are inconsistent and uncontrolled. Measurements are taken in many different directions, and to our knowledge, ethnicity is mentioned in few but assessed in none,9,10 In others, radiographic divergence is not given,5 and some studies have very small sample sizes.14 Dentate status is mentioned in few and analysed, to our knowledge, in only 2 despite the many studies that use cadavers of elderly people.1,3 We know of only one that examined the effect of sex on the site of the nerve,2 and none that have recorded its course from multiple bony landmarks and examined the association between age, dentate status, and sex in the same sample. Our study aims to provide comprehensive details of the anatomical site of the nerve and to provide information that may minimise the potential for iatrogenic damage during oral operations.
Method We divided 30 heads from elderly white cadavers (embalmed with a commercially available embalming mix) in the sagittal plane. The study followed the Declaration of Helsinki on medical protocol and ethics, and met the requirements of the University of Otago. Cadavers were donated in accordance with the New Zealand Human Tissue Act (2008). We excluded those with disease or damage to the area or the surrounding structures (particularly the submandibular gland), those that had lost genioglossal attachment to the superior mental spine, and those that had had resection or reconstructive operations in the area. A total of 46 hemimandibles remained. The deep primary incision began at the lingual aspect of the body of the mandible (in the region of the lower canine) along the mucogingival junction posteriorly and superiorly to the inferior part of the coronoid process. We made a superficial secondary incision in the mucosa that continued from the primary incision medially to meet the palatoglossal arch then made an incision inferiorly to the lateral border of the tongue that extended to the lower canine. This created a mucosal flap attached at the lingual sulcus in the lower canine region. We carefully removed the flap using blunt dissection so as not to displace any tissues. The nerve was exposed but not dissected to maintain its anatomical association with adjacent
Fig. 1. Medial view (A) and occusal view (B) of a left hemimandible showing landmarks and measurement details (1◦ = primary reference point; 2◦ = secondary reference point; LN = lingual nerve; X = emergence of lingual nerve below the lateral pterygoid muscle).
Fig. 2. Coronal section through the mandible at primary (A) and secondary (B) reference points showing measurement points (1◦ = primary reference point; 2◦ = secondary reference point; LN = lingual nerve).
structures. We then raised the periosteum over the mandibular alveolar ridge. Measurements from 2 hard-tissue reference points were taken with digital callipers. The primary reference point (1◦ ) (Fig. 1A) was the position of transition from the horizontal to the vertical on the internal oblique line (deepest point of the internal oblique line). Horizontal measurements were based on the occlusal plane; vertical measurements were perpendicular to the horizontal. Sagittal measurements were based on the plane of the mandibular ramus. The secondary reference point (2◦ ) (Fig. 1A) was 1 cm anterior to 1◦ in the sagittal plane on the alveolar ridge. The 6 measurements are shown in Table 1. All measurements were taken by all 3 operators and final values were agreed by consensus. Data were recorded on a spreadsheet. Pearson’s correlation coefficient was used to assess association with age, and multiple and paired t tests were done to assess for symmetry. Statistical analyses were done using STATA statistical software (StataCorp LP, College Station, USA). Probabilities of less than 0.05 were considered significant.
G.J. Dias et al. / British Journal of Oral and Maxillofacial Surgery 53 (2015) 347–351
349
Table 2 Summary of measurements (mm).
Results
No. of samples
Descriptive data
Mean (SD)
Range
There were 46 hemisectioned mandibles, 23 each from male and female cadavers. A total of 32 mandibles were edentulous in the molar and premolar area, 14 had either the second or the third molar present and they had minimal residual resorption of the ridge. There were 26 nerves from the left and 20 from the right. The mean age at death was 79 years (range 52–100). The mean (SD) and range for each variable are shown in Table 2. In all cases, the lingual nerve emerged below the lower border of lateral pterygoid muscle posterior to the primary reference point in the sagittal direction from the point S1◦ a. None were found above or at the level of the ridge at the primary reference point in the vertical direction. In the horizontal direction (H1◦ ), 9 of the 46 nerves (20%) were in direct contact with the lingual plate at the primary reference point. At the secondary reference point, 3 (7%) were above or level with the lingual crest, and the nerve was in contact with the lingual plate in 12 cases (26%). The closest point from the nerve to the lingual plate in relation to point 1◦ in the anteroposterior direction varied widely in the sagittal plane (−13.00 mm posterior to point 1◦ to 15.17 mm anterior to point 1◦ ) (Table 2).
Vertical (V1◦ ) Horizontal (H1◦ ) Sagittal (S1◦ a): Edentulous Dentulous Closest point (S1◦ b) Vertical from 2◦ (V2◦ ): Edentulous Dentulous Horizontal from 2◦ (H2◦ )
Dentate status
Descriptive data
To assess how resorption of the residual ridge affected the site of the nerve, we compared dentulous (n = 14) with edentulous (n = 32) samples. Differences in the sagittal measurement from the primary reference point (S1◦ a) (p < 0.001) and in the vertical measurement from the secondary reference point (V2◦ ) (p < 0.001) were significant. Where there were significant differences within the sample population these subpopulations are presented separately (Table 2). From the primary reference point in the sagittal direction in an edentulous mandible, the nerve often emerged 3.56 mm further back than in a dentulous mandible (t(31) = −4.05, p = 0.0003). Vertically from the secondary reference point, it was about
We found that the mean (SD) vertical distance of the lingual nerve from the alveolar ridge at the retromolar region was 9.1 mm (3.87), similar to observations by Pogrel et al.1 Of the 46 nerves, 9 were in contact with the lingual plate at the primary reference point, and 12 at the secondary reference point. For white people in New Zealand, the nerve therefore has some protection in the vertical dimension as it is usually suspended under the trigone area. In agreement with many other studies,2,3,9,15 it is very close to the lingual plate in the horizontal direction, and can lie in this position over a large anterior-posterior distance (28.17 mm). This suggests that great care is needed when operating in the lingual aspect
46 46
9.15 (3.87) 0.57 (0.56)
2.33–17.50 0–2.50
32 14 46
10.37 (3.20) 6.81 (2.51) 1.88 (6.42)
2.67–17.50
32 14 46
6.34 (5.6) 11.1 (3.31) 0.59 (0.64)
−13.00–15.17 –5.33–17.67 0–2.50
4.75 mm closer to the lingual crest in an edentulous than a dentulous mandible (t(40) = 3.58, p = 0.0009). Symmetry, age, and sex Differences in the site of the nerve between the left and right sides of the same cadaver (n = 16, 8 male) were not significant. Age or sex did not correlate significantly for any variable.
Discussion
Table 1 Measurements taken, abbreviation, and figure where illustrated.
1 2 3 4 5 6
Measurement
Abbreviation
Figures
Vertical distance from the alveolar crest to the superior-most part of the lingual nerve at 1◦ Vertical distance from the alveolar crest to the superior-most part of the lingual nerve at 2◦ Horizontal distance from the most medial part of the lingual plate of the mandible to the lateral-most part of the lingual nerve at 1◦ Horizontal distance from the most medial part of the lingual plate of the mandible to the lateral-most part of the lingual nerve at 2◦ Distance between the lingual nerve (where it emerges below the lower border of the lateral pterygoid muscle) and 1◦ in the sagittal plane Distance in the sagittal plane between 1◦ and the point in the sagittal plane that coincides with the closest horizontal distance between the lingual nerve and the lingual plate of the mandible
V1◦
2A
V2◦
2B
H1◦
2A
H2◦
2B
S1◦ a
1A
S1◦ b
1B
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of retromolar and molar areas in elderly white people, and surgeons should assume that the nerve is in contact with the lingual plate somewhere in this region. Other comparisons with existing data are not possible because of differences in measuring techniques. Our choice of primary reference point on the internal oblique ridge where it changes from a vertical to a horizontal course was based on easy identification. The landmark is also important to clinicians who may be operating in the retromolar area as it generally corresponds to the retromolar pad. Measurements at the secondary reference point provided us with further information on the spatial relation between the nerve and the mandible along the mandibular body (which is particularly important given the common nature of oral procedures in this region), and our results should help clinicians identify the nerve more easily in this area. Dentate status There were significant differences in the site of the nerve in relation to dentate status. We know of few studies that have previously reported on this variable, Pogrel et al.1 indicated no difference, but Hölzle and Wolff found the nerve closer to the lingual mandibular crest. Our findings support those of Hölzle and Wolff because the lingual crest is likely to approximate the position of the nerve as the alveolar bone becomes resorbed in edentulous mandibles. Surprisingly, in edentulous mandibles there was also a significant difference in the position between the primary reference point and the point at which the nerve emerged (below the lateral pterygoid) into the retromolar region. It is not clear why such a difference exists, but it is thought that the resorption of bone contributes to the reshaping of the mandible in such a way as to affect the measurement. Clinicians should be aware of potential differences in the site of the nerve between dentate and edentulous populations. Symmetry, age, and sex We found no significant differences for any variables measured between sides. This corroborates the findings of one study,2 and contradicts those of Pogrel et al.1 We found no significant differences between age or sex for the site of the nerve, although increased age was a risk factor for damage.6 This suggests that variables other than anatomical site may contribute to the association between injury and age. Limitations Donated cadavers were from an elderly population, so it is not clear how well the results will transfer to younger groups. Some anatomical variation may be attributed to racial or genetic factors,5 but as donated cadavers in New Zealand are consistently white,16 it gives some validity to our findings being representative of a single ethnic population. However, it is not clear whether the results are transferable to other ethnic
groups, and surgeons should be mindful of the potential for variation.17 Conclusion To provide additional information on the anatomical site of the lingual nerve, further research is required to investigate the variables studied across different ethnic groups. Conflict of interest The authors declare they have no conflict of interest. Ethics statement The study uses cadavers and complies with local University ethics requirements. Acknowledgements Prof. Peter Herbison (biostatistician) for assistance with statistical analyses, and Mr David Stiles for co-ordinating the dissections. References 1. Pogrel MA, Renaut A, Schimdt B, et al. The relationship of the lingual nerve to the mandibular third molar region: an anatomic study. J Oral Maxillofac Surg 1995;53:1178–81. 2. Behnia H, Kheradvar A, Shahrokhi M. An anatomic study of the lingual nerve in the third molar region. J Oral Maxillofac Surg 2000;58:649–53. 3. Hölzle FW, Wolff KD. Anatomic position of the lingual nerve in the mandibular third molar region with special consideration of an atrophied mandibular crest: an anatomical study. Int J Oral Maxillofac Surg 2001;30:333–8. 4. Gomes AC, Vasconcelos BC, de Oliveira e Silva ED, et al. Lingual nerve damage after mandibular third molar surgery: a randomized control trial. J Oral Maxillofac Surg 2005;63:1443–6. 5. Karakas P, Uzel M, Koebke J. The relationship of the lingual nerve to the third molar region using radiographic imaging. Br Dent J 2007;203:29–31. 6. Leung YY, Cheung LK. Risk factors of neurosensory deficits in lower third molar surgery: a literature review of prospective studies. Int J Oral Maxillofac Surg 2011;40:1–10. 7. Berini-Aytes L, Valmaseda-Castellon E, Gay-Escoda C. Lingual Nerve Damage After Third Lower Molar Surgical Extraction. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2000;90(5):567–73. 8. Renton T, McGurk M. Evaluation of factors predictive of lingual nerve injury in third molar surgery. Br J Oral Maxillofac Surg 2001;39:423–8. 9. Erdogmus S, Govsa F, Celik S. Anatomic position of the lingual nerve in the mandibular third molar region as potential risk factors for nerve palsy. J Craniofac Surg 2008;19:264–70. 10. Kim SY, Hu KS, Chung IH, et al. Topographic anatomy of the lingual nerve and variations in communication pattern of the mandibular nerve branches. Surg Radiol Anat 2004;26:128–35. 11. Benninger B, Kloenne J, Horn JL. Clinical anatomy of the lingual nerve and identification with ultrasonography. Br J Oral Maxillofac Surg 2013;51:541–4.
G.J. Dias et al. / British Journal of Oral and Maxillofacial Surgery 53 (2015) 347–351 12. Loescher AR, Smith KG, Robinson P. Nerve damage and third molar removal. Dent Update 2003;30:375–82. 13. Smith KG, Robinson PP. The re-innervation of the tongue and salivary glands after lingual nerve repair by stretch, sural nerve graft or frozen muscle graft. J Dent Res 1995;74:1850–60. 14. Trost O, Kazemi A, Cheynel N, et al. Spatial relationships between lingual nerve and mandibular ramus: original study method, clinical and educational applications. Surg Radiol Anat 2009;31:447–52.
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15. Kiesselbach JE, Chamberlain JG. Clinical and anatomic observations on the relationship of the lingual nerve to the mandibular third molar region. J Oral Maxillofac Surg 1984;42:565–7. 16. Cornwall J, Perry GF, Louw G, et al. Who donates their body to science? An international, multicenter, prospective study. Anat Sci Educ 2012;5:208–16. 17. Dennison J. Polynesian dentition. Athropol Anz 2007;65:353–63.
