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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: 333–338 doi:10.1054/ijom.2001.0064, available online at http://www.idealibrary.com on
Research paper: Dentoalveolar surgery
Anatomic position of the lingual nerve in the mandibular third molar region with special consideration of an atrophied mandibular crest: an anatomical study
F. W. Ho¨lzle, K.-D. Wolff Arzt fu¨r Mund-, Kiefer- und Gesichtschirurgie, Plastische Operationen, Knappschaftskrankenhaus, Klinikum der Ruhr-Universitat, In der Schornau 23–25, 44892 Bochum
F. W. Ho¨lzle, K.-D. Wolff: 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: 333–338. 2001 International Association of Oral and Maxillofacial Surgeons Abstract. The position of the lingual nerve in the mandibular third molar region was measured and documented in 68 cadaver dissections (34 adult cadaver heads). In 8.8% of the dissections, the lingual nerve was found at or above the level of the alveolar crest. In the horizontal plane, the nerve contacted the lingual plate of the third molar in 57.4% of the specimens. There was also a significant relationship between the degree of mandibular crest atrophy and the distance from the nerve to the molar region. The distance decreased with the degree of atrophy. There was no significant difference between the two sides of the head. These results demonstrate the vulnerability of the lingual nerve as it medially passes the mandibular third molar and may help avoid lingual damage during surgery in the third molar and retromolar region of the mandible.
The anatomic proximity of the lingual nerve to the mandibular third molar region plays an important role in planning and performing surgical interventions in this area. Nerve injury is possible during removal of the third molars, osteotomy of the mandibular branch, alveolar crest graft and by injection of local anaesthesia. Even excision during tumour removal or the sequelae of trauma may injure the nerve1,20,23. There are also reports of lingual par0901-5027/01/040333+06 $35.00/0
esthesia after surgical insertion of implants3. The risk of damaging the lingual nerve during mandibular wisdom tooth surgery differs in the literature. Horch reports an injury incidence of 0.05%10 and H 0.04%. About 250 000 wisdom teeth per year were removed in the 1980’s in the old federal states of Germany. An incidence of 0.05% means 125 nerve lesions per year. The probability of irreversible numbness and
Key words: third molar surgery; nerve injury; lingual paresthesia; protection of the lingual nerve; human anatomy. Accepted for publication 1 April 2001
hypogeusia of one half of the tongue is calculated to be 1:2 million after local anaesthesia9. The incidence of a persistent sensory deficit after osteotomy is reported to be 0.5–2% in English literature4,13,19. A-A gives an 11.5% incidence of reversible dysesthesia after mandibular wisdom tooth surgery2. Thus, extensive knowledge about the position of nerves in the mandibular third molar region is indispensable for surgery in this area.
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A survey of the literature revealed that virtually no detailed descriptions or measurements of the lingual nerve in the lower third molar region have been reported for many years21. In 1984, K & C were the first to perform an exact quantitative evaluation on cadaverous specimens and to attempt atraumatic in vivo exposure of the nerve in 256 wisdom tooth removals to study its course medial to the posterior alveolar crest in the retromolar region12. In 1995, P et al. measured in three dimensions the exact anatomic position of the lingual nerve for the wisdom tooth region. For this, they used a reproducible osseous point, taking the dentulous jaw into account17. There have not yet been any studies considering alveolar crest atrophy in addition to determining a reproducible osseous point as a fixed point for measuring and evaluating dental status. Thus, the aim of this study was to examine whether the lingual nerve has a relatively higher or closer position to the alveolar crest due to mandibular atrophy and is therefore exposed to a higher risk in surgery near the bone. Such an additional risk is possible especially in osteotomies or during implantation. Moreover, the aim was to measure the position of the nerve in the mandibular third molar region in all three dimensions and to examine it for bone contact. Another objective was to determine the distance of the lingual nerve to the typical incision in surgical wisdom tooth removal. According to N & H, the lingual nerve either has a mono- or oligofascicular structure in the pterygomandibular space15. The nerve begins to branch off medial to the posterior molars and has a polyfascicular structure there. The point of ramification is also examined in the present study and placed in relation to a distal fixed point, the mental foramen and the tooth region in dentulous patients. It was also necessary to check the assertion by R & M that anatomic lingual nerve variations are of secondary importance18. Material and methods Thirty-four formalin-fixed heads were divided sagittally. The 68 dissections were prepared as follows: In dentulous mandibles or in those with second molars, a 1 cm long distal relieving incision was made in the direction of the ascending mandibular branch. This
N. alveolaris inf.
N. mylohyoideus B' A' A
B
Distal incision
C
N. lingualis
D X
FK
K2 Foramen mentale
K1
Fig. 1. 3D-Illustration of the measured points and distances.
incision was marginally and mesially lengthened in the lingual region. Starting distally, the lingual mucosa and the periosteum were removed with a bone rasp in the mesial direction. The lingual nerve was demonstrated by blunt dissection but not exposed to prevent changing its anatomic relationship to the adjacent structures. The anterior measuring points and distances were recorded with a precision vernier gage and those more distal and difficult to reach were calipered with a measuring compass. Stepwise dissection was performed in such a way as to reliably obtain measurements without falsifying them by too great a change in the anatomic site. Distances to the nerves were measured from the boundary of the nerve inclining towards the other measuring point. Since the oblique line of the ramus mandibulae in the atrophied mandibular crest is frequently very indistinct, it cannot be used as an orientation or marking aid. Thus, the reproducible transition site of the horizontal to the vertical branch of the ramus mandibulae is more or less fixed as a retromolar pad and defined as osseous measuring point A. Starting at this point, the following measurements were performed, which are demonstrated by the illustration in Fig. 1: + The horizontal distance of the lingual nerve to the lingual mandibular crest surface at the level of point A. + The shortest distance of the lingual nerve to point A in the sagittal plane (defined as point B or segment AB).
+ The distance of the lingual nerve to point A in the vertical plane (defined as point C or segment AC). + The medial bending point of the nerve towards the tongue was defined as Point D and the distance to point B determined (segment BD). + The distance of the most cranial point of the lingual nerve in its mandibular course was measured to the upper edge of the mandibular crest. + The point of ramification was determined and defined as point X. + A B was defined as the shortest distance of the lingual nerve to the classical incision in the surgical removal of wisdom teeth. The soft tissue point A was dependent on the nerve position and was located on the incision line of the distal relief. + The shape of the nerve was characterized as round, oval or flat and its diameter was determined at point C. + The height of the mandibular crest was measured at the level of the foramen mentale (K1) as well as at its lowest point (K2). Moreover, the distance between the upper osseous edge of the foramen mentale and that of the mandibular crest (FK) was determined. The ratio FK to K1 was a good, objectifiable indicator of the degree of atrophy. + All measurements and the unilateral position of the nerve were compared to the opposite side and statistically analyzed taking the tooth status into consideration.
Anatomic position of the lingual nerve in the mandibular third molar region lingual
buccal
7.83 mm N. lingualis mandibular crest 0.86 mm Fig. 2. The frontal incision through the left third molar region shows the mean horizontal and vertical distance of the lingual nerve to the lingual surface and the mandibular crest at the level of the defined measurement point A.
Results After statistically analyzing 1088 measurements, the following results were obtained. The mean age of the prepared cadavers was 78.82 years and the median 80 years. Standard deviation was 7.63 years; the youngest was 52 and the oldest 94 years. There were 19 female and 15 male corpses. Forty four mandible dissections were edentulous; 10 had less and 14 more than 4 teeth. The degree of mandibular crest atrophy was high in 10 cadavers, moderate in 15 and slight in nine. The mean horizontal distance of the lingual nerve to the lingual mandibular crest surface at the level of point A was 0.86 mm with a standard deviation of 1.00 mm. In 57.4% of the cases, the nerve had direct contact with the bone. The greatest distance was 4 mm. The mean vertical distance of the nerve to point A was 7.83 mm with a mean deviation of 1.65 mm. The distances ranged from 4.5 mm to 14 mm. Figure 2 shows both the horizontal and vertical distance of the nerve to point A. The mean distance from point B to point A in the sagittal plane was 5.97 mm with a standard deviation of 1.29 mm. The measurements ranged from 2.5 mm to 10.5 mm. When the nerve was closest to point A, point B was always distal to A. The mean sagittal distance of the nerve from point B up to its medial bend toward the tongue (segment BD) was 21.47 mm. The shortest distance of the nerve over its entire course from point A in the mesial direction into the paralingual space towards the upper edge of the mandibular crest was a mean 5.91 mm with a standard deviation of 2.3 mm and considerable scattering of the values. The maximal distance with a very deeply coursing nerve was 12 mm. The nerve was at or above the alveolar crest level in four heads, two bilaterally, and thus in a total of 8.82% of the cases (Fig. 3). This very high and, therefore, exposed and
vulnerable nerve position significantly correlated to the degree of mandibular crest atrophy (right: P=0.003; left: P=0.001). In this connection, one corpse had a high atrophy in the area of the lower first molar, with no teeth present here, and there the nerve was only at the level of the mandibular crest or even 1 mm above it on one side. Mandibular crest atrophy could be measured and thus objectified as a quotient of the distance between the foramen mentale and the upper edge of the mandibular crest to the total height of the mandibular crest (FK/K1) at this site. The shortest distance of the lingual nerve to the distal relieving incision was a mean 4.41 mm with a standard deviation of 1.44 mm. The maximal distance was 9 mm, and in one head specimen the nerve was dissected by the distal relieving incision. The ramification site (X) was a mean mesial distance of 20.62 mm from point C. This point was 57.13% of the distance between C and the foramen mentale.
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The mean nerve diameter at point C was 2.74 mm (range: 1.9 mm to 3.6 mm; standard deviation: 0.3 mm). Fifty percent of the nerves were oval, 32.3% round and 17.7% rather flat. The shape of the nerves did not correlate to the distance from the mandibular bone. Osseous mandibular crest height at the level of the foramen mentale (K1) was a mean 22.89 mm. Values ranged from 11.8–32 mm with a standard deviation of 4.44 mm. The lowest height of the mandibular crest (K2) was always farther distal and a mean of 2.7 mm less than at the height of the foramen mentale. The distance from the upper edge of the foramen mentale to that of the mandibular crest (FK) was a mean of 8.97 mm with a maximum of 15.5 mm. On one side, the foramen mentale directly contacted the mandibular crest, which only had a total height of 14 mm. The foramen-mandibular crest distance was entered as 0 mm in the calculations. The degree of mandibular crest atrophy was determined as a ratio of FK to K1. The ratio of the foramenupper mandibular crest edge distance to the entire mandibular crest height at this site was a mean 39.19%. Dentulousness affects the nerve position as follows: the nerve was closer to point A in edentulous jaws and its mesial distance from that point to the upper mandibular crest edge was markedly shorter in partially dentulous and edentulous jaws. Comparison of the means with onesided variance analysis followed by the
Fig. 3. Superficial and exposed right lingual nerve position in the mandibular crest with pronounced atrophy and a fraction of the foramen-mandibular crest distance to the entire mandibular crest height <20%. l: N. lingualis, m: N. mentalis, F: Foramen mentale, t: tongue.
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Ho¨ lzle et al. unilateral stayed deep in the floor of the mouth and did not cross the lingual nerve. One cadaver unilaterally had an extremely thin lingual nerve with a diameter of 1.9 mm. In another corpse, the lingual nerve showed very high unilateral ramification and was doublestranded at the level of point C. Two cadavers each had an extremely deep lingual nerve on one side at 12 mm from the mandibular crest. In one corpse, the hypoglossal nerve was directly adjacent to the lingual nerve and submandibular duct. A pronounced paramandibular lipoma was seen in one head dissection. Discussion
Fig. 4. Double foramen mentale with two mental fascicles exiting from each. m: N. mentalis, F: Foramen mentale, c: top view of mandibular crest.
Fig. 5. Nerve anastomosis between the mylohyoid and lingual nerves. l: N. lingualis, y: N. mylohyoideus, a: nerve anastomosis, t: tongue, c: mandibular crest.
Scheffe test showed that the more dentulous the jaw, the less marked the mandibular crest atrophy (right: P=0.02; left P=0.06). Pre-existing variations
One corpse had a double foramen mentale on one side. There were two mental nerve fascicles exiting from each of the foramina. A bilateral double foramen mentale was seen in one head specimen. On the right side, two nerves each originated from the foramina and, on the left, two from the cranial and one from the caudally located foramen (Fig. 4).
Two corpses had a unilateral nerve anastomosis (as demonstrated in Fig. 5) between the sensory lingual nerve and the motor mylohyoid nerve from the inferior alveolar nerve. This corresponds to an incidence of just under 3%. In these cases, there was a pronounced anastomosis with a diameter of over 1 mm. In one case, the anastomotic branch to the lingual nerve was larger than the distal mylohyoid component. The submandibular duct (of Wharton) primarily crosses over the lingual nerve in the premolar region. In one corpse, the unilateral duct was tied off by a network of lingual branches. In a total of four corpses, Wharton’s duct
After the lingual nerve passes through the deep lateral facial region, it enters the floor of the mouth between the mandibular branch and the medial pterygoid muscle. Behind the dorsal edge of the mylohyoid muscle, the sublingual space is broadly connected to the submandibular space24. Like the styloglossus muscle, the nerve is also at the aboral end of the sublingual oral sinus at the level of the lower third molar just beneath the mucosa and is only separated by this and some connective tissue7. Nerve injuries in this region can predominately be attributed to dental interventions and the close spatial relationship of the nerve to the wisdom tooth region24. Numerous authors describe the nerve but discuss the variability of its position to a much lesser degree. Our measurements quantify the position of the nerve and provide information about its incidence and range. In the present study, the mean distance of the lingual nerve to the lingual mandibular crest surface is 0.86 mm1 mm at the level of point A. The nerve directly contacted the bone in 57.4% and the greatest distance was 4 mm. K & C, who also examined 34 heads, reported a distance of 0.59 mm0.9 mm. There was bone contact in 62% of the cases12. In 20 head specimens, P et al. found a horizontal distance of 3.45 mm1.48 mm. The values ranged from 1.0 mm to 7.0 mm17. Using MRI, M et al. examined the position of the lingual nerve in 10 volunteers aged 21–35 years. All subjects had rudimentary lower wisdom teeth and no maxillofacial surgery in their history. The horizontal distance here to the lingual aspect of the mandible in the wisdom
Anatomic position of the lingual nerve in the mandibular third molar region tooth region was 2.53 mm0.67 mm. In five of the 20 cases (25%), the nerve directly contacted the bone. The mean vertical distance of the nerve to upper mandibular crest edge was 2.75 mm 0.97 mm with range of 1.52–4.61 mm14. In our study, the vertical distance was 7.83 mm with a standard deviation of 1.65 mm and a range of 4.5–14 mm. P et al. found a vertical distance of 8.32 mm (standard deviation: 4.05 mm)17. K & C measured only 2.28 mm1.96 mm, although the values extended from 2 mm over to 7 mm below the crest12. All four studies mentioned deal with the distance of the nerve from the mandibular crest in its further mesial course in the paralingual space. In our study, the mean distance was 5.91 mm with a standard deviation of 2.3 mm. There was a considerable range of values with a maximal distance of 12 mm, and, in a total of six head dissections, the nerve was found at or above the alveolar crest. The authors largely agree on this finding. The percentage of nerves found at or above the mandibular crest and thus particularly endangered by this exposed position is 8.82% in our study, 10% in M et al. using MRI, 15% in P et al. and 17.6% in K & C12,14,17. The latter even reported one nerve that passed through the retromolar region 2 mm above the lingual crest border at the level of the occlusal surface of an impacted wisdom tooth and would, thus, have certainly been dissected by a classical incision12. The mean distance of point B from point A in the sagittal plane was 5.97 mm with a standard deviation of 1.29 mm. P et al. found a mean distance of 4.45 mm with a standard deviation of 1.48 mm17. At the shortest distance from the nerve to point A, point B was distal to point A in both studies. The mean sagittal course of the nerve from point B to its medial bend towards the tongue (segment BD) was 27.7 mm5.69 mm in P et al. and 27.47 mm3.3 mm in our study17. The shortest distance of the lingual nerve to the distal relieving incision was a mean 4.41 mm. In one head dissection, the nerve was bisected by the distal relieving incision. K & C reported a situation with similar superficial nerve course12. H, who studied lingual nerve damage in Schleswig-Holstein, the northern part of Germany, from 1981 to 1986, determined that an incision too far in the lingual direction promotes lingual
nerve damage8. Our incision directly up to the ascending branch is certainly the most medial that should be selected. In the surgical removal of wisdom teeth, it facilitates distolingual exposure of the mucoperiosteum flap and subsequent mobilization of the tooth, but carries the risk of a lingual lesion. In view of the results, a more buccal relieving incision is safer and is therefore recommended. There is a clear discrepancy in the mean nerve diameters given in the literature. M et al. reported the lingual nerve diameter to be 2.54 mm with a range of 1.58–3.13 mm. The shape of the nerve was round in 45% of the cases, oval in 30% and flat in 25%14. K & C found a mean nerve diameter of 1.86 mm. The nerves were round in 61.7% of the cases, oval in 17.6% and flat in 20.5%. Three of the flat nerves were only 0.5 mm thick. The shape did not correlate to the distance from the jaw bone12. P et al. reported a mean nerve diameter of 3.45 mm. The standard deviation was 1.00 mm with a range of 2.5–4.5 mm17. The mean nerve diameter in P et al. is 80% above that reported by K & C. Moreover, lowest value found by P et al. did not even reach the mean value of K & C. In our study the mean diameter was 2.74 mm with a standard deviation of 0.3 mm. Values ranged from 1.9– 3.6 mm. The nerves were oval in 50.0% of the cases, round in 32.3% and flat in 17.7%. The shape of the nerve did not correlate to the distance from the alveolar bone. Changes of shape of nerves may be due to post-mortem artefacts and/or formalin fixation. To this issue we neither found publications nor experienced anatomists or pathologists. To answer this question we looked at the shape of the lingual nerve in 15 fresh cadavers without fixative added. In this 30 nerves measured it was oval in 46.7%, round in 33.3% and flat in 20.0%. We therefore conclude the influence of postmortem formalin fixation on the shape of the nerve as minimal. The nerve started to ramify a mean of 20.62 mm mesially from point C. This site was 57.13% of the distance between C and the foramen mentale. In dentulous jaws, ramification was primarily located in the distal premolar region and is thus somewhat mesial to the position reported by N & H15. This site is clinically relevant if, for example, a sural nerve graft is required for reconstruction of a nerve lesion.
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Peripheral polyfascicular reconstruction of the lingual nerve can be done in individual cases and its fasciculus connected to that of the sural nerve with a perineural suture8. The correlation between the position of the lingual nerve to the upper mandibular crest edge and mandibular crest atrophy has hitherto not been the subject of extensive studies. Although this connection seems obvious, it is not necessarily the case. This study shows that the extent of atrophy is related to age but even more to edentulousness. However, since there is often a loss of muscle tone and connective tissue tension with advanced age, the nerve may also descend into the floor of the mouth and thus not change its relative position to the mandibular crest. Further studies are necessary to confirm this connection. The ratio of the foramen-upper mandibular crest edge to the entire mandibular crest height at this position is a very suitable measure of mandibular crest atrophy and agrees with the ‘prima vista’ estimation of atrophy into ‘high’, ‘moderate’ and ‘slight’. At this point it should be considered, whether this method would also be suited for radiological classification based on pantomograms. One only has to measure two lengths on the X-ray and divide them. Manufacturers of X-ray devices use different magnification factors. However, since both values are placed in relationship to each other with the same magnification, the ratio remains constant and can thus be compared to the diverse magnifications of other pantomograms. In addition, the foramen mentale is almost always clearly visible and usually located between the mandible premolars in dentulous jaws, so that the teeth do not interfere with the determination of the entire mandibular crest height. This would provide a simple method for classifying mandibular atrophy and promote understanding among dentists. A total of three double mental foramina, each with a nerve exit, were determined in 68 prepared mandibular dissections. In two mandibular dissections, atrophy was so severe that the mental nerve exited at the mandibular crest. It is exactly during abscess incision that the mental nerve is easily dissected, since there is no visualization as in other operations like apicectomy11. A preoperative X-ray should therefore always be performed.
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In two corpses, there was a pronounced nerve anastomosis on one side between the sensory lingual nerve and the motor mylohyoid nerve from the inferior alveolar nerve, in one case with a diameter of more than 1 mm. L & W also report a fiber change between these two nerves16,24. B described very fine anatomical branches between the lingual and mylohyoid nerves5. S even refers to ‘Bichat’s nerve’22. F also found a connecting branch between these two nerves6. R & M18, who studied the course of the lingual nerve in 48 head dissections, reported this connection in eight cases, thus in a third of their study specimens. They are of the opinion that the mylohyoid nerve is a mixed nerve, which gives off postganglionic vegetative fibres from the anastomotic branch to the lingual nerve. Due to the regularity of this anastomosis, they spoke about an ‘ansa mylohyoidea’ or ‘ansa sublingualis’. However, the rate of 2.94% in the present study was less than a tenth of the value reported by R & M18. The high variability of the nerve bed in the wisdom tooth region was demonstrated by M et al. in their MRI examinations in patients. There was no correlation between measurements made on the right or left side. In their opinion, this underlines the vulnerable position of this nerve during intraoral or maxilloK & facial surgery14. C also point out that the surgeon cannot depend on the lingual osseous lamella as a protective barrier during wisdom tooth removal, since the nerve may lie over the bone in the soft tissue12. The incision, especially the distal relieving incision for wisdom tooth osteotomy, should not be made medial to the ascending branch because the variability of the nerve and its possible surface positions may cause a lesion. The tangent to the distal surface of the third molar is also suited as a guideline for orientation. The incision should be made at a 45 angle to this tangent in the buccal direction. Moreover, during free fraising of the lower wisdom tooth, attention should be paid to the fact that a raspatory should be pushed distolingually between the periosteum and bone in order to protect the periosteum and lingual nerve9. Furthermore, a relatively high position of the nerves must be taken into account for surgical interventions even
in the mesial paralingual region, if there is marked mandibular crest atrophy. This is not only true for oral surgical procedures like osteotomies and excisions but also for the insertion of intraosseous implants. Acknowledgments. The authors would like to express their many thanks to Professor Graf, M.D., from the Institute of Anatomy of the Free University, Berlin for providing the study specimens as well as her kind support during the entire study. References 1. A CC. Dysesthesia of the lingual and inferior alveolar nerves following third molar surgery. J Oral Maxillofac Surg 1986: 44: 454–457. 2. A-A S, A A MG. Protection of the lingual nerve during operations on the mandibular third molar: a simple method. Br J Oral Maxillofac Surg 1997: 35: 170–172. 3. B A, L B G, M J, W H, N I. Lingual paresthesia following surgical placement of implants: report of a case. Int J Oral Maxillofac Implants 1993: 8: 580–582. 4. B CW, B PA. Lingual nerve damage associated with removal of lower third molars. Br Dent J 1989: 167: 103–107. 5. B X. Traite d’ A v natomie descriptive. Brossen Paris 1802, Nouvelle edition: 1819: 227–231. 6. F E. Zwei Sonderfa¨ lle des N. lingualis. Anat. Anz., Jena 1956: 103: 187–191. 7. G H. Anatomy descriptive and applied. London New York Toronto 1932: 994. 8. H B. Verletzung des Nervus lingualis—Eine klinische und tierexperimentelle Studie. Habilitationsschriften der Zahn-, Mund- und Kieferheilkunde, Quintessenz Verlags-GmbH, Berlin 1989: 21–22. 9. H B. Verletzung des Nervus lingualis—Eine klinische und tierexperimentelle Studie. Habilitationsschriften der Zahn-, Mund- und Kieferheilkunde, Quintessenz Verlags-GmbH, Berlin 1989: 81–82. 10. H HH. Iatrogene Nervla¨ sionen bei der zahna¨ rztlichen Behandlung. Zahna¨ rztl Mitt 1984: 7: 708–715. 11. H HH. Zahna¨ rztliche Chirurgie. Praxis der Zahnheilkunde 9. 3. Auflage, Urban & Schwarzenberg, Mu¨ nchen Wien Baltimore 1995: 51–52. 12. K JE, C JG. Clinical and anatomic observations on the relationship of the lingual nerve to the
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mandibular third molar region. J Oral Maxillofac Surg 1984: 42: 565–567. M D. Lingual nerve damage following lower third molar surgery. Int J Oral Maxillofac Surg 1988: 17: 290–294. M M, H LE, S HW, C DW. Assessment of the lingual nerve in the third molar region using magnetic resonance imaging. J Oral Maxillofac Surg 1997: 55: 134–137. N FW, H JE. Anatomische Untersuchungen zur faszikula¨ ren Struktur einzelner Hirnnerven als Grundlage zur Vermeidung von Mißerfolgen bei der Mikrochirurgischen Nervnaht. Fortschr Kiefer Gesichtschir 1985: 30: 51–54. P-T. Les NERFS en schemas. Anatomie et Physiolpathologie. Paris 1925: 118. P MA, R A, S B, A A. The relationship of the lingual nerve to the mandibular third molar region: an anatomic study. J Oral Maxillofac Surg 1995: 53: 1178–1181. R L, M T. Anatomische Variationen des Nervus lingualis beim Menschen. Anat Anz 1981: 149: 64–71. R JP. Permanent damage to inferior alveolar and lingual nerves during the removal of impacted mandibular third molars. Comparison of two methods of bone removal. Br Dent J 1992: 172: 108–110. S LJ. Lingual anesthesia following mandibular odontectomy. J Oral Surg 1973: 31: 918. S GC. Lingual exposure during mandibular third molar surgery. Int J Oral Surg 1977: 6: 334–337. S J. A propos du nerf de Zlobikowski. Fol morph Warzawa 1933: 4: 164–170. V G AV, T B JJ, B G. Clinical consequences of complaints and complications after removal of the mandibular third molar. Int J Oral Surg 1977: 6: 29. V L T, W W. Praktische Anatomie Bd.1, Teil 2: Hals. Berlin Go¨ ttingen Heidelberg: Springer Verlag 1955: 114–115.
Address: Dr. med. Dr. med. dent. Frank Ho¨ lzle Klinik fu¨ r Mund-, Kiefer- und Plastische Gesichtschirurgie Knappschaftskrankenhaus Klinikum der Ruhr-Universita¨ t Bochum In der Schornau 23–25 44892 Bochum Germany Tel.: +49 (0) 234-299 3500 Fax: +49 (0) 234-299 3509 E-mail: [email protected]
Research paper: Dentoalveolar surgery
Anatomic position of the lingual nerve in the mandibular third molar region with special consideration of an atrophied mandibular crest: an anatomical study
F. W. Ho¨lzle, K.-D. Wolff Arzt fu¨r Mund-, Kiefer- und Gesichtschirurgie, Plastische Operationen, Knappschaftskrankenhaus, Klinikum der Ruhr-Universitat, In der Schornau 23–25, 44892 Bochum
F. W. Ho¨lzle, K.-D. Wolff: 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: 333–338. 2001 International Association of Oral and Maxillofacial Surgeons Abstract. The position of the lingual nerve in the mandibular third molar region was measured and documented in 68 cadaver dissections (34 adult cadaver heads). In 8.8% of the dissections, the lingual nerve was found at or above the level of the alveolar crest. In the horizontal plane, the nerve contacted the lingual plate of the third molar in 57.4% of the specimens. There was also a significant relationship between the degree of mandibular crest atrophy and the distance from the nerve to the molar region. The distance decreased with the degree of atrophy. There was no significant difference between the two sides of the head. These results demonstrate the vulnerability of the lingual nerve as it medially passes the mandibular third molar and may help avoid lingual damage during surgery in the third molar and retromolar region of the mandible.
The anatomic proximity of the lingual nerve to the mandibular third molar region plays an important role in planning and performing surgical interventions in this area. Nerve injury is possible during removal of the third molars, osteotomy of the mandibular branch, alveolar crest graft and by injection of local anaesthesia. Even excision during tumour removal or the sequelae of trauma may injure the nerve1,20,23. There are also reports of lingual par0901-5027/01/040333+06 $35.00/0
esthesia after surgical insertion of implants3. The risk of damaging the lingual nerve during mandibular wisdom tooth surgery differs in the literature. Horch reports an injury incidence of 0.05%10 and H 0.04%. About 250 000 wisdom teeth per year were removed in the 1980’s in the old federal states of Germany. An incidence of 0.05% means 125 nerve lesions per year. The probability of irreversible numbness and
Key words: third molar surgery; nerve injury; lingual paresthesia; protection of the lingual nerve; human anatomy. Accepted for publication 1 April 2001
hypogeusia of one half of the tongue is calculated to be 1:2 million after local anaesthesia9. The incidence of a persistent sensory deficit after osteotomy is reported to be 0.5–2% in English literature4,13,19. A-A gives an 11.5% incidence of reversible dysesthesia after mandibular wisdom tooth surgery2. Thus, extensive knowledge about the position of nerves in the mandibular third molar region is indispensable for surgery in this area.
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A survey of the literature revealed that virtually no detailed descriptions or measurements of the lingual nerve in the lower third molar region have been reported for many years21. In 1984, K & C were the first to perform an exact quantitative evaluation on cadaverous specimens and to attempt atraumatic in vivo exposure of the nerve in 256 wisdom tooth removals to study its course medial to the posterior alveolar crest in the retromolar region12. In 1995, P et al. measured in three dimensions the exact anatomic position of the lingual nerve for the wisdom tooth region. For this, they used a reproducible osseous point, taking the dentulous jaw into account17. There have not yet been any studies considering alveolar crest atrophy in addition to determining a reproducible osseous point as a fixed point for measuring and evaluating dental status. Thus, the aim of this study was to examine whether the lingual nerve has a relatively higher or closer position to the alveolar crest due to mandibular atrophy and is therefore exposed to a higher risk in surgery near the bone. Such an additional risk is possible especially in osteotomies or during implantation. Moreover, the aim was to measure the position of the nerve in the mandibular third molar region in all three dimensions and to examine it for bone contact. Another objective was to determine the distance of the lingual nerve to the typical incision in surgical wisdom tooth removal. According to N & H, the lingual nerve either has a mono- or oligofascicular structure in the pterygomandibular space15. The nerve begins to branch off medial to the posterior molars and has a polyfascicular structure there. The point of ramification is also examined in the present study and placed in relation to a distal fixed point, the mental foramen and the tooth region in dentulous patients. It was also necessary to check the assertion by R & M that anatomic lingual nerve variations are of secondary importance18. Material and methods Thirty-four formalin-fixed heads were divided sagittally. The 68 dissections were prepared as follows: In dentulous mandibles or in those with second molars, a 1 cm long distal relieving incision was made in the direction of the ascending mandibular branch. This
N. alveolaris inf.
N. mylohyoideus B' A' A
B
Distal incision
C
N. lingualis
D X
FK
K2 Foramen mentale
K1
Fig. 1. 3D-Illustration of the measured points and distances.
incision was marginally and mesially lengthened in the lingual region. Starting distally, the lingual mucosa and the periosteum were removed with a bone rasp in the mesial direction. The lingual nerve was demonstrated by blunt dissection but not exposed to prevent changing its anatomic relationship to the adjacent structures. The anterior measuring points and distances were recorded with a precision vernier gage and those more distal and difficult to reach were calipered with a measuring compass. Stepwise dissection was performed in such a way as to reliably obtain measurements without falsifying them by too great a change in the anatomic site. Distances to the nerves were measured from the boundary of the nerve inclining towards the other measuring point. Since the oblique line of the ramus mandibulae in the atrophied mandibular crest is frequently very indistinct, it cannot be used as an orientation or marking aid. Thus, the reproducible transition site of the horizontal to the vertical branch of the ramus mandibulae is more or less fixed as a retromolar pad and defined as osseous measuring point A. Starting at this point, the following measurements were performed, which are demonstrated by the illustration in Fig. 1: + The horizontal distance of the lingual nerve to the lingual mandibular crest surface at the level of point A. + The shortest distance of the lingual nerve to point A in the sagittal plane (defined as point B or segment AB).
+ The distance of the lingual nerve to point A in the vertical plane (defined as point C or segment AC). + The medial bending point of the nerve towards the tongue was defined as Point D and the distance to point B determined (segment BD). + The distance of the most cranial point of the lingual nerve in its mandibular course was measured to the upper edge of the mandibular crest. + The point of ramification was determined and defined as point X. + A B was defined as the shortest distance of the lingual nerve to the classical incision in the surgical removal of wisdom teeth. The soft tissue point A was dependent on the nerve position and was located on the incision line of the distal relief. + The shape of the nerve was characterized as round, oval or flat and its diameter was determined at point C. + The height of the mandibular crest was measured at the level of the foramen mentale (K1) as well as at its lowest point (K2). Moreover, the distance between the upper osseous edge of the foramen mentale and that of the mandibular crest (FK) was determined. The ratio FK to K1 was a good, objectifiable indicator of the degree of atrophy. + All measurements and the unilateral position of the nerve were compared to the opposite side and statistically analyzed taking the tooth status into consideration.
Anatomic position of the lingual nerve in the mandibular third molar region lingual
buccal
7.83 mm N. lingualis mandibular crest 0.86 mm Fig. 2. The frontal incision through the left third molar region shows the mean horizontal and vertical distance of the lingual nerve to the lingual surface and the mandibular crest at the level of the defined measurement point A.
Results After statistically analyzing 1088 measurements, the following results were obtained. The mean age of the prepared cadavers was 78.82 years and the median 80 years. Standard deviation was 7.63 years; the youngest was 52 and the oldest 94 years. There were 19 female and 15 male corpses. Forty four mandible dissections were edentulous; 10 had less and 14 more than 4 teeth. The degree of mandibular crest atrophy was high in 10 cadavers, moderate in 15 and slight in nine. The mean horizontal distance of the lingual nerve to the lingual mandibular crest surface at the level of point A was 0.86 mm with a standard deviation of 1.00 mm. In 57.4% of the cases, the nerve had direct contact with the bone. The greatest distance was 4 mm. The mean vertical distance of the nerve to point A was 7.83 mm with a mean deviation of 1.65 mm. The distances ranged from 4.5 mm to 14 mm. Figure 2 shows both the horizontal and vertical distance of the nerve to point A. The mean distance from point B to point A in the sagittal plane was 5.97 mm with a standard deviation of 1.29 mm. The measurements ranged from 2.5 mm to 10.5 mm. When the nerve was closest to point A, point B was always distal to A. The mean sagittal distance of the nerve from point B up to its medial bend toward the tongue (segment BD) was 21.47 mm. The shortest distance of the nerve over its entire course from point A in the mesial direction into the paralingual space towards the upper edge of the mandibular crest was a mean 5.91 mm with a standard deviation of 2.3 mm and considerable scattering of the values. The maximal distance with a very deeply coursing nerve was 12 mm. The nerve was at or above the alveolar crest level in four heads, two bilaterally, and thus in a total of 8.82% of the cases (Fig. 3). This very high and, therefore, exposed and
vulnerable nerve position significantly correlated to the degree of mandibular crest atrophy (right: P=0.003; left: P=0.001). In this connection, one corpse had a high atrophy in the area of the lower first molar, with no teeth present here, and there the nerve was only at the level of the mandibular crest or even 1 mm above it on one side. Mandibular crest atrophy could be measured and thus objectified as a quotient of the distance between the foramen mentale and the upper edge of the mandibular crest to the total height of the mandibular crest (FK/K1) at this site. The shortest distance of the lingual nerve to the distal relieving incision was a mean 4.41 mm with a standard deviation of 1.44 mm. The maximal distance was 9 mm, and in one head specimen the nerve was dissected by the distal relieving incision. The ramification site (X) was a mean mesial distance of 20.62 mm from point C. This point was 57.13% of the distance between C and the foramen mentale.
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The mean nerve diameter at point C was 2.74 mm (range: 1.9 mm to 3.6 mm; standard deviation: 0.3 mm). Fifty percent of the nerves were oval, 32.3% round and 17.7% rather flat. The shape of the nerves did not correlate to the distance from the mandibular bone. Osseous mandibular crest height at the level of the foramen mentale (K1) was a mean 22.89 mm. Values ranged from 11.8–32 mm with a standard deviation of 4.44 mm. The lowest height of the mandibular crest (K2) was always farther distal and a mean of 2.7 mm less than at the height of the foramen mentale. The distance from the upper edge of the foramen mentale to that of the mandibular crest (FK) was a mean of 8.97 mm with a maximum of 15.5 mm. On one side, the foramen mentale directly contacted the mandibular crest, which only had a total height of 14 mm. The foramen-mandibular crest distance was entered as 0 mm in the calculations. The degree of mandibular crest atrophy was determined as a ratio of FK to K1. The ratio of the foramenupper mandibular crest edge distance to the entire mandibular crest height at this site was a mean 39.19%. Dentulousness affects the nerve position as follows: the nerve was closer to point A in edentulous jaws and its mesial distance from that point to the upper mandibular crest edge was markedly shorter in partially dentulous and edentulous jaws. Comparison of the means with onesided variance analysis followed by the
Fig. 3. Superficial and exposed right lingual nerve position in the mandibular crest with pronounced atrophy and a fraction of the foramen-mandibular crest distance to the entire mandibular crest height <20%. l: N. lingualis, m: N. mentalis, F: Foramen mentale, t: tongue.
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Ho¨ lzle et al. unilateral stayed deep in the floor of the mouth and did not cross the lingual nerve. One cadaver unilaterally had an extremely thin lingual nerve with a diameter of 1.9 mm. In another corpse, the lingual nerve showed very high unilateral ramification and was doublestranded at the level of point C. Two cadavers each had an extremely deep lingual nerve on one side at 12 mm from the mandibular crest. In one corpse, the hypoglossal nerve was directly adjacent to the lingual nerve and submandibular duct. A pronounced paramandibular lipoma was seen in one head dissection. Discussion
Fig. 4. Double foramen mentale with two mental fascicles exiting from each. m: N. mentalis, F: Foramen mentale, c: top view of mandibular crest.
Fig. 5. Nerve anastomosis between the mylohyoid and lingual nerves. l: N. lingualis, y: N. mylohyoideus, a: nerve anastomosis, t: tongue, c: mandibular crest.
Scheffe test showed that the more dentulous the jaw, the less marked the mandibular crest atrophy (right: P=0.02; left P=0.06). Pre-existing variations
One corpse had a double foramen mentale on one side. There were two mental nerve fascicles exiting from each of the foramina. A bilateral double foramen mentale was seen in one head specimen. On the right side, two nerves each originated from the foramina and, on the left, two from the cranial and one from the caudally located foramen (Fig. 4).
Two corpses had a unilateral nerve anastomosis (as demonstrated in Fig. 5) between the sensory lingual nerve and the motor mylohyoid nerve from the inferior alveolar nerve. This corresponds to an incidence of just under 3%. In these cases, there was a pronounced anastomosis with a diameter of over 1 mm. In one case, the anastomotic branch to the lingual nerve was larger than the distal mylohyoid component. The submandibular duct (of Wharton) primarily crosses over the lingual nerve in the premolar region. In one corpse, the unilateral duct was tied off by a network of lingual branches. In a total of four corpses, Wharton’s duct
After the lingual nerve passes through the deep lateral facial region, it enters the floor of the mouth between the mandibular branch and the medial pterygoid muscle. Behind the dorsal edge of the mylohyoid muscle, the sublingual space is broadly connected to the submandibular space24. Like the styloglossus muscle, the nerve is also at the aboral end of the sublingual oral sinus at the level of the lower third molar just beneath the mucosa and is only separated by this and some connective tissue7. Nerve injuries in this region can predominately be attributed to dental interventions and the close spatial relationship of the nerve to the wisdom tooth region24. Numerous authors describe the nerve but discuss the variability of its position to a much lesser degree. Our measurements quantify the position of the nerve and provide information about its incidence and range. In the present study, the mean distance of the lingual nerve to the lingual mandibular crest surface is 0.86 mm1 mm at the level of point A. The nerve directly contacted the bone in 57.4% and the greatest distance was 4 mm. K & C, who also examined 34 heads, reported a distance of 0.59 mm0.9 mm. There was bone contact in 62% of the cases12. In 20 head specimens, P et al. found a horizontal distance of 3.45 mm1.48 mm. The values ranged from 1.0 mm to 7.0 mm17. Using MRI, M et al. examined the position of the lingual nerve in 10 volunteers aged 21–35 years. All subjects had rudimentary lower wisdom teeth and no maxillofacial surgery in their history. The horizontal distance here to the lingual aspect of the mandible in the wisdom
Anatomic position of the lingual nerve in the mandibular third molar region tooth region was 2.53 mm0.67 mm. In five of the 20 cases (25%), the nerve directly contacted the bone. The mean vertical distance of the nerve to upper mandibular crest edge was 2.75 mm 0.97 mm with range of 1.52–4.61 mm14. In our study, the vertical distance was 7.83 mm with a standard deviation of 1.65 mm and a range of 4.5–14 mm. P et al. found a vertical distance of 8.32 mm (standard deviation: 4.05 mm)17. K & C measured only 2.28 mm1.96 mm, although the values extended from 2 mm over to 7 mm below the crest12. All four studies mentioned deal with the distance of the nerve from the mandibular crest in its further mesial course in the paralingual space. In our study, the mean distance was 5.91 mm with a standard deviation of 2.3 mm. There was a considerable range of values with a maximal distance of 12 mm, and, in a total of six head dissections, the nerve was found at or above the alveolar crest. The authors largely agree on this finding. The percentage of nerves found at or above the mandibular crest and thus particularly endangered by this exposed position is 8.82% in our study, 10% in M et al. using MRI, 15% in P et al. and 17.6% in K & C12,14,17. The latter even reported one nerve that passed through the retromolar region 2 mm above the lingual crest border at the level of the occlusal surface of an impacted wisdom tooth and would, thus, have certainly been dissected by a classical incision12. The mean distance of point B from point A in the sagittal plane was 5.97 mm with a standard deviation of 1.29 mm. P et al. found a mean distance of 4.45 mm with a standard deviation of 1.48 mm17. At the shortest distance from the nerve to point A, point B was distal to point A in both studies. The mean sagittal course of the nerve from point B to its medial bend towards the tongue (segment BD) was 27.7 mm5.69 mm in P et al. and 27.47 mm3.3 mm in our study17. The shortest distance of the lingual nerve to the distal relieving incision was a mean 4.41 mm. In one head dissection, the nerve was bisected by the distal relieving incision. K & C reported a situation with similar superficial nerve course12. H, who studied lingual nerve damage in Schleswig-Holstein, the northern part of Germany, from 1981 to 1986, determined that an incision too far in the lingual direction promotes lingual
nerve damage8. Our incision directly up to the ascending branch is certainly the most medial that should be selected. In the surgical removal of wisdom teeth, it facilitates distolingual exposure of the mucoperiosteum flap and subsequent mobilization of the tooth, but carries the risk of a lingual lesion. In view of the results, a more buccal relieving incision is safer and is therefore recommended. There is a clear discrepancy in the mean nerve diameters given in the literature. M et al. reported the lingual nerve diameter to be 2.54 mm with a range of 1.58–3.13 mm. The shape of the nerve was round in 45% of the cases, oval in 30% and flat in 25%14. K & C found a mean nerve diameter of 1.86 mm. The nerves were round in 61.7% of the cases, oval in 17.6% and flat in 20.5%. Three of the flat nerves were only 0.5 mm thick. The shape did not correlate to the distance from the jaw bone12. P et al. reported a mean nerve diameter of 3.45 mm. The standard deviation was 1.00 mm with a range of 2.5–4.5 mm17. The mean nerve diameter in P et al. is 80% above that reported by K & C. Moreover, lowest value found by P et al. did not even reach the mean value of K & C. In our study the mean diameter was 2.74 mm with a standard deviation of 0.3 mm. Values ranged from 1.9– 3.6 mm. The nerves were oval in 50.0% of the cases, round in 32.3% and flat in 17.7%. The shape of the nerve did not correlate to the distance from the alveolar bone. Changes of shape of nerves may be due to post-mortem artefacts and/or formalin fixation. To this issue we neither found publications nor experienced anatomists or pathologists. To answer this question we looked at the shape of the lingual nerve in 15 fresh cadavers without fixative added. In this 30 nerves measured it was oval in 46.7%, round in 33.3% and flat in 20.0%. We therefore conclude the influence of postmortem formalin fixation on the shape of the nerve as minimal. The nerve started to ramify a mean of 20.62 mm mesially from point C. This site was 57.13% of the distance between C and the foramen mentale. In dentulous jaws, ramification was primarily located in the distal premolar region and is thus somewhat mesial to the position reported by N & H15. This site is clinically relevant if, for example, a sural nerve graft is required for reconstruction of a nerve lesion.
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Peripheral polyfascicular reconstruction of the lingual nerve can be done in individual cases and its fasciculus connected to that of the sural nerve with a perineural suture8. The correlation between the position of the lingual nerve to the upper mandibular crest edge and mandibular crest atrophy has hitherto not been the subject of extensive studies. Although this connection seems obvious, it is not necessarily the case. This study shows that the extent of atrophy is related to age but even more to edentulousness. However, since there is often a loss of muscle tone and connective tissue tension with advanced age, the nerve may also descend into the floor of the mouth and thus not change its relative position to the mandibular crest. Further studies are necessary to confirm this connection. The ratio of the foramen-upper mandibular crest edge to the entire mandibular crest height at this position is a very suitable measure of mandibular crest atrophy and agrees with the ‘prima vista’ estimation of atrophy into ‘high’, ‘moderate’ and ‘slight’. At this point it should be considered, whether this method would also be suited for radiological classification based on pantomograms. One only has to measure two lengths on the X-ray and divide them. Manufacturers of X-ray devices use different magnification factors. However, since both values are placed in relationship to each other with the same magnification, the ratio remains constant and can thus be compared to the diverse magnifications of other pantomograms. In addition, the foramen mentale is almost always clearly visible and usually located between the mandible premolars in dentulous jaws, so that the teeth do not interfere with the determination of the entire mandibular crest height. This would provide a simple method for classifying mandibular atrophy and promote understanding among dentists. A total of three double mental foramina, each with a nerve exit, were determined in 68 prepared mandibular dissections. In two mandibular dissections, atrophy was so severe that the mental nerve exited at the mandibular crest. It is exactly during abscess incision that the mental nerve is easily dissected, since there is no visualization as in other operations like apicectomy11. A preoperative X-ray should therefore always be performed.
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In two corpses, there was a pronounced nerve anastomosis on one side between the sensory lingual nerve and the motor mylohyoid nerve from the inferior alveolar nerve, in one case with a diameter of more than 1 mm. L & W also report a fiber change between these two nerves16,24. B described very fine anatomical branches between the lingual and mylohyoid nerves5. S even refers to ‘Bichat’s nerve’22. F also found a connecting branch between these two nerves6. R & M18, who studied the course of the lingual nerve in 48 head dissections, reported this connection in eight cases, thus in a third of their study specimens. They are of the opinion that the mylohyoid nerve is a mixed nerve, which gives off postganglionic vegetative fibres from the anastomotic branch to the lingual nerve. Due to the regularity of this anastomosis, they spoke about an ‘ansa mylohyoidea’ or ‘ansa sublingualis’. However, the rate of 2.94% in the present study was less than a tenth of the value reported by R & M18. The high variability of the nerve bed in the wisdom tooth region was demonstrated by M et al. in their MRI examinations in patients. There was no correlation between measurements made on the right or left side. In their opinion, this underlines the vulnerable position of this nerve during intraoral or maxilloK & facial surgery14. C also point out that the surgeon cannot depend on the lingual osseous lamella as a protective barrier during wisdom tooth removal, since the nerve may lie over the bone in the soft tissue12. The incision, especially the distal relieving incision for wisdom tooth osteotomy, should not be made medial to the ascending branch because the variability of the nerve and its possible surface positions may cause a lesion. The tangent to the distal surface of the third molar is also suited as a guideline for orientation. The incision should be made at a 45 angle to this tangent in the buccal direction. Moreover, during free fraising of the lower wisdom tooth, attention should be paid to the fact that a raspatory should be pushed distolingually between the periosteum and bone in order to protect the periosteum and lingual nerve9. Furthermore, a relatively high position of the nerves must be taken into account for surgical interventions even
in the mesial paralingual region, if there is marked mandibular crest atrophy. This is not only true for oral surgical procedures like osteotomies and excisions but also for the insertion of intraosseous implants. Acknowledgments. The authors would like to express their many thanks to Professor Graf, M.D., from the Institute of Anatomy of the Free University, Berlin for providing the study specimens as well as her kind support during the entire study. References 1. A CC. Dysesthesia of the lingual and inferior alveolar nerves following third molar surgery. J Oral Maxillofac Surg 1986: 44: 454–457. 2. A-A S, A A MG. Protection of the lingual nerve during operations on the mandibular third molar: a simple method. Br J Oral Maxillofac Surg 1997: 35: 170–172. 3. B A, L B G, M J, W H, N I. Lingual paresthesia following surgical placement of implants: report of a case. Int J Oral Maxillofac Implants 1993: 8: 580–582. 4. B CW, B PA. Lingual nerve damage associated with removal of lower third molars. Br Dent J 1989: 167: 103–107. 5. B X. Traite d’ A v natomie descriptive. Brossen Paris 1802, Nouvelle edition: 1819: 227–231. 6. F E. Zwei Sonderfa¨ lle des N. lingualis. Anat. Anz., Jena 1956: 103: 187–191. 7. G H. Anatomy descriptive and applied. London New York Toronto 1932: 994. 8. H B. Verletzung des Nervus lingualis—Eine klinische und tierexperimentelle Studie. Habilitationsschriften der Zahn-, Mund- und Kieferheilkunde, Quintessenz Verlags-GmbH, Berlin 1989: 21–22. 9. H B. Verletzung des Nervus lingualis—Eine klinische und tierexperimentelle Studie. Habilitationsschriften der Zahn-, Mund- und Kieferheilkunde, Quintessenz Verlags-GmbH, Berlin 1989: 81–82. 10. H HH. Iatrogene Nervla¨ sionen bei der zahna¨ rztlichen Behandlung. Zahna¨ rztl Mitt 1984: 7: 708–715. 11. H HH. Zahna¨ rztliche Chirurgie. Praxis der Zahnheilkunde 9. 3. Auflage, Urban & Schwarzenberg, Mu¨ nchen Wien Baltimore 1995: 51–52. 12. K JE, C JG. Clinical and anatomic observations on the relationship of the lingual nerve to the
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Address: Dr. med. Dr. med. dent. Frank Ho¨ lzle Klinik fu¨ r Mund-, Kiefer- und Plastische Gesichtschirurgie Knappschaftskrankenhaus Klinikum der Ruhr-Universita¨ t Bochum In der Schornau 23–25 44892 Bochum Germany Tel.: +49 (0) 234-299 3500 Fax: +49 (0) 234-299 3509 E-mail: [email protected]