Risk factors associated with injury to the inferior alveolar and lingual nerves following third molar surgery—revisited

Vol. 109 No. 3 March 2010

ORAL AND MAXILLOFACIAL SURGERY

Editor: James R. Hupp

Risk factors associated with injury to the inferior alveolar and lingual nerves following third molar surgery—revisited Waseem Jerjes, MSc (OMFS), PhD (Surg),a Tahwinder Upile, FRCS,b Priya Shah, MFDS,c Farai Nhembe, MFDS,c Dipali Gudka, MFDS,c Panagiotis Kafas, MSc (OMFS),d Eileen McCarthy, MFDS,e Syedda Abbas, FDS, MRCS,f Shinali Patel, MFDS,c Zaid Hamdoon, MSc (OMFS),g Jesuloba Abiola, BSc,h Michael Vourvachis, MSc (OMFS), MFDS,i Maria Kalkani, MFDS,c Mohammed Al-Khawalde, MSc (OMFS),j Rachael Leeson, MSc, PhD, FDS,k Bilquis Banu, MSc, FDS,k Jubli Rob, BSc,h Mohammed El-Maaytah, MSc, PhD, FDS,k and Colin Hopper, MD, FDSRCS, FRCS,l London and Winchester, UK, Thessaloniki, Greece, and Amman, Jordan UNIVERSITY COLLEGE LONDON MEDICAL SCHOOL, UNIVERSITY COLLEGE LONDON EASTMAN DENTAL INSTITUTE, ROYAL HAMPSHIRE COUNTY HOSPITAL, UNIVERSITY COLLEGE LONDON HOSPITALS, ARISTOTLE UNIVERSITY, UNIVERSITY COLLEGE LONDON HOSPITALS HEAD AND NECK CENTRE, AND ROYAL MEDICAL SERVICES

Objective. Earlier reports, including a preliminary study within our unit, have shown that the surgeon’s experience is one of the most influential factors in determining the likelihood of both permanent inferior alveolar nerve (IAN) and lingual nerve (LN) paresthesia, following third molar surgery. The effect of this and other factors influencing such prevalence are assessed in this study. Study design. This prospective study involved 3236 patients who underwent surgical removal of impacted third molars. Patients’ demographics and radiological parameters were recorded along with the grade of the treating surgeon. The prevalence of inferior alveolar and lingual nerves paresthesia at 1 month, 6 months, and 18 to 24 months postoperatively were also traced. Results. At 1 month postoperatively, the incidence of IAN paresthesia was 1.5% and the LN was 1.8%. These figures decreased over time and 18 to 24 months postoperatively, the incidence of permanent dysfunction of the IAN was 0.6% and LN was 1.1%. With regard to inferior alveolar nerve paresthesia, risk factors included the patient’s age (2630 years), horizontally impacted teeth, close radiographic proximity to the inferior alveolar canal (IAC), and treatment by trainee surgeons. With regard to the lingual nerve, risk factors included male patients, distoangular impactions, close radiographic proximity to the IAC, and treatment by trainee surgeons. Conclusion. One of the main risk factors of developing permanent sensory dysfunction in the distribution of these nerves is related to the surgical skills/experience of the operator. Other factors are associated with the type of a

Senior Clinical Research Fellow, UCLH Head and Neck Centre; Senior Research Fellow, Department of Surgery, University College London Medical School; Lecturer, Unit of Oral and Maxillofacial surgery, UCL Eastman Dental Institute, London, UK. b Senior Lecturer, Department of Surgery, University College London Medical School, London; Consultant Head and Neck Surgeon, Royal Hampshire County Hospital, Winchester, UK. c Senior House Officer, Department of Oral and Maxillofacial Surgery, University College London Hospitals, London, UK. d Clinical Research Fellow, Department of Oral Surgery and Radiology, School of Dentistry, Aristotle University, Thessaloniki, Greece. e Senior House Officer, Department of Oral and Maxillofacial Surgery, Eastman Dental Hospital, University College London Hospitals, London, UK. f Specialist Registrar, UCLH Head and Neck Centre, London, UK. g Clinical Research Assistant, UCLH Head and Neck Centre, London, UK.

h

Clinical Researcher, Department of Medicine, University College London Medical School, London, UK. i Clinical Researcher, UCLH Head and Neck Centre, London, UK. j Specialist, Department of Oral & Maxillofacial Surgery, Royal Medical Services, Amman, Jordan. k Oral Surgeon, Department of Oral and Maxillofacial Surgery, Eastman Dental Hospital, University College London Hospitals, London, UK. l Head of the Academic Surgical Unit, Consultant Oral & Maxillofacial Surgeon, Eastman Dental Hospital and University College London Hospitals, London, UK. Received for publication Jul 4, 2009; returned for revision Sep 20, 2009; accepted for publication Oct 7, 2009. 1079-2104/$ - see front matter © 2010 Mosby, Inc. All rights reserved. doi:10.1016/j.tripleo.2009.10.010

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impaction and the radiographic proximity of the tooth to the inferior alveolar nerve. Such long-term complications can affect the patient’s quality of life; the impact on profession, education, and research is unknown. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2010;109:335-345)

It is well recognized that the surgical removal of third molars carries a risk of injury to both the inferior alveolar nerve (IAN) and lingual nerve (LN),1,2 In fact the most common cause of IAN and LN injury is traumatic third molar surgery, shown by Tay and Zuniga3 to account for 52% of referrals. Other less common etiologies include locoregional anesthetic injections, endodontic treatment, orthognathic surgery, and implant surgery.3-5 Paresthesia, anesthesia, and dysesthesia of the IAN and LN are unwanted complications of third molar surgery that are frequently disturbing to both the patient and the practitioner.6 Previous studies have shown there to be a wide range in the incidence of IAN and LN injuries causing paresthesia, from 0.4%7 to 8.4%8 and 0%9 to 23.0%,10 respectively. The inferior alveolar nerve travels within the inferior alveolar canal (IAC) in the mandible, and is thus supported by the alveolus and the neurovascular bundle. Anatomically the inferior alveolar vein is the most superior structure in the canal. When rotary instruments penetrate the canal, the bleeding will alert the surgeon that the superior aspect of the bony canal has been breached and the vein is injured. More profuse bleeding usually indicates damage to the inferior alveolar artery, which lies underneath the vein and superior to the nerve. Nonsurgical removal of the third molar is unlikely to cause any damage to the nerve unless excessive force has been used.11-13 If the IAN is injured, unless it is displaced by bony fragments from the roof of the IAC or displaced into the socket, it will remain within the canal and regenerate. Regeneration is relatively quick, healing is favourable, and good recovery of sensation is expected.1 The radiographic position of the third molar in relationship to the IAC has been shown to be useful in assessing the risk of damage to the IAN following extraction.11-13 The lingual nerve lies at first beneath the lateral pterygoid muscle, medial to and in front of the inferior alveolar nerve. The nerve then passes between the medial pterygoid muscle and the ramus of the mandible. Unlike the IAN, the LN is not supported by a bony canal. Following injury, the LN fibers retract and often become trapped within scar tissue. This may require surgical release and microneurosurgical repair; the success rate of this procedure is modest.1 Most studies have shown that paresthesia of the LN and IAN is likely to be temporary and resolve within

the first 6 months. This depends on the type of injury (i.e., stretch, crush, section) and presence of severe inflammation. However, if no improvement is seen after 2 years of follow-up, the altered sensation is likely to represent nerve dysfunction.12,14 Some studies have reported a lower rate of recovery of the injured LN compared with the IAN,15,16 but the results of other studies17,18 have failed to support this. The aim of this study was to develop upon the work of the preliminary study,19 collecting data from a larger patient group. The incidence of sensory impairment following third molar surgery was assessed and factors related to the surgical removal of third molars were recorded. The two were compared to assess which factors were influential in determining/predicting outcome. MATERIALS AND METHODS This prospective study involved 3236 patients who underwent surgical removal of impacted lower third molars from 1998 to 2006. Patients’ demographics were recorded along with the radiological characteristics for each case. The patients were randomized into 2 groups using a computer format. Patients included in the study had their third molars removed surgically at the University College Hospital, London. The study protocol was approved by the Joint University College London/University College London Hospital Committees of the Ethics for Human Research. All surgical procedures were performed in similar clinics, equipped with similar surgical instruments, rotary and irrigation devices, and materials (sutures and hemostatic agents). Prior to surgery, each patient was informed of the possible complications and provided fully informed consent. Local anesthesia was applied (2% lidocaine with 1:80,000 epinephrine) by local tissue infiltration and/or inferior alveolar nerve regional block. A standard surgical approach was implemented in all cases. An envelope mucoperiosteal flap was reflected and bone was removed buccodistally. Sectioning of the tooth was carried out when needed. The wound was carefully irrigated and any bony spicules removed. The flap was then repositioned and sutured with 4/0 Vicryl. Lingual flaps were not employed in any of the cases. No patient in this study underwent coronectomy, and no lingual or buccal split techniques were used. During the immediate postoperative phase, all patients were given written instructions about wound care

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and possible complications. All patients were prescribed the recommended analgesics and antimicrobials, and were reviewed postoperatively. The cases were distributed among specialists and residents randomly regardless of patient’s age, gender, or even complexity of surgery. Patients were excluded from the study if their records showed that they failed to follow-up during the postoperative review process. The procedures were performed by 12 surgical residents and 7 surgical specialists. No weight was given to the year of training; it is expected that junior specialists performed better surgery, with fewer complications, when they became senior specialists. The same principle applies to junior trainees in their first year and, for example, fourth year in the study. “Surgical specialist” refers to a specialist in oral surgery or a specialist registrar in oral and maxillofacial surgery; the surgical experience in third molar surgery is expected to vary between 5 and 15 years. Whereas “surgical resident” refers to a clinical assistant in oral surgery or a senior house officer in oral and maxillofacial surgery; the surgical experience in third molar surgery is expected to be less than 5 years. Data concerning alteration of sensation of the lip/chin and tongue were collected as originating from the inferior alveolar and lingual nerves, respectively. This was mainly volunteered by the patient, or the clinician inquired regarding the experience of “paresthesia,” “pins and needles,” or “numbness.” Patients who presented with paresthesia during the first month postoperatively were followed up to 18 to 24 months. Patients who continued to present with paresthesia beyond this period were considered to have a permanent nerve dysfunction. Data were collected upon proformas. A random sample of 100 proformas was taken and reviewed by an independent assessor to ensure quality of data entry. Statistical Package for Social Scientists (SPSS version 14.0, SPSS Inc., Chicago, IL, USA) was used. The outcomes of paresthesia affecting the lingual nerve and inferior alveolar nerves were summarized as frequencies for a series of time intervals after surgery (1 month, 6 months, 18-24 months). The results were then cross tabulated and the chi-squared statistic was used to test for differences in the incidence of paresthesia of the inferior alveolar and lingual nerves in relation to the various factors assessed. Fisher’s exact test was used for the analysis of contingency tables and therefore to measure the P value. RESULTS The 3236 patients treated had a mean age of 24.2 years. The age of the patients in this study ranged from 17 to 36 years. The 21- to 25-year age group had the largest number of patients (1594/3236, 49.2%). There

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Table I. Profile of treated cases Category

Description

Age, y

Mean Std. Error Mean Median SD Range Minimum Maximum 95% CI

Age groups

Group 1 (17-20y) Group 2 (21-25y) Group 3 (26-30y) Group 4 (⬎30y) Male Female Fully erupted Partially erupted Fully impacted Vertical Mesioangular Distoangular Horizontal ⬎2 mm ⱕ2 mm Trainee Specialist

Gender Degree of impaction

Type of impaction

Proximity to IAC Seniority of surgeon

Value, n (%) 24.2100 0.07441 22.0000 3.93294 19.00 17.00 36.00 (Lower 23.1641, Upper 23.4558) 852 (26.3) 1594 (49.2) 471 (14.6) 319 (9.9) 1445 (44.7) 1791 (55.3) 296 (9.1) 2572 (79.5) 368 (11.4) 1128 (34.9) 1518 (46.9) 318 (9.8) 272 (8.4) 705 (21.8) 2531 (78.2) 1565 (48.4) 1671 (51.6)

CI, confidence interval; IAC, inferior alveolar canal.

Table II. Prevalence of IANP and LNP at specific time intervals after surgery Time after surgery 1 month 6 months 18-24 months

IANP, n (%)

LNP, n (%)

48 (1.5) 45 (1.4) 20 (0.6)

57 (1.8) 52 (1.6) 37 (1.1)

IANP, inferior alveolar nerve paresthesia; LNP, lingual nerve paresthesia.

was a slight predominance of female patients in this study (1791/3236, 55.3%). Most of the teeth were partially impacted (2572/3236, 79.5%) with either vertical (1128/3236, 34.9%) or mesial (1518/3236, 46.9%) spatial relationship. Over three quarters (2531/3236, 78.2%) of the teeth were close to the IAC, when assessed on the 2-dimensional orthopantomograph (Table I). After 1 month, 48 patients (1.5%) experienced IAN paresthesia and 57 (1.8%) experienced LN paresthesia. The prevalence of paresthesia at 6 months had only slightly reduced to 45 (1.4%) and 52 (1.6%) in the distribution of the IAN and LN, respectively. At 18 to 24 months postoperatively, 20 patients (0.6%) still exhibited IAN paresthesia and 37 patients (1.1%) still exhibited LN paresthesia (Table II). Our study of the factors predictive of permanent IAN paresthesia after 18 to 24 months revealed that 0.8% of

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Table III. Predictors of temporary and permanent IANP Description

IANP prevalence, n (%) at 1 mo

IANP prevalence, n (%) at 6 mo

IANP prevalence, n (%) at 18-24 mo

Group 1 (17-20y) Group 2 (21-25y) Group 3 (26-30y) Group 4 (⬎30y) Male Female Fully erupted Partially erupted Fully impacted Vertical Mesioangular Distoangular Horizontal ⬎2 mm ⱕ2 mm Trainee Specialist

6 (0.7) 18 (1.1) 21 (4.5) 3 (0.9) 19 (1.3) 29 (1.6) 0 (0.0) 44 (1.7) 4 (1.1) 16 (1.4) 14 (0.9) 10 (3.1) 8 (2.9) 13 (1.8) 35 (1.4) 39 (2.5) 9 (0.5)

6 (0.7) 18 (1.1) 18 (3.8) 3 (0.9) 16 (1.1) 29 (1.6) 0 (0.0) 41(1.6) 4 (1.1) 13 (1.2) 14 (0.9) 10 (3.1) 8 (2.9) 13 (1.8) 32 (1.3) 36 (2.3) 9 (0.5)

5 (0.6) 2 (0.1) 12 (2.5) 1 (0.3) 5 (0.3) 15 (0.8) 0 (0.0) 16 (0.6) 4 (1.1) 4 (0.4) 7 (0.5) 4 (1.3) 5 (1.8) 8 (1.1) 12 (0.5) 19 (1.2) 1 (0.1)

Chi-squared (df) at 18-24 mo

P value at 18-24 mo (Fisher’s)

35.347 (3)

⬍.001

3.145 (1)

3.195 (2)

⫽.076 (⫽.112) ⫽.202

3.525 (1)

⬍.001 (⬍.001)

3.910 (1)

⫽.048 (⫽.058)

17.528 (1)

⬍.001 (⬍.001)

IANP, inferior alveolar nerve paresthesia.

the female and 0.3% of the male patients sustained permanent nerve impairment. This was more frequently associated with third molars recorded as fully impacted (1.1%) than with partially impacted teeth (0.6%). There was also a much higher prevalence of permanent IAN paresthesia in the group of patients with horizontally impacted third molars (1.8%), those treated by trainees (1.2%), and those in the 26- to 30-year age group (2.5%). These 3 factors were all found to be strongly statistically significant (P ⬍ .001) (Table III). Our study of the predictive factors of permanent LN paresthesia after 18 to 24 months revealed that 0.6% of the female and 1.8% of the male patients sustained permanent nerve impairment. This difference was statistically significant (P ⫽ .002). Permanent LN paresthesia was more frequently associated with third molars recorded as partially impacted (1.3%) than with fully erupted teeth (1.0%). There was also a much higher prevalence of permanent LN paresthesia in the group of patients with horizontally impacted third molars (6.3%) and those treated by trainees (2.0%). The percentage of patients with permanent LN paresthesia was higher when the third molar was radiographically less than or equal to 2 mm from the inferior alveolar canal (1.5%). Factors found to be highly significant in relation to permanent LN paresthesia were the third molar angulation, radiographic distance from the IAC, and grade of operator (P ⬍ .001) (Table IV). DISCUSSION In 1951, Sunderland20 proposed a classification of nerve injuries. It is based on the theory that the degree of sensory disturbance and subsequent recovery follow-

ing nerve injury depend on the severity of the insult. The classification involved neuropraxia, axonotmesis, rupture of endoneurium or perineurium, neurotmesis, and perineural inflammation. Injuries to the inferior alveolar nerve To some extent, the risk of injury to the IAN may be assessed preoperatively, through examination of the radiographic relationship of the third molar to the inferior alveolar canal. Although standard radiographs only provide a 2-dimensional image of the 3-dimensional anatomies, by using morphological and location characteristics, in some cases the higher likelihood of IAN injury may be anticipated.11-13 IAN injury and a subsequent sensory disturbance may occur after direct or indirect trauma during third molar removal.11,21 For example, it may result from compression of the nerve by root elevators leading to blunt nerve trauma or the elevated roots. The IAN may be damaged by rotating instruments used for the surgical procedure or after IAN regional anesthetic block injections.22 Other possible causes of trauma to the IAN during third molar surgery include clinical observation of the neurovascular bundle during surgery and excessive haemorrhage into the socket during surgery. Tay and Go23 found that if an intact inferior alveolar nerve bundle is observed during third molar surgery, this indicates an intimate relationship with the third molar and has a 20% risk of postoperative paresthesia, with a 70% chance of recovery within 1 year. Damage to the nerve is also more likely when the tooth is completely impacted in bone and/or the apices of the tooth extend into or below the level of the neurovascular bundle.

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Table IV. Predictors of temporary and permanent LNP Description

LNP prevalence, n (%) at 1 mo

LNP prevalence, n (%) at 6 mo

LNP prevalence, n (%) at 18-24 mo

Group 1 (17-20y) Group 2 (21-25y) Group 3 (26-30y) Group 4 (⬎30y) Male Female Fully erupted Partially erupted Fully impacted Vertical Mesioangular Distoangular Horizontal ⬎2 mm ⱕ2 mm Trainee Specialist

9 (1.1) 35 (2.2) 10 (2.1) 3 (0.9) 36 (2.5) 21 (1.2) 3 (1.0) 51 (2.0) 3 (0.8) 18 (1.6) 17 (1.1) 9 (2.8) 13 (4.8) 3 (0.4) 54 (2.1) 44 (2.8) 13 (0.8)

6 (0.7) 33 (2.1) 10 (2.1) 3 (0.9) 33 (2.3) 19 (1.1) 3 (1.0) 49 (1.9) 0 (0.0) 15 (1.3) 17 (1.1) 7 (2.2) 13 (4.8) 3 (0.4) 49 (1.9) 42 (2.7) 10 (0.6)

6 (0.7) 18 (1.1) 10 (2.1) 3 (0.9) 26 (1.8) 11 (0.6) 3 (1.0) 34 (1.3) 0 (0.0) 9 (0.8) 12 (0.8) 5 (1.6) 11 (4.0) 0 (0.0) 37 (1.5) 31 (2.0) 6 (0.4)

Chi-squared (df) at 18-24 mo

P value at 18-24 mo (Fisher’s)

5.573 (3)

⫽.134

9.938 (1)

4.987 (2)

⫽.002 (⫽.002) ⫽.083

3.428 (1)

⬍.001 (⬍.001)

10.434 (1)

⫽.001 (⬍.001)

18.804 (1)

⬍.001 (⬍.001)

LNP, lingual nerve paresthesia.

Hence, neuropraxia or axonotmesis can take place at any point during the procedure. If the IAN directly traverses the root of the tooth, when the tooth is elevated the IAN may be dissected, resulting in neurotmesis. The incidence of permanent paresthesia of the inferior alveolar nerve found in this study was found to be consistent with our preliminary study19 and some other studies,7,9,24,25 but inconsistent with others.8,13,26,27 Injuries to the lingual nerve The position of the lingual nerve is variable and although all efforts are made to avoid lingual nerve trauma during third molar surgery, lingual nerve damage may sometimes be inevitable. Kiesselbach and Chamberlain28 studied the variable position of the lingual nerve. In 17.6% of the dissections, the lingual nerve was found at the level of the alveolar crest or higher. Horizontally, the nerve contacted the lingual plate of the third molar in 62% of the specimens. Of 256 patients, the nerve was visualized above the height of the lingual plate of the lower third molar in 12 (4.6%). These results document the vulnerability of the lingual nerve as it passes medially to the mandibular third molar. As a result, clinicians cannot depend on the lingual plate to act as a protective barrier during third molar surgery. The inconsistent position of the lingual nerve in the region of the retromolar area means that it may be subject to damage throughout the procedure— during incision, buccal flap elevation, flap retraction, tooth sectioning and removal, and suturing. Minimal interference of the lingual soft tissues during third molar surgery is associated with a lower

incidence of lingual nerve trauma, compared with the incidence when lingual flaps are raised.29,30 Some studies have shown that the raising of a lingual mucoperiosteal flap, clumsy instrumentation, and lingual plate fracture may result in lingual nerve paresthesia.21,31-34 The lingual nerve may be protected from direct trauma with instruments, by positioning a periosteal elevator underneath the lingual periosteum. However, when this technique is used by less experienced surgeons, there is a greater chance of stretching the lingual nerve.18,21,34,35 There have been several reports of the use of lingual retractors17,36 and rotating instruments leading lingual nerve damage.37 Rood37 suggested that IAN and LN damage was significantly related to bone removal with a surgical drill, and the application of a Howarth’s periosteal elevator (retractor) is of no benefit. Absi and Shepherd38 also came to the same conclusions. The type of retractor used may also affect the outcome. Rood18 also found that even if the Howarth’s perisoteal elevator is carefully positioned, it is not wide enough to protect the lingual nerve along the whole length of the surgical field. He suggested that the retractor should be continually repositioned to provide optimum protection. Greenwood et al.39 compared the Howarth’s elevator with a broader retractor. They found that the use of the second resulted in a reduced incidence of tongue numbness 1 month postoperatively and thus offered greater protection of the lingual nerve. A systematic review by Pichler and Beirne40 concluded that the use of a lingual nerve retractor during third molar surgery was associated with an increased incidence of temporary nerve damage, but did not influence that rate of permanent

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nerve damage. Other studies have suggested that there is no indication for the use of periosteal elevators as retractors during third molar surgery.41,42 Lingual nerve injury has also been shown to be sometimes related to infection, haematoma formation, swelling,11,12 and IAN regional anesthetic block injections.43 The incidence of permanent paresthesia of the lingual nerve found in this study was found to be consistent with the preliminary study19 and some other studies7,44-46 but inconsistent with others.18,24,26,39 The findings of the preliminary study showed that the rate of recovery of patients who had LN damage was faster compared with patients with IAN damage and it has been previously suggested that this is because LN injury was due to neuropraxia.17-19 However, this was not true in the data collected from our patients, where the rate of recovery was similar in both groups. Degree and type of impaction and proximity of the tooth to the inferior alveolar canal Teeth were considered to be partially erupted if any part the crown was superior to the superior border of the alveolar ridge. Permanent IAN and LN sensory dysfunction was extremely low following the removal of fully erupted teeth. With regard to the IAN, it was slightly higher in teeth that were fully impacted compared with those that were partially impacted, but this was not found to be statistically significant. In the group of fully impacted teeth there were no cases of permanent lingual nerve injury. These findings are consistent with those of the preliminary and other studies.19,32,47 The prevalence of both IAN and LN permanent damage was significantly higher when teeth were horizontally impacted. The degree and angulation of the impacted tooth are likely to be directly related to the amount of bone needed to be removed to allow removal. However, unusually, some authors have found that mesioangularly impacted teeth are most closely positioned to the inferior alveolar canal and have suggested such teeth are more likely to be associated with nerve damage.12,48 When third molar surgery is of greater complexity and more bone removal is required, especially with horizontally and distally impacted teeth, some studies have found there is a greater risk of nerve damage.12,47,49 This may offer a possible explanation for our findings. A close radiographic proximity of the inferior alveolar canal to the third molar was (statistically) significantly associated with higher incidence of permanent IAN and LN damage. Although, in our preliminary study this relationship was identified, it was not found to be statistically significant. Interestingly, the signifi-

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cance was greater with LN damage (P ⬍ .001) than IAN damage (P ⫽ .048). Like some previous studies, the results of this study strongly suggest that there is a relationship between the incidence of permanent IAN and LN dysfunction and the anatomical position of the extracted tooth, which is directly related to the type of impaction and distance from the IAC, which may be assessed radiographically.32,47 Jerjes et al.49 assessed the likely surgical difficulty of third molar extraction and evaluated the relationship between preoperative findings on dental panoramic tomographs and postoperative inferior alveolar nerve paresthesia. They concluded that patients whose third molars were assessed to be “very difficult,” had a 95% chance of developing permanent numbness. Where third molars radiographically appeared to touch the inferior alveolar canal, patients had a 60% probability of experiencing numbness following extraction. Other studies have found that there is no relationship between the proximity of the third molar to the inferior alveolar canal and the incidence of paresthesia.27,50 Although no coronectomies were performed in this study, some authors have suggested that coronectomy as opposed to extraction of third molars that have radiological evidence of proximity to the inferior alveolar canal is preferable.51,52 Renton et al.51 found that coronectomy reduces the incidence of injury to the IAN, without other adverse effects. In their study, no patients who underwent successful coronectomy of the third molar experienced paresthesia, compared with 19% of the patients whose third molar was extracted. However, Pogrel et al.52 noted that hollowing coronectomy and subsequent migration of the third molar roots may be an issue in the long term. Studies have shown that preoperative treatment with a combination of dexamethasone and dyprone prevents sensory hypersensitivity of the inferior alveolar and lingual nerves following third molar extraction.53 These drugs may play a role in the management of patients at high risk of nerve injury, identified using the factors described, including radiographic assessment, although further research is necessary. Iatrogenic injury of the inferior alveolar and lingual nerves during third molar surgery may have legal implications, as it can lead to actions for damage and compensation for personal suffering. In a study by Pogrel and Thamby,54 40% of the patients who experienced nerve damage were involved in litigation. Informed consent about the risk of nerve damage should be obtained before surgery.17 If there are predictive factors seen on a radiograph that put an individual patient at higher risk of nerve damage, the patient should be informed.

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Patient’s age and gender Some work has shown that inferior alveolar nerve injury occurs more frequently in patients of an older age.25,47,55,56 However, this was not demonstrated by this study and in fact the prevalence of permanent IAN dysfunction was found to be significantly higher in patients between 26 and 30 years of age. This contradicts the suggestions of some authors who have advocated the prophylactic removal of third molars in younger patients to minimize complications such as permanent sensory disturbance.45,55 For example, Blondeau and Daniel56 suggested that surgery in patients older than 24 years of age should be avoided if possible. Previous studies have also suggested that nerve dysfunction and postoperative complications are more common in female patients.22,56 However, we failed to demonstrate this in both the preliminary study19 and this study. Other studies have also not confirmed any association between the prevalence of nerve damage and patient’s gender.35 Although in this study the proportion of female patients suffering from permanent inferior alveolar nerve paresthesia was greater, it was not statistically significant. Interestingly, permanent lingual nerve paresthesia was significantly higher (P ⫽ .002) in male patients. This is consistent with the findings of Tay and Go23 who found that male gender was a risk factor for paresthesia. In March 2000, the National Institute for Health and Clinical Excellence (NICE) issued to the National Health Service (NHS) their guidance on the removal of wisdom teeth. NICE recommended that the routine practice of prophylactic removal of pathology-free impacted third molars should be discontinued in the NHS. These guidelines aimed to reduce the prophylactic removal of third molars to reduce the rate of unnecessary postoperative complications. However, there is no evidence-based study, to date, which suggests that prophylactic removal of third molars could be associated with higher complications rate. The Royal College of Surgeons of England suggested that it is unreasonable to remove “pathology-free” impacted third molars in the absence of good evidence to support prophylactic surgery, whereas the Scottish (Royal College of Physicians of Edinburgh) and American Guidelines (American Association of Oral and Maxillofacial Surgeons) don’t prohibit prophylactic removal of third molars but recommend that each case should be dealt with on its own merit where benefits outweigh risks to avoid postoperative complications and litigation. Surgeon’s experience The percentage of patients with permanent IAN and LN damage in this study is similar to that of the patients in the preliminary study and consistent with most stud-

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ies, with regard to the experience of the operating surgeon.7,26,32,35,56-58 Throughout the follow-up period, patients treated by trainees showed a higher prevalence of both IAN and LN paresthesia. This is despite both groups of surgeons removing relatively equal numbers of teeth considered radiographically to be in close proximity to the IAC. In this study and the preliminary study,19 the number of patients with paresthesia is relatively small. Without performing multiple regression analysis to assess multiple factors simultaneously, it is not possible to eliminate the presence of potential confounding factors influencing the results. Follow-up and treatment Alling et al.15 reported spontaneous recovery at the level of 96% in the IAN and 87% in the LN in the first 4 to 8 weeks after third molar surgery. Meyer59 suggested that where there is recovery of sensation after 4 weeks, there is an excellent prognosis and the type of nerve injury is likely to have been neuropraxia. He also suggested where there is recovery of sensation between 1 and 3 months, nerve injury was likely to have resulted from axonotmesis and that any failure to recover after this time is suggestive of neurotmesis being the etiology. Pogrel60 suggested a follow-up regimen for patients complaining of lip and tongue numbness following third molar surgery. This consisted of review every 2 weeks for 2 months, every 6 weeks for 6 months, every 6 months for 2 years, and then on an annual basis indefinitely. If no active treatment is performed, the frequency of appointments in this regimen may be considered unwarranted. Although the recovery after nerve damage after 2 years has been reported in a small group of patients,61 generally if a patient still reports numbness at the end of a monitoring period of 2 years, permanent nerve damage is considered.62 Management and assessment of nerve-injury–induced anesthesia and dysesthesia are problematic. Monitoring recovery using simple sensory testing allows those patients who may benefit from intervention to be identified and there is good evidence that these patients may benefit from early intervention.63 Surgical exploration, decompression, or repair of the nerve may be considered. Various methods for assessing lingual nerve injury have been described. van der Glas et al.64 reported on an objective test based on inhibitory reflexes in masseteric electromygraphic activity following electrical stimulation of the oral tissue on the injured and control sides. They suggested that this test may have conclusive prognostic value or be used to influence surgical

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therapeutic decisions. The analysis of somatosensory evoked potentials in the assessment of inferior alveolar nerve following third molar removal was studied by Ghali et al.65 They found that, when compared with electrical stimulation, 2-point discrimination in the mental nerve area, visual analogue scale subjective ratings of electrical stimulation, and somatosensory evoked potentials were the most sensitive methods of analysis. The other advantage being that it provides an objective as opposed to subjective evaluation technique.65 Renton et al.66 showed that quantitative thermosensory testing may be useful in identifying patients with inferior alveolar and lingual nerve injuries. As explained earlier, permanent lingual nerve damage may sometimes require electrographic exploration. Direct recording of the lingual nerve requires its puncture at the foramen ovale, which can be extremely dangerous. Trost et al.67 recently proposed a novel method of reaching the lingual nerve through the intraoral puncture at the intermaxillary commisure, thus modifying the inferior alveolar technique. They suggest that this method may be performed as routinely as electrographic exploration of the lingual nerve. Loescher et al.1 suggested a few indications for surgical intervention of a damaged inferior alveolar nerve. These include if the nerve is completely divided and the severed ends misaligned, if a bony fragment has compressed the mandibular canal, or if the patient suffers from persistent neuropathic pain. In contrast, the same authors suggested that surgical intervention of a damaged lingual nerve is indicated when sensory testing demonstrates no neural recovery within 3 to 4 months.1 This would involve exploration of the injury site to assess the continuity and microsurgical repair of the damaged nerve.1,6,57 Yachouh et al.68 stress the importance of early repair and good-quality suturing of the damaged lingual nerve in increasing the likelihood of the return of sensation. However, when a patient reports improvement of sensation or acceptable sensory deficit, noninterventional follow-up is advised. Surgical intervention is contraindicated in patients with central neuropathic pain or medical neuropathy, who are medically compromised, or who have dysesthesia not resolved by a nerve block.59,69 Many novel techniques for the treatment of nerve damage and forms of microneurosurgical repair of damaged inferior alveolar and lingual nerves have been suggested.2 Farole and Jamal70 conducted a study on a small series of patients using a bioabsorbable collagen cuff for the repair of inferior alveolar and lingual nerve injuries following third molar surgery with good preliminary results. Ka et al.71 found that acupuncture may be useful in treating sensory injury following third

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molar surgery. However, other evidence to support this is limited. Psychosocial impact Much of the third molar surgery literature focuses on clinical assessment and management in order to achieve healing. Some third molar surgery complications should be classified as a chronic or long-term (defined as a condition, “that is currently not curable and therefore can only be managed”),72 although it is not generally acknowledged as such. There is an inadequate body of literature that focuses on the psychosocial issues that can affect the quality of life of patients with long-term complications. These include the emotional impact of pain, long-term sensory deficit, social support, coping mechanisms and response to stress, and treatment adherence. Health care professionals are becoming increasingly aware of the impact psychosocial issues may have on wound healing in general. There is need to consider alternative intervention measures for patients for whom healing may not be a realistic option. It is also wise to remember that some patients are more anxiety prone. This group of patients is more likely to develop postoperative complications and suffer poor wound healing, and hence have a troublesome recovery. If such patients are identified in the assessment phase, full psychological counseling is advised. The limited surgical experience can, sometimes, negatively affect the patient and might be related to a number of postoperative complications. Other factors that have been implicated include the practitioner’s approach to the patient. Anxiety and stress can be significant when training of an undergraduate or junior surgeon takes place in a clinic where the patient retains consciousness and can hear the conversation. Several studies have shown that psychological interventions can elevate the patient’s pain threshold and be associated with a lower complication rate.72 Impact on the profession, education, and research All UK dental schools provide undergraduate training in oral surgery in accordance with the guidelines provided by the General Dental Council (GDC). However, the courses vary with regard to the departments involved and the level of student participation. Training is likely to comprise basic familiarization with the principles of oral surgery and the factors that determine which patients should be referred for specialist advice. Nonsurgical removal of third molars is usually practiced at the undergraduate level; however, some dental schools have introduced a new scheme that allows dental undergraduates to perform surgical extractions. Irreversible anatomical damage has been reported and

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re-treatment may be complex or impractical. Usually these procedures take place under senior supervision or with the senior acting as an “assistant.” A number of issues underlie the practice of oral surgery, including the preparation and continuing surgical education of practitioners. In past times, the doctor was generally not troubled by litigation from patients presenting as emergency cases (i.e., severe jaw pain), but this aspect of practice has changed. Litigation by patients now significantly affects dental and surgical practice and vicarious liability often affects hospitals. It is expected that the development of national uniformity in the research, teaching, and assessment of clinical skills can lead to some progress in developing a high-standard service across the country and reduce the number of litigations. Hospitals need to adopt a risk management approach, including assessment of the competence of dental practitioners, particularly in procedural skills. CONCLUSIONS The findings of this study are similar to the preliminary study19 and to other studies, with permanent sensory loss of the inferior alveolar and lingual nerves to be 0.6% and 1.1%, respectively. Although these figures are relatively low, they are still of great significance for both patients and clinicians and may have legal implications. All patients must be warned of the risks of third molar surgery, including possible damage to the inferior alveolar and lingual nerves and informed consent must be obtained before the procedure. With regard to the inferior alveolar nerve, factors found to be associated with a significantly higher incidence of paresthesia included patients in the 26- to 30-year age group, with horizontal impactions, close radiographic proximity to the inferior alveolar canal, and treatment by trainee surgeons. With regard to the lingual nerve, factors found to be associated with a significantly higher incidence of paresthesia included male patients, distoangular impactions, close radiographic proximity to the inferior alveolar canal, and treatment by trainee surgeons. Therefore, this study also highlights the importance of careful preoperative clinical and radiographic assessment of patients where third molar surgery is planned. The surgical technique of third molar removal is also likely to have great impact on the outcome. Clinicians should have an adequate knowledge of how to assess and manage complications such as paresthesia. They should also know when specialist referral is appropriate, with regard to the possible need for microsurgical exploration and repair of the damaged nerve. The findings of this study in that permanent paresthesia of the inferior alveolar and lingual nerves is

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significantly higher when patients are treated by more junior surgeons may have implications on the provision of health care. All steps to minimize these complications must be undertaken to improve patient care. Further research into the influencing factors, prevention, assessment, and treatment of postoperative inferior alveolar nerve and lingual nerve paresthesia is necessary. The authors would like to stress that the impact of the findings from this study on the profession, education, and research is still unknown. Higher evidence-based trials are expected to reveal more parameters that can affect the complication rate in third molar surgery. Dentoalveolar surgery and in particular third molar removal form an integral element of training within the field of oral and maxillofacial surgery. Competence in third molar surgery forms a sound foundation for the skills necessary for some of the more complex surgical procedures performed by oral and maxillofacial surgeons. Because several hundreds of patients are treated per unit each year, this confers third molar removal to be an easily accessible field for the training of both junior and more senior surgeons. One of the main risk factors for developing permanent sensory dysfunction in the distribution of these nerves is related to the surgical skills/experience of the operator. Other factors are associated with the type of impaction and the radiographic proximity of the tooth to the inferior alveolar nerve. Such long-term complications can affect the patient’s quality of life; the impact on profession, education, and research is unknown. REFERENCES 1. Loescher AR, Smith KG, Robinson PP. Nerve damage and third molar removal. Dent Update 2003;30:375-82. 2. Ramadas Y, Sealey CM. Third molar removal and nerve injury. N Z Dent J 2001;97:25-8. 3. Tay AB, Zuniga JR. Clinical characteristics of trigeminal nerve injury referrals to a university centre. Int J Oral Maxillofac Surg 2007;36:922-7. 4. Hillerup S. Iatrogenic injury to oral branches of the trigeminal nerve: records of 449 cases. Clin Oral Investig 2007;11:133-42. 5. Libersa P, Savignat M, Tonnel A. Neurosensory disturbances of the inferior alveolar nerve: a retrospective study of complaints in a 10-year period. J Oral Maxillofac Surg 2007;65:1486-9. 6. Fielding AF, Rachiele DP, Frazier G. Lingual nerve paresthesia following third molar surgery: a retrospective clinical study. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1997;84:345-8. 7. Sisk AL, Hammer WB, Shelton DW, Joy ED Jr. Complications following removal of impacted third molars: the role of the experience of the surgeon. J Oral Maxillofac Surg 1986;44: 855-9. 8. Lopes V, Mumenya R, Feinmann C, Harris M. Third molar surgery: an audit of the indications for surgery, post-operative complaints and patient satisfaction. Br J Oral Maxillofac Surg 1995;33:33-5. 9. Chiapasco M, De Cicco L, Marrone G. Side effects and complications associated with third molar surgery. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1993;76:412-20. 10. Middlehurst RJ, Barker GR, Rood JP. Postoperative morbidity

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Reprint requests: Waseem Jerjes, BDS, MSc (OMFS), PhD (Surg) UCLH Head & Neck Centre 1st Floor East Wing 250 Euston Road London NW1 2PG, UK [email protected]