Risk Factors for Permanent Injury of Inferior Alveolar and Lingual Nerves During Third Molar Surgery

DENTOALVEOLAR SURGERY

Risk Factors for Permanent Injury of Inferior Alveolar and Lingual Nerves During Third Molar Surgery Edward Nguyen, BDSc, MBBS,* Dragan Grubor, BDSc, FRACDS(OMS),y and Arun Chandu, BDSc, MBBS, MDSc, FDSRCS(Eng), FRACDS(OMS)z Purpose:

The purpose of this study was to assess the incidence of and risk factors for permanent neurologic injuries to the inferior alveolar nerve (IAN) or lingual nerve (LN) after the removal of third molars. This report also describes the use of a Clinical Incident Review (CIR) process, allowing close monitoring of all patients with neurologic injuries as a result of dentoalveolar surgery.

Materials and Methods:

A database associated with a CIR process at the Royal Dental Hospital of Melbourne from January 2006 through December 2009 was assessed. Factors assessed included gender, age, operator class, method of anesthesia, spacial relation, depth of impaction, ramus relation, proximity of the IAN on orthopantomogram, cone-beam computed tomographic usage, and side of injury.

Results:

During this 4-year period, 11,599 lower third molars were removed in 6,803 patients. The incidence of an IAN injury was 0.68%, and the incidence of an LN injury was 0.15%. Important risk factors for permanent IAN injury were increasing age, surgery performed by staff dentists, type of anesthesia, and mesioangular impactions. The mean time of complete resolution was 4.3 months. No factors were found to statistically increase the risk of LN injury, although most injuries were seen in patients with a distoangular impaction.

Conclusion:

The overall incidences of IAN and LN injuries were low. Some risk factors for permanent IAN nerve injury were identified. Important risk factors for permanent IAN injury were increasing age ($25 yr old), surgery performed by staff dentists, surgery under general anesthesia, and mesioangular impaction. No factors were found to statistically increase the risk of LN injury. Ó 2014 American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg -:1-8, 2014

Dentoalveolar surgery, in particular the surgical removal of impacted third molars, is a common procedure in oral and maxillofacial surgery with predictable outcomes.1 However, it is well recognized that there are potential complications associated with their removal. These include the risk of injury to the inferior alveolar nerve (IAN) and the lingual nerve (LN).2 IAN and LN injuries also occur with other procedures,

including orthognathic surgery, dental implant surgery, endodontic treatment, and even needle trauma related to IAN blocks, but they occur most commonly after third molar surgery.3 The IAN is the largest branch of the mandibular division of the trigeminal nerve. The IAN arises from the posterolateral surface of the main mandibular trunk and descends deep to the lateral pterygoid muscle

*Registrar, Department of Oral and Maxillofacial Surgery, The

Received June 5 2013

Royal Dental Hospital of Melbourne, Carlton, Victoria, Australia.

Accepted June 25 2014

yConsultant, Department of Oral and Maxillofacial Surgery, The

Ó 2014 American Association of Oral and Maxillofacial Surgeons

Royal Dental Hospital of Melbourne, Carlton; Melbourne Dental School, The University of Melbourne, Melbourne, Victoria, Australia. zConsultant, Department of Oral and Maxillofacial Surgery, The

0278-2391/14/01110-0

Royal Dental Hospital of Melbourne, Carlton; Melbourne Dental School, The University of Melbourne, Melbourne, Victoria, Australia.

http://dx.doi.org/10.1016/j.joms.2014.06.451

Address correspondence and reprint requests to Dr Chandu: Melbourne Dental School, The University of Melbourne, Melbourne, VIC, Australia; e-mail: [email protected]

1

2 and then passes between the sphenomandibular ligament and the ramus of the mandible to the mandibular foramen. The IAN enters the mandibular foramen slightly anterior and superior to the inferior alveolar artery. Then, the IAN passes through the body of the mandible within a bony canal that carries and protects the neurovascular bundle, comprised of a vein, an artery, and a nerve. The nerve gives off branches to supply the teeth and continues as the mental nerve to supply sensation to the lower lip, chin, and mucosa. During surgery, profuse bleeding from the surgical site may indicate damage to the inferior alveolar artery, which lies between the vein and nerve, and therefore also may indicate damage to the IAN.4 The LN branches from the mandibular nerve, traveling medially to the IAN, between the medial pterygoid muscle and the ramus of the mandible. Unlike the IAN, the LN is not supported by a bony canal, and in up to 17.6% of cases the LN can be found at the level of the alveolar crest or higher in the third molar area.5 If lingual tissue injury occurs, the fibers of the LN can be inadvertently damaged, resulting in nerve fiber entrapment in scar tissue. It has been well documented in the literature that the risk factors for IAN and LN injuries include increasing age, unerupted teeth, deep impaction, distoangular impaction, irregular root morphology, lack of clinician experience, lingual flap and retraction, and radiographic signs of proximity of the third molar to the IAN canal.1,6-11 The main forms of altered sensation that can occur include paraesthesia, anesthesia, or dysesthesia, which may be temporary or permanent. The literature reports an incidence of temporary IAN and LN injury ranging from 0.26 to 8.4% and from 0.1 to 22%, respectively, whereas permanent damage ranges from 0.3 to 0.9% for these 2 nerves.1,7,8,10,12 Most studies have reported paraesthesia resolving in the first 6 months. However, the rate of recovery depends on the type of injury and the surrounding inflammatory process initiated.1,7-10 Neurosensory testing is commonly used to assess sensory deficits in maxillofacial procedures, including orthognathic surgery and third molar surgery. These tests consist of subjective assessment of neurosensory function with a visual analog scale (VAS), brush stroke directional discrimination, 2-point discrimination, contact detection, pinprick nociception, and thermal discrimination.13 A classification of neurologic injuries based on mechanism of injury has been described by Sunderland.14 These include compression injury (neurapraxia), severe compression, crush or stretch injury (axonotmesis), complete section of the nerve trunk (neurotmesis), and other injuries (perineural inflammation). The damaged nerve will react by going through stages of Wallerian degeneration and an attempt at axon regener-

PERMANENT NERVE INJURY IN THIRD MOLAR SURGERY

ation, but the altered sensation is likely to remain permanent if there is no change after 1 to 2 years.9,10 In contrast, some researchers have claimed that patients with persistent symptoms are classified as having a permanent nerve injury if there has been no change after 3 months.2,15 It also has been reported that the LN has a lower rate of recovery compared with the IAN.5,16 Permanent altered sensation is more likely to occur where the nerve was severed (neurotmesis) or crushed as a result of sectioning with a rotary instrument or crushing of the nerve as a result of displacement of root tips into the IAN canal. Traditionally, preoperative assessment of the nerve position and risk level for third molar surgery has included a clinical examination and an orthopantomogram (OPG). With cone-beam computed tomographic (CBCT) scanning widely available, imaging in coronal, sagittal, and axial views with 3-dimensional reconstructions is more commonly used in third molar surgery to potentially improve diagnostic assessment and accuracy of anatomic forms and structures and evaluation of risk.17 The purpose of this study was to record the incidence of IAN or LN injuries as a result of third molar surgery at the Royal Dental Hospital of Melbourne (RDHM; Melbourne, Australia) using a Clinical Incident Review (CIR) process and to assess for factors that might influence the rate of permanent neurologic injury.

Materials and Methods A database of patients who have had neurologic complications related to the IAN and LN at the RDHM was assessed. The RDHM is the main public dental referral center for the state of Victoria. Cases were excluded from the study if there was insufficient clinical or radiographic information or if neurologic injuries were not related to the removal of third molars. The database and medical records from January 2006 through December 2009 were reviewed. This study was approved by the human research ethics committee of Dental Health Services Victoria. A database of neurologic complications exists as a result of a CIR system set up by the Department of Oral and Maxillofacial Surgery at the RDHM. Any surgical complications were documented as part of this system manually in the patient’s records and electronically in a register and were assessed in a meeting held on a monthly basis. The team consisted of the head of oral and maxillofacial surgery, surgical trainees, nursing staff, and administrative staff. Each month, reported clinical incidents were discussed, the progress and outcomes were monitored, and strategies were developed to improve patient safety and to refine clinical

3

NGUYEN, GRUBOR, AND CHANDU

guidelines. Insurers of the hospital also were informed of patients added to the CIR database. Preoperative clinical and radiographic data were collected in an attempt to identify predictive risk factors for IAN and LN injuries. These included gender, age, operator type, method of anesthesia, lateral spatial relation, depth of impaction, ramus relation, root morphology, and radiologic proximity to the inferior alveolar canal. These factors are defined in Table 1. With regard to spatial relation, tooth angulation was Table 1. PREDICTIVE PREOPERATIVE CLINICAL AND RADIOGRAPHIC RISK FACTORS FOR INFERIOR ALVEOLAR NERVE AND LINGUAL NERVE INJURIES

Variable (Definition) Gender Age Operator class Method of anesthesia Spatial relation (angulation in relation to long axis of second molar)

Depth of impaction (occlusal level of third molar in relation to second molar)

Ramus relation (distance between third molar and ascending ramus)

Root morphology

Radiologic proximity to inferior alveolar nerve

iCAT (cone-beam computed tomography)

Classification 1. male 2. female 1. <25 yr old 2. $25 yr old 1. dentist or BST 2. AST or specialist 1. GA 2. LA 1. mesioangular 11-79

2. horizontal 80-100 3. vertical 10 to 10 4. distoangular 11 to 79 1. high occlusal level

2. medium occlusal level 3. lower occlusal level 1. sufficient space

2. reduced space 3. no space 1. incomplete root formation 2. conical 3. curved 4. bulbous 1. distant 2. touching 3. crossing 1. yes

2. no Abbreviations: AST, advanced surgical trainee; BST, basic surgical trainee; GA, general anesthesia; LA, local anesthesia. Nguyen, Grubor, and Chandu. Permanent Nerve Injury in Third Molar Surgery. J Oral Maxillofac Surg 2014.

established by measuring with a protractor the long axis of the third molar in relation to the adjacent second molar. To identify depth of impaction, third molars were scored a high, medium, or low occlusal level based on the crown of the third molar in relation to the adjacent erupted tooth. The ramus also was used to define the difficulty of surgery by measuring the distance between the crown of the third molar and the ascending ramus, and third molars were classified as having sufficient, reduced, or no space. With regard to proximity of the third molar to the IAN based on OPG findings, this was classified as distant, touching, or crossing the radiographic IAN canal. Patients who were deemed at high risk of IAN injury, based on the radiographic principles of Rood and Shehab,18 were referred for CBCT scanning to provide additional anatomic information with regard to the proximity of the nerve to the root, and the use of CBCT scanning was documented. All operations were performed under general anesthesia (GA) or local anesthesia (LA) by different operators. During consultation, patients were allocated to surgery under LA or GA depending on several factors, including difficulty and risk of surgery, comorbidities, and psychosocial issues. Operators were classified as staff dentist, basic surgical trainee (BST; first year of oral and maxillofacial surgical [OMS] training), advanced surgical trainee (final 3 years of OMS training), or an oral and maxillofacial surgeon. Staff dentists were nonspecialist or non-OMS trainee dentists working in the department. All trainees were registered with the Royal Australasian College of Dental Surgeons as OMS trainees. During a weekly preoperative planning session, patients are allocated to operators based on estimated surgical difficulty and risk. Surgical procedures performed were standardized with a buccal flap with bone removal and tooth division facilitated by an electric handpiece (40,000 rpm) for procedures completed under LA or a Hall 5058 Surgairtome pneumatic surgical handpiece (100,000 rpm; Conmed Linvetec, Sydney, Australia) was used for those procedures performed under GA; all procedures were performed with saline irrigation. Patients who experienced altered neural sensation in the distribution of the IAN or LN were documented and monitored as part of the CIR process. The standard follow-up protocol for all patients included reviews at 2 weeks and 1, 2, 3, 6, and 12 months after surgery. The level of retained sensation in the affected area was expressed by the patient using a detailed VAS with division of the affected area into 10 fields and assessment of the remaining sensation on a scale from 0 to 10 (Fig 1). Outcomes were categorized as complete resolution, partial resolution, or no improvement. The presence of dysesthesia or pain also was recorded. After 3 months of little or no improvement,

4

PERMANENT NERVE INJURY IN THIRD MOLAR SURGERY

Table 2. DISTRIBUTION OF CASES

Inferior alveolar nerve Lingual nerve

Unilateral Cases

Bilateral Cases

Total Cases

65

2

69

13 78

1 3

15 84

Nguyen, Grubor, and Chandu. Permanent Nerve Injury in Third Molar Surgery. J Oral Maxillofac Surg 2014. FIGURE 1. Stamp diagram used to quantify inferior alveolar nerve distribution sensation. Nguyen, Grubor, and Chandu. Permanent Nerve Injury in Third Molar Surgery. J Oral Maxillofac Surg 2014.

patients were given the option to be referred to a neurosurgery department at an external hospital for assessment with regard to nerve repair surgery. Review appointments for patients experiencing nerve injury were concluded if they experienced complete resolution, were content with the outcome, or were referred to and accepted for treatment in another hospital. At 12 months, the condition was considered permanent. All data were entered into a computer database. Analysis of factors affecting complete, partial, or no resolution was assessed using SPSS 18 (IBM Corporation, Somers, NY). Data were presented in a descriptive fashion. For analysis, outcome was divided into temporary neurologic injury with complete resolution or permanent neurologic injury as a result of partial or no resolution of the neurologic insult. Cross-tabulated analysis of factors associated with permanent nerve injury was assessed using the Pearson c2 test. A P value less than .05 was considered statistically significant.

Results From January 1, 2006 through December 31, 2009, 11,599 mandibular third molars were removed in 6,803 patients. Of these cases, 10,160 involved surgical removal. Eighty-one patients who sustained 84 neurologic injuries were included in the study. Table 2 presents the distribution of cases. The overall incidence of acquiring any nerve injury after the removal of lower third molars was 0.72%. For third molars requiring surgical removal, the incidence of an IAN injury was 0.68%, and the incidence of an LN injury was 0.15%. The incidence of temporary injury to the IAN and LN was 0.44% and 0.069%, respectively. The incidence of permanent injury to the IAN and LN was 0.24% and 0.079%, respectively. Table 3 presents the outcomes of patients reviewed by the CIR process. Of all 69 cases with IAN injuries, 3 (4.3%) reported no improvement in their symptoms during the review period and 21 (30.4%) reported par-

tial resolution. Of the 15 cases of LN injuries, 8 patients acquired permanent nerve injury, with 5 (33.3%) of these patients experiencing partial resolution and 3 (20%) patients reporting no improvement during the review period. The follow-up period for IAN and LN injuries ranged from 1 month to 2 years (mean, 6.7 months). Although most nerve injuries resolved completely in the first month, the mean complete resolution time was 4.3 months (range, 2 weeks to 14 months for the IAN; range, 1 to 4 months for the LN). Table 4 presents factors assessed for permanent IAN injury. Tabulation of data showed that important risk factors for permanent IAN injury were increasing age ($25 yr old), surgery performed by staff dentists, surgery under GA, and mesioangular impactions. No factors were found to statistically increase the risk of LN injury, although most injuries were seen in patients with a distoangular impaction. Fourteen of 15 LN injury cases (93.3%) occurred under GA, with 6 of these cases (40%) resulting in permanent numbness of the tongue. These surgeries were performed by a dentist or BST operators. Three patients with altered nerve sensation opted for neurosurgery referral after a 3-month period of no reported sensation postoperatively and no improvement. The remainder of patients with permanent neurologic deficit declined referral. There were no reported cases of dysesthesia or pain in the IAN and LN groups.

Discussion Proper preoperative assessment of third molar surgery is imperative to minimizing the risk of neurologic Table 3. OUTCOMES OF PATIENTS REVIEWED BY THE CLINICAL INCIDENT REVIEW PROCESS

Inferior alveolar nerve Lingual nerve

Temporary Sensory Loss, n (%)

Permanent Sensory Loss, n (%)

45 (65.2) 7 (46.7)

24 (34.8) 8 (53.3)

Nguyen, Grubor, and Chandu. Permanent Nerve Injury in Third Molar Surgery. J Oral Maxillofac Surg 2014.

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NGUYEN, GRUBOR, AND CHANDU

Table 4. FACTORS AFFECTING PERMANENT IAN NUMBNESS

Temporary Injury

Permanent Injury

Variable

Classification

n

%

n

%

P Value

Gender

1. male 2. female 1. <25 yr old 2. $25 yr old 1. dentist 2. BST 3. AST 4. specialist 1. GA 2. LA 1. mesioangular 2. horizontal 3. vertical 4. distoangular 1. high occlusal level 2. medium occlusal level 3. lower occlusal level 1. sufficient space 2. reduced space 3. no space 1. distant from tooth root 2. crossing or touching tooth root 1. yes 2. no left-hand side right-hand side

7 39 24 22 12 10 9 15 42 4 24 8 10 4 8 22 16 16 28 2 24 22 13 33 21 25

10.1 56.5 34.8 31.9 17.4 14.5 13 21.7 60.9 5.8 34.8 11.6 14.5 5.8 11.6 31.9 23.2 23.2 40.6 2.9 34.8 31.9 18.8 47.8 30.4 36.2

6 17 4 19 12 7 0 4 15 8 8 3 3 9 4 13 6 7 16 0 7 16 2 21 14 9

8.7 24.6 5.8 27.5 17.4 10.1 0 5.8 21.7 11.6 11.6 4.3 4.3 13.0 5.8 18.8 8.7 10.1 23.2 0 10.1 23.2 2.9 30.4 20.3 13.0

NS

Age Operator class

Method of anesthesia Spatial relation

Depth of impaction

Ramus relation

Proximity of IAN on OPG Cone-beam computed tomography Side of injury

.006 .026

.007 .025

NS

NS

.087 NS NS

Abbreviations: AST, advanced surgical trainee; BST, basic surgical trainee; GA, general anesthesia; IAN, inferior alveolar nerve; LA, local anesthesia; NS, not significant; OPG, orthopantomogram. Nguyen, Grubor, and Chandu. Permanent Nerve Injury in Third Molar Surgery. J Oral Maxillofac Surg 2014.

complications. Altered sensation and pain can interfere with a patient’s daily social interaction and functioning, such as speaking, eating, and drinking, and can have a major negative impact on a person’s quality of life.19 Information gained from clinical and radiologic examinations is vital to make an informed decision on surgical difficulty and thus operator suitability. This is most important in the RDHM, a tertiary teaching institution with different levels of operator ability and experience. Therefore, increasingly complex cases are assigned to operators with increasing levels of experience. Clinical incident reporting and reviewing is aimed at minimizing adverse outcomes and improving patient care and safety. However, it has been well documented that difficulties remain with incident reporting in improving patient outcomes. These include operators fearing punitive action, poor safety culture in an organization, lack of understanding among clinicians about what should be reported, lack of awareness of how the

reported incidents will be analyzed, and how the reports will ultimately lead to changes that will improve patient safety.20 In a recent medical review process assessing adverse events and causative factors in all hospital admissions, it was found that 63% of contributing causes to adverse events were undetected by current medical review processes.21 This does not correlate directly with third molar surgery because risk factors for nerve damage are well documented, but it does emphasize the importance of timely and accurate clinical incident reporting. Different factors were identified in this study that predicted an increased risk of permanent IAN injury. These were increasing age ($25 yr old), surgery performed by staff dentists as opposed to OMS trainees or specialists, surgery performed under GA, and teeth with a mesioangular impaction. A consensus of the literature supports the statement that the risk of surgical and postoperative complications increases with age.11,22-24 In the present study, the mean

6 age of the patients with nerve damage was 34 years (median age, 25 yr). Although most permanent IAN injuries occurred in patients older than 45 years, it was found to be a statistically important risk in those older than 25 years. This can be attributed to increased operative difficulty associated with agerelated changes, including increased bone density, decreased bone elasticity, decreased vascularization impairing the nerve regeneration process, and a higher incidence of hypercementosis and thus more bone removal.25 Having third molar surgery after 25 years of age is a positive predictor for permanent neurologic injury, which is in keeping with other studies in the literature.23,26-29 With regard to operator class, the overall incidence of IAN injuries was highest in the staff dentist group (34.8%) followed by specialist oral and maxillofacial surgeons (27.5%); however, 50.0% of injuries in the staff dentist group were permanent compared with 14.3% in the specialist group. As part of the preoperative allocation of patients, those patients considered at high risk of neurologic injury or increased surgical difficulty were allocated to specialists only, which may explain the natural bias of increased neurologic injuries in this group. However, the large number of permanent injuries in the staff dentist group may reflect a lack of experience, different surgical techniques, poor training, improper use of force, and instrument handling. The findings from this study are supported by previous documented studies with regard to surgical training and skills.30,31 A large proportion of third molar surgeries is performed under GA at the authors’ institution and its safety has been previously assessed.32 The day-surgery facilities at the RDHM were considered safe and an optimal method for managing difficult surgical and psychosocial patients and is associated with a low incidence of morbidity. This may explain a higher incidence of permanent injuries under GA than LA in the present study and similar findings have been published previously.11,33 In contrast, Rehman et al,34 using logistic regression, found no difference in neurologic injury rate between different forms of anesthesia. Multiple indices and assessment models have been proposed to establish a reliable method of determining surgical risk and difficulty for third molar removal. The WHARFE assessment calculates a score based on the Winter lines, height of mandible, angle of second molar, root shape and development of the third molar, follicle size, and exit path.35 It has been argued that radiologic assessment alone provides an inaccurate measurement of actual surgical difficulty.36 Although spatial relation, depth of impaction, ramus relation and root morphology were assessed and have been shown to be statistical risk factors in previous studies,2,8,10 the present study showed that third

PERMANENT NERVE INJURY IN THIRD MOLAR SURGERY

molars with a mesioangular angulation contributed to the increased risk of permanent neurologic injury. The proximity of the tooth roots to the IAN has been traditionally assessed by OPGs. Several investigators have assessed the radiographic signs of this association, which include increase in radiolucency, deflection or narrowing of the roots, interruption of the canal lamina dura, or diversion or narrowing of the IAN canal.18,37 In the present study, tooth roots touching or crossing the IAN showed a trend toward increased permanent nerve injury, which is in keeping with the literature.18,37 Recently, it has been suggested that CBCT scanning is an effective method of assessing nerve proximity and can allow risk stratification and thus surgical technique modification.36 In the present study, patients were referred for CBCT scanning if there were high-risk signs on OPG based on the radiographic principles of Rood and Shehab.18 The use of a CBCT image did not alter the risk of permanent nerve injury. To help those at high risk, the coronectomy technique has been advocated to minimize the risk of IAN injury.38-40 In the present study, only a few cases of coronectomy were performed, of which 1 resulted in a temporary paraesthesia. Although this technique has the potential for retained teeth roots to migrate, they can be removed with considerably lower risk to the IAN. The VAS is a common tool in the assessment of neurosensory deficits of the IAN.13 In the present study, not all patients were subject to 2-point discrimination, direction sense testing, or pinprick testing; however, all patients were subject to a standardized subjective VAS. This allowed the longitudinal follow-up of nerve injuries to be quantifiable for trend and outcome. The definition of a permanent nerve injury is a controversial area. In previous studies, it was reported that in the first 4 to 8 weeks after surgery, 96% of IAN and 87% of LN injuries spontaneously resolve and these can be attributed to neuropraxia.41,42 The findings of the present study are in keeping with this finding, because most neurologic disturbances resolved completely within the 4- to 8-week follow-up period. Several investigators have reported that a nerve injury has a poor prognosis and is unlikely to recover after 3 to 9 months if there has been no improvement and is therefore suggestive of neurotmesis.42 Although the resolution of nerve injuries has been reported up to 2 years after surgery,43 some investigators consider the injury permanent if numbness remains at the end of 3 months.2,15,19 This definition of permanent injury may be a little premature because the present data showed that one third of all temporary paraesthesia of the IAN that persisted for longer than 3 months did resolve completely by 4 to 14 months, and the mean time for complete resolution was 4.3 months. In the LN data, there was no resolution after the 3-month follow-up period, which suggests that the LN may be

NGUYEN, GRUBOR, AND CHANDU

at greater risk of neurotmesis or the reparative potential of the special sensory nerve is poorer. In the present study, no factors were statistically meaningful for permanent LN injury. However, risk factors approaching importance included surgery performed by staff dentists, surgery performed under GA, and third molars with a distoangular impaction. Other studies have shown that lingual angulation of the third molar, the use of lingual flap retraction, vertical sectioning of teeth, and surgical inexperience increase the risk of LN damage.10,11 The follow-up regime in the present study provides an opportunity to closely monitor the patient’s recovery for improvement. This is similar to the regime suggested by Pogrel,44 which consists of reviews every 2 weeks for 2 months, every 6 weeks for 6 months, every 6 months for 2 years, followed by annual review indefinitely. However, current practice advocates referral for assessment for microneurosurgical repair at 3 months after surgery, if there is no improvement of complete anesthesia at 3 months, paraesthesia or dysesthesia beyond 4 months, or immediately when the nerve has been severed.45,46 Despite 1 case of complete resolution at 14 months, the present study does not propose that patients be reviewed indefinitely beyond 1 year because improvement is unlikely thereafter.41 Injury to the IAN or LN during third molar surgery can result in major morbidity and negatively affect a patient’s quality of life. Therefore, careful preoperative clinical and radiographic assessments of risk factors are essential to minimize the risk of permanent nerve injury to a patient. This report also describes the use of a CIR process, allowing close monitoring of all patients with neurologic injuries as a result of dentoalveolar surgery. The risk factors for permanent IAN injury after third molar surgery were increasing age ($25 yr old), surgery performed by staff dentists, surgery performed under GA, and teeth with a mesioangular impaction. There were no statistically important risk factors for permanent LN injury.

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