Does Early Repair of Lingual Nerve Injuries Improve Functional Sensory Recovery?

Clinical insights into traumatic injury of the inferior alveolar and lingual nerves: a comprehensive approach from diagnosis to therapeutic interventions

OBJECTIVES

This scoping review explores the risk and management of traumatic injuries to the inferior alveolar and lingual nerves during mandibular dental procedures. Emphasizing the significance of diagnostic tools, the review amalgamates existing knowledge to offer a comprehensive overview.

MATERIALS AND METHODS

A literature search across PubMed, Embase, and Cochrane Library informed the analysis.

RESULTS

Traumatic injuries often lead to hypo-/anesthesia and neuropathic pain, impacting individuals psychologically and socially. Diagnosis involves thorough anamnesis, clinical-neurological evaluations, and radiographic imaging. Severity varies, allowing for conservative or surgical interventions. Immediate action is recommended for reversible causes, while surgical therapies like decompression, readaptation, or reconstruction yield favorable outcomes. Conservative management, utilizing topical anesthesia, capsaicin, and systemic medications (tricyclic antidepressants, antipsychotics, and serotonin-norepinephrine-reuptake-inhibitors), proves effective for neuropathic pain.

CONCLUSIONS

Traumatic nerve injuries, though common in dental surgery, often go unrecorded. Despite lacking a definitive diagnostic gold standard, a meticulous examination of the injury and subsequent impairments is crucial.

CLINICAL RELEVANCE

Tailoring treatment to each case's characteristics is essential, recognizing the absence of a universal solution. This approach aims to optimize outcomes, restore functionality, and improve the quality of life for affected individuals.

Assessing the Efficacy of Allogeneic Nerve Grafts in Trigeminal Nerve Repair: A Systematic Review

PURPOSE

Our primary objective was to assess the efficacy of allogeneic nerve grafts in inferior alveolar nerve or lingual nerve repair. We hypothesized that using allogeneic nerve grafts would be effective, as evidenced by achieving high rates of functional sensory recovery (FSR). Additionally, we looked if sex, time from injury to repair, etiology of nerve damage, and graft length affected outcomes.

METHODS

A systematic review following Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines was conducted. PubMed and Scopus databases were searched using specific search strategies to generate eligible studies. Inclusion criteria encompassed studies reporting use of allogeneic grafts, assessing FSR using either Medical Research Council Scale or Neurosensory Testing, and published within the past 15 years.

RESULTS

Across 10 studies conducted between 2011 and 2023, analysis was performed on 149 patients and 151 reconstructed nerves. Allogeneic nerve grafts showed an average FSR rate of 88.0%. Kaplan-Meier analysis of time to FSR postoperatively revealed that of those achieving FSR, 80% achieved it within 6 months and 98% achieved it by 1 year. The mean graft length was 29.92 mm ± 17.94 mm. The most common etiology for nerve damage was third molar extractions (23.3%). Sex distribution among patients revealed that 85 were female (57.0%) and 64 were male (43.0%).

CONCLUSION

Our primary hypothesis was supported as nerve allografts achieved high rates of FSR. FSR was achieved in normative timeframes, which is 6 to 12 months postoperatively. Furthermore, allografts reduced the risk of posttraumatic trigeminal neuropathy. Time from injury to repair, graft length, etiology of nerve damage, and sex did not affect FSR. As the assessed variables in our study did not affect outcomes, there needs to be a more nuanced approach to understanding and addressing various factors influencing sensory recovery.

Relationship of the Degree of Nerve Exposure and Surgical Manipulation and Short-Term Neurosensory Disturbance Following Sagittal Split Ramus Osteotomy: A Prospective Study

BACKGROUND

Neurosensory disturbance (NSD) is a common complication after sagittal split ramus osteotomy (SSRO) due to inferior alveolar nerve (IAN) injury. The impact of intraoperative nerve manipulation on NSD remains debated.

PURPOSE

The purpose of this study was to evaluate the influence of IAN exposure and manipulation during SSRO on functional sensory recovery (FSR).

STUDY DESIGN

This was a single-center, prospective cohort study of 40 patients undergoing SSRO at Mahidol University from December 2020 to December 2021. The inclusion criteria were patients aged 20-34, ASA Class I-II. The exclusion criteria were patients with systemic bone disease, history of head and neck or neurological pathology, previous SSRO, or incomplete data collection.

PREDICTOR VARIABLE

Degree of intraoperative nerve manipulation was divided by the attending surgeon as follows; 1) Nerve fully encased in distal segment and not visible (NS); 2) Nerve encased in distal segment but partially visible (DS); and 3) Nerve partially encased in proximal segment and fully dissected free (PS).

OUTCOME VARIABLES

The area of interest was divided into the lip and chin. The primary outcome was time to FSR. The secondary outcome was subjective patient report, using a visual analogue scale, compared to FSR.

COVARIATES

The covariates were sex, age, skeletal diagnosis, degree of movement, and concomitant genioplasty/subapical procedure.

ANALYSES

Kaplan-Meier survival analysis, Cox proportional hazards regression, and Mcnemar test were utilized. P-value < .05 was significant.

RESULTS

In the lip, the median times to FSR were NS, 2 days; DS, 45 days; PS, 102 days. (Interquartile range: 77,127, 114, respectively) In the chin, the median times to FSR were NS, 23 days; DS, 92 days; PS, 87 days. (Interquartile range: 77, 161, 101, respectively.) Nerve manipulation significantly affected FSR in the lip and chin (P = .001, <0.001, respectively. Cox hazard ratios for DS and PS were lower compared to NS. Patients consistently reported more NSD compared to FSR as per Mcnemar test.

CONCLUSION AND RELEVANCE

After SSRO, FSR in the lip is prolonged when the IAN is partially encased in the proximal segment and released. This raises the question of the efficacy of surgically releasing a partially encased IAN.

Application of Tinel's test combed with clinical neurosensory test distinguishes spontaneous healing of lingual nerve neuropathy after mandibular third molar extraction

BACKGROUND

Extraction of the mandibular third molar, the most frequent and important surgical procedure in the clinical practice of oral surgery, is associated with the risk of injury of the lingual nerve. Neuropathy of the lingual nerve poses diagnostic challenges regarding the transient or permanent nature of the injury. No consensus or criteria have been established regarding the diagnosis of lingual nerve neuropathy. We applied both Tinel's test and clinical neurosensory testing together, which can be easily used at the bedside in the early stages of injury. Therefore, we propose a new method to differentiate between lesions with the ability to heal spontaneously and those that cannot heal without surgery.

RESULTS

Thirty-three patients (29 women,  4 men; mean age, 35.5 years) were included in this study. For all patients, the median interval between nerve injury and initial examination was 1.6 months and that between nerve injury and the second examination before determining the need for surgical management was 4.5 months. The patients were assigned to either group A or B. The spontaneous healing group (group A, n = 10) revealed a tendency for recovery within 6 months after tooth extraction. In this group, although there were individual differences in the degree of recovery, a remarkable tendency for recovery was observed based on clinical neurosensory testing in all cases. None of the patients were diagnosed with allodynia. In seven cases, the Tinel test result was negative at the first inspection, and in three cases, the result changed to negative at the second inspection. Conversely, in group B(n = 23), no recovery trend was observed with regard to clinical neurosensory testing, and nine patients had allodynia. Further, the Tinel test result was positive for all patients in both examinations.

CONCLUSIONS

Our findings indicate that in case of transient lingual nerve paralysis, clinical neurosensory testing findings deteriorate immediately after tooth extraction and gradually recover, while Tinel's test shows a negative result. Using Tinel's test and clinical neurosensory testing together enabled early and easy identification of the severity of the lingual nerve disorder and of lesions that would heal spontaneously without surgical management.

Post-traumatic Trigeminal Neuropathic Pain: Factors Affecting Surgical Treatment Outcomes

Post-traumatic trigeminal neuropathic pain (PTTNp) is a painful condition that may result from injury to the sensory division of the trigeminal nerve. Treatment of this condition is challenging and consensus on treatment to resolve neuropathic pain has yet to be standardized. Equally as challenging is the identification of surgical outcome variables to guide surgical treatment of PTTNp. This is partly due to the variability in pain characteristics, severity of nerve injury, location, and duration from injury to surgery. In those with neuropathic pain prior to microsurgical intervention, the incidence of neuropathic pain after microsurgical intervention is 67%. It is unclear why nerve repair surgery is effective in resolving or decreasing neuropathic pain in some patients, whereas it has no effect on pain relief in others. Psychological, medical, and age-related factors have been identified as risk factors for developing chronic post-surgical pain due to post-traumatic neuropathic pain. Two factors: injury to surgery time and preoperative visual analog scale score have recently been identified as variables that influence surgical outcomes in the treatment of PTTNp.

Comparison of prognosis in two methods for the lingual nerve repair: direct suture with vein graft cuff and collagen allograft method

Background

No studies have compared the outcomes of direct perineurial suture with vein graft cuff repair and indirect collagen allograft repair of the lingual nerve following an injury. Therefore, we evaluated and compared the outcomes of each over a 1-year observation period. We retrospectively assessed 20 patients who had undergone microneurosurgical repair of unilateral lingual nerve injuries at the Wakayama Medical University Hospital between May 2015 and March 2019. We utilized two different methods for lingual nerve repair, i.e., direct perineurial repair with a vein graft cuff and interpositional collagen allograft repair. Sensory and taste function in the lingual nerve were preoperatively evaluated using a static two-point discrimination test, superficial pain/tactile sensation test, tests for the pressure pain threshold (Semmens-Weinstein monofilament), test for thermal discrimination hot and cold sensation, and a taste discrimination test. These tests were performed again at 6 and 12 months postoperatively.

Results

Compared to the preoperative conditions, all patients showed improved sensory reactions. Functional sensory recovery outcomes were defined by Pogrel’s criteria, Medical Research Council Scale grades, and functional sensory recovery. In each group, all patients improved after the operation. However, the operation time was significantly shorter for an interpositional collagen allograft repair as compared to that for a direct perineurial repair with a vein graft cuff.

Conclusions

There were no statistically significant differences between the two repair Methods, except for the operation time. Both methods led to satisfactory results for all criteria. From an economic point of view, direct perineurial repair with a vein graft cuff is meaningful; however, the esthetic effect on the donor site should be considered. Conversely, interpositional collagen allograft repair has the advantage of a greatly shortened operation time.

Type I Collagen-Based Devices to Treat Nerve Injuries after Oral Surgery Procedures. A Systematic Review

The regeneration of nerve injuries after oral surgery procedures is a quite often attempted procedure in dental medicine. Despite several proposed technical approaches, there is still a lack of consensus on which should be considered the gold standard procedure, even-though in the last decades, the use of collagen-based devices allowing a tension-free direct neurorrhaphy has been used. A systematic search of multiple electronic databases and hand searching was conducted to assess the level of evidence behind the use of type I collagen devices to treat nerve injuries after oral surgery procedures. After screening, four articles (one case series and three retrospective studies) including overall 65 patients suffering from inferior alveolar (IAN)/lingual nerve (LN) injury after mandibular wisdom tooth extraction, met the inclusion criteria and could be included. The Oxford Centre for evidence-based medicine (OCEBM) scaling system was used to evaluate the quality of the included studies. Positive clinical results in terms of sensorial improvements were recorded at least 3 months after surgery, even-though the overall level of evidence is low. The use of collagen membranes to enhance nerve regeneration in oral surgery results in promising results. Nevertheless, additional clinical comparative trials with larger sample sizes are needed.

Factors Affecting Functional Sensory Recovery After Inferior Alveolar Nerve Repair Using the Nerve Sliding Technique

PURPOSE

The nerve sliding technique (NST) was introduced for repairing inferior alveolar nerve (IAN) defect and overcoming the disadvantages of conventional surgical treatment methods such as nerve graft. This study was conducted to identify factors associated with functional sensory recovery (FSR) following inferior alveolar nerve repair using the NST.

PATIENTS AND METHODS

This was a retrospective cohort study including all patients who underwent IAN repair using the NST at Seoul National University Dental Hospital, Department of Oral and Maxillofacial Surgery from February 2009 to March 2020. The damaged part of the IAN was excised, and the incisive branch was transected intentionally to perform direct anastomosis without tension. Cox proportional hazard analysis was utilized to determine the relationships between predictor variables (age, gender, chief complaints, preoperative sensory results, duration from injury to repair, length of nerve tissue resected during the procedure, and neuroma formation) and outcome variable (time to FSR).

RESULTS

The sample was composed of 16 patients with a mean age of 56.1 ± 10.1 years, 25% were males and 75% were females. The mean nerve gap deficit was 7.69 mm (3-15 mm). Ten patients (62.5%) achieved FSR with a median time from operative treatment to FSR of 84.5 days. Dental implant placement was found as the main cause for IAN injury (93.8%) and 56.2% of patients complained of hypoesthesia and dysesthesia. Factors associated with time to FSR at 1 year were age, chief complaint, and early repair. Younger patients (P = .041) and patients without dysesthesia (P = .019) were more likely to achieve FSR. Higher proportion of early repair group achieved FSR, although not statistically significant (P = .068).

CONCLUSIONS

The use of NST in repair of IAN defects up to 15 mm achieved 62.5% FSR. Younger age and absence of dysesthesia were associated with higher FSR.

Neurosensory Recovery Following Mental Nerve Skeletonization in Intraoral Open Reduction and Internal Fixation of Mandible Fractures

PURPOSE

The purpose of this study was to evaluate neurosensory recovery after mental nerve skeletonization in open reduction and internal fixation (ORIF) of mandible fractures.

METHODS

This was a prospective nonrandomized observation study of adult subjects treated at a Level I trauma center between April 1, 2016 and December 31, 2019, with mental nerve skeletonization for ORIF of mandible fractures. Age, sex, and mandibular injury severity score (MISS), and functional sensory recovery (FSR) and subjective neurosensory recovery of skeletonized mental nerve were recorded at preoperative and regularly scheduled follow-up appointments. Uninomial and multinomial logistic regressions were conducted with a significance level of < 0.05.

RESULTS

Twenty-six subjects (all male) completed all the postoperative protocol requirements and were included in this study. All subjects had a loss of FSR (S0) and subjective neurosensation immediately after surgery. Half of the subjects achieved FSR (S3) and subjective neurosensory recovery (VAS < 4) an average of 42 days after surgery. All subjects improved FSR (S4) by 57 days and subjective neurosensory recovery by 90 days after surgery. These were independent of MISS but had decreased recovery time with increased age. No incidences of mental nerve neuropathic pain during the trial period were found.

CONCLUSIONS

FSR and subjective neurosensory recovery from mental nerve skeletonization in intraoral ORIF of mandible fractures was achieved in all subjects by the end of this study. Neurosensory recovery was independent of MISS but decreased with increased age. Initial inverse correlations between objective and subjective neurosensory assessments were insignificant at study completion. No incidences of neuropathic pain were identified during the time of this study. Mental nerve skeletonization in ORIF of mandible fracture may be performed with an anticipated return of functional and subjective neurosensory recovery within 3 months of surgery.

Clinical outcomes of lingual nerve repair

Lingual nerve injury, a well-described complication of third molar removal, may result in permanent lingual sensory deficit leading to symptoms including lost or altered sensation, inadvertent tongue biting, and the development of unpleasant neuropathic pain, with consequent impaired quality of life. We analysed outcomes of a prospective case series to determine whether direct anastomosis of the lingual nerve results in improved sensory recovery and reduced neuropathic pain, and whether delayed surgery is worthwhile. In 114 patients who underwent nerve repair at our nerve injury clinic following damage sustained during mandibular third molar removal, sensory deficit was assessed before and after surgery using a questionnaire and visual analogue scales (VAS) to assess pain, tingling, and discomfort. Neurosensory tests were utilised to evaluate light touch, pin-prick, and two-point discrimination thresholds. Subjectively, 94% patients felt their sensation had improved following nerve repair, with significant reductions in the incidence of tongue biting (p<0.0001), impaired speech (p<0.0001), and neuropathic pain (p=0.0017). Quantitative neurosensory data showed highly significant improvements in light touch, pin-prick, and two-point discrimination (all p<0.0001), and VAS scores for pain (p=0.0145), tingling (p<0.0025), and discomfort (p<0.0001) were significantly reduced. Patients with high levels of pain preoperatively (VAS>40) showed highly significant reductions in pain (p<0.0001). No correlation was found between surgical outcome and patient's age or delay until surgery. Lingual nerve repair results in good sensory outcomes and significant improvements in the incidence and degree of neuropathic pain, even when delayed.

Outcomes of Direct Lingual Nerve Repair After an Injury: A Systematic Review

PURPOSE

The purpose of this study was to conduct a systematic review with meta-analysis to investigate the outcomes of direct lingual nerve repair after injury.

MATERIALS AND METHODS

The studies in this review were compiled by using PubMed/Medline and ScienceDirect, which were searched by a single reviewer (M.K.) from their inception until March 10, 2020. Two independent reviewers (M.K. and V.B.Z.) who were blinded to each other's assessments reviewed full-text articles to assess for study inclusion. Outcomes were dichotomized as either functional sensory recovery (FSR) or no FSR. Clinical testing must have been assessed at a minimum of 6 months postoperatively. FSR was defined as grade S3, S3⁺, or S4 on the British Medical Research Council scale of neurosensory function. Studies were only eligible if they provided the number of patients treated with conduits or time from injury to repair and the associated rates of FSR with each intervention.

RESULTS

The initial search using the key terms yielded 4,921 results, which was then eventually filtered down to 6 articles after multiple levels of appraisal. Five articles were retrospective cohort studies and 1 was a randomized controlled study. Four of the 6 studies reported an FSR of grade S3 or higher in 85% or more of the patients. Conduit use was not associated with a significantly greater likelihood of achieving FSR (pooled risk ratio = 1.10; 95% confidence interval, 0.96 to 1.27; P = .17). Repair within 6 months was associated with significantly improved likelihood of achieving FSR (pooled risk ratio = 0.84; 95% confidence interval, 0.71 to 0.99; P = .04).

CONCLUSIONS

The use of conduits during repair was not associated with clinically significant increased FSR. Early repair was associated with a beneficial effect on FSR; however, heterogeneity was an issue with the studies. There is a lack of strong evidence owing to the nature of studies analyzed and the need for further research is required.

Neuromodulation of the lingual nerve: a novel technique

Acute injury of the trigeminal nerve or its branches can result in posttraumatic trigeminal neuropathy (PTTN). Affected patients suffer from chronic debilitating symptoms long after they have recovered from the inciting trauma. Symptoms vary but usually consist of paresthesia, allodynia, dysesthesia, hyperalgesia, or a combination of these symptoms. PTTN of the trigeminal nerve can result from a variety of traumas, including iatrogenic injury from various dental and maxillofacial procedures. Treatments include medications, pulsed radiofrequency modulation, and microsurgical repair. Although trigeminal nerve stimulation has been reported for trigeminal neuropathy, V3 implantation is often avoided because of an elevated migration risk secondary to mandibular motion, and lingual nerve implantation has not been documented. Here, the authors report on a patient who suffered from refractory PTTN despite multiple alternative treatments. He elected to undergo novel placement of a lingual nerve stimulator for neuromodulation therapy. To the best of the authors' knowledge, this is the first documented case of lingual nerve stimulator implantation for lingual neuropathy, a technique for potentially reducing the risk of electrode migration.

Effect of duration from lingual nerve injury to undergoing microneurosurgery on improving sensory and taste functions: retrospective study

Background

The prognosis of recovery following microneurosurgery for injured lingual nerves varies among individual cases. This study aimed to investigate if recovery ratios of sensory and taste functions are improved by the microneurosurgery within 6 months after lingual nerve injury.

Methods

We retrospectively assessed 70 patients who underwent microneurosurgery at the Wakayama Medical University Hospital for lingual nerve injuries between July 2004 and December 2016. Sensory and taste functions in lingual nerves were preoperatively evaluated using a static two-point discrimination test, an intact superficial pain/tactile sensation test, and a taste discrimination test. They were evaluated again at 12 and at 24 months postoperatively. The abundance ratio of Schwann cells in the excised traumatic neuromas was analyzed with ImageJ software following immunohistochemistry with anti S-100β antibody.

Results

In early cases (microneurosurgery within 6 months after the injury), recovery ratios of sensory and taste functions were not significantly different at 24 months after microneurosurgery compared with later cases (microneurosurgery more than 6 months after the injury). Meanwhile, the ratio of patients with taste recovery within 12 months after microneurosurgery was significantly decreased in late cases compared with early cases. The abundance ratio of Schwann cells in traumatic neuroma was also significantly lower in later cases.

Conclusion

Microneurosurgery more than 6 months after lingual nerve injury did not lead to decreased recovery ratio of sensory and taste functions, but it did lead to prolonged recovery of taste. This delay may be associated with a decrease in the abundance ratio of Schwann cells in traumatic neuromas.

Remnant neuromuscular junctions in denervated muscles contribute to functional recovery in delayed peripheral nerve repair

Schwann cell proliferation in peripheral nerve injury (PNI) enhances axonal regeneration compared to central nerve injury. However, even in PNI, long-term nerve damage without repair induces degeneration of neuromuscular junctions (NMJs), and muscle atrophy results in irreversible dysfunction. The peripheral regeneration of motor axons depends on the duration of skeletal muscle denervation. To overcome this difficulty in nerve regeneration, detailed mechanisms should be determined for not only Schwann cells but also NMJ degeneration after PNI and regeneration after nerve repair. Here, we examined motor axon denervation in the tibialis anterior muscle after peroneal nerve transection in thy1-YFP mice and regeneration with nerve reconstruction using allografts. The number of NMJs in the tibialis anterior muscle was maintained up to 4 weeks and then decreased at 6 weeks after injury. In contrast, the number of Schwann cells showed a stepwise decline and then reached a plateau at 6 weeks after injury. For regeneration, we reconstructed the degenerated nerve with an allograft at 4 and 6 weeks after injury, and evaluated functional and histological outcomes for 10 to 12 weeks after grafting. A higher number of pretzel-shaped NMJs in the tibialis anterior muscle and better functional recovery were observed in mice with a 4-week delay in surgery than in those with a 6-week delay. Nerve repair within 4 weeks after PNI is necessary for successful recovery in mice. Prevention of synaptic acetylcholine receptor degeneration may play a key role in peripheral nerve regeneration. All animal experiments were approved by the Institutional Animal Care and Use Committee of Tokyo Medical and Dental University on 5 July 2017, 30 March 2018, and 15 May 2019 (A2017-311C, A2018-297A, and A2019-248A), respectively.

A case report of a long-term abandoned torn lingual nerve injury repaired by collagen nerve graft induced by lower third molar extraction

Background

The lingual nerve plays an important role in multiple functions, including gustatory sensation and contact sensitivity and thermosensitivity. Misdiagnosed conservative treatments for serious lingual nerve (LN) injuries can induce the patient to serious mental disability. After continuous observation and critical diagnosis of the injury, in cases involving significant disruption of lingual nerve function, microneurosurgical reconstruction of the nerve is recommended. Direct anastomosis of the torn nerve ends without tension is the recommended approach. However, in cases that present significant gaps between the injured nerve ends, nerve grafts or conduits (tubes of various materials) are employed. Recently, various reconstruction materials for peripheral nerves were commercially offered especially in the USA, but the best method and material is still unclear in the world. There currently exists no conventional protocol for managing LN neurosensory deficiency in regard to optimal methods and the timing for surgical repair. In Japan, the allograft collagen nerve for peripheral nerves reconstruction was permitted in 2017, and we tried to use this allograft nerve and got a recommendable result.

Case presentation

This report is a long-term abandoned torn LN reconstructed with allograft nerve induced by the lower third molar extraction.

Conclusions

In early sick period, with the exact diagnosis, the LN disturbance should be managed. In a serious condition, the reconstruction with allograft nerve is one of the recommendable methods.

MRI of the inferior alveolar nerve and lingual nerve-anatomical variation and morphometric benchmark values of nerve diameters in healthy subjects

OBJECTIVE

Since MRI using dedicated imaging sequences has recently shown promising results in direct visualization of the inferior alveolar nerve (IAN) and the lingual nerve (LN) with high spatial resolution, the aim of this study was to generate suitable standard specifications to reliably depict the IAN and LN in MRI and to delineate the anatomy and its variants of these nerves in healthy subjects.

METHODS

Thirty healthy volunteers were examined on a 3-T scanner (Elition, Philips Healthcare, Best, the Netherlands). The sequence protocol consisted of 3D STIR, 3D DESS, and 3D T1 FFE "black bone" sequences.

RESULTS

The study reconfirmed a good feasibility of direct visualization of proximal and peripheral portions of the IAN and of the proximal course of the LN. The STIR sequence showed the highest apparent signal to noise ratio (aSNR) and best apparent nerve-muscle contrast to noise ratio (aNMCNR) for IAN and for the LN. The applied MRI sequences allowed to differentiate the tissue composition of the neurovascular bundle inside the mandibular canal.

CONCLUSION

Dedicated MRI sequence protocols proved effectively to detect the IAN and LN and their course in healthy volunteers. The tissue composition of the mandibular neurovascular bundle was conclusively distinguishable as was the varying topography inside multiple bony channels.

CLINICAL RELEVANCE

The presented data on the precise and valid visualization of the IAN and LN have clinical implications in respect to local anesthesia prior to dental treatments in the mandible but also regarding surgical procedures and implant insertion in the molar region.

Resveratrol Promotes Nerve Regeneration via Activation of p300 Acetyltransferase-Mediated VEGF Signaling in a Rat Model of Sciatic Nerve Crush Injury

Peripheral nerve injuries are generally associated with incomplete restoration of motor function. The slow rate of nerve regeneration after injury may account for this. Although many benefits of resveratrol have been shown in the nervous system, it is not clear whether resveratrol could promote fast nerve regeneration and motor repair after peripheral nerve injury. This study showed that the motor deficits caused by sciatic nerve crush injury were alleviated by daily systematic resveratrol treatment within 10 days. Resveratrol increased the number of axons in the distal part of the injured nerve, indicating enhanced nerve regeneration. In the affected ventral spinal cord, resveratrol enhanced the expression of several vascular endothelial growth factor family proteins (VEGFs) and increased the phosphorylation of p300 through Akt signaling, indicating activation of p300 acetyltransferase. Inactivation of p300 acetyltransferase reversed the resveratrol-induced expression of VEGFs and motor repair in rats that had undergone sciatic nerve crush injury. The above results indicated that daily systematic resveratrol treatment promoted nerve regeneration and led to rapid motor repair. Resveratrol activated p300 acetyltransferase-mediated VEGF signaling in the affected ventral spinal cord, which may have thus contributed to the acceleration of nerve regeneration and motor repair.

Iatrogenic trigeminal post-traumatic neuropathy: a retrospective two-year cohort study

With the growing demand for dental work, trigeminal nerve injuries are increasingly common. This retrospective cohort study examined 53 cases of iatrogenic trigeminal nerve injury seen at the Department of Oral and Maxillofacial Surgery, University Hospitals of Leuven between 2013 and 2014 (0.6% among 8845 new patient visits). Patient records were screened for post-traumatic trigeminal nerve neuropathy caused by nerve injury incurred during implant surgery, endodontic treatment, local anaesthesia, tooth extraction, or specifically third molar removal. The patients ranged in age from 15 to 80years (mean age 42.1years) and 68% were female. The referral delay ranged from 1day to 6.5years (average 10months). The inferior alveolar nerve (IAN) was most frequently injured (28 cases), followed by the lingual nerve (LN) (21 cases). Most nerve injuries were caused during third molar removal (24 cases), followed by implant placement (nine cases) and local anaesthesia injuries (nine cases). Pain symptoms were experienced by 54% of patients suffering IAN injury, compared to 10% of patients with LN injury. Persistent neurosensory disturbances were identified in 60% of patients. While prevention remains the key issue, timely referral seems to be a critical factor for the successful treatment of post-traumatic neuropathy.

Evaluation of a Nerve Fusion Technique With Polyethylene Glycol in a Delayed Setting After Nerve Injury

PURPOSE

Polyethylene glycol (PEG) has been hypothesized to restore axonal continuity using an in vivo rat sciatic nerve injury model when nerve repair occurs within minutes after nerve injury. We hypothesized that PEG could restore axonal continuity when nerve repair was delayed.

METHODS

The left sciatic nerves of female Sprague-Dawley rats were transected and repaired in an end-to-end fashion using standard microsurgical techniques at 3 time points (1, 8, and 24 hours) after injury. Polyethylene glycol was delivered to the neurorrhaphy in the experimental group. Post-repair compound action potentials were immediately recorded after repair. Animals underwent behavioral assessments at 3 days and 1 week after surgery using the sciatic functional index test. The animals were sacrificed at 1 week to obtain axon counts.

RESULTS

The PEG-treated nerves had improved compound action potential conduction and animals treated with PEG had improved sciatic function index. Compound action potential conduction was restored in PEG-fused rats when nerves were repaired at 1, 8, and 24 hours. In the control groups, no compound action potential conduction was restored when nerves were repaired. Sciatic functional index was superior in PEG-fused rats at 3 and 7 days after surgery compared with control groups at all 3 time points of nerve repair. Distal motor and sensory axon counts were higher in the PEG-treated rats.

CONCLUSIONS

Polyethylene glycol fusion is a new adjunct for nerve repair that allows rapid restoration of axonal continuity. It effective when delayed nerve repair is performed.

CLINICAL RELEVANCE

Nerve repair with application of PEG is a potential therapy that may have efficacy in a clinical setting. It is an experimental therapy that needs more investigation as well as clinical trials.

Chronic Oral Capsaicin Exposure During Development Leads to Adult Rats with Reduced Taste Bud Volumes

INTRODUCTION

Cross-sensory interaction between gustatory and trigeminal nerves occurs in the anterior tongue. Surgical manipulations have demonstrated that the strength of this relationship varies across development. Capsaicin is a neurotoxin that affects fibers of the somatosensory lingual nerve surrounding taste buds, but not fibers of the gustatory chorda tympani nerve which synapse with taste receptor cells. Since capsaicin is commonly consumed by many species, including humans, experimental use of this neurotoxin provides a naturalistic perturbation of the lingual trigeminal system. Neonatal or adults rats consumed oral capsaicin for 40 days and we examined the cross-sensory effect on the morphology of taste buds across development.

METHODS

Rats received moderate doses of oral capsaicin, with chronic treatments occurring either before or after taste system maturation. Tongue morphology was examined either 2 or 50 days after treatment cessation. Edema, which has been previously suggested as a cause of changes in capsaicin-related gustatory function, was also assessed.

RESULTS

Reductions in taste bud volume occurred 50 days, but not 2 days post-treatment for rats treated as neonates. Adult rats at either time post-treatment were unaffected. Edema was not found to occur with the 5 ppm concentration of capsaicin we used.

CONCLUSIONS

Results further elucidate the cooperative relationship between these discrete sensory systems and highlight the developmentally mediated aspect of this interaction.

IMPLICATIONS

Chronic exposure to even moderate levels of noxious stimuli during development has the ability to impact the orosensory environment, and these changes may not be evident until long after exposure has ceased.

Nerve Sharing Between the Lingual and Mental Nerve to Restore Lower Lip Sensation After Segmental Resection of the Mandible

This report demonstrates a successful new procedure for reconstructing the inferior alveolar nerve by transplanting the great auricular nerve (GAN) between the mental nerve and the remaining submandibular ganglion to achieve nerve sharing of the lingual nerve. A 59-year-old woman with discomfort in the left mandibular retromolar region and ipsilateral neck was referred to our hospital by a local dentist. Physical examination showed mild swelling and redness at the left mandibular retromolar region. The histologic diagnosis showed central mucoepidermoid carcinoma of the jaw. With the patient under general anesthesia, segmental resection of the mandible followed by level 1 selective neck dissection was performed. The resected mandible was reconstructed with a titanium plate. The submandibular incision was extended to the lower edge of the tragus for harvesting of the GAN. The GAN was grafted, and an epineural neurorrhaphy was carried out with the mental nerve, as well as the submandibular ganglion, under a microscope. After the operation, submental sensation was evaluated with a Semmes-Weinstein pressure esthesiometer. The Semmes-Weinstein pressure esthesiometer test showed a loss of perception at the third week after surgery. Within 12 months, nerve sensation was substantially improved and the patient was free from discomfort.

Longitudinal Treatment Outcomes of Microsurgical Treatment of Neurosensory Deficit after Lower Third Molar Surgery: A Prospective Case Series

Objective

To prospectively evaluate the longitudinal subjective and objective outcomes of the microsurgical treatment of lingual nerve (LN) and inferior alveolar nerve (IAN) injury after third molar surgery.

Materials and Methods

A 1-year longitudinal observational study was conducted on patients who received LN or IAN repair after third molar surgery-induced nerve injury. Subjective assessments (“numbness”, “hyperaesthesia”, “pain”, “taste disturbance”, “speech” and “social life impact”) and objective assessments (light touch threshold, two-point discrimination, pain threshold, and taste discrimination) were recorded.

Results

12 patients (10 females) with 10 LN and 2 IAN repairs were recruited. The subjective outcomes at post-operative 12 months for LN and IAN repair were improved. “Pain” and “hyperaesthesia” were most drastically improved. Light touch threshold improved from 44.7g to 1.2g for LN repair and 2g to 0.5g for IAN repair.

Conclusion

Microsurgical treatment of moderate to severe LN injury after lower third molar surgery offered significant subjective and objective sensory improvements. 100% FSR was achieved at post-operative 6 months.

Recovery of Impaired Somatosensory Evoked Fields After Improvement of Tongue Sensory Deficits With Neurosurgical Reconstruction

Somatosensory evoked fields (SEFs) induced by tongue stimulation can be useful as an objective parameter to assess sensory disturbances in the tongue. However, whether tongue SEFs can be useful as a clinical, objective follow-up assessment method of tongue sensation after oral surgery is unknown. We describe 2 cases in which tongue SEFs were successfully used in clinical assessment. Two patients with unilateral tongue sensory deficits caused by lingual nerve injury during lower third molar extraction were recruited. Both patients underwent surgery to repair the damaged nerve, and all tongue sensory evaluations were performed once before and once after surgery. SEFs were recorded by stimulating the affected and unaffected sides of the tongue separately, and cortical activity was evaluated over the contralateral hemisphere. The unilaterality of the deficit also was assessed. In both patients, stimulation of the unaffected side evoked reproducible cortical responses before and after surgery. Both patients also recovered some sensation after surgery, given that presurgery stimulation of the affected side failed to evoke cortical activity whereas postsurgery stimulation evoked cortical activity on both sides. Sensation was initially highly lateralized in both patients but was restored to approximately normal in the postsurgery evaluation. Finally, both patients rated their subjective tongue sensations on the affected side over 50% better after the surgical intervention. These cases indicate that tongue SEFs may have a clinical use as an objective parameter for assessing the course of tongue sensory recovery.

Surgical management of damaged inferior alveolar nerve caused by endodontic overfilling of calcium hydroxide paste

AIM

To evaluate the neurosensory outcome of management of damaged inferior alveolar nerves caused by endodontic overfilling and to assess the efficacy of delayed surgical intervention.

METHODOLOGY

Nine patients who underwent surgical removal of extruded endodontic material were included. All patients were evaluated for neurosensory function using a set of standardized tests. The outcome of surgical intervention was evaluated through patient interview and quantitative statistical analysis.

RESULTS

Surgical procedures included foreign body removal, microsurgical external/internal decompression, excision of neuroma followed by nerve repair, and excision of damaged nerve segment with interpositional nerve graft. Seven of the nine patients had significant improvement according to the follow-up neurosensory assessment. Four patients reported significant improvement, three patients reported mild improvement and two patients reported no appreciable improvement in the Visual Analog Scale (VAS). Two patients who reported no appreciable improvement in VAS also did not achieve FSR. In these patients, calcium hydroxide was spread widely along the IAN and a surgical approach was obtained via sagittal spit osteotomy. The mean time to reach FSR was 222.7 (±41.8) days with a range of 106-397 days. In the early repair group who received surgery within 60 days, three out of five patients achieved FSR in a mean time of 198.0 (±76.2) days. The mean time to FSR in all four subjects who received surgical attention over 60 days after injury was 241.3 (±139.8) days with a range of 106-397 days. As all four cases in the late repair group with limited amount of nerve injury achieved FSR, only 3 of 5 early repair cases with wide-spread injury achieved a similar outcome.

CONCLUSION

The results of this case series confirmed the notion that surgical management of the inferior alveolar nerve is effective in the treatment of nerve injuries caused by endodontic extrusion of calcium hydroxide paste. Delayed surgical repair of the inferior alveolar nerve can be indicated and helpful for the neurosensory recovery of damaged IAN, however, the surgical management was less effective in case of widespread nerve injuries.

The prognostic value of histopathology on lingual nerve neurosensory recovery after micro-neurosurgery

OBJECTIVE

Micro-neurosurgical repair is considered in permanent nerve damage but the outcome is unpredictable. We examined if histopathologic parameters of traumatic neuromas have a prognostic value for recovery in relation to lingual nerve micro-neurosurgery.

MATERIALS AND METHODS

Retrospective case study on neurosensory recovery after micro-neurosurgery. Outcome variables were as follows: pain perception, two-point discrimination, and sum score of perception, before and 12 months after micro-neurosurgery. Predictive histopathology variables included size, nerve tissue, and inflammation. Statistics are as follows: logistic and correlation analyses (P < 0.05).

RESULTS

Sixty-five patients with lingual nerve damage were included in the study. Improved two-point discrimination was associated with small size of resected tissue (P = 0.0275). No normal appearing distal nerve tissue was associated with improved sum score of perception (P = 0.0185), higher final sum score of perception value (P = 0.0475) and final pain perception (P = 0.0324). Foreign body reaction was associated with no final pain perception (P = 0.0492).

CONCLUSIONS

Small size, absence of distal nerve tissue, and no foreign body reaction were associated with improvement of the neurosensory functions.

CLINICAL RELEVANCE

Histological parameters of the traumatic neuromas in routine preparation appeared to have some prognostic value for neurosensory functions as improvement of the neurosensory functions was associated with small size of resected tissue, no distal normal appearing nerve tissue, and no foreign body reaction.

Evidence-based outcomes following inferior alveolar and lingual nerve injury and repair: a systematic review

The inferior alveolar nerve (IAN) and lingual (LN) are susceptible to iatrogenic surgical damage. Systematically review recent clinical evidence regarding IAN/LN repair methods and to develop updated guidelines for managing injury. Recent publications on IAN/LN microsurgical repair from Medline, Embase and Cochrane Library databases were screened by title/abstract. Main texts were appraised for exclusion criteria: no treatment performed or results provided, poor/lacking procedural description, cohort <3 patients. Of 366 retrieved papers, 27 were suitable for final analysis. Treatment type for injured IANs/LNs depended on injury type, injury timing, neurosensory disturbances and intra-operative findings. Best functional nerve recovery occurred after direct apposition and suturing if nerve ending gaps were <10 mm; larger gaps required nerve grafting (sural/greater auricular nerve). Timing of microneurosurgical repair after injury remains debated. Most authors recommend surgery when neurosensory deficit shows no improvement 90 days post-diagnosis. Nerve transection diagnosed intra-operatively should be repaired in situ; minor nerve injury repair can be delayed. No consensus exists regarding optimal methods and timing for IAN/LN repair. We suggest a schematic guideline for treating IAN/LN injury, based on the most current evidence. We acknowledge that additional RCTs are required to provide definitive confirmation of optimal treatment approaches.

Lingual Nerve Repair: To Graft or Not to Graft?

PURPOSE

Since no studies have compared direct and graft repair of the lingual nerve, we examined the subjective and objective outcomes of lingual nerve repair by direct epineurial repair and indirect graft repair, assessed the effect of other confounding variables, and compared the outcomes of autograft and allograft repairs.

PATIENTS AND METHODS

All patients who had undergone microneurosurgical repair of the lingual nerve from 2000 to 2012 by 1 surgeon (M.M.) were asked to complete an online questionnaire regarding their current neurosensory status at least 2 years after nerve repair. A direct comparison was made between patients who had undergone direct epineurial repair and those who had undergone interpositional nerve graft repair. Student's t test and χ(2) test were used to determine whether a significant difference existed in the success between the 2 techniques and whether age, gender, race, delay from injury to repair, or degree of initial nerve deficit influenced the success of nerve repair.

RESULTS

Of the 72 patients identified, 43, who had undergone 47 nerve repairs (18 direct, 29 indirect graft repairs [4 bilateral]; 28 female and 19 male patients; mean age 28.3 years), were interviewed. The objective results of functional sensory recovery, defined by a Medical Research Council Scale grade of S3, S3+, or S4, was 89% for the graft repairs and 85% for the direct repairs (P = .01). The subjective patient satisfaction score (0 to 10 scale) was 8.9 for the graft repairs and 8.1 for the direct repairs (P = .02). The autograft and allograft repairs performed comparably, and the other variables (ie, age, gender, race, delay from injury to nerve repair, gap length, and initial Sunderland grade injury) were not found to be significant (P > .05).

CONCLUSION

Graft repair of the lingual nerve provides superior long-term (>2 years) objective and subjective outcomes compared with direct repair. This might be because of the lack of tension at the repair site, more freedom with nerve stump preparation, and the addition of neurotropic and neurotrophic factors from the donor nerve graft at the site of injury to augment neurosensory recovery.

Lingual nerve injury after third molar removal: Unilateral atrophy of fungiform papillae

BACKGROUND

Pain and sensory changes due to lingual nerve injury are one of the most common alterations that follow surgical removal of third molar. They are usually transient but other less common complications, such as the atrophy of fungiform papillae, have an uncertain prognosis.

CASE DESCRIPTION

We report a case of a 34-year-old woman who presented a unilateral lingual atrophy of fungiform papillae after third molar extraction accompanied by severe dysesthesia that altered her daily life significantly during the following months and how this complication evolved over time. We conducted a literature review on the different factors that can lead to a lingual nerve injury.

CLINICAL IMPLICATIONS

The clinical evolution of temporary and permanent somatosensitve injuries is an important fact to take into consideration during the postoperative management because it will indicate the lesion prognosis. Key words:Lingual nerve, third molar removal, somatosensitive alteration, papillae atrophy, permanent injury, temporary injury.

Lingual nerve deficit following mandibular third molar removal: review of the literature and medicolegal considerations

The removal of mandibular third molars is probably the most frequently performed procedure in oral and maxillofacial surgery, and it is the most common surgical procedure associated with lingual nerve deficit. Lingual sensory impairment remains a clinical problem in oral and maxillofacial surgery and has serious medical and legal implications. In fact, damage to the lingual nerve is a common cause of litigation in dentistry. The purpose of this article was to review the literature about lingual nerve deficit following mandibular third molar removal and discuss the associated medicolegal aspects.

Effect of delayed peripheral nerve repair on nerve regeneration, Schwann cell function and target muscle recovery

Despite advances in surgical techniques for peripheral nerve repair, functional restitution remains incomplete. The timing of surgery is one factor influencing the extent of recovery but it is not yet clearly defined how long a delay may be tolerated before repair becomes futile. In this study, rats underwent sciatic nerve transection before immediate (0) or 1, 3, or 6 months delayed repair with a nerve graft. Regeneration of spinal motoneurons, 13 weeks after nerve repair, was assessed using retrograde labeling. Nerve tissue was also collected from the proximal and distal stumps and from the nerve graft, together with the medial gastrocnemius (MG) muscles. A dramatic decline in the number of regenerating motoneurons and myelinated axons in the distal nerve stump was observed in the 3- and 6-months delayed groups. After 3 months delay, the axonal number in the proximal stump increased 2–3 folds, accompanied by a smaller axonal area. RT-PCR of distal nerve segments revealed a decline in Schwann cells (SC) markers, most notably in the 3 and 6 month delayed repair samples. There was also a progressive increase in fibrosis and proteoglycan scar markers in the distal nerve with increased delayed repair time. The yield of SC isolated from the distal nerve segments progressively fell with increased delay in repair time but cultured SC from all groups proliferated at similar rates. MG muscle at 3- and 6-months delay repair showed a significant decline in weight (61% and 27% compared with contra-lateral side). Muscle fiber atrophy and changes to neuromuscular junctions were observed with increased delayed repair time suggestive of progressively impaired reinnervation. This study demonstrates that one of the main limiting factors for nerve regeneration after delayed repair is the distal stump. The critical time point after which the outcome of regeneration becomes too poor appears to be 3-months.

Treatment modalities of neurosensory deficit after lower third molar surgery: a systematic review

PURPOSE

To conduct a systematic review to answer the clinical question, "What are the available treatment modalities and their outcomes of neurosensory deficit after lower third molar surgery?"

MATERIALS AND METHODS

A systematic search, including a computer search of several databases with specific keywords, a reference search, and a manual search of 3 key maxillofacial journals were performed. Relevant articles were then evaluated and those that fulfilled the 6 predetermined criteria were chosen to enter the final review. The various treatment modalities and their outcomes of neurosensory deficit after lower third molar surgery, in the selected studies in the final review, were analyzed.

RESULTS

Ten articles entered the final review. Six treatment modalities of lingual nerve or inferior alveolar nerve deficit after lower third molar surgery were identified. External neurolysis, direct suturing, autogenous vein graft, and a Gore-Tex tube as a conduit were the 4 surgical treatments. Significant improvement after surgical treatment ranged from 25% to 66.7%. Acupuncture and low-level laser therapy were 2 available nonsurgical treatment modalities that were found to have produced significant improvement in sensation after treatment in more than 50% of subjects. There was insufficient information to determine the best timing of treatment of nerve injury after third molar surgery.

CONCLUSIONS

Four surgical treatments and 2 nonsurgical treatments were identified in the management of neurosensory disturbance after lower third molar surgery. Most treatments showed an improvement in sensation but the outcomes were variable. Complete recovery was uncommon in all kinds of available treatments.

Management of mandibular nerve injuries from dental implants

Treatment of the patient who has sustained a nerve injury from dental implant procedures involves prompt recognition of this complication, evaluation of sensory dysfunction, the position of the nerve vis-à-vis the implant, and timely management of the injured nerve. In some patients, removal or repositioning of the implant and surgical exploration and repair of the injured nerve will maximize the implant patient's potential for a successful recovery from nerve injury.