Management of Nerve Injury

Nerve injury following implant therapy often results in paraesthesic or anaesthesic effects that affect quality of life of the patient. Patients usually experience postoperative changes in sensation, including pain, even though the intraoperative procedures were uneventful. In cases of uneventful clinical implant placement procedures, a postoperative telephonic interview, as soon as the effects of anaesthesia have dissipated, will enable the clinician to determine possible nerve injury and hence initiate management protocols. Postoperative radiography would be essential to assess whether the inferior alveolar nerve canal or mental foramen have been traversed, however it must be noted that absence of radiographic findings do not preclude nerve injury. Management protocols aim to alleviate pain, loss of normal sensation and overall discomfort following nerve related injuries, with varying degrees of success depending on the nature of injury. Hence, it is clearly identified that the importance of comprehensive pre-planning mitigates the need for management of nerve related injuries. Nerve injuries in the maxilla are relatively uncommon compared to mandible. Branches of the greater palatine nerve, posterior superior alveolar nerve, and the nasopalatine nerve, which supply the gingival issues in the anterior and posterior palate and buccal mucosa of the maxilla, are inevitably damaged due to flap procedures in implant therapy. Due to the rich anastomosis between these nerves, very rarely does this damage result in neural deficit. Numerous academic studies have been attributed to implant related nerve injury of the mandibular branch of the trigeminal nerve, more importantly, the inferior alveolar nerve, mental nerve, and the lingual nerve.

Interventions can be broadly classified as,

a. Non-surgical

b. Surgical, and

c. alternate treatments.

a. Non-Surgical Therapy

This form of therapy should be mandated as soon as signs and / or symptoms of nerve injury be suspected, whether intraoperatively or postoperatively. Corticosteriods, dexamethasone (8mg daily for 3 days) or prednisolone (1mg/kg/day up to 80mg day), in high doses have been shown to minimize neuropathies in acute nerve injuries if administered within 1 week of the injury. A non-steriodal anti-inflammatory drug (NSAID) could be added to the regimen or prescribed as an alternative. Ibuprofen, 800mg three times daily for 3 weeks, is a suitable NSAID. Corticosteriods and NSAIDs reduce the inflammatory response with corticosteroids having the added effect of preventing ectopic discharges from injured axons and preventing neuroma formation (Juodzbalys et al, 2011). Pain and temperature are the first sensations to resolve with other sensations taking longer (Alhassani and Alghamdi, 2010: 405; Juodzbalys et al, 2011).

The use of topical applications has not been broadly researched. Capsaicin and clonidine patches along with EMLA paste (4% lignocaine) are some of the products used to treat hyperalgesia with varying success. Topical clonazepam, 0.5mg to 1.0 mg 3 times day was shown to be effective in relieving burning oral pain (Graff-Radford and Evans, 2003: 979, Fukada et al, 2012).

Tricyclic antidepressants (TCAs), antiepileptic drugs, and muscle relaxants have been effective in treating cases with neuropathic pain and intermittent pains which exhibit an “electric shock” – like symptoms (Graff-Radford and Evans, 2003: 980). An example of a TCA is amitriptyline although other antidepressants can be used. In patients where TCAs are contraindicated, serotonin and norepinephrine reuptake inhibitor (Venlafaxine) can be prescribed. Gabapentin and topiramate are antiepileptic drugs which stabilize the injured nerve membrane. It must be noted that this class pharmacological agents depress the activity in the central and peripheral nervous systems. Hence patients on these therapies can expect side effects including, drowsiness, loss of memory, and somnolence. It can be expected that some patients cannot manage the side effects of these drugs and opt to live with pain or altered sensations (Renton et al, 2012; Park et al, 2010: 345).

Cryotherapy is effective treatment to minimize swelling over the osteotomy site and hence minimizing secondary nerve damage due to swelling. Use of ice packs in the first 24 hours promotes post-surgical recovery and reduces nerve degeneration and neuroma formation (Juodzbalys et al, 2011).

A stellate ganglion block is a treatment modality that used to treat patients experiencing chronic neuropathic pain and to relieve subjective symptoms. If performed early,1 to 2 month post nerve injury, it accelerates neurophysiological repair by blocking the sympathetic nervous system hence increasing blood flow and decreasing oedema (Fukada et al,2012;).

A more recent non-surgical, non-invasive approach includes the use low level laser therapy (LLLT), also known as cold laser therapy, for inducing tissue repair. The initial concept, now available for mainstream commercial use, has been gaining interest as research with over 200 random clinical trials have been already published, 50% of which were aimed at pain relief, but it must be noted fewer studies have investigated its efficacy in the head and neck region. LLLT broadly aims to reduce inflammation and provide analgesia by blocking peripheral axonal transmission and stimulating nerve regeneration / healing. After repeated treatments with LLLT, decreased central sensitization is acheived (ThorLaser). [ABDUL PLEASE ASSIST ME WITH THAT REFERENCE FROM THORLASER]. In animal studies, LLLT has shown positive results in enhancing myelination of axons and nerve function. In the Midamba and Haanaes 1993 study, similar protocols were used on patients with long standing inferior alveolar or lingual nerve neurosensory deficits, an average of 71,1% improvement was noticed in subjective symptoms (cited in Ozen et al, 2006: 7).

The use of vitamin B12 as an adjunct with routine pharmacotherapy is thought to promote the regeneration of nerve terminals. Modalities that increase blood flow to the injured nerve also promote healing. These include near infrared therapy to increase local blood flow and adenosine triphosphate by causing vasodialation.

b.Surgical Therapy

Microsurgical repair includes procedures that involve internal neurolysis, external neurolysis, and removal of the neuroma. Microsurgical repair of the injured nerve carries its own risk as permanent anaesthesia is a possibility. Hence, these procedures are carried out with aid of a microscope by specialist neurosurgeons or trained maxillo-facial surgeons.

Microsurgical repair of the lingual or inferior alveolar nerve has been shown to have significantly improved sensory outcomes in most patients with total recovery in a fewer patients. Zicchardi et al (2009: 300) have concluded that statistically, there were no significant differences between the microsurgical neurosensory outcomes between the inferior alveolar and lingual nerves. It has been reported that 55% to 82% of patients show improved neurosensory outcomes of microsurgical repair of the inferior alveolar nerve (Strauss et al, 2006: 1769; Bagheri et al, 2012: 1983). This wide range leads to hypothesize that other factors play a role in the outcomes of microsurgical nerve repair.

Time between the nerve injury and microsurgical repair has been a topic of debate with regards to sensory outcomes. Some groups advocate early repair (6 month or earlier post-injury), and some groups finding no statistical difference in sensory outcomes between early or later repairs. However, in a retrospective cohort study undertaken by Bagheri et al, a cohort of 167 patients were evaluated post-microsurgical repair, where it was deduced that early repairs were directly related to better outcomes. Younger patients (patients less than 51 years) also yielded a more favourable outcome than older patients. Neurosensory testing will also give insight into the severity of damage and hence the outcome of microsurgical repair, if indicated.

In cases where it has been clearly established that nerve damage has occurred post implant therapy, removal of the implant within 24 to 30 hours has been shown to resolve neuropathy (Renton et al, 2012).

c. Other Treatment Modalities

It is clear from above that nerve injury post implant therapy has an effect on the quality of life of affected patients. Some patients even lose confidence in their treating physician / dentist / specialist as a result, and opt for alternate management strategies.

Psychotherapeutic interventions, including cognitive behavioural therapy, aim to manage the resulting depression, if diagnosed. When combined with psycho-active chemotherapy, stress management techniques, and hypnosis, has been shown to be effective in managing neuropathic pain. Patients are taught to modify their behaviours according to their symptoms, psychological traits and ultimately decreasing patients’ pain-related disability (Dickenson et al, 2010: 1644).

Further investigation into treatment modalities for nerve injuries, iatrogenic or otherwise, make mention of other procedures, that are beyond the topic of this discussion, but include the use of epidural injections, neuromodulation, transcutaneous electrical stimulation, spinal cord stimulation and deep brain stimulation.

There are no clearly defined management protocols for the management of nerve injury post implant therapy, however, Juodzbalys et al, (2011), have constructed a management guideline that incorporates some of the treatment modalities described above (See Table 1).

REFERENCES

Alhassani, A., Alghamdi, A.S.T., 2010. Inferior alveolar nerve injury in implant dentistry: Diagnosis, causes, prevention, and management. Journal of Oral Implantology, 36 (5), 401 – 407, viewed 30 April 2014, (Ebsco online / Allen Press).

Bagheri, S.C, Meyer, R.A, Cho, S,H, Thoppay, J, Khan, H.A, Steed, M, 2012. Microsurgical repair of the inferior alveolar nerve: Success rate and factors that adversely affect outcome. Journal of Oral Maxillofacial Surgery, 70, 1978 – 1990, viewed 30 April 2014, (online Science Direct).

Dickinson, B.D, Head, A, Gitlow, S, Osbahr III, A.J, 2010. Maldynia: Pathophysiology and management of neuropathic and maladaptive pain – A report of the AMA Council on Science and Public Health. Pain Medicine, 11, 1635 – 1653, viewed 24 May 2014, (Ebsco online / Wiley Blackwell).

Fukuda, K, Ichinohe, T, Kaneko, Y, 2012. Pain management for nerve injury following dental implant surgery at a Tokyo dental college hospital. International Journal of Dentistry. vol. 2012, Article ID 209474, viewed 22 April 2014, (Ebsco online / Hindawi Corporation).

Graff-Radford, S.B, Evans, R.W, 2003. Lingual nerve injury. Headache, 43, 975 – 983, viewed 21 April 2014, (Ebsco online / Wiley Blackwell).

Juodzbalys, G., Wang, H-L, Sbalys, G., 2011. Injury of the inferior alveolar nerve during implant placement: a literature review. Journal of Oral Maxillofacial Research , 2 (1), 1 – 20, viewed 22 April 2014, (Ebsco online).

Ozen, T, Orhan, K, Gorur, I, & Ozturk, A, 2006. Efficacy of low level laser therapy on neurosensory recovery after injury to the inferior alveolar nerve. Head & Face Medicine, 2, 3-9, viewed 01 June 2014, (Ebsco online / BioMed Central).

Park, J.H, Lee, S.H, Kim, S.T, 2010. Pharmacological management of trigeminal nerve pain after implant surgery. International Journal of Prosthodontics, 23, 342 – 346, viewed 22 April 2014, (Ebsco online, Quintessence)

Renton, T., Dawood, A., Shah, A., Searson, L., Yilmaz, Z., 2012. Post-implant neuropathy of the trigeminal nerve. A case series. British Dental Journal, 212 (E17), 1 – 6, viewed 30 April 2014, (online Nature Group).

Strauss, E.R, Ziccardi, V.B, Janal, M.N, 2006. Outcome assessment of inferior alveolar nerve microsurgery : a retrospective review. Journal of Oral Maxillofacial Surgery, 64, 1767 – 1770, viewed 05 May 2014, (Ebsco online/ Quintessence).

Ziccardi, V.B, Riviera, L, Gomes, J, 2009. Comparison of lingual and inferior alveolar nerve microsurgery outcomes. Quintessence International, 40, 295 – 301, viewed 02 May 2014, (Ebsco online/ Quintessence).

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