3.4 Complications of Local Anaesthesia and Endodontic Treatment

3.4.1 Possible Mechanism of LA Nerve Injury

Nerve injury due to LA is complex. The nerve injury may be physical (needle, compression due to epineural or perineural haemorrhage) or chemical (haemorrhage or LA contents). Thus the resultant nerve injury may be a combination of peri-, epi- and intraneural trauma causing subsequent haemorrhage, inflammation and scarring resulting in demyelination (loss of nerve lining (Fig. 3.3) [39]. Local anaesthesia practice can cause injury to nerves in many ways. The location of nerve injury may also be important as well as mechanism. Factors that need to be considered are that only 1.3–8.6% of patients get an ‘electric shock’ type sensation on application of an IAN block and 57% of patients who suffer from prolonged neuropathy have not experienced the discomfort on injection, thus this is not a specific sign [78].

3.4.2 Damage to the IANB

3.4.2.1 Neuropathy

Any damage to sensory nerve tissue may cause a mixture of anaesthesia (numbness), paraesthesia (altered sensation which is not painful), dysaesthesia (altered sensation which is uncomfortable/painful) and neuropathic pain. Neuropathy in the orofacial region must be taken seriously and the cause established, as there are some serious conditions that need to be eliminated if a cause is not obvious [42]. Often there is a history that helps determine the origin. Sensory deficits should be mapped on the face so that an estimate can be made of resolution or expansion of the deficit. Any patient with an expanding area of paraesthesia for which a cause has not been established should be referred for specialist evaluation. Amongst other things, paraesthesia can result from trauma, nerve injury, surgery, infections and prolonged reactions to local anaesthesia, viruses, malignancy or serious pathoses. If a dental cause is suspected, patients require reassurance, careful documentation and follow-up.

Unilateral paraesthesia and facial paralysis can occur in a misdirected block where local anaesthetic solution is deposited in the parotid gland. It usually occurs when the depth of needle penetration is nearly to the hub of a long needle. It is more likely to happen when the ramus of the mandible is flared laterally making it difficult for the operator to ‘hit the bone’. The unilateral paralysis of facial muscles is reversible. This resolves over hours. The patient needs to be reassured, and the eye has to be protected until the blink reflex returns, as corneal reflex is often lost.

3.4.2.2 Neurological Injuries Resulting from Untreated Periapical Infections

It is not uncommon in endodontic practice to encounter patients with apical periodontitis of endodontic origin leading to sensory impairment of the inferior alveolar or mental nerve. This invariably resolves with the reduction in inflammation and local swelling. A number of authors have reviewed and documented clinical cases of neurological disorder with paraesthesia and hypaesthesia of the mental nerve resulting as a sequel of apical periodontitis of a mandibular second premolar and second molar teeth [40–42].

3.4.2.3 Motor Nerve Palsy Due to Endodontic Treatment

There are reports of facial motor nerve deficit as a result of endodontic treatment due to extrusion of endodontic irrigants, hydrogen peroxide and ethanol rinses [43, 44].

3.4.2.4 Paraesthesia and Pain Associated with Endodontically Related Nerve Injuries

Endodontic treatment of premolar and mandibular teeth has the potential to damage the inferior alveolar nerve via direct trauma, pressure or neurotoxicity. Trigeminal nerve injury is the most problematic consequence of dental surgical procedures with major medicolegal implications [44]. While incidence of lingual nerve injury has remained static over many years, the incidence of inferior alveolar nerve injury has increased; the latter likely being due to implant surgery and endodontic therapy [45].

Iatrogenic injuries to the third division of the trigeminal nerve remain a common and complex clinical problem (Fig. 3.4). Altered sensation and pain in region may interfere with speaking, eating, kissing, shaving, applying make-up, tooth brushing and drinking, in fact just about every social interaction we take for granted [46, 78]. Thus these injuries have a significant negative effect on the patient’s quality of life, and the iatrogenesis of these injuries lead to significant psychological effects [47].

Persistence of any peripheral sensory nerve injury depends on the mechanisms, the severity of the injury, the increased age of the patient, the time elapsed since the injury and the proximity of the injury to the cell body (the more proximal lesions are having a worse prognosis). Most sensory nerve injuries related to dentistry are permanent. LA-induced nerve injuries have nearly 80% likelihood of recovery. Many authors recommend referral of injuries before 4 months [50], but this may be too late for many endodontically related peripheral sensory nerve injuries. Inferior alveolar nerve injuries related to endodontic treatment, particularly where there is extrusion of filling material, require immediate attention with permanency likely after 24–30 h [50]. After 3 months, permanent central and peripheral changes occur within the nervous system subsequent to such injury, and they are unlikely to respond to surgical intervention [48].

The IAN is at risk from a variety of endodontic procedures. The IAN is contained within a bony canal, predisposing it to ischemia, trauma and subsequent injury in relation to dental procedures. This may explain the higher incidence of permanent damage for inferior alveolar nerve injuries compared with lingual nerve injuries [45]. Inferior alveolar nerve injury during endodontic treatment can result from local anaesthetic accidents, from irrigant extrusion and from over instrumentation or overfilling, in all cases resulting in one or a combination of mechanical injury, haemorrhagic, ischaemic or chemical injury to the nerve.

There are relatively few detailed reports on nerve injuries resulting from endodontic treatment [42]. The largest series of endodontic-related trigeminal nerve injuries included 61 patients reviewed over an 8-year period [9], with most of these patients presenting with persistent pain. There are relatively few reports of persistent pain subsequent to endodontic procedures [49]. In a recent study of 216 patients with trigeminal nerve injuries related to dentistry, 70% are reported to have chronic neuropathic post-traumatic pain [50].

Neuropathic pain (NP) syndromes are chronic pain disorders that develop after a lesion involving the peripheral or central nervous structures that are normally involved in signalling pain. The characteristics of NP differ substantially from those of other chronic pain states, i.e. chronic nociceptive pain, which develops while the nervous system that is involved in pain processing is intact. Apart from the existence of negative somatosensory signs (deficit in function), there are other features that are characteristic of neuropathic conditions (allodynia, hyperalgesia and hyperpathia) [51]. Paraesthesia is typically described by patients as bothersome but not painful. Furthermore, NP states require different therapeutic approaches such as anticonvulsants, which are not effective in nociceptive pain [52].

Thus symptoms experienced by patients with post-traumatic neuropathy of the trigeminal nerve can range from next to no symptoms, such as minimal anaesthesia in a small area to devastating effects on the patient’s quality of life [53].

3.4.2.5 Local Anaesthesia-Related Neuropathy During Endo Procedures

As stated earlier, local anaesthesia is often complex in endodontics as the patients often experience difficulty in achieving analgesia. Patients undergoing endodontic treatment often have multiple injections and may be more at risk of local anaesthetic-related nerve injuries [54]. More recently the incidence of nerve injury in relation to IANBs has been calculated as 1:609,000 but with a reported increase in injury rate when 4% anaesthetic agents are used [55]. These LA injuries are associated with a 34–70% incidence of neuropathic pain, which is lower when compared with endodontic-related nerve injuries. Recovery is reported to take place at 8 weeks for 85–94% of cases [56].

LA injuries may have a better prognosis than nerve injuries resulting from endodontic treatment. In both cases, the nerve injury may be physical (compression due to epineural or perineural haemorrhage or extruded material) or chemical (haemorrhage or local anaesthetic or endodontic compound contents). There may be elements of direct mechanical trauma, which generally would be worse in endodontically caused nerve injuries.

Intraoperatively all clinicians should document unusual patient reactions occurring during application of local analgesic blocks (such as sharp pain or an electrical shock-like sensation), and multiple blocks should be avoided if possible as they may also increase the risk of local anaesthetic-related nerve injuries.

3.4.3 Assessment of Trigeminal Nerve Injuries

The emphasis in trigeminal neuro-functional studies has been on using conventional mechanical tests, which are subjective. Due to the variability in methodology and reporting, they are of limited value for inter-study comparisons and little clinical significance in relation to a patient’s pain and functionality. Recently several investigators have recommended the use of the patient’s report alone [53], in combination with subjective and objective neurosensory tests [50] or utilising quality of life questionnaires (OHIP 14–31) for a more holistic approach for the assessment of patients with trigeminal nerve injury [57]. In this way hopefully to make studies easier to compare.

3.4.4 Management of Neuropathy Related to Endodontics

Differentiation between the possible causes of nerve injury, whether it is of local anaesthetic, periapical inflammation [50] or endodontically origin, is difficult. An accurate diagnosis is dependent on a thorough history and specific identification of the neuropathic area distribution. On occasions the use of adjunctive antibiotics or NSAIDS and paracetamol may enable the clinician to exclude inflammatory or infection-related pain as against post-traumatic NP.

3.4.4.1 Management

Patients who report severe electric-like pain (though it is not a definite sign) following the administration of an IANB should be followed up [63]. What is important, however, is to inform all patients of the risks of problems that may result from IANB, however slight the risk, beforehand and do everything in your power to minimise the risks. Such as minimising repeat blocks and using supplementary techniques.

Acute Management

Should endodontically induced nerve injuries be suspected, acute management involves urgent referral. Some patients may require surgery. The largest series reported to date is by Pogrel [65], who described the management of 61 patients with endodontically induced nerve injuries over an 8-year period. Eight patients were asymptomatic and received no treatment. Forty-two patients exhibited only mild symptoms or were seen more than 3 months after undergoing root canal therapy. They received no surgical treatment. Only 10% of these patients experienced any resolution of symptoms. Eleven patients underwent surgical exploration. Five of these patients underwent exploration and received treatment within 48 h, and all recovered completely. The remaining six patients underwent surgical exploration and received treatment between 10 days and 3 months after receiving endodontic therapy. Of these six patients, four experienced partial recovery and two experienced no recovery at all. Thus Pogrel [65] concludes that early surgical exploration and débridement may reverse the side effects (pain and paraesthesia) of endodontic treatment on the inferior alveolar nerve. If the patient has continued symptoms of paraesthesia or pain once the local anaesthetic has worn off and the radiograph obtained after endodontic therapy shows sealant in the inferior alveolar canal (Fig. 3.5), then immediate referral to an oral and maxillofacial surgeon is indicated. Immediate surgical exploration and débridement may provide satisfactory results.

Escoda-Francoli et al. [66] described a case of endodontic treatment of a permanent right mandibular first molar in which the sealer cement overextended in large amounts and damaged the right inferior alveolar nerve. The condition reverted a few months after the surgical removal of the material. There are several reports of nerve injury in relation to over instrumentation and overfilling [67, 68]. Endodontic retreatment for inferior alveolar nerve injury was also reported by Yatsuhashi et al. [67]. Gatot and Tovi [68] recommended steroid therapy for early postoperative neuritis. More recently Grotz et al. [69] described the management of 11 patients with endodontic-associated neuropathy. They similarly reported that the neurological findings were dominated by hypaesthesia and dysaesthesia with 50% of patients reporting pain. Initial X-rays showed root filling material in the area of the mandibular canal. Nine cases were treated with apicectomy and decompression of the nerve; in two cases, extraction of the tooth was necessary. Only one patient reported persistent pain after surgery. Both Scolozzi et al. [70] and Brkic et al. [71] describe a limited series of patients successfully treated with surgical decompression (removal of material within the canal or apicecting the tooth) resulting in resolution of the endodontically related nerve injury. As stated earlier, patients must be assessed on a case-by-case basis, but immediate surgical exploration and débridement may provide satisfactory results.

Delayed Management

If the neuropathy is longer standing and the patient has chronic pain, then post-traumatic neuropathy must be diagnosed and appropriate treatment prescribed. Most patients accept a full explanation and reassurance for their symptoms. Many patients can find the explanation for their neuropathic pain symptoms very helpful. Antibiotics may be prescribed to exclude apical infection. NSAIDs and paracetamol will also exclude inflammatory pain, but neuropathic pain due to post-traumatic nerve injury will not respond to these medications.

Oshima et al. [72] reported that 16 patients of 271 patients presenting with chronic orofacial pain were diagnosed with chronic neuropathic tooth pain subsequent to endodontic retreatment. Most of these patients were treated for maxillary teeth, and 70% of the patients responded to tricyclic antidepressant therapy which highlights the importance of establishing whether the patient has neuropathic pain to start with. A recent Cochrane review highlights the lack of robust evidence in managing trigeminal nerve injuries [73]. Recommendations for treatment of trigeminal neuropathic pain are also well described by Truelove [52].

3.4.5 Recommendations Based on the Current Evidence