Causes of trigeminal alveolar nerve injury (TNI) are varied, but many occur that are related to restorative dentistry. Professor Tara Renton, specialist in oral surgery, looks into ‘prevention first’ and then recommended management of nerve injuries.

Prevention

Neuropathy caused by local block injections is a well-recognised complication throughout medicine, anaesthesia and dentistry. However, dentistry is the only specialty that still trains clinicians to aim for nerves rather than avoid neural contact (often using ultrasound), which likely explains the continued prevalence of local anaesthetic (LA)-related nerve injuries in dentistry.

There is evidence, using ultrasound, that the benefits of a proximal injection of LA to the inferior alveolar nerve (IAN) are not related to efficacy of the inferior dental block (IDB). A close injection to the nerve is therefore not required. However, what is frequently overlooked is the need to wait for eight to ten minutes for optimal pulpal anaesthesia, and additional repeated IDBs will not improve the success of anaesthesia.

A recent report highlights that the prevalence of IDB-related nerve injuries in UK general dental practice is 1:14,000 blocks for temporary nerve injury, or 1:56k IDBs with patients experiencing permanent lingual or inferior alveolar nerve injury, of which 25% of nerve injuries are permanent.¹

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 resulting nerve injury may be a combination of peri-, epi- and intra-neural trauma causing subsequent haemorrhage, inflammation and scarring, resulting in demyelination (loss of nerve lining).

Only 1.3-8.6% of patients get an ‘electric shock’ type sensation on application of an IAN block and 57% of patients suffer from prolonged neuropathy having not experienced the discomfort on injection, so this is not a specific sign.²

Routine practice in Europe and USA involves warning patients of potential nerve injury in relation to dental injections.

Infiltration dentistry avoiding block anaesthesia

A 2014 survey of German dental LA practice found that 74% of dentists were using infiltration dentistry routinely, avoiding the use of inferior dental blocks (IDBs). Improved comfort was reported by patients who had a preference for having full lingual sensation and shorter duration LA anaesthesia after dental treatment.³

Further evidence to support infiltration dentistry successfully includes a study by Evans, Nusstein and Drum et al⁴, which found 4% articaine to be more effective than 2% lidocaine for lateral incisors but not molars, and a recent randomised and controlled trial, which found a statistically significant difference supporting use of 4% articaine in place of 2% lidocaine for buccal infiltration in patients experiencing irreversible pulpitis in maxillary posterior teeth.⁴ Other studies however– such as that conducted by Oliveira et al – reported no clinical superiority for this injection.

There is evidence supporting the significantly increased rates of pulpal anaesthesia using infiltration anaesthesia, when compared with IDB anaesthesia, particularly for premolar and incisor teeth¹. Similarly, a recent systematic review reports that articaine is 3.4 times more effective for pulpitic mandibular molars when compared with lidocaine, but there is no difference between articaine and lidocaine maxillary infiltrations or IDBs.⁵

Several reports of supra periosteal infiltration anaesthesia suggest that it is not only sufficient for posterior mandible implant surgery but may be protective of the IAN.⁶ When it comes to periodontal and implant surgery, the standard care is infiltration LA, while intraligamental anaesthesia for extractions and avoiding IDBs is also gaining population.⁷ Paedodontic extractions do not require IDBs as the bone is very porous and susceptible to absorption of infiltrative anaesthesia.

Subhead: Prevention of LA nerve injuries is possible

These simple steps may minimise LA-related nerve injuries:

• Avoid high concentration LA for IDBs (use 2% lidocaine as standard). There is increasing evidence that higher concentration agents are more neurotoxic and therefore more likely to cause persistent IDB related neuropathy.
• Avoid multiple blocks where possible.
• Avoid IAN blocks by using high concentration agents (articaine) with infiltration-only anaesthesia. Infiltration dentistry avoids the use of IDBs, therefore preventing LA-related nerve injury, for which there is no cure.

There are two main issues currently for LA: changing practice in using tailored LA techniques rather than always reaching for the IDB, and consenting patients regarding potential nerve injury.

Consent for LA

Patients are routinely warned of the risk of nerve injury when undergoing epidural or spinal injections. Reports estimated that nerve injury from neuroaxial blocks (epidurals, spinals and combined epidural with spinals) resulted in sensory or motor nerve injury in 1 in 24-54,000 patients (and paraplegia or death in 1 in 50-140,000 patients.⁸

Germany already has a legal precedent to warn all patients of the risk – something that was originally suggested in the US.⁹ With Montgomery setting consent principles based upon what is material to the patient, warning patients of the risk of TNIs, and their unpleasant consequences, should now be routine.

Tailored LA technique

Infiltration dentistry avoids the use of IDBs in most cases. IDBs may only be needed for lower posterior molar complex endo, restorative and extraction procedures, thus preventing LA-related nerve injury.

By avoiding IDBs there is less risk of injury to the lingual and inferior alveolar nerves which, though rare, is debilitating to the patients and has no cure. This technique requires less skill, causes less discomfort for the patient during the injection and avoids unnecessary lingual anaesthesia after dental treatment.

References

1. Renton T, Adey-Viscuso D, Meechan J et al. Trigeminal nerve injuries in relation to the local anaesthesia in mandibular injections. British Dental Journal 2010;209:E15-E15. doi:10.1038/sj.bdj.2010.978
2. Smith MH, Lung KE. Nerve injuries after dental injection: a review of the literature. Journal of the Canadian Dental Association 72 (6) 559-564
3. Pogrel M, Schmidt B, Sambajon V et al. Lingual nerve damage due to inferior alveolar nerve blocks. The Journal of the American Dental Association 2003;134:195-199. doi:10.14219/jada.archive.2003.0133
4. Evans G, Nusstein J, Drum M et al. A Prospective, Randomized, Double-blind Comparison of Articaine and Lidocaine for Maxillary Infiltrations. Journal of Endodontics 2008;34:389-393. doi:10.1016/j.joen.2008.01.004
5. Kung J, McDonagh M, Sedgley C, Does Articaine Provide an Advantage over Lidocaine in Patients with Symptomatic Irreversible Pulpitis? A Systematic Reviewand Meta-analysis, Journal of Endodontics November 2015 Volume 41, Issue11, Pages 1784–1794. https://doi.
org/10.1016/j.joen.2015.07.001
6. Etoz OA, Nilay E, Demirbas AE. Is supraperiosteal infiltration anesthesia safe enough to prevent inferior alveolar nerve during posterior mandibular implant surgery? Medicina Oral Patologia Oral y Cirugia Bucal 2011 May 1;16 (3)e386-9. doi: 10.4317/medoral.16.e386
7. Dumbridge HB, Lim MV, Rudman RA, Serraon A. A comparative study of anesthetic techniques for
mandibular dental extractions. American Journal of Dentistry 1997;10:275.
8. The National Royal College of Anaesthetists. Audit Recipe Book 3rd edition. 2012. Accessed 31/07/2019 at: https:// www.rcoa.ac.uk/document-store/audit-recipe-book-3rdedition-2012
9. Orr DL, Curtis WJ. Obtaining written informed consent for the administration of local anesthetic in dentistry. Journal of the American Dental Association 1939 136(11):1568-71.
doi: 10.14219/jada.archive.2005.0090
10. Montgomery v Lanarkshire Health Board [2015] SC 11 [2015] 1 AC 1430