Claire Wilson, Simon Atkins
Whilst inferior alveolar and lingual nerve damage are very uncommon but well-documented risks from local anaesthetic injections, injury to the chorda tympani nerve in isolation has rarely been reported. The chorda tympani, a branch of the facial nerve, provides taste sensation to the anterior two-thirds of the tongue and joins the lingual nerve approximately 10-20mm below the skull base.
A 20 year old male was referred to the hospital with a two-month history of left tongue ageusia following root canal treatment of the lower left second premolar and first molar. His General Dental Practitioner reported that they had administered a mandibular block with 4% Articaine local anaesthetic using the Gow-Gates technique. The patient experienced left lingual nerve anaesthesia that resolved after 48 hours. However the patient had no return of taste sensation on the left side of the tongue. A diagnosis of aguesia secondary to local anaesthetic injection was made.
This case demonstrates a rare complication of a block injection resulting in an isolated chorda tympani injury and aguesia. The infrequency of this specific injury is likely due to the position where the chorda tympani joins the lingual nerve being anatomically superior to the intended area of administration of local anaesthesia using a standard inferior alveolar nerve (IAN) block technique. However the Gow-Gates technique directs local anaesthetic to a position anteromedial to the condyle, thus superior to the standard IAN block position. This case demonstrates that such injuries are possible with the use of superior angled blocks such as the Gow-Gates technique. Moreover, the use of 4% Articaine has been reported to be associated with increased incidence of permanent sensory disturbance following neuropraxia. This case highlights the need for further review of the risks associated with different block techniques and different local anaesthetic agents.