Higher concentration local anaesthetics causing prolonged anaesthesia. Do they? A literature review and case reports.

Higher concentration dental local anaesthetics (3% and 4%) have become more available in Australia in recent years. Benefits claimed include a faster onset of anaesthesia and improved success with injections compared to 2% solutions. Recent reports suggest that the higher concentration carries a greater risk of prolonged anaesthesia to the mandibular and particularly the lingual nerves. The literature was reviewed and those studies which demonstrated adverse effects of different concentrations of local anaesthetics were analysed. Recent cases are presented. There is an extensive international literature which confirms increased concentration of local anaesthetic does show an increased risk, by about ×6, of prolonged anaesthesia. Five case reports illustrate the impact of this complication on patients' quality of life. Careful consideration needs to be given before using higher concentration local anaesthetic agents for mandibular and lingual blocks as lower concentration local anaesthetics are safer. If acceptable to individual patients, avoidance of block injections or any local anaesthetic for minor restorative tasks could be encouraged given the severity of the complication. It is safe to use the higher concentration agents for infiltrations away from major nerves.