Sir, we read with great interest the article (BDJ 2015;219: 439–445) on symptomatic irreversible pulpitis. The intrapulpal injection technique (IPI) is commonly preferred in situations where patients encounter pain during pulp extirpation, especially in a hot tooth condition. The most significant factor contributing to the success of IPI is that its administration must be done under pressure. Monheim has suggested that prolonged pressure may lead to degeneration of nerve fibres in many instances leading to profound anaesthesia.1 Various suggested methods that aid in pressure build up in such cases include obliteration of a large pulpal opening with either gutta-percha or a cotton pellet.2

In the BDJ article, under the section: Step Three – Intrapulpal Injection (IPI), a variation of the conventional IPI technique is given, ie use of a gutta-percha bung to aid in pressure build up for profound anaesthesia, which has been developed and used by the restorative team at the Leeds Dental Institute. However, no reference was cited with regards to this. The paper also states that after access and de-roofing of the pulp chamber, IPI is administered followed by effective haemostasis achieved with a cotton wool pledge (CWP) soaked with local anaesthetic or haemostatic agents or sodium hypochlorite (NaOCl). However, Vidhya et al. studied the chemical interaction between lignocaine hydrochloride (with and without adrenaline) and NaOCl by using nuclear magnetic resonance (NMR) spectroscopy and reported the formation of a toxic precipitate, 2,6-xylidine, which is a known carcinogen.3 Hence, the immediate use of NaOCl for achieving haemostasis following intrapulpal injection with lignocaine hydrochloride (with or without adrenaline) should be avoided.

As stated by Birchfield and Rosenburg, the anaesthetic effect of the intrapulpal technique is mainly due to the back-pressure of the solution, independent of the type of solution injected.4 Hence, 0.9% normal saline can be employed for achieving intrapulpal anaesthesia to avoid potential interactions between lignocaine hydrochloride and NaOCl.