The vast majority of dental procedures are carried out under local anaesthetic so that the patient feels no pain. Which one of the following constituents of a local anaesthetic cartridge is present to allow a reasonable shelf life and period of use?

A preservative is included in local anaesthetic cartridges to extend their shelf life and maintain their efficacy over time. Over time, anaesthetic agents can degrade or become less effective if not properly preserved. The presence of a preservative helps to prevent bacterial growth and chemical breakdown, ensuring that the anaesthetic remains safe and effective for the duration of its use.

The other constituents, while important to the overall effectiveness of the anaesthetic, do not serve the same purpose. The anaesthetic itself is what provides pain relief, the buffer helps to maintain a neutral pH for better tissue compatibility and absorption, and the vasoconstrictor works to minimize bleeding and prolong the action of the anaesthetic. However, none of these components directly contribute to extending the shelf life of the product.