Which constituent of a local anaesthetic cartridge maintains a neutral pH of 7?

The constituent of a local anaesthetic cartridge that maintains a neutral pH of 7 is the buffer. Buffers are important in local anaesthetic formulations because they help to adjust the pH of the solution to ensure that it is compatible with the body's tissues. A neutral pH is crucial as it helps to enhance the efficacy of the anaesthetic agent, allowing for better penetration through cell membranes and improving patient comfort during injection.

In many cases, local anaesthetics are weak bases, and their effectiveness can be compromised if the pH is too acidic. A buffer helps to stabilize the pH and can enhance the amount of drug in its uncharged form, which can diffuse across nerve membranes more easily. Consequently, the use of a buffer is key to achieving optimal performance of the local anaesthetic during dental procedures.