The patient may experience burning pain upon a local anesthesia injection because:

The experience of burning pain during a local anesthesia injection is commonly attributed to the pH of the solution being low. Local anesthetics are typically formulated as salts, and when they are in a more acidic solution, such as those with a low pH, the ionized form predominates. This ionized form does not penetrate nerve membranes as effectively, which can lead to discomfort and a burning sensation upon injection.

Additionally, the acidity can enhance the irritation of the surrounding tissues, contributing to the feeling of pain during the injection. Ideally, local anesthetic solutions should have a pH that is close to physiological pH to minimize discomfort for the patient. In contrast, factors such as the rate of injection, nerve contact, or high concentrations of the anesthetic itself may not directly relate to the burning sensation felt during the injection process as significantly as the pH of the solution does.