Final answer:
Local anesthesia can fail in endodontic treatments due to excessive bleeding that dilutes the anesthetic or a lowered tissue pH which affects anesthetic absorption. Overdose is a less common cause for anesthetic failure.
Step-by-step explanation:
Local anesthesia given in preparation for endodontic treatments can fail for various reasons. The failure may not necessarily indicate that the patient is experiencing an overdose, as this is a relatively rare occurrence compared to other factors that could affect the efficacy of the anesthetic. One possible reason is excessive bleeding at the site, which can dilute the anesthetic solution and prevent it from effectively numbing the area. Another reason could be a change in the tissue environment, such as when the pH of the tissue has been lowered. Inflammation or infection can lead to acidic conditions which reduce the efficacy of local anesthetics because they rely on a certain pH level to be properly absorbed into the nerve membranes.
The drill's trauma causes the release of chemical messengers like cytokines, serotonin, and prostaglandins from damaged cells. These chemical messengers bind to nociceptors, signaling pain that is transmitted by A and C fibers to the central nervous system. If local anesthesia does not work properly, these messages cannot be effectively blocked, leading to pain during endodontic procedures.