It works by blocking the nerve supplying the particular tooth under treatment. It is also necessary to allow time for the local anesthetic to work. This is very often the reason why LA appears not to work. See section on Local Anesthesia. Fear due to a bad experience from previous dental treatment.
Childhood experiences such as a previous general anesthetic.
A fear of choking due to incorrect positioning of the patients head or poor suction by the dental assistant. Long dental procedures leading to jaw stiffness. Poor access due to a small mouth leading to difficult procedures at the back of the mouth. Fear that the local anesthetic will produce side effects such as dizziness. Considering the number of dental injections given there are remarkably few reports of side effects worldwide and indeed local anesthetic is considered one of the safest drugs of all.