Topical anesthesia: differentiating the pharmacological and psychological contributions to efficacy.

Pain can be influenced by both pharmacologic and psychologic factors. The purpose of this study was to investigate the pharmacologic and psychologic factors. The purpose of this study was to investigate the pharmacologic and psychologic processes that may play a role when topical anesthesia is used to reduce the pain of dental injections. Subjects were assigned to one of two belief manipulation conditions: one-half of the subjects were led to believe they would receive a placebo, while the remaining subjects were told they would receive the active agent. In reality, all subjects received two separate injections at contralateral sites, one preceded by a placebo and the other by a 20% benzocaine gel. The order in which injections were given was associated with differences in pain report. Second injections were more painful than first injections. Whether injections were preceded by an active or placebo agent did not alter subjects' experienced pain. Likewise, the belief manipulation did not affect the pain report. However, subjects who believed they would receive the active agent anticipated significantly less pain than subjects who thought they would receive placebo. The widespread belief that topical anesthetics are effective at reducing injection pain may serve to reduce the anticipatory anxiety associated with an impending dental injection, thus making the injection experience less aversive.