Effect of Time on Clinical Efficacy of Topical Anesthesia

Intraoral topical local anesthetic is used to reduce the discomfort of injection. OBJECTIVES: To determine the effect of time on the clinical efficacy of the topical anesthetic 5% lidocaine, and to determine whether it is as effective in reducing pain in the palate upon injection compared with needle insertion alone. METHODS: This randomized, double blind, placebo controlled, split-mouth, clinical trial enrolled 90 subjects, equally divided into 3 major groups based upon time of topical anesthetic application (2, 5 or 10 minutes). Each group was further subdivided into 2 groups: needle insertion only or needle insertion with deposition of anesthetic (0.5mL 3% mepivacaine plain) in the palate. Each subject received drug on one side of the palate and placebo on the other. Subjects recorded pain on a 100mm VAS scale. RESULTS: For needle insertion only, 5% lidocaine reduced pain as determined by a significant difference in mean VAS after 2 minutes (20.1mm, p<0.002), 5 minutes (15.7mm, p<0.022) and 10 minutes (13.7mm, p<0.04), as analyzed by paired t-tests. For needle insertion plus injection of local anesthetic, a significant difference in mean VAS was noted only after 10 minutes (14.9mm, p<0.031), but not at 2 minutes (8.0mm, p=0.2) or 5 minutes (9.3mm, p=0.17) as analyzed by paired t-tests. Time of application did not result in a significant difference in effect for either needle insertion (p=0.73) or needle insertion plus injection of local anesthetic (p=0.7), as analyzed by one-way ANOVA. CONCLUSIONS: Topical anesthetic application relieves pain from needle insertion in the palate after any one of 2, 5 or 10 minutes of application, but requires 10 minutes in order to reduce pain from local anesthetic injection. This study was funded in part by the Ontario Dental Society of Anesthesiology.