Factors that modulate the efficacy of topical anesthetic agents to reduce needle-insertion pain include (1) concentration and formulation of the topical anesthetic agent, i.e., viscous, ointment, liquid, spray, patch; (2) duration of application; (3) site of application, i.e., keratinized versus non-keratinized tissue and maxillary versus mandibular sites; and (4) technical issues related to the administration of the LA, e.g., the depth of needle placement, the gauge of needle used, and contact with the periosteum.34
Four studies found lidocaine 5%, benzocaine 20%, and EMLA patch (lidocaine 2.5% w/prilocaine 2.5%), to be more effective than placebo.35-38 Three other studies concluded that benzocaine 20%, benzocaine 18%, tetracaine 2% w/benzocaine 20%, and lidocaine 5% were no more effective than a placebo.39-41 While there were other variables, it is of note that the needles used in the first four studies were no larger than 27 gauge; while in the last three studies the needles were 25 gauge.
Two randomized, double-blind, placebo-controlled studies evaluated the efficacy of lidocaine patches containing lidocaine 10% (23 mg) and lidocaine 20% (46.1 mg) placed on the buccal mucosa of the maxillary premolar area, and maxillary and mandibular premolar areas, respectively, prior to the insertion of a 25-gauge needle intentionally contacting the periosteum.42,43 Both formulations were superior to the placebo, but the 20% patch produced more profound anesthesia of longer duration.
Two cm2 mucoadhesive lidocaine (20%) patches containing 46.1 mg of lidocaine base are available (DentiPatch™, Noven Pharmaceuticals, Inc.).44 Anesthesia occurs within 2.5 minutes of application and after an application period of 15 minutes anesthesia persists for approximately 30 minutes. Peak plasma concentration with the 20% patch, after an application period of 15 minutes, is 10 times less than that associated with the administration of lidocaine 2% (36 mg) w/1:100,000.42,43