Comparison of topical EMLA 5% oral adhesive to benzocaine 20% on the pain experienced during palatal anesthetic infiltration in children

Resident: J. Hencler
Date: 01/19/2011

Article title: Comparison of topical EMLA 5% oral adhesive to benzocaine 20% on the pain experienced during palatal anesthetic infiltration in children

Author: Primosch, DDS, MS, MEd; Roland-Asensi, DDS
Journal: Pediatric Dentistry-23:1, 2001

Major topic: Topical anesthetic
Type of Article: Scientific

Main Purpose:
Compare the pain responses of children during local anesthetic injection at bilateral palatal sites prepared with the topical application of benzocaine 20% oral adhesive (Orabase-B®) versus benzocaine 20% gel (Hurricaine®) or EMLA 5% oral adhesive (EMLA 5% cream on Orabase Plain®).

Overview of method of research:
In the first phase, subjects compared injection pain experience at bilateral palatal sites anesthetized topically with Hurricaine vs. Orabase-B. The second phase was conducted with Orabase-B vs. EMLA 5% manually mixed with Orabase Plain (sodium carboxymethylcellulose oral adhesive). Collected data included the subject’s gender, age, and heart rate (pre-, intra-, and post-injection), pain assessments by the subject using a visual analogue scale (VAS), by the operator using a modification of the Children’s Hopital of Eastern Ontario Pain Scale (CPS), and a post-trial questionnaire comparing overall comfort, taste acceptability, and agent preference. For both the VAS and CPS, the higher the score, the higher the subject’s pain intensity.

Findings:
Forty subjects were selected for the study aged 7-15 years old. When Hurriciane was compared to Orabase-B (Phase I) no significant differences during palatal injection were found for the subject’s pain perception (VAS) and the operator’s assessment of the subject’s pain using CPS. There was an increased mean heart rate during the injection when compared with the mean pre- and post-injection heart rate values but no significant differences in heart rates were shown between the two agents. There were no significant differences in the discomfort reported by the subjects, but Hurricaine was rated slightly better for taste acceptance and agent preference. When Orabase-B was compared to EMLA cream in Orabase plain (Phase II), no significant differences during palatal injection were found for the subject’s pain perception (VAS) and operator assessment of subject’s pain using CPS. There was an increased mean heart rate during the injection when compared with the mean pre- and post-injection heart rate values but no significant differences in heart rates were shown between the two agents. No significant differences in the discomfort reported by the subjects, but subjects expressed greater taste acceptance and agent preference for Orabase-B.

Key points in the article discussion:
The prior application of topical anesthetic helps to alleviate, but does not eliminate, pain associated with needle insertion and anesthetic injection. Widespread belief among patients that topical anesthetics are effective at reducing injection pain may serve to reduce the anticipatory anxiety associated with impending dental injection. The most popular topical anesthetic is benzocaine 20% gel due to rapid onset (30sec), acceptable taste, and lack of systemic absorption. EMLA 5% cream is an acronym for “eutectic mixture of local anesthetics” and contains lidocaine 2.5% and prilocaine 2.5%. Preliminary trials were promising for the effectiveness of EMLA 5% cream on the palatal mucosa of adults, this site has not been tested in children. The palatal site is notorious for its inability to acquire adequate topical anesthesia due to poor drug penetration through highly keratinized tissue. The eutectic mixture found in EMLA cream allows it to be in liquid form at oral temperature and thus facilitates absorption into tissue. The practical disadvantages of EMLA 5% cream intraorally include a bland taste (a pH of 9 may even create a bitter taste), low viscosity with resulting difficulty in retaining it at the desired site, prolonged time of application (5 min vs. 2 min w/ benzocaine), and product cost. This study did not reveal superior effectiveness in reducing injection pain for children using EMLA 5% oral adhesive when compared to benzocaine 20% in gel and adhesive forms.

Summary of conclusions:
EMLA 5% cream in Orabase Plain was equally effective as Orabase-B, which displayed a similar efficacy as Hurricaine. Although all agents tested were equivalent in injection pain response comparisons, Hurricaine had a slight advantage in expressed subject preference and taste acceptance over the other agents. The lack of demonstrated efficacy and subject preference, the necessity to custom mix the cream into an oral adhesive paste, the extended duration of time required for onset of action, the greater potential for complication associated w/ systemic absorption, and the product cost preclude to use of EMLA 5% oral adhesive over other products containing benzocaine 20%.

Assessment of article:
Good article. VAS and CPS scales to report pain perception are subjective and could lead to over or under reporting of pain perception. Everyone has a different threshold for pain. Overall a good study design. Authors could have also tested EMLA 5% cream alone and not mixed into a paste with Orabase Plain. I was surprised by the results of this study.