Title: 0147 - Double-Blind Concealment Inadequate When Administering Local Anesthetic and Non-Active Control


Olivia Edvinsson, Malmö University
Johanna Ekelund, Malmö University
Donald Nixdorf, University of Minnesota
Lene Vase Toft, Aarhus University
Thomas List, Malmö University
Maria Pigg (Presenter)
Malmo University


Objectives: Patients’ expectations and beliefs are known to affect treatment outcomes, but it is unknown how they affect the experience of local anesthetic agents administered to anesthetize dentoalveolar tissues. This study aimed to examine the relationship between type of agent administered, the anesthetizing effect/response to injection, and the belief of the recipient.

Methods: This double-blind randomized clinical experimental study included pain-free adults. Participants received a 2ml-infiltration injection of either 1% lidocaine (active group AG; n=10) or 0.9% NaCl (non-active group NAG; n=10) on oral mucosa in the right upper premolar region. Mechanical pain sensitivity (MPS; rating of pain intensity 0–10/10 with 512mN pinprick stimulus) and stimulus quality (sharp/blunt) was assessed before and 5 min after injection. Participants were instructed that chances of receiving active versus non-active agent were equal, 50%. The following day, each participant’s belief regarding administered agent was obtained. Paired and independent t-test (pain intensity) and chi-2 test (stimulus quality) analyzed within- and between-group differences. Spearman’s rho analyzed agent–stimulus quality correlation.

Results: Average pre-injection MPS was 3.0(SD 2.4) in AG and 3.1(SD 1.3; p=0.909) in NAG, and post-injection 0.1(SD 0.3) in AG and 3.1(SD 2.0; p<0.001) in NAG. Within-group MPS difference was significant only for AG (p=0.003). 60% in AG versus 70% in NAG perceived the stimulus as blunt pre-injection (p=1.000), and 90% in AG versus 40% in NAG post-injection (p=0.057). The correlation between rating the post-injection stimulus quality as blunt and receiving active agent was r=0.52 (p=0.019). All participants correctly identified their group allocation, thus injection response in relation to beliefs could not be analyzed.

Conclusions: When equally expecting to receive active/non-active agent, participants could correctly identify which agent was given; thus, double-blind concealment was ineffective. Pain sensitivity to pinprick decreased after injection with active but not non-active agent. The correlation between agent and perceived stimulus quality was weak.

Disclosure Statement:
The submitter must disclose the names of the organizations with which any author have a relationship, the nature of the relationship, and the clinical or research area involved. The following is submitted: NONE