Laird Harrison

April 05, 2012

April 5, 2012 (Tampa, Florida) — A topical anesthetic with tetracaine numbed subjects' pulps better than benzocaine in a study reported here at the American Association for Dental Research 2012 Annual Meeting.

A new topical anesthetic is needed because what's already available doesn't work very well, said Bradley Carn, a fourth-year dental student at Southern Illinois University School of Dental Medicine in Alton.

Benzocaine has not been shown to be more effective than placebo, and the US Food and Drug Administration has expressed concern about compounded anesthetics.

A team of dentists and pharmacists in southern Illinois has developed a formulation of 6% tetracaine, an ester-type anesthetic also known as amethocaine, pontocaine, and dicaine.

They combine the tetracaine with propylene glycol as a penetration enhancer and a plasticized base as a mucoadhesive. The resulting compound they call tetracaine anesthetic paste (TAP).

"Currently it's being used in select dental offices," said Carn. "Those clinicians are reporting anecdotal evidence that it's giving 45 to 90 minutes of soft tissue anesthesia. They are using it to cut off crowns and for scaling and root planing and gingivectomy."

In one preliminary study, researchers conducted a head-to-head comparison of TAP and benzocaine applied prior to a maxillary buccal infiltration and asked subjects to rate their pain. The difference was not statistically significant.

For their study, Carn and his colleagues divided 45 subjects into 3 groups — 21 received TAP, 17 received 20% benzocaine, and 7 received a placebo.

The researchers measured the subjects' sensitivity with a pulp tester, which zaps teeth with an electric current. They gradually increased the current until the subjects said they felt pain.

They then applied 25 mg of 1 of the treatments to the buccal and palatal mucosa of each subject's tooth number 6.

After 10 minutes, they wiped off the treatment, rinsed with water, and retested with the pulp tester at 10, 15, and 20 minutes.

The subject and the investigator who performed the pulp testing were blinded to the treatment.

Nine of the subjects (42.8%) in the TAP group reached at least double their score before feeling pain. In comparison, 2 of the benzocaine subjects (11.7%) and 3 of the placebo subjects (42.8%) doubled their scores.

The high scores for patients receiving placebo could be from endogenous opioids released when a constant current is applied, Carn said.

Looking at the numbers another way, 6 of the TAP subjects (28.5%) reach the maximum current possible in the pulp tester; none of those receiving benzocaine or placebo reached that limit.

The difference between benzocaine and TAP was statistically significant, but the difference between TAP and placebo was not, Carn said. He hopes to expand the study to more subjects to increase its statistical power to compare TAP and placebo.

The duration of the anesthesia was short — only about 5 minutes in most patients. "Whether that's clinically [relevant] is a valid question," Carn said. He suggested adding a vasoconstrictor or leaving TAP in place longer to extend the longevity of the numbness.

The presentation stimulated a lively discussion. "I'm rather impressed that you get any pulpal anesthesia with a topical anesthetic," said Paul Moore, DMD, PhD, MPH, professor of dental anesthesiology at the University of Pittsburgh School of Dental Medicine in Pennsylvania.

Peter Milgrom, DDS, professor of dental public health sciences at the University of Washington in Seattle, questioned the reliability of pulp testers in general.

And Daniel Haas, DDS, PhD, professor of dental anesthesia at the University of Toronto in Ontario, Canada, asked how much of the tetracaine is absorbed systemically.

Carn said his team has not done that research yet.

Dr. Moore disclosed that he is a paid consultant to Septodont, which markets articaine. Mr. Carn, Dr. Milgrom, and Dr. Haas have disclosed no relevant financial relationships.

American Association for Dental Research (AADR) 2012 Annual Meeting: Abstract 80. Presented March 22, 2012.

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