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BOSTON, USA: Although local anesthesia was introduced in dentistry more than 130 years ago, little is known about associated brain mechanisms. New data has now pinpointed brain regions that appear to play a distinct role in dental pain and its relief.
The study aimed to investigate task-related brain activity and functional connectivity patterns after onset of a regional anesthetic nerve block during continuous noxious dental stimulation. According to the researchers, pain relief was accompanied by a significant activity reduction in the posterior insula and an enhanced connectivity to the midbrain. These results confirm previous reports demonstrating that direct electrical stimulation of this brain region evokes bodily pain sensations. However, this effect was not observed in other regions of the brain. Hence, the investigation adds further evidence to the theory that the posterior insula plays a unique role in nociceptive processing.
The placebo-controlled fMRI study involved 28 male participants with a mean age of 27. The participants were subjected to repetitive electrical stimuli applied to the left mandibular canine. The intensity of these stimuli was rated as 5 out of a possible 11.
In the first stage of the experiment, the participants received 30 stimuli for 5 minutes. One half of the participants then received a submucosal injection of 4% articaine, while the other half received a sodium chloride placebo. In the second stage, electrical tooth stimulation was applied for 16 minutes, during which participants indicated pain offset by pressing an alarm ball. Brain activity before and after the injection of the anesthetic was then compared intra-individually on group level.
Pain relief was shown to occur 4.5 minutes after the injection in the articaine group, while there were no similar responses of relief from the placebo group. Between-group analysis in the second stage of the experiment demonstrated a significant activation cluster in the ipsilateral posterior insula in the placebo group. Using the posterior insula as a seed region, the context-dependent psychophysical interaction analysis yielded a significantly enhanced coupling to the midbrain after the pain relief onset in the articaine group only, which suggests a distinct role of both brain regions in dental pain and its relief.
The findings of the study, titled "Distinct Brain Mechanisms Related to Dental Pain Relief," were presented at the 2015 International Association for Dental Research general session on March 12 by Dr. Michael L. Meier, a research fellow at the Center for Dental Medicine, University of Zurich, Switzerland.
