Although local anesthesia has made dental patients more comfortable since 1884, little is known about brain mechanisms related to dental pain relief. At the 93rd General Session and Exhibition of the International Association for Dental Research (IADR), researcher Michael L. Meier, Center for Dental Medicine, University of Zürich, Switzerland, presented a placebo-controlled and age matched functional magnetic resonance imaging study aimed to investigate task-related brain activity and functional connectivity patterns following onset of a regional anesthetic nerve block during continuous noxious dental stimulation. The study involved a total of 28 male subjects with a mean age of 27.09, SD ± 7.06. Repetitive electric stimuli evoking an intensity perception of 5 on an 11-point numeric intensity rating scale were applied to the left mandibular canine. Two phases were involved; in phase one, 30 stimuli with a duration of 5 minutes was followed by a submucosal injection of the anesthetic articaine 4% (group A) or 0.9% sodium chloride as placebo (group P) at the left mental foramen. Phase 2 involved electric tooth stimulation which continued for 16 minutes, with subjects indicating pain offset by pressing an alarm ball. Task-related activation and connectivity analysis was performed using SPM8 and context-dependent psychophysical interactions (PPI). The study found that in group A, pain relief was reported 4.5 minutes after the injection. In group P, no subject reported pain relief. The between-group analysis of phase 2 demonstrated a significant activation cluster in the ipsilateral posterior insula (pIns) in group P. Using the pIns as a seed region the PPI analysis yielded a significant enhanced coupling to the midbrain (periaqueductal gray/ventral tegmental area) after analgesia onset in group A only. This study demonstrated that dental pain relief was accompanied by a significant activity reduction in the posterior insula and an enhanced connectivity to the midbrain. This data suggests a distinct role of these brain regions in dental pain and its relief.
(Source: Medical News Today, March 17, 2015)