The Human Brain Response to Dental Pain Relief

Abstract

Local anesthesia has made dental treatment more comfortable since 1884, but little is known about associated brain mechanisms. Functional magnetic resonance imaging is a modern neuroimaging tool widely used for investigating human brain activity related to sensory perceptions, including pain. Most brain regions that respond to experimental noxious stimuli have recently been found to react not only to nociception alone, but also to visual, auditory, and other stimuli. Thus, presumed functional attributions have come under scrutiny regarding selective pain processing in the brain. Evidently, innovative approaches are warranted to identify cerebral regions that are nociceptive specific. In this study, we aimed at circumventing known methodological confounders by applying a novel paradigm in 14 volunteers: rather than varying the intensity and thus the salience of painful stimuli, we applied repetitive noxious dental stimuli at constant intensity to the left mandibular canine. During the functional magnetic resonance imaging paradigm, we suppressed the nociceptive barrage by a mental nerve block. Brain activity before and after injection of 4% articaine was compared intraindividually on a group level. Dental pain extinction was observed to correspond to activity reduction in a discrete region of the left posterior insular cortex. These results confirm previous reports demonstrating that direct electrical stimulation of this brain region-but not of others-evokes bodily pain sensations. Hence, our investigation adds further evidence to the notion that the posterior insula plays a unique role in nociceptive processing. The human brain response to dental pain relief AbstractLocal anesthesia has made dental treatment more comfortable since 1884, but little is known about associated brain mechanisms. Functional magnetic resonance imaging (fMRI) is a modern neuroimaging tool widely used for investigating human brain activity related to sensory perceptions, including pain. Recently, most brain regions that respond to experimental noxious stimuli have been found to react not only to nociception alone, but also to visual, auditory and other stimuli. Thus, presumed functional attributions have come under scrutiny regarding selective pain processing in the brain. Evidently, innovative approaches are warranted to identify cerebral regions that are nociceptivespecific. In this study, we aimed at circumventing known methodological confounders by applying a novel paradigm in 14 volunteers: rather than varying the intensity and thus the salience of painful stimuli, we applied repetitive noxious dental stimuli at constant intensity to the left mandibular canine.During the fMRI paradigm we suppressed the nociceptive barrage by a mental nerve block. Brain activity before and after injection of 4% articaine was compared intra-individually on a group level.Dental pain extinction was observed to correspond to activity reduction in a discrete region of the left posterior insular cortex. These results confirm previous reports dem...

Tracking local anesthetic effects using a novel perceptual reference approach

“…This aspect would be best addressed by applying a series of stimuli without intervention. Yet, our previous electric tooth stimulation studies using 7-12-s intervals did not indicate habituation or sensitization effect (Brügger et al, 2012;Meier et al, 2014Meier et al, , 2015.…”

“…The idea behind selecting a tooth as a target site for evoking a pure pain experience is not new (Chatrian et al, 1975) and relies on the observation that repetitive electric stimuli reliably evoke short and sharp painful sensations (A-␦-fiber-mediated pain) and no superimposed mechanosensations or thermosensations (Brügger et al, 2011(Brügger et al, , 2012Meier et al, 2014Meier et al, , 2015Närhi et al, 1992). A-␦-and C-nociceptors dominate intrinsic tooth innervation.…”

“…Mandibulary splints were fabricated from dental impressions made of Blu-Mousse [Blu-Mousse is a fast-setting vinyl polysiloxane material produced by Parkell (Edgewood, NY)] (Brügger et al, 2012;Meier et al, 2014Meier et al, , 2015. Stainless-steel electrodes were embedded into each splint at the labial and palatal centers of the left and right mandibular canine (Fig.…”

“…Its underlying psychophysical concept requires subjects to self-adjust the stimulus strength to a nonanesthetized tooth every 5 s, so that it matches the perceived intensity in an homologous tooth that received a LA injection, while perpetually stimulated with a given stimulus strength. Since electric tooth stimulation evokes reliable and stable pain perceptions (Brügger et al, 2012;Meier et al, 2014Meier et al, , 2015, we opted for this experimental model, but the current approach might be applied to other body sites.…”

Brain activity and connectivity attributable to nociceptive signal block

“…Converging evidence from animal and human studies using central (intracortical) and peripheral stimulation suggests the existence of nociceptive afferents passing the thalamus, the cerebellum, the S1 and S2, the midcingulate cortex and the posterior insula (pINS) (Kenshalo et al 2000; Moulton et al 2010; Shyu et al 2010; Garcia-Larrea 2012b; Mazzola et al 2012a; Vierck et al 2013; Craig 2014). In humans, the pINS and the adjacent parietal operculum (S2 region) show the uppermost preference for nociceptive signal processing, constituting a promising “core nociceptive node” (Eickhoff et al 2006a; Garcia-Larrea 2012a; Mazzola et al 2012b; Mazzola et al 2012a; Segerdahl et al 2015; Cowan 1977; Mano and Seymour 2015; Meier et al 2015; Davis et al 2015). Yet, while the theory of a single pain center is still not falsifiable by current neuroimaging technology, the validation of distinct brain mechanisms for acute pain and its relief is ongoing and highly dependent on the employed experimental design.…”