Cold Air Heats the Brain: fMRI of Dentine Hypersensitivity

Objectives: Dentine hypersensitivity (DH) is commonly evoked by cold temperatures. This study aimed at clarifying the following two questions: 1) Is the DH threshold stable across a four week time period and 2) what brain responses are generated during cold stimulation of hypersensitive and control teeth in general and by comparison ?
Methods: A sensitive and an insensitive (control) tooth were identified in 12 subjects (8 female, 4 male, mean 31. 2 y, sd 9.6). The cold pain threshold of the sensitive tooth was determined at weekly intervals for four weeks by means of an MR-compatible custom-built cold air stimulator. Perceived stimulus intensities were recorded on a modified BORG scale. Additionally, during an fMRI experiment, 40 cold stimuli (max. duration 3s; inter stimulus interval 10s) evoking moderate pain in the sensitive tooth were applied to both, the sensitive and insensitive tooth.
Results: Mean stimulus temperature required for evoking DH was -16.9 °C (sd 1.9) with a mean stimulus duration of 2.7 s (sd 0.1). Repeated psychophysical assessments revealed a robust intraindividual threshold stability across the four week period (icc = 0.93, p < .001). fMRI responses related to DH revealed significant activity changes in bilateral insula, thalamus, and anterior mid-cingulate cortex/supplemental motor area (SMA). Equi-intense stimulation of the control tooth resulted in significant activation changes in bilateral insula and SMA. Differential responses to cold stimulation between sensitive and control tooth were observed in perigenual anterior cingulate cortex (pgACC)(p < .05, FWE-corrected).
Conclusions: Stability of DH threshold across four weeks was robust. fMRI data revealed a differential brain response to cold stimuli between sensitive and insensitive teeth. These pilot results suggest a prominent role of the pgACC in differentiating DH pain from painless sensations.