CNS Representation of Different Kinds of Orofacial Pain: fMRI Study

Objectives: To investigate the activation pattern of central nervous system (CNS) of different kinds of orofacial pain in order to analyze the characteristics of pain (psychogenic or somatic pain). Methods: Four groups of subjects were included in this study: 10 normal adult volunteers without orofacial pain (No.1 group), normal group with an experiment occlusal high spot (0.5 mm in height) which was placed on the right lower first molar and remained for 3 days (No.2 group), 7 patients with orofacial pain arising after iatrogenic sudden occlusal changes, who complained physical symptoms but have no corresponding physical conditions (No.3 group) and 7 temporomandibular disorder (TMD) patients with inflammatory pain (No.4 group). All the subjects scored orofacial pain on a 10-cm visual analogue scale (VAS). Blood-oxygenation-level-dependent (BOLD)-functional magnetic resonance imaging (fMRI) was used to observe the cerebral neuronal activities evoked by mastication among the four groups. Results: With less than moderate orofacial pain(mean VAS±s.d. = 3.7±0.5) induced by experimental occlusal interference, the activated cerebral regions of No.2 group were different from No.1 group and included bilateral significantly activated thalamus. Although the VAS scores received from No.3 and No.4 groups were approximate (P>0.05), the cerebral activation patterns of the two groups were significantly different. The activated pain regions for the patients in No.3 group were bilateral thalamus and anterior cingulate cortex. Otherwise, the No.4 group activated a quite different pain network, including postcentral gyrus, cingulate gyrus and prefrontal cortices. Conclusions: The experimental occlusal interference may induce the excessive attention of pain in No.2 group. The No.3 group presented psychogenic orofacial pain while the No.4 group presented somatic orofacial pain. The cerebral processing of different kinds of orofacial pain wasn't the same, which indicated that antalgic mechanisms and pain management couldn't be the same.