The cerebral representation of temporomandibular joint occlusion and its alternation by occlusal splints

Abstract

Occlusal splints are a common and effective therapy for temporomandibular joint disorder. Latest hypotheses on the impact of occlusal splints suggest an altered cerebral control on the occlusion movements after using a splint. However, the impact of using a splint during chewing on its cerebral representation is quite unknown. We used functional magnetic resonance imaging (fMRI) to investigate brain activities during occlusal function in centric occlusion on natural teeth or on occlusal splints in fifteen healthy subjects. Comparisons between conditions revealed an increased activation for the bilateral occlusion without a splint in bilateral primary and secondary sensorimotor areas, the putamen, inferior parietal and prefrontal cortex (left dorsal and bilateral orbital) and anterior insular. In contrast, using a splint increased activation in the bilateral prefrontal lobe (bilateral BA 10), bilateral temporo-parietal (BA 39), occipital and cerebellar hemispheres. An additionally applied individually based evaluation of representation sites in regions of interest demonstrated that the somatotopic representation for both conditions in the pre- and postcentral gyri did not significantly differ. Furthermore, this analysis confirmed the decreasing effect of the splint on bilateral primary and secondary motor and somatosensory cortical activation. In contrast to the decreasing effect on sensorimotor areas, an increased level of activity in the fronto-parieto-occipital and cerebellar network might be associated with the therapeutic effect of occlusal splints.

Figure 1

Illustration on an individually segmented brain of the anatomical ROIs selected. Blue: precentral gyrus, Red: postcentral gyrus, orange: secondary somatosensory cortex (S2); green: area of the superior cerebellum selected. Picture of the Michigan splint: left in an overview, right: implemented for the upper alignment. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

Figure 2

Main effect of both conditions; projection of group maps on a high‐resolution segmented brain (CG‐brain; P < 0.01; FDR corrected). Top row: Bilateral occlusal movements without a splint; Bottom row: Group representation for occlusion with the usage of an occlusal splint. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

Figure 3

Comparison between conditions; Top row: Cortical differences projected on a segmented high‐resolution brain (CG‐brain; P < 0.05; FDR corrected). Bottom row: slices projected on the averaged T1‐weighted structural datasets of all 15 subjects. Occlusion (“bilateral”) minus occlusional splint (“splint”): The bilateral occlusion without a splint showed increased activation in bilateral M1, S1, and S2, anterior insula, inferior parietal lobe, putamen and medial cingulate cortex. Occlusional splint (“splint”) minus occclusion (“bilateral”): The usage of a occlusal splint involved increasing activation in bilateral prefrontal lobe (BA 46, left BA 10, right BA 45), bilateral temporo‐parietal junction, bilateral occipital lobe and bilateral cerebellar hemispheres.

Figure 4

Group analysis based on individual activation sites and magnitude revealed differential activation magnitude in bilateral M1 (P < 0.05), S1 (P < 0.005), and S2 (P < 0.05) but not in the anterior cerebellar hemispheres (n.s.). [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]