Objectives: In 1937 Penfield and Boldrey demonstrated the medial-lateral representation of the upper lip, lower lip, intraoral cavity and tongue in the somatosensory homunculus using electrical stimulation. Even today, however, very little is known about the projection of the teeth on the human cerebral cortex. In the present study, functional magnetic resonance imaging (fMRI) was used to investigate the somatosensory (SI and SII) brain areas that are involved in the perception of tooth vibration. Methods: On 6 subjects, a piezoelectric crystal driven plastic stimulator with a rubber-coated tip was used to apply a 20 Hz vibration to the left upper central incisor. The stimulation was presented at an amplitude of 3dB above the subjects individual threshold while fMRI experiments were performed on a 3.0T echo-planar imaging scanner. The stimulus was presented for a 9s ‘ON' period followed by 27s ‘OFF'. This was repeated for 10 cycles. Coronal images were acquired with a 128 x 64 matrix size, 3 x 3 mm in-plane resolution and 8 mm slice thickness. Group analysis was conducted with SPM99. Results: The group data yielded an SPM standard space mean co-ordinate of the centre of mass of activation for contralateral SI of (56, -52, 36; p<0.001) and ipsilateral SI of (-54, -38, 32; p<0.001). For SII the mean contralateral activation was found at (56, -32, 10; p<0.001) and ipsilateral SII at (-58, -34, 10; p<0.005). Conclusions: It has been shown that it is possible to investigate brain responses to dental vibration using fMRI. Bilateral activation was found in SI and SII and the contralateral activation of SI was greater than that in the ipsilateral cortex.

This work was supported by Unilever Research and MRC Sweden (No. 13291).

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