Brain plasticity and cortical correlates of osseoperception revealed by punctate mechanical stimulation of osseointegrated oral implants during fMRI

Purpose: Our aim was to unveil the cortical neural correlates of osseoperception, i.e. the tactile sensation perceived when loading a bone-anchored implant, by taking oral implants as a model. This was performed in a cross-sectional observational study with 9 volunteering patients and 10 age-matched controls. For each patient, functional magnetic resonance imaging (fRMI) recordings were made during punctate mechanical stimulation of either teeth or osseointegrated implants in the maxillary incisor area. Materials and methods: During fMRI recordings, 1 Hz punctate tactile stimuli were applied either on a maxillary left central incisor, canine tooth or central incisor implant. A block design paradigm was used to stimulate, in 9 patients, maxillary left central incisor implants (I21-p) and maxillary left canines (T23-p). In 10 control subjects, maxillary left central incisors and canines (T21-c, T23-c) were stimulated. Random effect group analyses were performed for each stimulated site, and differences in cortical activity elicited when loading teeth or implants were examined using ANOVA. Results: As a group, patients activated somatosensory area S2 bilaterally for both I21 and T23, while controls activated S1 and S2 bilaterally for T21 and T23. At an individual level, S1 was activated by 4/9 implants, mainly on the ipsilateral side. The stimulated implants activated a larger bilateral cortical network outside the somatosensory areas: in parietal, frontal and insular lobes, the main clusters being located in the inferior frontal gyri. Stimulation of T23 in patients resulted in an activation pattern intermediate between that of the implants and that of natural teeth. Conclusion: This study demonstrates that punctate mechanical stimulation of oral implants activates both primary and secondary cortical somatosensory areas. It also suggests that brain plasticity occurs when extracted teeth are replaced by endosseous implants. This cortical activation may represent the underlying mechanism of osseoperception. Keywords: dental, fMRI, neuroplasticity, oral implant, osseoperception, periodontal, somatosensory cortex