Detection of the piezoelectricity effect in nanocrystals from human teeth

Direct and converse piezoelectric effects have been observed in human tooth enamel and dentin. In this study, organic material was removed from dentin and enamel using a chlorinated solution to measure the sole contribution of the inorganic phase. In the direct mode, piezoelectricity is observed when a force applied to the sample produces a voltage. A variable load was applied to the samples with a Shimadzu universal testing machine. In the converse mode, mechanical deformation of the sample occurs under an electric field, which was detected using an atomic force microscope in the piezoelectric mode (piezoresponse force microscope, PFM). For comparison, measurements were also performed on samples where organic (collagen) and inorganic (hydroxyapatite) phases were present. Although a decrease in of the electromechanical response of the organic free sample was observed, the results indicate that the inorganic phase contributes to the piezoelectric property in dentin and in a lesser extent in enamel. This suggests that tooth dentin and enamel apatite nanocrystals present piezoelectric non-centrosymmetric (P6₃ and P2₁), as with centrosymmetric (P6₃/m) structure domains in different percentages.