Piezoelectric Effect in Dentin

It was reported recently (J. M. MUMFORD and A. V. NEWTON, J Dent Res 48:226-229, 1969) that there is considerable transduction of mechanical force to electric potential in whole teeth. In the same paper, a tentative model for this phenomenon was presented, which involved the streaming potential in capillaries (the periprocessal space in dentinal tubules). An alternate explanation for this effect, namely, the piezoelectric response of dentin is possible. Piezoelectricity, long regarded as a classical phenomenon in physics (W. G. CADY, Piezoelectricity, 1964) has, in the last few years, been found in a variety of biologic materials (V. A. BAZHENOV, Piezoelectric Properties of Wood, 1961; M. H. SHAMOS, and L. S. LAVINE, Clin Orthop 35:177-188, 1964; E. FUKADA, Biorheology (Oxford) 5:199-208, 1968) and it must be recognized as a fundamental property of biologic tissues (M. H. SHAMOS and L. S. LAVINE, Nature 213:267-269, 1967.). This and other groups have previously reported (SHAMOS, LAVINE, 1964; M. BRADEN ET AL, Nature 212: 1565-1566, 1966; G. V. B. COCHRAN, R. J. PAWLUK, and C. A. L. BASSETT, Arch Oral Biol 12: 917-920, 1967) a decided piezoelectric effect in human dentin. However, these were qualitative results and were difficult to interpret because of the specimen size available from humans. A recent determination has been made on horse dentin cubes cut so the dentinal tubules were all approximately parallel. The expression governing the electric polarization, Ps (coulombs/m2), resulting from the application of stress, Sj (newtons/M2), is Pi= doSe, where the 18 elements (dil) are referred to as the piezoelectric moduli. The index j takes on the values 1 -e 6, corresponding to the six possible stresses on a cube, and the index i takes on the values 1, 2, 3, corresponding to the three Cartesian directions. Depending on the crystal system, most of the dij are zero. It is generally agreed that the greatest piezoresponse in collagenous systems