THE EFFECTS OF ACETONE, ETHANOL, HEMA, AND AIR ON THE STIFFNESS OF HUMAN DECALCIFIED DENTIN MATRIX

During resin-bonding procedures, dentin surfaces are treated with acid ic conditioners to remove the smear layer and decalcify the surface to expose the collagen fibrils of the underlying matrix. These decalcifi ed surfaces are then either air-dried or treated with dehydrating solv ents, procedures which may modify the physical properties of the denti n matrix. The purpose of this study was to evaluate the effects of deh ydration on the stiffness of the decalcified dentin matrix. Small (8 x 1.7 x 0.9 mm) beams of dentin were prepared from mid-coronal, dentin of extracted human molars. The ends were covered with varnish for prot ection, and the specimens were placed in 0.5 M EDTA for 5 days to deca lcify. The stiffness was measured by both the cantilever technique and by conventional stress-strain testing. Specimens tested by the cantil ever technique were sequentially exposed to water, acetone, alcohol, H EMA, and glutaraldehyde. Specimens tested by conventional stress-strai n testing were exposed either to water, acetone, or HEMA, or were allo wed to air-dry. The results indicate that the stiffness of decalcified human dentin matrix is very low (ca. 7 MPa), if the specimens are wet with water. As they are dehydrated, either chemically in water-miscib le organic solvents or physically in air, the stiffness increases 20- to 38-fold at low strains or three- to six-fold at high strains. These increases in modulus were rapidly reversed by rehydration in water. E xposure to glutaraldehyde also produced an increase in stiffness that was not reversible when the specimens were placed back in water.