ATOMIC-FORCE MICROSCOPIC STUDY OF DIMENSIONAL CHANGES IN HUMAN DENTINDURING DRYING

Six 1-mm thick sections of human dentine, three parallel to the occlus al surface and three perpendicular to the buccal surface, were prepare d from non-carious third molars. The enamel was ground off, and the se ctions were polished with alumina powder to remove the smear layer. Ea ch section was imaged by atomic-force microscopy with 20 nm horizontal and 0.1 nm vertical resolutions, initially while the samples were imm ersed in deionized water and then periodically during drying at room t emperature. No dimensional changes over microscopic fields of view (sc anned areas smaller than 50 x 50 mum) could be detected within the pre cision of the measurements (< 0.5%). Across the entire sample, however , vertical displacements of 10-20 mum were measured. Elasticity (Berno ulli beam) theory was used to calculate the engineering strain require d to produce these displacements. The magnitude of the strain was 0.04 % (SD = 0.01) in the buccal sections in the direction of the tubule ax is and 0.09% (SD = 0.02) in the direction normal to the tubule axis. A lso, the strain alternated between tension and compression across the samples. It was concluded that, as determined by using microscopic tec hniques, drying-induced strain is too small to require corrections for tubule size and tubule density.