Dimensional changes of demineralized human dentine during preparation for scanning electron microscopy

Dentine rods measuring approx. 0.7 x 0.7 x 5.0mm were prepared from the crowns of extracted human third molars. The specimens were demineralized in 0.5 M EDTA (pH 7.0) for 3 days and their volume measured with a digital micrometer under a dissecting microscope. The specimens were randomly assigned to experimental groups and were chemically dehydrated in acetone. Next they were dried using either hexamethyldisilazane, Peldri II, or critical-point drying techniques. The dimensions of the specimens were measured again after each step and the changes in volume were expressed as a percentage of the original demineralized volume. The effects of fixing the specimens in 10% buffered formalin before dehydration with acetone were also investigated for every drying procedure. Dehydration in acetone caused a small but significant reduction in the volume of demineralized formalin-fixed specimens but unfixed specimens did not change significantly. In general, all three drying procedures caused some shrinkage in demineralized dentine specimens. Unfixed specimens exhibited a volumetric shrinkage of approx. 15-20% after drying with any of the methods. Fixed specimens shrank more than unfixed specimens after drying (25-35%). Regardless of the drying technique, the specimens shrank a further 10-20% when measured in the vacuum chamber of the scanning electron microscope. Among the three drying techniques employed, hexamethyldisilazane seems to be a very useful alternative to critical-point drying for the preparation of dentine specimens for scanning electron microscopy.