Application of ion etching to the study of dental restorative materials

An electrostatic ion source has been incorporated into the specimen stage of a scanning electron microscope to measure the absolute and relative etching rates of dental materials, using a cryogenic stage to control the sample temperature. It has been found that the etching rates of tooth enamel, amalgam and composite fillings are 1.3, 6.0 and 4.7 μm/hr respectively using argon ions of current density of about 0.1 mA/cm 2 at an energy of 4.5 keV. This approach has been used to study the enamel/restoration interface. It has been shown that after ion etching a gap of 10–20 μm is revealed between the enamel and the amalgam. This suggests that a thin bridge of amalgam, thickness about 50 μm, adjacent to the enamel at the surface is removed during the ion bombardment. Thus, although good adaptation between the amalgam and enamel is indicated on the surface, this is in fact not the case down the whole depth of the cavity wall. A similar study using composite fillings has shown very little evidence for the existence of any gap and thus demonstrates that these composite fillings adapt better to the cavity walls.