Material-specific contrast in the ESEM and its application in dentistry

Abstract

The Environmental Scanning Electron Microscope (ESEM) equipped with a Gaseous Secondary Electron Detector (GSED) was used to image and analyze materials of different density, composition and structure applied in dentistry. Under ESEM conditions (at a H₂O vapor pressure of 1–10 Torr) the hydrated surfaces of native teeth, which were coated with different polymers, generated a topographic and also a material specific contrast. The backscattered (BSE) and the secondary (SE) electrons involved into the imaging process produced a cascade-dependent mixed signal at the GSED. The material-specific contrast, generated by the BSE cascade, depends mainly on the atomic number z of the investigated material. The topographic contrast is based principally on the SE cascade. For the exact differentiation of the specific signal components inside of the ESEM, we additionally used a backscattered electron detector (BSED), the application of which allowed us to detect pure BSEs and no signals from cascade-dependent electrons. Conventional scanning electron microscopy (CSEM) used to investigate and image the structures of teeth and applied dental materials needs time-consuming and often artifact-inducing preparation steps before the partially hydrated specimen can be investigated, whereas the ESEM technology permits the imaging of hydrated organic structures with no prior specimen preparation. In the ESEM the interfaces between the hydrated organically structured tooth surfaces and the artificially applied polymer materials with its specific bond characteristics can be analyzed very fast and repeatedly (e.g. after etching series) at a reproducible high quality level.