Comparison of human and bovine dental enamel by TEM and t-EBSD investigations

The microstructures of human dental enamel and bovine enamel are compared to each other. To obtain samples for transmission electron microscopy (TEM), focused ion-beam (FIB) milling is used. The preparation of such TEM-slices is found to be very effective when operating the FIB with adapted parameters. After the milling process, the TEM-slices are then thinned by means of the ion beam to achieve samples being transparent for the electron beam. With a home-built sample holder, the electron backscatter diffraction (EBSD) can be operated in the scanning electron microscope (SEM) in transmission mode called t-EBSD. This technique enables the crystallographic orientation measurement on nanometer-sized, non-conducting enamel grains with a reasonable quality. Both TEM and t-EBSD images reveal a similar arrangement of the apatite crystals within the enamel, but it is obvious that the nanostructure of human enamel follows a more complex construction principle. The grain sizes of bovine enamel are much larger, and it is difficult to recognize the chain arrangement as found previously in the human enamel. As a result of the comparison, one can state that the nanostructure of human enamel is clearly more complicated than the bovine counterpart.