Ultrastructure of Human Enamel Specimens Prepared by Ion Micromilling

Ion-thinning techniques for the preparation of transmission electron microscope samples of mature enamel were used to examine ul-trastructural details that included crystallite size and orientation in relation to the enamel rod geometry. The three-quarter arcade of the sheath is visible as the perim-eter of the keyhole. Diffraction studies in-dicate a preferred orientation in the c axis of the crystallites in the head and tail of the keyhole and in other directions in the head region. The ultrastructural elements of mature hu-man dental enamel have been studied ex-tensively by transmission electron micros-copy. Meckel, Griebstein, and Neal ' suc-cessfully sectioned fully mature enamel with the use of a special microtome.2 The tech-niques have not been applied widely, how-ever, and most investigators have used various indirect methods to study adult tooth ultrastructure. Some of the methods used have been replication of fractured or chemically etched surfaces,3-5 sectioning of artificially demineralized tissue,6 8 and sec-tioning of hypomineralized teeth that are a result of pathologic processes (for example, amelogenesis imperfecta,9 caries10 11) or are formed during natural developmental stages. '-14 The purpose of this investigation was to develop further the use of ionized gas bom-bardment of mature human enamel for the preparation of thin specimens for trans-mission electron microscopy. This procedure would allow direct observation and diffrac-tion study of the tissue and would be fre