Alan E. Nelson

Surface Analysis of Etched Molar Enamel by Gas Adsorption

Much research has been devoted to the study of etched enamel, since it is critical to bonding. Currently, there are no precise data regarding the etched-enamel specific surface area. The aim of this study was to characterize, by two different methods, the surface of human dental enamel in vitro after being etched. It was hypothesized that differences would be observed between specimens in terms of specific surface area and grade of etching. Sixteen third molar enamel samples were etched for 30 sec with 37% phosphoric acid prior to being viewed by SEM. Etched enamel surfaces were graded according to the Galil and Wright classification. The total surface area of etched samples was determined by the BET gas absorption method. A substantial variability in total surface area was observed between and among samples. A Pearson’s Correlation Coefficient showed a lack of relationship between etch pattern and total surface area.

Mature Dental Enamel [Calcium Hydroxyapatite, Ca10(PO4)6(OH)2] by XPS

The dental enamel from the buccal surface of a human premolar tooth (maxilla) was analyzed by x-ray photoelectron spectroscopy (XPS). Mature dental enamel has a crystalline structure containing up to 96 wt% inorganic material, and is principally comprised of calcium hydroxyapatite [Ca10(PO4)6(OH)2, HAP]. The XPS analysis was performed with a Kratos Analytical Axis 165 spectrometer using a monochromatic Al Kα source. In addition to a survey spectrum, core level spectra of the Ca 2p, O 1s, P 2p, and C 1s orbitals were collected. The data are consistent with the surface being predominately calcium hydroxyapatite, with trace contaminants (Na, Si, N, S) observed.

Chemical composition of enamel surface as a predictor of in-vitro shear bond strength.

INTRODUCTION Orthodontic bond failure varies between patients. It has been speculated that the chemical composition of the enamel surface might play a role in the variations in bond failure. METHODS X-ray photoelectron spectroscopy was used in analyzing the surface chemical composition of 49 pairs of maxillary right and left first premolars from patients requiring extractions as part of the orthodontic treatment. After x-ray photoelectron spectroscopy analysis, 49 enamel samples were randomly selected for an in-vitro shear bonding study with a materials testing system, Synergie 400 machine (MTS Systems, Eden Prairie, Minn). RESULTS The in-vitro shear bond strength was found to have a mean of 6.93 +/- 2.71 MPa. Twelve elements were detected; the major ones were calcium, phosphorus, oxygen, nitrogen, and carbon. Regression analysis with the 12 elements explained 33.3% of the variations in bond strength. However, the contribution was not significant (P = 0.170). CONCLUSIONS The chemical composition of the buccal surface of maxillary first premolars was not significant in predicting in-vitro mean shear bond strength. Other factors are likely to be important contributors to the large variations frequently seen in bond strength studies.

Analysis of Cerium–Zirconium Mixed Metal Oxides by Auger Electron Spectroscopy

Auger electron spectra of cerium–zirconium mixed metal oxides over a kinetic energy range of 50–1200 eV are presented. The cerium–zirconium metal oxides were prepared via co-precipitation of nitrate precursors. The precipitate compositions were confirmed to ± 5 at. % with x-ray fluorescence and the crystalline structures were determined with x-ray diffraction. The precipitates were formed into 0.1 mm thick specimens and analyzed in wafer form.

Analysis of Cerium–Zirconium Mixed Metal Oxides by X-Ray Photoelectron Spectroscopy

Survey and high-resolution x-ray photoelectron spectra of cerium–zirconium mixed metal oxides prepared by co-precipitation are presented. The spectra were collected using a Mg Kα (1253.6 eV) source operated at 300 W and 15 kV over a binding energy range of 1100–0 eV. The compositions of the mixed metal oxides were confirmed with x-ray fluorescence and Auger electron spectroscopy prior to XPS characterization. The precipitates were formed into 100 μm thick specimens and analyzed in wafer form.