M. B. Kruger

Raman Imaging of Dental Adhesive Diffusion

The clinical success of dental composites depends critically upon the adhesive bond that secures it to the tooth. Previous efforts to characterize the adhesive/dentin interface have generally required sample preparation that alters or damages the interface. Using micro-Raman spectroscopy, we have collected chemical and morphologic information on the dentin/adhesive interface with minimal sample preparation. Results from this technique have provided direct evidence of adhesive penetration and demineralization depth for two adhesive systems.

Raman Mapping of the Dentin/Adhesive Interface

The degree of adhesive penetration into dentin has been studied through micro-Raman spectroscopic examination of the dentin/adhesive interface. In contrast to previous studies, for the specimen examined in this work the adhesive penetrates less than 2 μm into the acid-etched and, thus, decalcified dentin. There is strong spectroscopic evidence that, upon acid etching of the dentin surface, which is typically performed immediately before the adhesive is applied, the collagen matrix collapses upon itself.

High pressure X-ray diffraction study of β-Si3N4

Abstract X-ray diffraction data collected at quasi-hydrostatic pressures of 5–34 GPa yield an average zero-pressure bulk modulus and pressure derivative of K 0 = 270(±5) GPa and K 0 ′ = 4.0(±1.8) for β-Si 3 N 4 at room temperature. Similar linear incompressibilities along the a and c crystallographic directions document that compression is nearly isotropic.

Nanocrystalline iron at high pressure

X-ray diffraction measurements were performed on nanocrystalline iron up to 46 GPa. For nanocrystalline epsilon-Fe, analysis of lattice parameter data provides a bulk modulus, K, of 179±8 GPa and a pressure derivative of the bulk modulus, K[prime], of 3.6±0.7, similar to the large-grained control sample. The extrapolated zero-pressure unit cell volume of nanocrystalline epsilon-Fe is 22.9±0.2 A^3, compared to 22.3±0.2 A^3 for large-grained epsilon-Fe. No significant grain growth was observed to occur under pressure.

Nanoparticle fabrication of hydroxyapatite by laser ablation in water

Synthetic polycrystalline hydroxyapatite was ablated in water with 337 nm radiation from a UV nitrogen pulsed laser. According to transmission electron microscopy micrographs, the ablated particles were approximately spherical and had a size of ∼80 nm. Raman spectroscopic analysis demonstrated that particles had the same structure as the original crystal. X-ray photoelectron spectroscopy showed that the surface chemical composition was close to that of the original material. The characteristics of the ablated particles and estimations of the temperature rise of the hydroxyapatite surface under laser irradiation are consistent with the mechanism of explosive boiling being responsible for ablation. The experimental observations offer the basis for preparation of hydroxyapatite nanoparticles by laser ablation in water.

High-pressure studies of titanium pyrophosphate by Raman scattering and infrared spectroscopy

High-pressure investigations of titanium pyrophosphate, TiP2O7, in diamond anvil cell have been performed at room temperature using in situ Raman scattering and Fourier transform infrared spectroscopy (FTIR). The endeavor was to acquire information on pressure-induced structural transformations such as phase transitions and amorphization occurring in the crystal lattice. The pressure-stimulated alterations in the spectral profile, the position, and the intensity of the stretching and bending modes Of PO4 tetrahedral structural units have been investigated up to 42.8 and 49.4 GPa for Raman and infrared-active modes, respectively. The spectral changes pointed mostly to the densification and partial amorphization of the crystal lattice. FTIR spectra confirmed that the investigated compound, TiP2O7, compressed smoothly up to the highest investigated pressures. The spectroscopic studies did not indicate an unambiguous structural transformation matching to a pressure-driven phase transition. The reversibility to ambient pressure structure upon decompression was implied by FTIR but was not confirmed by Raman spectroscopy. The mode Gruneisen parameters were calculated for the various Raman and infrared-active vibrational modes. The results obtained are consistent with our previous high-pressure synchrotron radiation-based X-ray diffraction investigations

Spectroscopic and Morphologic Characterization of the Dentin/ Adhesive Interface

The potential environmental risks associated with mercury release have forced many European countries to ban the use of dental amalgam. Alternative materials such as composite resins do not provide the clinical function for the length of time characteristically associated with dental amalgam. The weak link in the composite restoration is the dentin/adhesive bond. The purpose of this study was to correlate morphologic characterization of the dentin/adhesive bond with chemical analyses using micro-Fourier transform infrared and micro-Raman spectroscopy. A commercial dental adhesive was placed on dentin substrates cut from extracted, unerupted human third molars. Sections of the dentin/adhesive interface were investigated using infrared radiation produced at the Aladdin synchrotron source; visible radiation from a Kr+ laser was used for the micro-Raman spectroscopy. Sections of the dentin/adhesive interface, differentially stained to identify protein, mineral, and adhesive, were examined using light microscopy. Due to its limited spatial resolution and the unknown sample thickness the infrared results cannot be used quantitatively in determining the extent of diffusion. The results from the micro-Raman spectroscopy and light microscopy indicate exposed protein at the dentin/adhesive interface. Using a laser that reduces background fluorescence, the micro-Raman spectroscopy provides quantitative chemical and morphologic information on the dentin/adhesive interface. The staining procedure is sensitive to sites of pure protein and thus, complements the Raman results.

Dentin etch chemistry investigated by Raman and infrared spectroscopy

Micro-Raman and infrared spectroscopy were used to investigate the influence of surface treatment on the diffusion of a dental adhesive into dentin. The commercial dentin adhesive Scotchbond MultiPurpose Plus (3M) was placed on coronal dentin substrates that were cut from extracted, unerupted third molars. Prior to placement of the adhesive, one surface was treated with a phosphoric acid etch and the other with a citric acid–iron(III) chloride etch. Thin sections, ∼3 μm in thickness, were prepared and mounted on silver chloride disks for infrared spectroscopic studies with the remaining bulk sample being used for the Raman studies. The infrared studies were performed at the Aladdin Synchrotron radiation source at the Synchrotron Radiation Center, Stoughton, WI, USA. The Raman studies employed a krypton ion laser in conjunction with a microscope equipped with a 100× objective and confocal aperture. In both studies the sample was translated in 1 μm steps at the focus of the respective radiation, providing a line scan across the interface. The infrared results clearly show the interface but owing to the diffraction limit of ∼15 μm, accurate dimensional information could not be obtained. The Raman results clearly indicate a broad interface associated with the sample etched with phosphoric acid and the presence of a much more abrupt interface with the citric acid etch. Additionally, a thin layer of exposed collagen exists at the dentin–adhesive interface. Copyright  2000 John Wiley & Sons, Ltd.

Effects of Sample Preparation on the Mechanical Properties of AlMgB14

Using synchrotron-based x-ray diffraction we have studied the behaviour of two different preparations of the super hard material AlMgB14 at pressures up to 41 GPa. Analysis of lattice parameter data from the high-pressure x-ray measurements provides a bulk modulus (K) of 196 GPa and a pressure derivative of the bulk modulus (K′) of 4.2 for sample 1, which was prepared by comminuting the elements and then hot pressing the sample. For sample 2, which was prepared by comminuting the elements and then cold pressing, K=264 GPa and K′=3.7. The differences in K and K′ clearly demonstrate that sample preparation significantly affects the mechanical properties of AlMgB14.

High-pressure synchrotron X-ray diffraction study of the pyrochlores: Ho2Ti2O7, Y2Ti2O7 and Tb2Ti2O7

Synchrotron-based X-ray diffraction was used to study the phase diagrams and determine the compressibilities of the pyrochlore rare-earth titanates Ho2Ti2O7, Y2Ti2O7 and Tb2Ti2O7 to ∼50 GPa. The bulk moduli of the cubic phase of these materials were calculated to be 213±2, 204±3 and 199±1 GPa, respectively. The onset of a structural phase change from cubic to monoclinic was observed near 37, 42 and 39 GPa, respectively. The bulk modulus for the high pressure monoclinic phase of Y2Ti2O7 has been determined to be 185±3 GPa.