Comparison by X-ray diffraction and infrared spectroscopy of two samples of alpha quartz with the NIST SRM 1878a alpha quartz.

The aim of this study was to compare the X-ray diffraction and infrared spectrophotometric patterns of two samples of alpha quartz (QUIN1 and QUIN2) with that of NIST SRM 1878a alpha quartz certified 100% crystalline. As it is known that the intensity diffracted and the absorbance per mass unit for a given type of alpha quartz depend on its particle size, this factor was taken into account. To do this, different types of alpha quartz were sampled on filters using a Dorr-Oliver cyclone to select particle size. Variation in the flow rate of the cyclone in the range 1.2-2.8 l/min allowed the volume median diameter of the sampled particles to be varied. For the four strongest diffraction lines it was observed that the intensity per mass unit increased with the volume median diameter of the particles. For infrared spectrophotometry for analytical band wavelengths close to 12.5 micro m, it was observed that the absorbance per mass unit decreased as particle size increased. The opposite effect was noted for analytical band wavelengths >14.4 micro m. Compared with SRM 1878a alpha quartz, certified 100% crystalline, the purity of QUIN1 alpha quartz was 93.1% (confidence interval 92.4-93.8%) when measured by X-ray diffraction and 91.5% (confidence interval 90.1-92.9%) when measured by infrared spectrophotometry. In the case of QUIN2 alpha quartz the purity was globally lower.

Clinical evaluation of posterior composite restorations: the 10-year report.

PURPOSE: To summarize all clinically relevant data of a 10-year prospective evaluation of posterior glass-ionomer cement/composite restorations (Ketac Bond/Visio-Molar radiopaque). MATERIAL AND METHODS: For this study 194 hybrid composite fillings (115 Class I, 79 Class II) were applied in 73 adult patients. The exposed dentin was covered with glass-ionomer cement. The clinical evaluation was carried out at baseline, after 6 months and at 1-year intervals up to 10 years. The USPHS-compatible CPM Index was used with the C and P criteria presented here for anatomic form, color match, surface quality, wear, marginal integrity, marginal ledge, marginal discoloration, secondary caries, and clinical acceptability. Thermal and electrical sensitivity testing were recorded annually. RESULTS: At baseline, 194 restorations were rated. The drop-out of patients comprised 108 fillings after 10 years. During this time, 24 restorations could not be followed up because of new carious lesions at different sites and/or prosthodontic treatment (drop-out of teeth). Forty-six composite restorations were longitudinally controlled over 10 years, and 16 more fillings failed before the end of the study (3 filling fractures, 7 partial filling losses, 1 total filling loss, 5 cases of secondary caries). Only Class II composite restorations exhibited secondary caries (4 fillings after 7 years and 1 filling after 9 years). After 10 years, the correct anatomic form was preserved in 44 fillings, but all restorations showed rough surface and wear. The majority of restorations (26 fillings) was free of marginal discoloration, and the color match showed only 3 fillings being too dark. The marginal integrity was optimal at baseline and during the first year. During the second year a continuing degradation started and lasted until the end of the study. Thirteen restorations showed optimal marginal integrity after 10 years. CONCLUSION: The USPHS-compatible CPM Index represents a sensitive rating system for long-term observation of posterior composite restorations. The early risk of failure is attributed to bulk fractures and partial loss of filling material. The longevity over 10 years is a maximum of 74.2%, and the very low secondary caries rate and the high percentage of correct anatomical form confirm the clinical safety of posterior composite restorations.

A comparison of international silica (alpha-quartz) calibration standards by Fourier transform-infrared spectrophotometry.

Seven international silica (alpha-quartz) standards were examined for relative purity to the US National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 1878 Respirable alpha-quartz by Fourier Transform-Infrared Spectrophotometry (FT-IR). The standards examined have been used in North America, the UK, Australia and Germany. The 189 samples analyzed included NIST-SRM 1878, Min-U-Sil 5, Ottawa Silica Sand, Sikron F-600, A9950 (AUST 1), DQ12-Robock, DQ12-Bergbau. Size distributions of the standards were determined by Coulter Counter to be broadly similar with equivalent spherical volume median diameter ranging between 1.2 and 3 microm. The results showed the standards to differ by as much as 30% in relative purity. Consequently, an internationally agreed upon calibration standard is urgently needed. Min-U-Sil 5 based NIST-SRM 1878 or Sikron F-600 are the two most likely candidates. Any agreed standard must have a well characterized size distribution and closely match the respirable dust criteria. It should also be studied by both infrared spectrophotometry and X-ray diffraction techniques.

Creep of posterior dental composites.

The creep of microspecimens of posterior dental composites was studied using a torsional creep apparatus. Shear stresses were maintained for 3 h and recovery was followed for 50 h. Creep curves were obtained at 21, 37, and 50 degrees C and four torque levels. The effect of conditioning the specimens in water up to 8 weeks was studied. The posterior composites exhibited linear viscoelastic behavior at low deformations. They had higher shear moduli and greater resistance to creep than conventional and microfilled composites. In aging experiments, maximum shear moduli occurred when specimens were 48 h to 1 week old. Subsequent softening was attributed to water absorption. Residual strain was highest when the composites were stressed within 24 h of initiating polymerization. Residual strain was very low in specimens 48 h to 8 weeks of age.

[Studies on the refractory coating materials for preventing scale formation (author's transl)].

In casting of high-fusing alloys such as cobalt-chrome and nickle-chrome alloys, the reaction between the investing mold and high-fusing molten alloys suffers the disadvantage of the scale formation. The various coating materials are used to prevent the scale formation. The experiments have been carried out to prove the effectiveness of seven commercialized coating materials. And the reaction between the coating materials and high-fusing molten alloys was analyzed by X-ray diffractometer. Results were as follows: 1) The refractory compositions of seven commercialized coating materials were composed of alpha-quartz (SiO2), zircon (ZrSiO4) and zirconium oxide (ZrO2). 2) Dainainvest (Ohara) mainly containing zircon indicated the reduction in surface roughness due to coating. Although zircon was slightly observed on the cast surface, the product of reaction was not detected. 3) Liquid investment (Nobilium) and Paint investment (Shofu) having about equal amounts of alpha-quartz and zircon showed as reduction in surface roughness as Dainainvest. The product of reaction was not observed and the cast surface was smooth. 4) Quick request (Shiken), Pre-coat (Niranium) and Ethymay B (Kamemizu) composed of alpha-quartz had not appreciably effectiveness. The cast surface was rough due to production of picrochromite (MgCr2O4) and eskolaite (Cr2O3)in the reaction between molten alloys and coating materials. 5) Hi-coat with zirconium oxide did not point out the advantage in spite of high refractory composition and showed little reduction in surface roughness due to coating.