Wayne T. Wozniak

The need for standardization of test protocols

This article reviews the current status of standardization in orthodontic products. The role of the American National Standards Institute and the American Dental Association is described. A review of laboratory testing for the evaluation of frictional forces and bond strength in orthodontics is discussed. The need for standardization in test protocols is emphasized to obtain valuable interpretation and use of data generated by researchers. Standardization of test protocols will lead to improved standards for orthodontic products and ultimately higher-quality products for orthodontists and their patients.

Color comparisons of composite resins of various shade designations

Abstract The purpose of this investigation was to compare the measured color of commercial composite resins of various shade designations (L, LG, LY, Y, U). Three samples of 11 composite resins were prepared according to manufacturers instructions. Diffuse reflectance measurements were made on a Pye Unicam dual-beam spectrophotometer equipped with an integrating sphere to provide CIE 1976 L * a * b * values using both black and white backgrounds. Differences within shade designations were as follows: ΔL * varied from 19.45 for Y to 4.75 for LG; Δa * ranged from 7.46 for U to 3.26 for LG: and Δb * ranged from 16.23 for Y to 4.73 for LY. Total color difference was greatest within the Y shade designation and least for the LY shade. Contrast ratios ranged from 0.811 for Command (LG) to 0.961 for Spectrafil (Y) and varied considerably within shade designations. Color differences between brands of identical shade designations were visually perceptiable in all groups. The results of this study indicate the need for improved standardization of shade designations for composite resins.

Ultraviolet light stability of composite resins

The ultraviolet light color stability of seven commercial composite resins was evaluated after 1, 8, and 15 days of exposure. Color differences between exposed and unexposed specimens stored for identical time periods were determined. Samples exposed to ultraviolet light showed large changes in Munsell Hue and Chroma, with smaller but significant changes in Value. Unexposed samples showed small changes in the Munsell components in some cases opposite those observed for the exposed samples. Statistical analysis showed that although significant color changes were observed, brands of composite resins could not be distinguished by length of storage in the dark. Time of exposure was a significant variable at 24 hours and 8 days. At 15 days a number of composite resins did not undergo additional significant color change. Scanning electron microscope showed a significant roughening of the surface of exposed composites with resin breakdown and exposure of the composite filler.

Use of an in vitro model to assess the effects of APF gel treatment on the staining potential of dental porcelain

Porcelains and resin composites exposed to acidulated phosphate fluorides (APF) have been reported to result in increased roughness, loss of weight, and loss of specular reflectance (gloss). Six samples of five commercial porcelains were subjected to five four-minute treatments with APF gels. Samples were then subjected to a nine-day cyclic staining procedure that utilized a tea, coffee, and mucin mixture. Changes in reflectance were then measured by means of a Minolta Chromameter (CR121) and converted to CIE L* a* b* values at illuminant D65 against a white background. delta L*, delta a*, delta b*, and delta E values were calculated. There was a substantial decrease in the L* value (lightness) for all porcelains. The average L* value for APF-treated and then stained porcelains was 43.6, for the stained-untreated samples, 48.2, and for untreated-unstained porcelain, 53.5. For three of the five porcelains, the differences in L* between treated and untreated stained porcelains were statistically significant. Changes in a* and b* values were also found to be consistent with but not as large as the changes in L*.

International dental standards-order out of chaos?

UNLABELLED The history, scope, structural components, generation, and purpose of international dental standards are concisely surveyed by three researchers active in standards development. SIGNIFICANCE Standards have an important role to play within dental materials research alongside more specialist scientific instruments and methods. For all that are concerned with the wider business and safety issues of manufacture, marketing, selection and use of dental biomaterials and devices, knowledge of the vital role of standards is indispensable.

Color mixing in dental porcelain

For esthetic reasons, pigments and opacifiers are added to porcelains used in restorative dentistry. The purpose of this study was to use Kubelka-Munk theory (Kubelka and Munk, 1931) to predict and analyse the colors of porcelains modified by the addition of two pigments and an opacifying agent. The base porcelain was composed of 88% potassium feldspar, 6% quartz and 6% kaolin. The porcelain was modified by the addition of a yellow (Pr-Zr-Si) or a brown (Fe-Cr-Zn) stain and an opacifier (10% SnO in base porcelain). After firing at 1200 degrees C for 30 min, reflectance spectra of the various combinations were obtained with a spectrophotometer. Reflectance spectra, except at low wavelengths, were influenced by increased scattering due to the addition of the opacifier. Calculated values from Kubelka-Munk theory for absorption coefficients and scattering coefficients with appropriate correction factors were compared with the values from the reflectance spectra of the combinations. In general, good agreement was obtained if the scattering coefficient of the opacifier is set equal to 1.0. Using the L*a*b* transform of the CIE color space, it was found that this transform provided uniform color intervals for equal changes in pigment concentration.