John W. Stanford

Alternative Interpretations of Water Sorption Values of Composite Resins

Water sorption values for direct filling resins and an unfilled resin were much more similar at 30 days when expressed as mg/g organic matrix than as mg/cm2 or weight percent. This interpretation is indicative of the water sorption characteristics of resin matrices. The values are even more indicative when solubility or leaching is taken into consideration. With the specimen sizes used in this study, the effect of the kinetics of water sorption could be minimized by using values obtained after immersion in water for 30 days.

Effects of Backing Reflectance and Mold Size on Polymerization of Photo-activated Composite Resin

The in vitro depth of cure of a visible-light-activated microfilled composite, as influenced by backing reflectance and mold size, was investigated using microhardness measurements. More extensive polymerization was obtained with higher values of backing reflectance. Mold size larger than the cross-sectional area of the photo-activating beam also increased the degree of polymerization. Backing reflectance and mold size are influential factors and need to be defined in depth-of cure evaluations if in vitro measurements are to be valid predictors of clinical performance.

Tarnish and Corrosion Behaviour of Dental Gold Alloys

For many years the specification of alloy composition, particularly high gold and platinum contents, was considered sufficient to guarantee the stability of dental prostheses in the oral environment. This article reveals a considerably more complex situation and stresses the need for extensive laboratory and clinical testing of new alloy formulations before these may be unreservedly recommended to practitioners.

Application of Electrochemical Techniques to Characterize the Corrosion of Dental Alloys

Electrochemical techniques involving potentiostatic and potentiodynamic (hysteresis) polarization have been employed to evaluate the corrosion resistance of dental amalgams and dental casting alloys in a 1.0 percent sodium chloride solution. Unlike conventional dental amalgams, where corrosion is associated mainly with the presence of the tin-mercury (γ 2 ) phase, the corrosion of γ 2 -free dental amalgams results from the presence of silver-copper eutectic or copper-tin or both. The corrosion of silver-base and gold-base dental casting alloys stems from the presence of silver-rich micro-segregations with a possible minor contribution from a copper-rich phase. These results agree with the results obtained from long-term laboratory and clinical studies and thus demonstrate the usefulness of relatively quick, convenient electrochemical techniques in the evaluation of the corrosion resistance of dental alloys.

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.

Analysis of the Organic Portion of Dental Calculus

SYNOPSIS IN INTERLINGUA ANALYSE DEL PORTION ORGANIC DE CALCULO DENTAL.—Specimens de composite e de separate calculos supra- e subgingival e de calculos ab dentaturas esseva decalcificate per le uso de 0,1 N de HCl e de un solution de 15 pro cento de tetraacetato ethylenediaminic a un pH de 7,0 a 7,5. Analyses chromatographic del hydrolysatos acide monstra que le mesme amino-acidos compone le portion proteinic del calculos supragingival como del calculos subgingival. Le aminoacidos trovate in mucina precipitate es simile a illos presente in calculos salivari. Le fraction carbohydratic del matrice organic del calculos esseva studiate per chromatographia a papiro. Galactosa, glucosa, mannosa, rhamnosa, e fucosa esseva detegite. In plus, il pare esser presente un hexosamina, un deoxy-sucro, e un acido sialic.