R.G. Craig

The sensitivities of Fourier transform infrared spectroscopy, Knoop hardness, water sorption, and resin leaching were compared for their ability to distinguish differences between composite samples cured through different thicknesses of overlying resin. The method developed allowed samples of light-cured composite to be made with controlled conversion for parameter testing, and eliminated effects of resin lost to slurry during polishing or an increase in conversion as a result of heat generated during grinding. Sensitivity to differences was greatest and equal for FTIR spectroscopy and Knoop hardness, while resin leaching proved to have moderate sensitivity, and water sorption none. The ability of these parameters to predict monomer conversion as measured by FTIR spectroscopy was also determined. Knoop hardness proved the best conversion predictor, resin leaching the next best, and water sorption the worst. Water sorption values did not vary with changes in specimen conversion.

The objectives of this study were to determine the cytotoxic concentrations of 11 components of resin composites on monolayers of cultured Balb/c 3T3 fibroblasts, to study the inhibitory effects of these components on DNA synthesis, total protein content, and protein synthesis, and to determine whether effects were reversible when the components were withdrawn from the medium. These data were reported as concentrations which inhibited 10% (ID10) and 50% (ID50) of a particular metabolic process as well as the range of concentrations over which cell metabolism was irreversibly inhibited. For any individual component, the ID50 values for all three metabolic parameters were of the same magnitude. The same was true for the ranges of irreversibility. Ethoxylated Bis-phenol A dimethacrylate (E-BPA) was the most toxic molecule of the group (ID50 being between 1 and 10 mumol/L). The ID50 concentrations for three of the components, including Bis-GMA, UDMA, TEGDMA, and Bis-phenol A, ranged between 10 and 100 mumol/L, while the ID50 values of three components (N,N dihydroxyethyl-p-toluidine, camphoroquinone, and N,N dimethylaminoethyl methacrylate) were above 100 mumol/L. The concentrations to which the cells and tissues are exposed in vivo are not known. This study should help to identify the concentrations of organic composite components which pose clinical cytotoxic hazards.

Peer Reviewed

THE hardness of enamel and dentin has been determined by a variety of methods including abrasion, " 2 pendulum, ' scratch,4-7 and indentation" teehnics. Since the hardness of enamel and dentin has been shown to have con-siderable local variations, the methods using a microscratch or microindentation have been preferred. One of the more common types is the Knoop diamond in-denter14 which has been used by a number of investigators.', 12, 15, 16 It should be mentioned, however, that in spite of the fact that the indentations are ex-tremely small, they still represent a macroindentation when compared to the microstructure of enamel and dentin. The majority of the published hardness data for enamel and dentin has been measured on ground sections, although several papers'0 13 reported the hardness of intact enamel surfaces. The conclusions in regard to the difference in hardness from one section of a tooth to another are at times in variance with each other. This study of dentin and enamel was undertaken in an attempt to establish any trends in hardness existing from one area of a tooth to another

The compressive properties of human enamel and dentin have been reported by Stan-ford, Paffenbarger, Kumpula, and Sweeney. ' The elastic modulus of occlusal, side, and cusp enamel was reported to be 1.8, 6.0, and 8.2 X 106 psi, respectively. The corre-sponding values for the proportional limit were 16,800, 21,000, and 34,200 psi and, for the compressive strength, 19,400, 28,300, and 40,200 psi. An improved procedure for preparing compressive specimens of hard tooth tissues and some restorative materials was published by Stanford, Weigel, Paffenbarger, and Sweeney.2 The compressive properties of enamel were within the experimental error of the earlier values, and additional values relating compressive properties to environment of development and orientation were reported. In addition, the compressive properties of plastics, amalgam, silicate cement, zinc phosphate cements, and dental golds were listed. Tyldesley3 determined the mechanical properties of enamel by using a transverse type of loading system. The elastic modulus of enamel was reported to be 19 X 106 psi in bending. The proportional limit and compressive strength were found to coincide at