The purpose of this study was to investigate the effect of repeated machining up to 51 times using the same diamond bu: on machining accuracy of inner and outer surfaces of CAD/CAM (computer-aided designing and computer -aided manufactur ing) machined ceramic crowns. The surface topography of machined crowns was examined using photographs . It was fount that machining accuracy was not affected by the number of machining times . In all measuring points, the inner surface wa; machined to a dimension larger than the die model (i.e., increased gap) , whereas the outer surface was machined to a dimen sion smaller than the crown model (i.e., smaller crown) . Photo observation showed that cervical contour was machined it a clear, rounded form from 1st to 11th crowns.

This study was designed to determine the effects of the heat curing time on a urethane tetramethacrylate (UTMA)-based hybrid resin and specifically on the degree of conversion (DC) and cytotoxicity. The materials used in this study were Estenia, a new-generation hybrid resin, and an experimental fiber reinforcement, Br-100. The DC values of the hybrid resin samples were measured using a Fourier transform infrared (FTIR) spectrophotometer after 180 s of light curing followed by heat curing (0, 15, 30, and 60 min). A method comparing intensities of C=C and N-H vibrations of the sample was used to calculate the final DC values. FTIR spectra were measured both inside and on the surface of the sample. The calculated DC values increased by increasing the heat curing times. After light curing only and after 15-min heat curing, the DC values inside the samples were smaller than the corresponding DC values at the surfaces of the samples. After 60 min of heat curing, the samples achieved homogeneous polymerization (DC% = 65). The cytotoxicity of the material was studied from the glass fiber-reinforced hybrid resin samples, which were first light cured and then heat cured (15, 30, and 60 min). Cytotoxicity was tested using both direct contact and extract methods. For the extract tests, the test specimens were incubated in a cell culture media at 37 degrees , 54 degrees , or 72 degrees C for 24 h. The heat curing times used had no effect on cytotoxicity. The incubation temperature, however, did have a significant effect. The extract obtained from 72 degrees C incubation showed a cytotoxic effect whereas the others did not. The direct contact test did not show cytotoxicity.

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The results of notched tensile tests and smooth and V-notched fatigue tests are reported for beryllium copper, AM350 corrosion-resistant steel, and A-286 heat and corrosion resistant steel, and for open-hole notched specimens of 17-7PH corrosion-resistant steel. Cyclic loading tests also are reported for dimpled and riveted sheet specimens of AM350 steel which simulate typical single-lap riveted aircraft joints. Other tests are reported for 17-7PH steel specimens containing unloaded rivet-filled holes. The results of the tests are discussed from the point of view of a materials engineer in the aircraft industry. The need is discussed for additional useful information about the new materials now being developed and, also, about the less common older materials which are required now and then for specific designs.