We measured the push-out and diametral tensile strength of dental restorative composites following aging under environmental conditions relevant to the oral cavity; air (A), artificial saliva (AS), acidified (50 mM CH 3 COOH, pH = 4.7) artificial saliva (AS + HAc), and AS with esterase enzyme (AS + ENZ). Cylindrical test specimens (6.3 mm diameter by 5.1 mm long) were prepared by placing 0.3 g of nanofilled composite in an epoxy ring and cured. Twenty samples were aged in each environment for 163-186 days at 37 C. The push-out strengths (mean AE standard error of the mean [SEM], in MPa) for specimens were: A-2.4 AE 0.2, AS-7.3 AE 0.5, AS + HAc-7.2 AE 0.9, and AS + ENZ-6.0 AE 0.6. Following the push-out test, the diametral tensile strength and elasticity were immediately determined. The diametral tensile strengths (mean AE SEM, in MPa) for specimens were: A-54.0 AE 1.6, AS-31.4 AE 1.3, AS + HAc-34.3 AE 1.2, and AS + ENZ-22.5 AE 0.7. The push-out strength was lowest for the A environment due to shrinkage of the composite. The push-out strength increased significantly as water diffused into the specimens (AS and AS + HAc) but decreased significantly in the enzyme environment (AS + ENZ). The diametral tensile strength was highest for specimens in the A environment, which was significantly higher than both the AS and AS + HAc specimens and > 2× higher than the AS + ENZ specimens. The results indicated that a water environment (with or without acid) caused a significant decrease in the mechanical properties of this composite, but the greatest decrease was seen in water with esterase. This is the first study to demonstrate that esterase enzymes affect the bulk strength of a commonly used commercial dental composite.
Understanding the amount of degradation using nondestructive evaluation (NDE) methods provides an effective way of determining the fitness to service and the residual life of structural components. Due to uncertainties introduced by the single NDE method, a combined damage index using multi-sensor data increases the reliability of damage assessment. In this paper, the outputs of three NDE methods including acoustic emission (AE), linear ultrasonics (LUT), and nonlinear ultrasonics (NLUT) are merged to identify the amount of plastic deformation in aluminum 1100. The sensitivities of individual and combined methods to microstructural changes are evaluated. The coupon samples are loaded up to different strain levels and then unloaded. AE data is recorded in real time and ultrasonic data is recorded from the unloaded samples. The major features combined in the damage index are cumulative AE absolute energy and nonlinear coefficient. The microstructural state is verified with microscopic analysis and hardness testing. The developed damage index can nondestructively assess the amount of plastic deformation with higher reliability.
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