Abstract
ObjectiveOver time dental composites age due to mechanical impacts such as chewing and chemical impacts such as saliva enzymes and food ingredients. For this research, the focus was placed on chemical degradation. The objective of this study was to simulate hydrolysis by using different food simulating liquids and to assess their impact on the mechanical parameter Vickers microhardness (MHV) and the physicochemical parameter contact angle (CA).MethodsSpecimen of three composites (d = 6 mm, h = 2 mm; n = 435) classified with respect to their filler content (wt%), namely low-filled, medium-filled and highly-filled, were stored for 0, 14, 30, 90 and 180 days in artificial saliva (pH 7), citric acid (pH 3; pH 5), lactic acid (pH 3; pH 5) and ethanol (40%vol; 60%vol) and assessed regarding to MHV and CA. Statistics: Kruskal-Wallis test, stepwise linear regression, bivariate Spearman Rank Correlation (p < 0.05).ResultsWhile stored in artificial saliva, acid and ethanol the CA decreased especially for the low- and medium-filled composites. It was shown that rising the filler content caused less surface changes in the CA. Storage in ethanol led to a significant decrease of MHV of all composites. Regression analysis showed that the effect of in vitro aging on MHV was mainly influenced by the composite material and therefore by filler content (R2 = 0.67; p < 0.05). In contrast, the CA is more influenced by incubation time and filler content (R2 = 0.2; p < 0.05) leading to a higher risk of plaque accumulation over time. Significance: In vitro aging showed significant changes on the mechanical and physicochemical properties of dental composites which may shorten their long-term functionality. In conclusion, it can be stated, that the type of composite material, especially rising filler content seems to improve the materials’ resistance against the processes of chemical degradation.
Highlights
Dental composites have gained increasing importance and usage over the last several years, caused especially by rising demands on aesthetic restorations [1, 2, 3]
It was shown that rising the filler content caused less surface changes in the contact angle (CA)
Regression analysis showed that the effect of in vitro aging on MHV was mainly influenced by the composite material and by filler content (R2 = 0.67; p < 0.05)
Summary
Dental composites have gained increasing importance and usage over the last several years, caused especially by rising demands on aesthetic restorations [1, 2, 3]. These dental composites mainly consist of a methacrylate based resin matrix filled with organic and inorganic particles of different shapes and sizes (macro-, micro- and nano-fillers). Changes in filler size and content have improved the mechanical properties (e.g. flexure strength, fracture toughness, tensile strength, polymerization shrinkage, Vickers microhardness (MHV)) and enabled further application in posterior restorations [3, 4]. The surface of a restoration is relevant to clinical performance. Due to strong chewing forces, wear resistance is another important clinical parameter [4], especially over the long operational lifespan of modern composites with annual failure rates of 2.4% after ten years [7]
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