Objectives: The increased usage of composite dental restorations underscores the need for continued improvements in material properties. Well-controlled sample fabrication and reproducible methods to quantify and compare material properties will accelerate material design and optimization. Our objectives were to fabricate samples encompassing a range of processing parameters and develop techniques that systematically quantify multiple properties of these samples, thus reducing sample-to-sample variation while concurrently testing numerous processing conditions.
Methods: Gradient samples were prepared to evaluate the effects of composition and irradiation time. Comonomer ratio of 2,2-bis[p-2'-hydroxy-3'-methacryloxypropoxy]-phenyl]propane (BisGMA) and triethylene glycol dimethacrylate (TEGDMA) was varied discretely, and irradiation time was varied continuously across each composition. Degree of conversion was measured using infrared spectroscopy, mechanical properties were evaluated using nanoindentation, and cell viability and density were quantified using fluorescence microscopy.
Results: Higher BisGMA contents increased elastic moduli while higher TEGDMA contents increased conversions. Cell response depended only on irradiation time and not composition, with conversions of at least 52% and 60% required for unaffected viability and cell density, respectively. A single composition-irradiation combination to achieve all of the 'best' properties (highest conversion, highest elastic modulus, lack of cytotoxicity) was not identified, illustrating the necessity of testing all combinations for multiple relevant properties.
Significance: Simultaneously screening composition and conversion increased the experimental throughput and allowed for the quantification of chemical, mechanical, and biological properties in a controlled, reproducible fashion. This 2D gradient approach is useful for optimizing compositions and processing parameters to achieve the desired combination of properties.