High-throughput modulus measurements for screening of dental materials
Elizabeth A. Wilder and Joseph M. Antonucci (Mentor)
Division: Polymers (854), Materials Science and Engineering Laboratory
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Introduction: Typical methods for measuring the moduli of dental materials such as tensile and compressive tests require relatively large specimens and are both labor-intensive and inefficient. While these methods are widely accepted for establishing standards for dental and other polymeric materials, they are not practical for wide-spread screening to establish structure-property relationships. The aim of this study is to evaluate the applicability of existing high-throughput techniques for measuring the moduli of dental polymers.
Materials and Methods: Various dental polymers were characterized by two different techniques that are amenable to high-throughput modulus measurements: nanoindentation and Strain-Induced Elastic Buckling Instability for Mechanical Measurements (SIEBIMM)1. Results were compared to those acquired through more traditional tensile methods.
Results and Discussion: Nanoindentation studies on Bis-GMA/TEGDMA films with mass fraction ratios of 30/70, 50/50 and 70/30 yielded moduli of (2.44 ± 0.06) GPa, (2.93 ± 0.03) GPa and (3.70 ± 0.07) GPa, respectively. Results from three-point bend testing indicated the same trend of increasing stiffness with increasing concentration of Bis-GMA, but values were significantly lower, ranging from (1.7 ± 0.1) GPa to (2.2 ± 0.2) GPa. Preliminary SIEBIMM measurements on PMMA yielded a modulus value of (2.2 ± 0.3) GPa, which is statistically identical to the value of (2.5 ± 0.1) GPa measured by traditional 3-point bend techniques. Efforts to perform SIEBIMM studies on crosslinked dental materials are in progress, but involve a more complicated sample preparation technique. Concurrent efforts are focused on applying a reverse-SIEBIMM procedure to measure the moduli of soft biomaterials and early studies on polydimethylsiloxane films indicate that reverse-SIEBIMM correctly predicts the behavior of these types of materials.
Conclusion: Moduli measurements on polymers are very sensitive to not only the sample composition, but also the geometry of the sample and the conditions of the test. High-throughput methods may not consistently yield results identical to those obtained through traditional techniques, but they can be valuable for rapid, automated screening of a wide variety of dental materials. Support: NIST/NIDCR Interagency agreement Y1-DE-1021-04 and the National Research Council.
1C.M. Stafford, C. Harrison, K. L. Beers, et al., Nature Materials 3, 545 (2004).