PubMed · 12524772
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K W Toal. 2000. Solving problems.. https://pubmed.ncbi.nlm.nih.gov/12524772/
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In a previous study, we reported the upper limit of Young's modulus of the unprotected protein at the dentin/adhesive interface to be 2 GPa. In this study, to obtain a more exact value of the moduli of the components at the d/a interface, we used demineralized dentin collagen with and without adhesive infiltration. The prepared samples were analyzed using micro-Raman spectroscopy (micro RS) and scanning acoustic microscopy (SAM). Using an Olympus UH3 SAM (Olympus Co., Tokyo), measurements were recorded with a 400 MHz burst mode lens (120 degrees aperture angle; nominal lateral resolution, 2.5 microm). A series of calibration curves were prepared using the relationship between the ultrasonically measured elastic moduli of a set of known materials and their SAM response. Finally, both the bulk and bar wave elastic moduli were computed for a set of 13 materials, including polymers, ceramics, and metals. These provided the rationale for using extensional wave measurements of the elastic moduli as the basis for extrapolation of the 400 MHz SAM data to obtain Young's moduli for the samples: E = 1.76 +/- 0.00 GPa for the collagen alone; E = 1.84 +/- 0.65 GPa for the collagen infiltrated with adhesive; E = 3.4 +/- 1.00 GPa for the adhesive infiltrate.
OBJECTIVES: The study investigates the influence of two-step curing of a BisGMA/TEGDMA based polymer on degree of conversion (DC) and on hardness before and after 1 day ethanol storage. METHODS: The specimens were pre-cured at 25, 50, 100, 200, or 400 mW/cm(2) for 10, 20, or 40 s. The final cure as well as the cure of the control group was carried out at 750 mW/cm(2) for 20 s. DC was determined on thin films by FTIR. Hardness was determined on disks by the method of Wallace. RESULTS: At intermediary energy densities of the pre-cure, the DC was reduced as compared to that of the control group. The hardness before ethanol storage was not influenced by the curing mode. Except for the lowest and the two highest energy densities of the pre-cure, the two-step curing mode resulted in polymers that after ethanol storage were softer than the control polymer. SIGNIFICANCE: Two-step curing of resin composites may result in polymers with increased susceptibility to the action of softening substances in food and beverage.
OBJECTIVES: The aims of the study were to synthesize derivatives of Bis-GMA having pendant n-alkyl urethane substituents and to characterize and evaluate their physicochemical properties. METHODS: Stoichiometric amounts of Bis-GMA and n-alkyl isocyanates were reacted in dichloromethane with dibutyltin dilaurate as a catalyst. Volumetric shrinkage, water uptake, degree of vinyl conversion, refractive index and viscosity of resulting urethane monomers and those of Bis-GMA were measured. The flexural strengths of their corresponding homopolymers and that of Bis-GMA were also measured. RESULTS: These types of urethane derivatives of Bis-GMA exhibited lower viscosities and were more hydrophobic than Bis-GMA. Generally, the viscosity of these experimental monomers decreased with increasing chain length of the alkyl urethane substituent. Photopolymerization of the new monomers gave high degrees of vinyl conversion compared to Bis-GMA. The experimental monomers also yielded polymers with lower polymerization shrinkages at equivalent degrees of vinyl conversion, than Bis-GMA. The refractive indices of these urethane derivatives were similar to Bis-GMA, but the flexural strengths of their polymers were lower than that of the Bis-GMA homopolymer, decreasing with increasing chain length of the alkyl urethane substituent. SIGNIFICANCE: Because of their excellent overall properties, these new derivatives of Bis-GMA have potential as dental monomers that can improve many properties of resin based dental materials that utilize methacrylate monomer systems.