PubMed · 2146007
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D W Jones. 1990. Composite restorative materials.. https://pubmed.ncbi.nlm.nih.gov/2146007/
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OBJECTIVES: The bond of adhesive luting cements to the tooth tissues and restorative materials is expected to hinder their transverse contraction for the layer thickness applied in dental restorations. It was hypothesized that the hindering of the transverse deformation will influence the relation between stress and strain (the stiffness) in the direction perpendicular to the substrate surface. The aim of this study was to investigate the relation between cement layers with different ratio between bonded and free surface (C-factor) and the stiffness of these layers, i.e. an apparent increase of the Young's modulus of the dental luting cement. METHODS: A commercial luting cement RelyX ARC (3M, St Paul, MN, USA) was used in this study. The 'real" Young's modulus and the Poisson ratio were determined and these values were used in models with layers with different C-factors (0.5, 1.0, 2.0, 3.0, 4.0, 5.0 and 6.0) in a three-dimensional Finite Element Analysis program (FEMAP, E.S.P., Maryland Height, MO, USA). The apparent Young's modulus was measured for layers with thicknesses of 0.5 mm (C = 6.0) and 6.0 mm (C = 0.5) and compared with the results of the Finite Element Analysis (FEA) analysis. RESULTS: The apparent Young's modulus in the 0.5 mm layer was 20% higher than the apparent Young's modulus in the 6.0 mm layer. This result was confirmed by the results of the F.E. analysis. For very thin layers the stiffness will be 25% higher than the Young's modulus. SIGNIFICANCE: The hindering of the transverse contraction has to be taken into account studying the mechanical properties of dental luting cements because it influences the behavior of these luting cements in thin layers.
OBJECTIVES: The objective of this study was to simulate the elastic modulus and polymerization shrinkage of a light activated polymer matrix composite using a generalized method of cells (GMC) micromechanics model. Two hypotheses were tested: (1) the micromechanics model provides estimates of elastic modulus vs filler fraction with greater accuracy than the rule of mixtures, Hashin-Shtrikman and phenomenological models; (2) Micromechanics Analysis Code/Generalized Method of Cells accurately simulates experimental benchmarks of polymerization shrinkage strain. METHODS: The study applied mathematical algorithms to a representative volume element of a model polymer composite to yield value estimates of the elastic modulus and contraction strain. Mechanical properties of the composite constituents were derived from thermomechanical and dynamic mechanical analysis of BisGMA and TEGDMA filled and unfilled resins. Data from the micromechanics model were compared to results of other analytical methods as well as experimental benchmarks. RESULTS: Predictions of elastic modulus vs filler fraction from the micromechanics model provided greater accuracy than the rule of mixtures and the Hashin-Shtrikman models. Predictions of polymerization shrinkage strain were within 13% of experimental values. SIGNIFICANCE: The elastic micromechanics model presented accurately predicted elastic modulus and polymerization shrinkage strain as a function of filler fraction, superior to other analytical methods.
The purpose of this study was to evaluate the effect of the various light curing units (plasma arc, halogen and light-emitting diodes) and irradiation methods (one-step, two-step and pulse) using different light energy densities on the leachability of unreacted monomers (Bis-GMA and UDMA) and the surface hardness of a composite resin (Z250, 3M). Leachability of the specimens immersed for 7 days in ethanol was analysed by HPLC. Vicker's hardness number (VHN) was measured immediately after curing (IC) and after immersion in ethanol for 7 days. Various irradiation methods with three curing units resulted in differences in the amount of leached monomers and VHN of IC when light energy density was lower than 17.0 J cm(-2) (P = 0.05). However, regardless of curing units and irradiation methods, these results were not different when the time or light energy density increased. When similar light energy density was irradiated (15.6-17.7 J cm(-2)), the efficiency of irradiation methods was different by the following order: one-step > or = two-step > pulse. These results suggest that the amount of leached monomers and VHN were influenced by forming polymer structure in activation and initiation stages of polymerization process with different light source energies and curing times.