PubMed · 6955831
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J Kielmann. 1982. ["3M Posterior"].. https://pubmed.ncbi.nlm.nih.gov/6955831/
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The purpose of this work was to propose a new numerical model for glass-fiber-reinforced composites. The proposed numerical model was constructed with orthotropic shell, isotropic shell, and beam elements representing glass fiber cloth, silica filler, and the remaining matrix resin, respectively. The proposed model was applied to failure analysis under three-point bending conditions. The validity of the numerical model was checked through comparisons with experimental results. Four types of specimens were used: composite resin, and composite resin with neutral, upper, and lower glass-fiber cloth reinforcement insertions. For all types, close agreement between the analytical and experimental results was confirmed. This indicates that the proposed numerical model is effective for evaluating the mechanical behaviors of glass-fiber-reinforced composites.
OBJECTIVES: [corrected] To microscopically evaluate the structural characteristics of post-and-core units made with a fiber post and different types of composite resins used as build-up materials. MATERIALS AND METHODS: Forty endodontically treated human maxillary incisors were prepared for receiving a fiber post (Aesthetic Post Plus, RTD). One-Step (Bisco) was used as a bonding material, and C&B resin cement (Bisco) for luting the post. The posted roots were randomly divided into eight groups. In each group a different material or technique was applied to build up the abutment. The materials on trial were Z100 (3M-ESPE), Lumiglass (RTD), Gradia (GC), Build-it! (Jeneric Pentron). On the specimens of Groups 5-8, the same materials were used for build-ups, with the addition of a preshaped plastic shell (Composipost, Core Form, RTD). All the post-and-core specimens were cut perpendicular to their long axis and processed for SEM observation. The objective was to detect the presence of voids/bubbles within the resin abutment, and of gaps at the interface between the post surface and the core material. These aspects were quantified with reference to indexes. The differences among the scores were tested for statistical significance (p<0.05). RESULTS: In the absence of any matrix, cores built up with Gradia showed the highest integrity, and those made with Z100 the best adaptation onto the post. In the presence of shells, Build-it! provided the most satisfactory result. Build-it! was the only material to perform better when used in combination with a shell. SIGNIFICANCE: When hybrid composites are used to build up a core onto a fiber post, a higher homogeneity of the abutment and a better post-core integration are achieved if the build up is done in the absence of any matrix.
The water uptake characteristics of resins and composites based on an ethoxylated bisphenol A glycol dimethacrylate (Bis-EMA) and a polycarbonate dimethacrylate (PCDMA) were studied in detail. Polydimethacrylate resins were prepared by photopolymerization of the neat monomers and mixtures of them with various weight ratios, using the camphoroquinone/N,N-dimethylaminoethyl methacrylate system as initiator, while the composites were prepared from the light-curing of commercial samples (Sculpt-It and Alert). Water sorption/desorption was examined both in equilibrium and dynamic conditions in two adjacent sorption-desorption cycles. The equilibrium water uptake from all resins was very small with a trend to increase as the amount of PCDMA was increased. The inverse effect was observed in the solubility values. The composites studied exhibited also very low water uptake values in comparison to other composite materials reported in the literature. It was also observed that the equilibrium uptake decreased with increasing filler loading. Slightly larger equilibrium water uptake and much smaller solubility values were obtained during the second sorption-desorption cycle in comparison to the first one. Concerning the sorption rate data, it was observed that the resin materials followed Fickian diffusion during almost the whole sorption or desorption curve, while the composites showed this behavior until only M(t)/M( infinity ) congruent with 0.5. The diffusion coefficients calculated for the resins were larger than those of the composites and always higher during desorption compared to sorption. The values of the diffusion coefficients for both resins and composites were in the same order of magnitude with the values of the corresponding materials reported in the literature.