PubMed · 15412110
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F A PEYTON. 1950. Packing and processing denture base resins.. https://doi.org/10.14219/jada.archive.1950.0089
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OBJECTIVES: To evaluate the mechanical behavior of resin cements used for luting fiber post. The influence of the curing mode is analysed. METHODS: Nanoindentation techniques have been applied to determine hardness and Young's modulus of disc-shaped specimens of three types of cements: chemical- , photo- and dual-cured, provided by Ivoclar-Vivadent. Results obtained have been compared with measurements performed inside the post-cement-dentin system. Mechanical properties are evaluated together with scanning electron micrographs showing the post-cement and dentin-cement interfaces. RESULTS AND SIGNIFICANCE: Differences have been detected between mechanical measurements performed inside the post-cement-dentin system and those carried out in laboratory disc-shaped specimens. The close presence of post and dentin boundaries has a lot of influence on the cement behavior. The nanoindentation measurements indicate that the photo-cured cement exhibits a high hardness and stiffness, but with a more marked tendency to brittle failure. The chemically cured cement is the material with higher ability to bear deformation without damage, although its hardness and elastic modulus are significantly lower. Dual-cured cements present the best combination of properties.
Although a lower curing rate is often cited as the reason why a chemical cured (CC) dental composite produces lower polymerization contraction stress (PCS) than a light cured (LC) composite, the exact mechanism is still unclear. In addition, the comparison is often made by using different brands of composites. The comparison's fairness is questionable because the two composites have different compositions and preparation procedures. The goal of the present work was to determine if the curing mode alone can produce different PCS. We formulated a dual cured composite and prepared it the same way for both CC and LC modes. We measured PCS by a strain gauge method, shrinkage by a video-imagining technique, degree of conversion (DC) by infrared spectroscopy, and flexural modulus by the three-point bending test. The CC specimens showed lower PCS and lower flexural modulus than the LC specimens, although both possessed an identical chemical composition and physical texture before cure. This finding indicates that the curing mode alone can affect PCS. Because the CC and LC specimens produced a similar shrinkage and DC, the lower modulus is considered to be one of the reasons for the lower stress. Using a structural inhomogeneity model, we explained how a resin composite with an identical DC can have different physical properties such as the modulus.
The objective of this article was to review the articles on the interaction of salivary organic substances with resin-based dental materials and on the interaction of these organic substances with exogenous chemical agents, which results in discoloration. Original scientific articles or reviews on the saliva, acquired pellicle, and the interaction with pellicle and chemical agents related to dental resin-based materials were reviewed. Salivary esterases can increase or decrease the internal and external discoloration. The formation of acquired pellicle on the surface of a material varies by the properties of material, and the pellicle interacts with denaturation agents, such as tannin and chlorhexidine, to form stains and also adsorbs staining substances. Therefore, for the quality and longevity of restorations, protocols for the evaluation of the influence of organic substances on the extrinsic staining of restorative materials should be included in the evaluation of aesthetic restorative materials.