"Compomers" are recently introduced products marketed as a new class of dental materials. These materials are said to provide the combined benefits of composites (the "comp" in their name) and glass ionomers ("omer"). Based on a critical review of the literature, the author argues that "compomers" do not represent a new class of dental materials but are merely a marketing name given to a dental composite. (+info)
Resin content in cement liquids of resin-modified glass ionomers.
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Qualitative and quantitative analyses were conducted on four kinds of resin-modified glass ionomer (RMGI) cement liquids, LC, LC II, LC III (hereinafter referred to as LCs) and VM, using HPLC and laser Raman spectroscopic methods. HPLC revealed that among the RMGI liquids LCs contain 31-32% HEMA (2-Hydroxyethyl methacrylate), and VM contains 18% of the same. The composition of RMGI cement liquids varied significantly between manufacturers. In Raman spectroscopic analyses, the spectra of liquids of various ratios of polyacrylic acid and HEMA were measured, and calculations were made on the peak intensity ratios of C=C stretch vibration to C=O stretch vibration, common in both HEMA and polyacrylic acid. The composition ratio of polycarboxylic acid to HEMA of commercial glass ionomer cements was assessed by the regression curve generated by a combination of peak intensity ratios and composition ratios. In addition, Raman spectroscopy was able to identity the differences in form of the methacryloyloxy group. (+info)
The influence of configuration factors on cavity adaptation in compomer restorations.
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The effect of configuration factor (C-factor) on cavity adaptation was investigated in three compomer and one resin composite restorations. Eighty-four cylindrical dentin cavities (C-factor: approximately 2.5, 3.0 or 4.0) prepared on flat coronal dentin surfaces were filled with the materials in combination with their proprietary adhesive systems. Cavity adaptation was microscopically examined after 15 minutes storage in water at the top surface and at other four sites along the cavity walls. Additionally, indentation testing was performed for each material at 20 minutes and 24 hours after irradiation. Regression analysis revealed no relationship between C-factor and gap dimension in compomer restorations at any of the measuring sites, while a logarithmic relation was found only at the cavity floor of the composite fillings. All materials showed maturation of mechanical properties. The elastic component of the indentation was smaller in compomers than in the composite. It was concluded that C-factor had no influence on the cavity adaptation for compomer restorations. This might be due to reduced stress generation at the bonding interface caused by relatively low mechanical properties immediately after curing, less elasticity, and water absorption in compomers. (+info)
The effect of primers on bond strength of polyacid-modified resin composites (compomers).
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This study evaluated the effect of primer on shear bond strength and marginal gaps of six new compomers immediately after light-activation. A resin-modified glass ionomer cement, a conventional glass-ionomer cement and a microfilled composite were used for comparison. The marginal gap widths of each of the four compomers and a microfilled composite used with the primer were significantly smaller compared with those used without the primer. The bond strength values of five compomers used with the primer were significantly higher than those used without the primer. The bond strength of conventional glass-ionomer was not affected by the primer (or the conditioner). (+info)
Release and recharge of fluoride by restorative materials.
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This study investigated the release and recharge of fluoride by restorative materials. Resin-modified glass ionomers (RGIs), polyacid-modified composite resins (PMCRs) and resin composite containing fluoride were used for comparison of fluoride release. Non-fluoride-releasing resin composite was used as a control. The amounts of fluoride release from RGIs and PMCRs remarkably increased in the citrate-phosphate acid buffer compared with distilled water. The amounts of fluoride recharged in RGIs increased with the concentration of NaF solution, but those of PMCRs exposed to all concentrations of NaF solutions were less than 1.5 ppm. Neither resin composite containing fluoride and non-fluoride-releasing resin composite gave any evidence of recharge. RGIs and PMCRs affected by acid buffer solution could not recharge much fluoride even if they were immersed in the 1000 ppmF NaF solution. The results suggested that the matrix of RGIs and PMCRs functioned as a reservoir of fluoride, but the functions were lost by acid attack. (+info)
An ex vivo assessment of resin-modified glass ionomer bonding systems in relation to ceramic bracket debond.
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This ex vivo study assessed three new resin-modified glass ionomer cements (Fuji ORTHO LC, Vitremer, and Dyract-Cem) in relation to ceramic bracket removal. It was hypothesized that the use of these cements would facilitate bracket removal and eliminate debond complications Eighty extracted premolar teeth were divided into four groups of 20 teeth and bonded with Intrigue brackets using each of the resin-modified cements (groups 1, 2, and 3), the control group 4 was bonded with Concise chemically-cured adhesive. The teeth were debonded by applying a shear load using an Instron universal testing machine. The mean force to debond was calculated for each group and each tooth was examined under the stereomicroscope to record the site of bond failure and the Adhesive Remnant Index (ARI). The results showed that the resin-modified cements were very effective at eliminating ceramic bracket debond problems. Bracket fracture was eliminated compared with a 40 per cent fracture rate with the control and the ARI scores were all reduced. The elimination of debond problems appears to be related to the significantly reduced (P < 0.001 using ANOVA and Tukey tests) mean and maximal debond forces compared with the control. (+info)
Evaluation of the surface roughness of compomer by laser scanning microscopy.
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The purpose of this study was to evaluate the effect of alcoholic and low pH soft drinks on the surface roughness of compomer restorative materials. There were five tested materials and four immersion media. Specimens were immersed in test solutions for a 10-day period at a temperature of 37 degrees C. Measurement of the surface texture was carried out using a laser scanning microscope (a non-contact laser stylus tracing method). This was also used to produce the Laser Scanning Microscope Image (LSM Image). Specimens immersed in orange juice and whisky displayed higher values for Ra & Rz than specimens immersed in soft drinks and deionized water. LSM Image showed a difference between the control and the examined side, especially for specimens immersed in low pH soft drinks this could be due to the erosive effect of the media. Alcoholic and low pH soft drinks caused deterioration of the materials surface, which may lead to a clinically detectable rough and dull surface. (+info)
Fatigue of restorative materials.
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Failure due to fatigue manifests itself in dental prostheses and restorations as wear, fractured margins, delaminated coatings, and bulk fracture. Mechanisms responsible for fatigue-induced failure depend on material ductility: Brittle materials are susceptible to catastrophic failure, while ductile materials utilize their plasticity to reduce stress concentrations at the crack tip. Because of the expense associated with the replacement of failed restorations, there is a strong desire on the part of basic scientists and clinicians to evaluate the resistance of materials to fatigue in laboratory tests. Test variables include fatigue-loading mode and test environment, such as soaking in water. The outcome variable is typically fracture strength, and these data typically fit the Weibull distribution. Analysis of fatigue data permits predictive inferences to be made concerning the survival of structures fabricated from restorative materials under specified loading conditions. Although many dental-restorative materials are routinely evaluated, only limited use has been made of fatigue data collected in vitro: Wear of materials and the survival of porcelain restorations has been modeled by both fracture mechanics and probabilistic approaches. A need still exists for a clinical failure database and for the development of valid test methods for the evaluation of composite materials. (+info)