In vitro comparison of peak polymerization temperatures of 5 provisional restoration resins.
(17/354)
BACKGROUND: The heat produced by provisional restoration materials may injure the dental pulp. This study measured and compared peak temperatures during polymerization of 5 materials used in the fabrication of provisional restorations. METHODS: The tested materials were 2 self-curing resins (Integrity and Protemp) and 3 dual-cure resins (Iso-Temp, TCB Dual Cure and Provipont DC). A mould the size of a maxillary molar tooth was fabricated to contain 0.5 cc of resin. The temperature rise of the different materials was recorded every 10 seconds over a 10-minute period. RESULTS: The rise in temperature of Integrity (peak temperature of 33.8 degrees C) and Protemp Garant (35.6 degrees C) was significantly higher than the rise in temperature of Iso-Temp (29.5 degrees C), TCB Dual Cure (28.4 degrees C) and Provipont DC (29.5 degrees C). CONCLUSION: Use of the dual-cure resins in provisional restorations may reduce the risk of pulp injury. (+info)
Estrogenic activity of dental materials and bisphenol-A related chemicals in vitro.
(18/354)
Twenty-eight chemicals used as dental materials and bisphenol-A related chemicals were diluted with DMSO to concentrations ranging from 10(-7) to 10(-3) M and tested for estrogenicity. Bisphenol-A (BPA), bisphenol-F (BPF) and bisphenol-A-bischloroformate (BPACF) showed estrogenic activity using the yeast two-hybrid system, and BPA, BPF, BPACF and bisphenol-S (BPS) showed estrogenic activity using the fluorescence polarization system. However, none of the remaining chemicals and none of the dental materials showed any activity at concentrations between 10(-7) and 10(-3) M. Although BPA, BPF, BPACF, bisphenol-A-dimethacrylate and BPS showed estrogenic activity in the E-screen test, the remaining chemicals did not. Thus, most of the chemicals showed consistent results, either positive or negative, by the three testing methods, while two chemicals showed conflicting results. Further studies, together with in vivo and epidemiological examinations, are required. Elucidation of the structure-activity relationships of these chemicals is also needed to estimate the estrogenicity of a chemical from its structure. (+info)
Analysis of major components and bisphenol A in commercial Bis-GMA and Bis-GMA-based resins using high performance liquid chromatography.
(19/354)
The purpose of this study was to examine the quality of commercially available Bis-GMA because concerns about Bis-GMA and Bis-GMA-based resins have been recently expressed in dentistry. Four major components and bisphenol A, which is a compound of recent controversy, were quantitatively analyzed using high performance liquid chromatography (HPLC) in three commercial Bis-GMA and six Bis-GMA-based composite resins. The contents of genuine Bis-GMA, Iso-bis-GMA, Bis-GMA-H, and Bis-GMA-M as well as the total content of the four monomers were 45.7-57.5%, 19.9-26.2%, 1.8-5.0%, 0.6-15.0% and 83.7-85.6% in the commercial Bis-GMAs, or 3.8-9.1%, 1.7-4.3%, 0.1-0.5%, 0.1-2.0% and 5.8-14.0% in composite resins, respectively. There were some differences in the composition of the major components between domestic and foreign materials. Bisphenol A contents in the unpolymerized composite resins were 1.5-10.2 micrograms/g resin. (+info)
WDX study of resin-dentin interface on wet vs. dry dentin.
(20/354)
The purpose of the present study was to determine the resin-dentin Interface conditions in Wet vs. Dry Dentin. Dentin disks were prepared from extracted human premolars. Sectioned dentin surfaces were used for SEM studies of wet vs. dried acid-etched dentin. These specimens were cut perpendicular to the surface into two equal halves. One-half of the sectioned specimen was observed by SEM in three treatment groups and the other half was observed for micromorphological differences in the resin-dentin interface using Wavelength Dispersive X-ray Spectrometer (WDX). SEM photomicrographs of the dentin surface showed the collapse of collagen fibrils in the demineralized layer and enlargement of the tubule orifices. A collagen rich layer approximately 8-10 microns thick (WDX) was observed at the resin-dentin interface when treated with the conventional dry-bonding technique. Dentin surfaces treated by the wet-bonding technique (SB), as observed by SEM, showed an uncollapsed collagen layer, while the collagen-rich layer was approximately 1-2 microns thick (WDX). The present findings suggest that moist bonding is required for optimum infiltration of adhesive resin into the demineralized layer. (+info)
Detection of bisphenol-A in dental materials by gas chromatography-mass spectrometry.
(21/354)
The xenoestrogenic substance bisphenol-A is widely used as a synthetic precursor of resin monomers, such as bisphenol-A diglycidyl methacrylate. Reports describing the release of bisphenol-A from polymerized resin into saliva have aroused considerable concern regarding exposure to xenoestrogen by dental treatment. The purpose of the present study was to demonstrate a reliable methodology of detecting the trace amounts of bisphenol-A in dental materials. Bisphenol-A was separable from bisphenol-A diglycidyl methacrylate, which is often employed as the principal dimethacrylate monomer, by selective extraction with a Sep-Pak C18 cartridge. Using this extraction method in combination with a gas-chromatography mass-spectrometry, we have obtained evidence that all unpolymerized materials used in this study were contaminated with bisphenol-A. Quantitative analysis using a deuterium-labeled compound as an internal standard revealed bisphenol-A contents in commercial dental materials ranging from < 1 microgram/g material to about 20 micrograms/g material. The polymerized dental materials released up to 91.4 ng bisphenol-A/g material into phosphate buffered saline during 24-h incubation. These results indicate that bisphenol-A can be released from dental materials, however the leachable amount would be less than 1/1000 of the reported dose (2 micrograms/kg body weight/day) required for xenoestrogenisity in vivo. (+info)
Elution of bisphenol A from composite resin: a model experiment.
(22/354)
To understand the leaching characteristics of bisphenol A (BPA) from composite resins, we prepared experimental composite resins containing known amounts of BPA and examined the BPA elution from the resins in water and methanol at 37 degrees C. The concentration of BPA in each eluate was determined by high performance liquid chromatography. Cumulative BPA release was calculated and plotted against extraction time. The elution of BPA was rapid during a 6-hr period for both solvents, and then declined and continued steadily. Plots of square root of the amount of BPA leached against logarithm of extraction time produced good linear relationships from a 6-hr period thereafter. Extrapolation of the relationship enabled prediction of the amount of BPA to be leached in the long term. The present results suggested that little or no estrogenic effect due to long-term elution of BPA from commercial Bis-GMA-based resins is expected in practice. (+info)
Acid and base-catalyzed hydrolysis of bisphenol A-related compounds.
(23/354)
In order to ascertain whether an estrogenic bisphenol A is produced from bisphenol A-related monomers by chemical-induced hydrolysis and to clarify their hydrolytic mechanisms, bisphenol A dimethacrylate (Bis-DMA) and bisphenol A bis(glycidyl methacrylate) (Bis-GMA) were reacted with phosphoric acid, hydrochloric acid, and sodium hydroxide in methanol or methanol/water mixed media at 37 degrees C. Amounts of monomethacrylate intermediates as well as bisphenol A (BPA) were determined by the use of high-performance liquid chromatography (HPLC), and time-conversion curves of hydrolytic products were prepared. BPA and bisphenol A monomethacrylate were produced by acid-catalyzed hydrolysis of Bis-DMA. Bis-GMA was partly converted into monomethacrylate by phosphoric acid and into monomethacrylate and 2,2-bis[4-(2,3-dihydroxypropoxy) phenyl]propane (BHP) by hydrochloric acid. Hydrolytic reactions by sodium hydroxide were completed almost within 1 day, resulting in the production of BPA from Bis-DMA, and BHP from Bis-GMA. No BPA was formed from Bis-GMA by chemical-induced hydrolysis. The hydrolytic behaviors of these monomers were discussed. (+info)
Effect of NaClO treatment on bonding to root canal dentin using a new evaluation method.
(24/354)
The purposes of this study were to investigate the reliability and efficiency of a new evaluation method for resin bonding to root canal dentin, which measures both marginal adaptation and shear bond strength simultaneously, and to determine the effects of root canal irrigants on resin bonding. A wet bonding system (Single Bond) and a self-etching primer system (Clearfil Mega Bond) were employed; NaClO was used as a root canal irrigant. No gaps or changes in bond strength were observed despite the NaClO treatment when the wet bonding system was employed, while the gap formation ratio increased, and bond strength decreased with longer NaClO treatment time when the self-etching primer system was employed. These findings suggested that this new experimental method was effective for evaluating resin systems to the root canal wall dentin which is affected by irrigation with NaClO. (+info)