Detection of bisphenol-A in dental materials by gas chromatography-mass spectrometry.
(65/1129)
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)
Acid and base-catalyzed hydrolysis of bisphenol A-related compounds.
(66/1129)
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 the adhesive layer thickness on the fracture toughness of dental adhesive resins.
(67/1129)
We investigated how the thickness of an adhesive layer between two Co-Cr alloy plates affected the mode I fracture toughness of dental adhesive resin by varying the type of resin using a double cantilever beam (DCB) test. Two typical adhesive resins (PV and SB) were used. The adhesive layers of the DCB test specimens were 20, 100 and 200 microns thick. The fracture modes of PV differed with the thickness of the adhesive layer, such as interface fracture at 20 microns thickness, and similar cohesive fracture at 100 and 200 microns thickness. In the case of SB, crack-propagating areas were observed as cohesive fractures in all test specimens with different adhesive layer thickness, and the surfaces of these areas became remarkably rougher as the thickness of the adhesive layer increased. The fracture toughness of PV was not affected by the differences in thickness between the 100 and 200 microns adhesive layers, but there was a notable decrease in fracture toughness when the adhesive layer decreased to a thickness of 20 microns. That of SB showed a tendency to increase as the adhesive layer became thicker. (+info)
New initiation system for resin polymerization using metal particles and 4-META.
(68/1129)
Fifteen kinds of metal particles were examined to establish whether they could induce the setting of UDMA-based monomer containing BPO without amine under the presence of 4-META at room temperature. FT-IR spectra of the resultant set samples and the monomer were analyzed to see if the setting was caused by the polymerization. The effects of 4-META and BPO concentrations on the setting time were also studied using the metal particles that induced the setting very effectively. As-received Cu, Zn, Mo, Sn, Co, and In particles could initiate the polymerization of the monomer in combination with BPO and 4-META when they were moistened with water. All the three kinds of silver alloy particles examined also could initiate the polymerization, although pure silver metal particles could not. The presence of 4-META drastically shortened the setting time of the mixture of Cu particles and the monomer containing BPO, while higher concentration of BPO in the monomer significantly shortened the setting time. (+info)
Polymerization of UDMA using zinc particles and 4-META with and without BPO.
(69/1129)
The polymerization phenomena of zinc particles moistened with a small amount of water, 4-META, and UDMA without amine in the presence and absence of BPO were investigated. The effects of 4-META and BPO on the setting time and the degree of conversion (DC) were studied. Moreover, the effect of zinc ion amount on the setting time was investigated. As-received zinc particles could induce the polymerization either with or without BPO. A higher concentration of 4-META shortened the setting time and increased DC when BPO was absent. However, the presence of BPO generally retarded the setting time and decreased DC, although its effect was dependent on the 4-META concentration. A higher amount of zinc ion retarded the setting reaction in the presence of 4-META. The zinc particles mixed with 10% zinc sulfate and acetic acid solutions could induce the polymerization of UDMA containing BPO when the amine and 4-META were absent. (+info)
Development of metal-resin composite restorative material. Part 3. Flexural properties and condensability of metal-resin composite using Ag-Sn irregular particles.
(70/1129)
Powder-liquid type metal-resin composites, using Ag-Sn irregular particles as the filler, 4-META as coupling agent and UDMA + TEGDMA as resin matrix, were experimentally prepared under 9 different conditions (three different particle sizes and three different filler contents). The flexural strength and flexural modulus were measured. Three different irregular particle size MRCs without redox-initiator at 94% filler content, as well as amalgam, conventional hybrid composite and Ag-Sn spherical particle MRC were evaluated for condensability. The flexural strength of the Ag-Sn irregular particle MRC was significantly influenced by both the filler particle size and filler contents (p < 0.01). It increased when either the filler content increased or the particles size decreased. The highest flexural strength (97.6 MPa) was obtained from the condition of particles size < 20 microns and 94% filler content. The flexural modulus was significantly influenced by filler content and it increased with increasing filler content. The condensability of the Ag-Sn irregular particle MRC was lower than that of amalgam but much higher than presently available conventional composites and spherical particle MRC. (+info)
Restoration of endodontically treated teeth with carbon fibre posts--a prospective study.
(71/1129)
BACKGROUND: A prospective study was started in 1995 to evaluate the success of carbon fibre reinforced epoxy resin (CFRR) posts used to restore endodontically treated teeth. All the teeth in the study had lost more than 50% of their coronal structure. METHODS: Fifty-nine carbon fibre Composiposts cemented with Metabond and built up with Core Paste cores were placed into the teeth of 47 patients. Each tooth received a full-coverage restoration (porcelain fused to metal crown) and was followed for 6.7-45.4 months (average = 28.0 months, standard deviation = 10.7). RESULTS: Results for 52 teeth in 42 patients were analyzed. There were no fractures. The overall failure rate was 7.7% and the cumulative survival rate was 89.6% at the end of the follow-up period. The only statistically significant finding (p = 0.04) was that posts in lower premolars were at higher risk of failure. CONCLUSION: CFRR posts are among the most predictable systems available today. CFRR posts in the upper anterior teeth are associated with a higher success rate and longer life than those placed in premolars, especially lower premolars. This study contributes to the growing body of evidence that supports the use of CFRR posts in the restoration of endodontically treated teeth. (+info)
Comparative xenobiotic metabolism between Tg.AC and p53+/- genetically altered mice and their respective wild types.
(72/1129)
The use of transgenic animals, such as v-Ha-ras activated (TG:AC) and p53+/- mice, offers great promise for a rapid and more sensitive assay for chemical carcinogenicity. Some carcinogens are metabolically activated; therefore, it is critical that the altered genome of either of these model systems does not compromise their capability and capacity for metabolism of xenobiotics. The present work tests the generally held assumption that xenobiotic metabolism in the TG:AC and p53+/- mouse is not inherently different from that of the respective wild type, the FVB/N and C57BL/6 mouse, by comparing each genotype's ability to metabolize benzene, ethoxyquin, or methacrylonitrile. Use of these representative substrates offers the opportunity to examine arene oxide formation, aromatic ring opening, hydroxylation, epoxidation, O-deethylation, and a number of conjugation reactions. Mice were treated by gavage with (14)C-labeled parent compound, excreta were collected, and elimination routes and rates, as well as (14)C-derived metabolite profiles in urine, were compared between relevant treatment groups. Results of this study indicated that metabolism of the 3 parent compounds was not appreciably altered between either FVB/N and TG:AC mice or C57BL/6 and p53+/- mice. Further, expression of CYP1A2, CYP2E1, CYP3A, and GST-alpha in liver of naive genetically altered mice was similar to that of corresponding wild-type mice. Thus, these results suggest that the inherent ability of TG:AC and p53+/- mice to metabolize xenobiotics is not compromised by their altered genomes and would not be a factor in data interpretation of toxicity studies using either transgenic mouse line. (+info)