PubMed · 16729503
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
Kenneth Koch, Dennis Brave. 2006. A new endodontic obturation technique.. https://pubmed.ncbi.nlm.nih.gov/16729503/
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
A commercial photopolymerizable resin-modified glass-ionomer (Fuji II LC) was studied using a variety of nuclear magnetic resonance (NMR) techniques. (1)H and (19)F stray-field imaging (STRAFI) enabled to follow the acid-base reaction kinetics in self-cured (SC) samples. Gelation and maturation processes with 25 min and 40 h average time constants, respectively, were distinguished. In self- & photo-cured (SPC) samples, two processes were also observed, which occurred with 2 s and 47 s average time constants. (1)H, (27)Al and (29)Si magic angle spinning (MAS) NMR, (13)C cross-polarization (CP)/MAS NMR and (27)Al multiple quanta (MQ)MAS NMR spectroscopy were used to obtain structural information on the glass and cements that were either SC or SPC. The presence of methacrylate groups was identified in the solid component. Unreacted hydroxyl ethylmethacrylate (HEMA) was detected in self-cured cement. (27)Al data showed that approximately 28% and 20% of Al is leached out from glass particles in SC and SPC samples, respectively. The upfield shift detected in (29)Si MAS NMR spectra of the cements is consistent with a decrease in the number of Al species in the second coordination sphere of the silicon structures. Scanning electron microscopy (SEM) showed existence of 3D shrinkage of the cement matrix in photo-cured cements.
Explore the source record for details and available documents.
A glass-ionomer cement containing an acrylic acid/vinyl phosphonic acid copolymer, has been investigated for its interaction with water and with aqueous lactic acid and the results compared with those from conventional glass-ionomers based on polyacrylic acid. Cylindrical specimens (12 mm high x 6 mm diameter) were placed in 8 cm3 of aqueous lactic acid (20 mmol dm(-3); pH 2.7) for 1 week, at the end of which the pH was determined. Each specimen was then placed in a fresh 8 cm3 volume of lactic acid and the pH determined after a further week. This procedure was continued for a total of 13 weeks for each specimen. Experiments were also carried out on similar specimens exposed to 8 cm3 of water for 1 week only. Further experiments were carried out in which discs of cement were exposed to thin films (0.15 mm) of lactic acid at pH 4.5, with pH values determined at 30 s, 1, 2, 5 and 10 min. After 1 week, cements had changed the pH of the lactic acid to a mean value of 3.63 (SD 0.08) while in weeks 2-13 they changed it to a mean value of 3.31 (SD 0.11). After 1 week in aqueous lactic acid the cements had gained mass by a mean of 1.26% (SD 0.59%) compared with 1.22% (SD 0.14%) in water. After 13 weeks in lactic acid, cements had lost a mean of 2.83% (SD 0.74%) in mass. Thin films of aqueous lactic acid changed from pH 4.5-5.1 at 30 s and to a steady value of 5.6 (SD 0.3) between 2 and 10 min. These results were similar to those for conventional glass-ionomer cements based on carboxylic acid polymers. Hence, it was concluded that the presence of the vinylphosphonic acid units made no significant difference to the interaction of cements with aqueous solutions.