Factors affecting dimensional instability of alginate impressions during immersion in the fixing and disinfectant solutions.
To clarify the factors determining the dimensional stability of alginate impressions during immersion in disinfectant and fixing solution, the weight change of impressions in solutions of glutaraldehyde (GA), NaClO, Na2SO4, K2SO4, CaCl2, and ZnSO4 was measured. In the nonelectrolytic solution, GA, the weight decreased in proportion to concentration, possibly due to the gradient of osmotic pressure between the impression and solution. In monovalent metallic salt solutions the weight change decreased with increased concentration. Especially at lower concentrations the rate of weight loss was high. A chemical action of the solution might also be involved, in addition to the osmotic pressure difference. The weight loss in divalent metallic salt solutions was greater than in monovalent solutions, implicating crosslinking reactions between the impression and solution. (+info)
Formulation of glutaraldehyde disinfectant for alginate impressions.
The effect of buffer agents incorporated in glutaraldehyde disinfectants on the surface quality of dental models was examined by the measurement of surface roughness, X-ray diffraction analysis and SEM observation. Seven experimental glutaraldehyde disinfectants were prepared using two buffer agents, potassium acetate alone or potassium acetate and sodium hydrogen carbonate in combination. Four kinds of sulfate--zinc, calcium, potassium and magnesium sulfate--were added to these disinfectants in order to accelerate the hydration of calcium sulfate hemihydrate. The impressions treated with the experimental disinfectants for 1 h produced stone surfaces which had significantly lower surface roughness values than those treated with the commercial disinfectants (p < 0.05). The X-ray diffraction analysis and SEM observation showed that these superior surfaces were produced as a result of significant reductions in the amount of residual calcium sulfate hemihydrate. Replacement of buffer agents in commercial glutaraldehyde disinfectants with chemicals such as those studied in the present study will improve the surface quality of dental stone. (+info)
Disinfection/sterilization of extracted teeth for dental student use.
Extracted human teeth are used in many preclinical courses. While there has been no report of disease transmission with extracted teeth, sterilization of teeth used in the teaching laboratory should be a concern. The purpose of this study was to determine the effectiveness of different sterilization/disinfection methods of extracted human teeth using Bacillus stearothermophilus, a bacteria resistant to heat and frequently used to test sterilizers. In this study, 110 extracted molars with no carious lesions were collected and stored in buffered saline. An endodontic occlusal access preparation was cut into the pulp chamber of each tooth. Pulp tissue in the chamber was removed with a broach. Approximately 1 x 10(5) B. stearothermophilus endospores in culture medium were injected into the pulp chamber, sealed with Cavit G, and then placed in sterile saline for twelve hours. Ten teeth were placed into each of eleven groups. Seven groups were immersed for one week in one of the following solutions: a) sterile saline (control group), b) 5.25% NaOCl, c) 2.6% NaOCl, d) 1% NaOCl, e) 10% buffered formalin, f) 2% gluteraldehyde, g) 0.28% quaternary ammonium. Four additional groups were treated by h) 10% formalin for two days, i) 10% formalin for four days, j) autoclaving at 240 degrees F and 20 psi for twenty minutes, and k) autoclaving at 240 degrees F and twenty psi for forty minutes. Each tooth was then aseptically split and placed in an individual test tube with growth medium. Samples were examined for evidence of growth (turbidity) at forty-eight hours. Only autoclaving for forty minutes at 240 degrees F and 20 psi or soaking in 10 percent formalin for one week were 100 percent effective in preventing growth. A chi-square analysis of the data indicates these two methods were significantly better than all other methods (p<0.001). (+info)
Swelling/deswelling mechanism of calcium alginate gel in aqueous solutions.
To elucidate the mechanism of dimensional changes in alginate impression in solutions, the relationship between the ion concentrations in three types of solutions (nonelectrolyte and monovalent and divalent metallic salts) and change in gel volume was examined. The gel in the monovalent metallic salt solution expanded and a decrease in monovalent cation and an increase in Ca2+ were observed. This suggests that the crosslinking density of the gel reduced due to dissociation of Ca2+ from the calcium alginate gel. In divalent metallic salt solutions, the shrinkage occurred according to crosslinking of unreacted residue. In the nonelectrolytic solution, gel, neither ethylene glycol nor acetonitrile showed any volume changes, while that in glutaraldehyde contracted. It is speculated that the former two solutions were affected by the fact that the gel has no semipermeability, and that the latter result was due to chemical interaction between the gel and solution. (+info)
Evaluation of the efficacy of Alpron disinfectant for dental unit water lines.
AIMS: To assess the efficacy of a disinfectant, Alpron, for controlling microbial contamination within dental unit water lines. METHODS: The microbiological quality of water emerging from the triple syringe, high speed handpiece, cup filler and surgery hand wash basin from six dental units was assessed for microbiological total viable counts at 22 degrees C and 37 degrees C before and after treatment with Alpron solutions. RESULTS: The study found that the use of Alpron disinfectant solutions could reduce microbial counts in dental unit water lines to similar levels for drinking water. This effect was maintained in all units for up to six weeks following one course of treatment. In four out of six units the low microbial counts were maintained for 13 weeks. CONCLUSIONS: Disinfectants may have a short term role to play in controlling microbial contamination of dental unit water lines to drinking water quality. However, in the longer term attention must be paid to redesigning dental units to discourage the build up of microbial biofilms. (+info)
Waterborne biofilms and dentistry: the changing face of infection control.
Interest in and concern about the biofilms that occur in dental equipment and waterlines have been increasing in recent years. Dental unit waterlines are ideal environments for the growth of microorganisms entering dental units from the municipal water supply. This article describes the conditions in waterline tubing that favour development of biofilms and discusses the level of risk that such microbial growth poses for both dental professionals and their patients. It is stressed that very few cases of infection have been linked directly to contamination in dental unit waterlines. Finally, potential solutions for minimizing risks are presented and discussed. (+info)
In vitro evaluation of different chemical agents for the decontamination of gutta-percha cones.
This study evaluated the effectiveness of three disinfectants used in Dentistry for decontamination of gutta-percha cones. Sixty gutta-percha cones were contaminated with standardized pure cultures of five species of microorganisms (Enterococcus faecalis ATCC 29212, Staphylococcus aureus ATCC 25923, Candida albicans ATCC CBS-ICB/USP 562, Bacillus subtilis spores ATCC 6633 and Streptococcus mutans ATCC 25175). The cones were treated with 10% polyvinylpyrrolidone-iodine aqueous solution (PVP-I; Groups 1 and 2), 5.25% aqueous sodium hypochlorite (Groups 3 and 4) and paraformaldehyde tablets (Group 5). All chemical agents were efficient for the cold sterilization of gutta-percha cones in short time periods. (+info)
Corrosion behavior of dental alloys in various types of electrolyzed water.
The corrosion behavior of dental alloys was examined in electrolyzed strong acid water, weak acid water and neutral water using a 7-day immersion test. The precious metal alloys, gold alloy. Au-Ag-Pd alloy and silver alloy showed the greatest surface color change and dissolution of constituents in the strong acid water and the smallest in the neutral water. The release of Au from gold alloy was especially marked in the strong acid water. Co-Cr alloy showed greater corrosion and tarnish resistance in the strong acid water rather than in the weak acid water and the neutral water. X-ray microanalysis revealed that the corrosion products on the precious metal alloys were silver chloride crystals and the thin brown products on Co-Cr alloy were cobalt and chromium oxides. Ti was sound in all three types of electrolyzed water. The neutral water appeared the least corrosive to metals among the three types showing equivalent bactericidal activity. (+info)