ABSTRACT
The effect of exposing glass ionomer cement to water during the first 48 hours after mixing was studied. The strength of the set cement was only reduced if exposure to water occurred within the first hour after mixing. The gel matrix formed during the setting reaction was shown to be the source of fluoride ions released when glass ionomer cement is placed in water. The degree of hydration, rate of fluoride release, and degree of cross-linking of the gel matrix were all shown to be affected by the water ingress during the setting reaction. Finally the fluoride release from the cements was found to cease within six months of exposure to water indicating that only fluoride ions released into the gel matrix during the setting reaction are available to protect surrounding tooth structure.
Subject(s)
Dental Cements , Glass Ionomer Cements , Chemical Phenomena , Chemistry, Physical , Fluorides , Models, Chemical , Pressure , WaterABSTRACT
Strength characteristics of dental poly(methyl methacrylate) were studied in terms of the fracture surface energy and inherent flaw size, using the methods of Berry.2-9 Dental poly(methyl methacrylate) is weaker than the corresponding bulk polymer because the former has a lower energy and higher inherent flaw size.
Subject(s)
Dental Stress Analysis , Methylmethacrylates/standards , Chemical Phenomena , Chemistry , Molecular Weight , Surface Properties , Viscosity , Water/pharmacologyABSTRACT
Treatment of freshly-cut dentine with fluoride ions or high concentrations of metal ions produced changes ranging from mineralization of tubule contents to precipitation of adherent surface layers. Combinations of these treatments with application of fluoridated and non-fluoridated polycarboxylate cements and glass ionomer cements produced both increases and reductions in bond strength which are explained by ionic diffusion at the interface prior to setting.
Subject(s)
Acrylic Resins , Dental Bonding , Dentin/ultrastructure , Polycarboxylate Cement , Aluminum/pharmacology , Calcium/pharmacology , Chlorides/pharmacology , Dentin/drug effects , Diffusion , Fluorides/pharmacology , Humans , Ions , Magnesium/pharmacology , Sodium/pharmacology , Stress, Mechanical , Tin/pharmacologyABSTRACT
Dithiocarbamate is used as a preservative or vulcanizing accelerator in the manufacturing process of latex gloves. Twenty-five types of gloves were tested for the presence of this additive by three methods: using an iodide/azide reagent; elemental analysis; and investigating the inhibition of the setting reaction of a vinyl polysiloxane putty. The results of these tests confirm that dithiocarbamates are the chemical components which cause the inhibition of the setting of a vinyl polysiloxane putty. Given this finding, and concerns regarding the possible effects of dithiocarbamate on skin, the use of dithiocarbamate-free gloves is recommended.
Subject(s)
Dental Impression Materials , Gloves, Surgical , Latex/chemistry , Thiocarbamates/chemistry , Electron Probe Microanalysis , Humans , Least-Squares Analysis , Polyvinyls/chemistry , Siloxanes/chemistry , Thiocarbamates/analysis , Time Factors , Zinc Compounds/analysis , Zinc Compounds/chemistryABSTRACT
A recently released dentine adhesion promoter, based on a HEMA/maleic acid primer, was found to bond exceptionally well to dentine (14.1 MPa) if the adhesion promoter layer was applied thickly enough. Air inhibition of the promoter layer during its initial cure was seen to reduce the bond strength by a half if the promoter layer was air-thinned prior to curing. The adhesion promoter was found to greatly enhance the bond strength of composite to glass ionomer, removing the necessity to acid etch the glass ionomer prior to applying the composite. The failure of the composite/glass ionomer bond was always within the glass-ionomer cement itself, with the higher bond strengths resulting in a greater incidence of oblique cracks at 45 degrees to the bond surface than had been previously observed.
Subject(s)
Acrylates , Adhesives , Dental Bonding , Dentin , Maleates , Methacrylates , Resin Cements , Acid Etching, Dental , Composite Resins , Dental Cements , Glass Ionomer Cements , Humans , Materials Testing , Stress, Mechanical , Surface PropertiesABSTRACT
Forty molar and premolar teeth had non-retentive cavities prepared and restored with amalgam using (1) copal varnish (control), (2) a pin, (3) Amalgambond or (4) Panavia-Ex. The forces and energy required to dislodge the restorations were recorded and compared, and the mode of failure noted for each group. Although the pinned restorations required significantly higher loads to dislodge them, the mode of failure and energy required to dislodge the restorations in the Amalgambond and Panavia-Ex groups indicated that these types of restorations had significant advantages over pinned restorations, particularly where the pulp might be compromised. The film thickness of the retentive systems in these two groups, however, indicated a substantial operator or technique sensitivity.