Studies on electrical and thermal properties of dental glass ionomer cement
A commercially available dental Glass Ionomer Cement (GIC) was studied after setting at room temperature (300 K) to understand its DC electrical conductivity, dielectric and thermal properties. The dental GIC’s are supposed to have free mobile charge carriers like F- ions. Interestingly this material loses its conductivity above 80°C and behaves like a non-polar substance. The frequency dependent dielectric studies also indicate the loss of mobile charge carriers in the samples annealed at 80°C. The DSC and TGA studies indicate that the material loses H2O exothermically at 100°C. This is attributed to the onset of a secondary setting reaction.
New Insights into the Setting Processes of Glass Ionomer Cements from Analysis of Dielectric Properties
The setting processes in the commercial glass ionomer cement (Fuji IX Fast) and resin modified glass ionomer cement (Fuji II LC) were investigated by the dielectric spectroscopy. The changes in the real and imaginary parts of the dielectric permittivity [e*(ω)] as well as dielectric loss (tan δ) with time for Fuji IX Fast show several distinct regions which are related to the different stages of the acid–base reaction. Interestingly, the first stage that lasts for approximately 12 min terminates with a sharp decrease in dielectric parameters which is most probably related to the instantaneous (micro)fracturing of the sample due to a rapid build–up of the shrinkage stress. On the other hand, evolution of the dielectric properties during the setting of Fuji II LC indicates fast reaction in the initial stage (within few minutes) followed by the slow gradual change as a result of the competing nature of the acid–base reaction and light-activated polymerization.
Factors influencing the setting reaction of glass polyalkenoate (ionomer) cements.
Abstract The setting reaction of a number of commercially available glass polyalkenoate cements has been investigated using differential thermal analysis. There were significant differences in the rates of setting between the materials under test, with a lining material setting most rapidly. The setting reaction of these materials is associated with a mild to moderate increase in temperature of the cement, which was greatest for a fast-setting glass polyalkenoate lining material (12·5°C), mixed at a higher powder: liquid ratio than recommended by the manufacturer (P: L 4·08 : 1). The rate of set is influenced by the powder: liquid ratio for hand-mixed materials, and may be influenced by both the type and the presentation of the polyacid used by the manufacturer.