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.
Thermal and mechanical properties of glass ionomer cement
Glass ionomer cement is used as a restorative material. This study evaluated some physical properties such as specific heat, thermal conductivity, vickers hardness and breaking strength of Glass ionomer cement (GC Fuji II - Tokyo). The specific heat and thermal conductivity were determined using the principal of method of mixtures and Lee's apparatus respectively. Micro hardness measurements were performed using a Vickers cum Brinell hardness tester and measurement of breaking strength was carried out using a universal testing machine, operated at a head speed of 10 mm per minute. Glass ionomer cement has several desirable properties such as high specific heat, low thermal conductivity and thermal diffusivity apart from greater Vickers hardness and breaking strength. In presence of these advantages it may be a cement of choice for filling of cavities.
Dielectric properties of glass ionomer cements.
A study of the dielectric properties of dental cements is interesting for two reasons: It provides information about the setting reaction of the cement, and about the likely function of the cement as an electrical insulator. The idea was borrowed from industry where electrical resistance measurements are a sensitive and non-destructive method of determining change in a setting cement. Thus, Callejal used such techniques to study the setting and hardening of high-alumina and Portland cements. Wilson and Kent2,3 were the first to apply the method in their work on silicate and phosphate cements. Braden and Clarke4,5 followed with their studies on zinc oxide-eugenol and polycarboxylate cements. In this latter study the changes in relative permittivity (dielectric constant) and resistivity during the setting of glass ionomer cements were measured.