Temperature-dependent properties of resin-composites before and during the setting process

• Main Author: Alnazzawi, Ahmad
• Other Authors: Watts, David; Silikas, Nikolaos
• Published: University of Manchester 2012
• Subjects: 617.6
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.566582

Dental Resin-Composites contain inorganic particles, coated with organic coupling agent, dispersed in an organic resin-matrix. In their precured state they are viscous pastes that change rapidly to a hardened mass after photo-activation. Temperature change is expected to modify several physical properties.The aims were to determine the extent to which increasing temperature from ambient (23 oC) to body temperature (37 oC) may affect properties before and during the setting process. Six representative resin-composites were selected [GRO, GCK, VDD, FXE, GDP, and GDA].Temperature-dependence of handling properties (packing stress and viscosity) of pre-cured resin composites was examined using a penetrometer instrument at 23 oC, 30 oC, and 37 oC. Viscosity was reduced significantly by up to 93 % at 37 oC compared to 23 oC. Temperature-dependence of degree-of-conversion (DC) was measured by FTIR spectroscopy at 23 oC and 37 oC. DC was also time-dependent after photo-activation at both temperatures, with all examined materials having higher DC at 1 h than 0 h.A modified bonded-disk instrument was used for simultaneous measurement of: shrinkage-strain, exotherm, and Coefficient of Thermal Expansion (CTE) at 23 oC. Shrinkage-strain, exotherm, and CTE were all found to correlate negatively with filler-load. Positive correlation was found also between shrinkage-strain and CTE.Temperature-dependence of shrinkage-strain kinetics, at 23 oC and 37 oC, was examined with the bonded-disk instrument. Mean 1h shrinkage-strains at 37 oC were numerically and significantly greater (p<0.05) than those at 23 oC for all cases except GDA and GDP. The activation energy (EA) of the shrinkage-strain kinetic process was calculated for each material, and a positive correlation was found between EA and the percentage of total organic material, calculated from the combustion technique.The Bioman instrument was used, for the first time, to measure temperature-dependence of shrinkage-stress kinetics at 23 oC and 37 oC. At 23 oC, all materials demonstrated a greater stress at 1h than 2 min after photo-activation. At 37 oC, there were no significant stress differences between 2 min and 1h. VDD composite showed a reduced stress 1h after photo-activation at 37 oC than at 23 oC. This suggests a pronounced visco-elastic character. Understanding the effects of temperature on dental composites can influence the possible adoption of clinical preheating regimes, prior to light-curing.