ABSTRACT
OBJECTIVES: To determine temperature dependence of shrinkage stress kinetics for a set of resin composites formulated with dimethacrylate monomer matrices. METHODS: Six representative resin composites with a range of resin matrices were selected. Two of them were considered as low shrinking resin composites: Kalore and Venus Diamond. The shrinkage stress kinetics at 23°C and 37°C were measured continuously using a Bioman instrument for 60min. Stress levels between materials were compared at two intervals: 2min and 60min. Specimen temperatures were controlled by a newly designed heating device. Stress measurements were monitored for 1h, after irradiation for 40s at 550mW/cm(2) (energy density=22J/cm(2)). Three specimens (n=3) were used at each temperature per material. RESULTS: Shrinkage stress at 23°C ranged from 2.93MPa to 4.71MPa and from 3.57MPa to 5.42MPa for 2min and 60min after photo-activation, respectively. The lowest stress-rates were recorded for Kalore and Venus Diamond (0.34MPas(-1)), whereas the highest was recorded for Filtek Supreme XTE (0.63MPas(-1)). At 37°C, shrinkage stress ranged from 3.27MPa to 5.35MPa and from 3.36MPa to 5.49MPa for 2min and 60min after photo-activation, respectively. Kalore had the lowest stress-rate (0.44MPas(-1)), whereas Filtek Supreme XTE had the highest (0.85MPas(-1)). Materials exhibited a higher stress at 37°C than 23°C except for Kalore and Venus Diamond. Positive correlations were found between shrinkage stress and stress-rate at 23°C and 37°C (r=0.70 and 0.92, respectively). SIGNIFICANCE: Resin-composites polymerized at elevated temperature (37°C) completed stress build up more rapidly than specimens held at 23°C. Two composites exhibited atypical reduced stress magnitudes at the higher temperature.
Subject(s)
Composite Resins , Polymerization , Stress, Mechanical , Temperature , KineticsABSTRACT
OBJECTIVES: To measure shrinkage strain, exotherm, and coefficient of thermal expansion (CTE), simultaneously for a set of representative resin-composites. METHODS: Six commercially available resin-composites with different filler loadings were selected. A modified bonded-disk instrument that includes temperature-monitoring apparatus was used to measure simultaneously: shrinkage strain, exotherm, and CTE. Shrinkage strain and temperature of disk specimens (n=3/materials) were monitored for 1h after irradiation for 20s at 1200mW/cm(2) (energy density=24J/cm(2)). Disks were irradiated for a second time 60min after the first irradiation. Axial expansion strain and temperature were monitored for 3min. Exotherm was obtained from differences between temperature rise during 1st and 2nd irradiations. CTE was calculated from disk axial expansion due to irradiation heat (ΔL) and rise in temperature (ΔT) during the second irradiation. RESULTS: The final shrinkage strain values ranged from 1.7% to 2.34%, exotherm values ranged from 4.66 to 9.43°C, and CTE ranged from 18.44 to 24.63 (10(-6)/°C). Negative correlations were found between filler loading and shrinkage strain, exotherm, and CTE. Positive correlation was apparent between shrinkage strain and CTE. SIGNIFICANCE: The modified bonded-disk instrument could be used to measure simultaneously shrinkage strain, exotherm, and CTE of resin-composites.
