Temperature-dependent polymerization shrinkage stress kinetics of resin-composites

ObjectivesTo determine temperature dependence of shrinkage stress kinetics for a set of resin composites formulated with dimethacrylate monomer matrices.MethodsSix 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 60 min. Stress levels between materials were compared at two intervals: 2 min and 60 min. Specimen temperatures were controlled by a newly designed heating device. Stress measurements were monitored for 1 h, after irradiation for 40 s at 550 mW/cm2 (energy density = 22 J/cm2). Three specimens (n = 3) were used at each temperature per material.ResultsShrinkage stress at 23 °C ranged from 2.93 MPa to 4.71 MPa and from 3.57 MPa to 5.42 MPa for 2 min and 60 min after photo-activation, respectively. The lowest stress-rates were recorded for Kalore and Venus Diamond (0.34 MPa s−1), whereas the highest was recorded for Filtek Supreme XTE (0.63 MPa s−1). At 37 °C, shrinkage stress ranged from 3.27 MPa to 5.35 MPa and from 3.36 MPa to 5.49 MPa for 2 min and 60 min after photo-activation, respectively. Kalore had the lowest stress-rate (0.44 MPa s−1), whereas Filtek Supreme XTE had the highest (0.85 MPa s−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).SignificanceResin-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.