Effects of Pre-Heating on the Properties of a Silorane-Based Composite

Objectives: The purpose of this study was to evaluate the effects of pre-heating on the properties of a silorane-based composite restorative material (Filtek LS, 3M/ESPE) and methacrylate-based composites (Esthet-X, Dentsply; Durafill VS, Kulzer; Filtek Supreme Ultra, 3M/ESPE; PermaFlo, Ultradent).  Methods: Viscosity, compressive strength, depth of cure, and polymerization shrinkage were examined.  The viscosity was measured using a rheometer (TA Instrument).   The temperature of the plate assembly and the environmental test chamber was set at 23^oC or 68^oC.  The composites were injected between the plates of the rheometer.  For compressive strength, depth of cure, and shrinkage, heated specimens were created using a CalSet (Addent) unit set at 68°C.  Unheated compules were held at room temperature (23°C) before insertion.  . Molds were held at oral temperature (37^oC) using a digital hot plate.  For compressive strength testing, specimens were made by injecting the heated and unheated composite into a 6-mm thick x 4-mm diameter stainless-steel mold.  The specimens were light cured, stored 24-hours in 37^oC water, and loaded in a universal-testing machine.  For depth of cure (ISO 4049), specimens were created by injecting the heated or unheated composite into a 10-mm thick x 4-mm diameter stainless-steel mold.  After 24-hours of storage, uncured resin was scraped with an instrument and the remaining thickness was measured with a micrometer and divided by two.   For polymerization-shrinkage testing, heated and unheated composites were placed on a heated pedestal (37^oC) in the AcuVol shrinkage-device (Bisco) and light cured.   Data were analyzed with ANOVA/t-tests per physical property and composite type.  Results:   Except for the flowable composite, significant reductions in viscosity were found between heated and unheated composites (p<0.001) with no significant difference in other properties.   Conclusions:  In general, heating the restorative composites decreased viscosity, but did not affect compressive strength, depth of cure, or shrinkage per composite type.

 

Restorative Material (Shade A-2) Physical Property   Mean (st dev) Viscosity (Pa S) Compressive Strength (MPa) Depth of Cure (mm) Shrinkage (%) Heated Room Heated Room Heated Room Heated Room Filtek LS (3M/ESPE)  6,123 (5,288) 189,360 (25,305) 158.6 (20.9) 180.7 (26.3) 2.72 (0.05) 2.63 (0.10) 3.32 (0.38) 3.03 (0.46) Esthet-X (Dentsply) 46,048 (31,278) 199,220 (40,519) 233.6 (37.4) 207.9 (25.4) 2.64 (0.07) 2.72 (0.09) 5.07 (0.44) 4.61 (0.35) Durafill VS (Kulzer) 7,664 (722) 38,892 (5,421) 174.9 (25.6) 192.4 (24.2) 3.51 (0.14) 3.53 (0.11) 4.16 (0.68) 4.24 (0.34) Filtek Supreme (3M/ESPE) 8,981 (2,440) 159,760 (28,530) 243.5 (41.2) 250.9 (29.8) 3.32 (0.09) 3.44 (0.06) 4.71 (0.37) 4.22 (0.57) PermaFlo (Ultradent) 56 (27) 62 (14) 186.6 (49.0) 202.1 (38.3) 3.13 (0.08) 3.20 (0.10) 10.88 (0.73) 11.16 (1.93)