The Linear Shrinkage and Microhardness of Packable Composites Polymerized by QTH or PAC Unit

Abstract

This study evaluated the effectiveness of a plasma arc curing (PAC) unit for packable resin composite curing. The amount and speed of polymerization shrinkage and the microhardness of packable composites were evaluated in order to compare the PAC unit's effectiveness with a quartz tungsten halogen (QTH) unit. Sure Fil (Dentsply Caulk), Pyramid (BISCO Inc) and Synergy Compact (Colténe/Whaledent) were used as the packable composites. In the case of curing with the PAC unit, the composites were light cured with Apollo 95E (DMD System Inc) for 1 second (Group 1), 2 seconds (Group 2), 3 seconds (Group 3), 6 seconds (Group 4) and 12 seconds (Group 5). For light curing with the QTH unit, the composites were light cured for 60 seconds using XL3000 (Group 6). The linear polymerization shrinkage of each composite was measured using a custom made linometer, and the data was stored in a computer every 0.5 to 0.55 seconds for a total of 60 seconds. For each composite, the amount of polymerization was compared using one-way ANOVA with Tukey at the 95% confidence level. In order to compare the speed of polymerization, the peak time (PT), showing the highest speed of polymerization and maximum speed of polymerization (Smax), were determined from the data and compared using one-way ANOVA with Tukey at the 95% confidence level for each material. Based on the statistical analysis among the PAC-cure groups (Groups 1 through 5), the group that was not statistically different from the QTH-cure group (Group 6) in the amount of linear polymerization shrinkage was determined for each material, and the corresponding curing time of the group was defined as the tentative minimum PAC-curing time (TMPT). For microhardness measurements, the samples were placed in a 2-mm thick Teflon plate. Twenty specimens, randomly divided into the PAC-cure group (Group 1) or the QTH-cure group (Group 2), were prepared for each material. In Group 1, each composite was light cured for TMPT with the PAC unit. In Group 2, each composite was light cured for 60 seconds with the QTH unit. Microhardness was measured on the upper and lower surface. For each material, the microhardness of the upper and lower surface of Groups 1 and 2 was analyzed using two-way ANOVA with Tukey at the 95% confidence level. The amount of polymerization was Group 1<Group 2<Group 3<Group 4<Groups 5, 6 in the Sure Fil composite (p<0.05); Groups 1, 2<Group 3<Groups 4, 6<Group 5 in the Synergy Compact composite (p<0.05) and Group 1 <Group 2 <Group 3 <Groups 4, 6 <Group 5 in the Pyramid composite (p<0.05) Regarding the speed of polymerization, the order of PT was G1, G2, G3<G4, G5<G6 (p<0.05). The order of Rmax was G6<G1, G2, G3, G4, G5 in Sure Fil; G6<G1<G2, G3, G4<G5 in Synergy Compact (p<0.05) and G6<G1<G2, G3<G4, G5 in Pyramid (p<0.05) On the upper surface, there was no statistical difference in microhardness between Groups 1 and 2 in all materials. On the lower surface, the microhardness of Group 2 was significantly higher than Group 1 in all materials. In all materials in Group 1 and the Synergy Compact of Group 2, microhardness of the upper surface was significantly higher than the lower surface (p<0.05). In Sure Fil and Pyramid of Group 2, there was no difference in microhardness between the upper and lower surfaces.