The influence of delayed light curing on the polymerization contraction stress and degree of conversion in dual-cured resin luting agents

Abstract

The purpose of this study was 1) To determine the impact of eliminating or delaying the photo-activation procedure on the polymerization contraction stress (PCS)and degree of conversion (DC) of a dual-cured resin luting agent, and 2) To determine the amount of delay in photo-initiation of the dual-cured resin cements that can achieve a reduced PCS value with the highest possible DC. The amount of PCS and DC of a dual-cured resin luting agent was determined using a tensometer and ATR spectroscopic technique, respectively. Photo-activation delay in seven tested groups was 0 min, 2 min, 4 min, 6 min, 8 min, 10 min and no photoactivation. Five samples for each group were tested. There were two hypotheses for this study: 1) A significant decrease in the amount of PCS associated with delayed photo-activation, and 2) A significant increase in DC associated with delayed photo-activation.The PCS of the chemical-cure luting agent had significantly lower value than all of the light-cure groups. For the light-cure groups, those with a 4-min delay had higher PCS than those with delays of 0 min, 2 min, 6 min, 8 min, and 10 min. The zero (0)-min and 2-min delay had higher PCS than the 6-min, 8-min, and 10-min delay; and the 6-min delay had higher PCS than the 8-min and 10-min delay. The PCS decreased 0.086 MPa per minute of delay. The DC of the chemical-cure luting agent had significantly lower value than the 2-min, 4-min, 6-min, 8-min, and 10-min delaylight cure. For the light-cure groups, 0-min delay had a lower DC than the 2-min, 4-min, 6-min, 8-min, and 10-min delay; 2-min delay had lower DC than 4-min, 6-min, 8-min, and 10-min delay. The 4-min and 6-min delay had lower DC than the 8-min and 10-min delay; and the 8-min delay had a lower degree of conversion by peak area than the 10- minute delay. The DC increased 0.021 per minute of delay. Extending the stress relief period of the dual-cured luting agents by delaying light activation has a significant impact on PCS and DC values. There was significant decrease in PCS with the delayed light curing of the resin luting agent. Significant increase in DC was noticed when light activation was delayed in the dual-cured resin luting agents.