Objectives: The initial dynamic kinetics of photopolymerization of three light-cured dental composite resins (APX, CharmFil, Solitaire2) were studied with the use of two techniques: laser triangulation method for measuring the polymerization shrinkage strain and Photocalorimetry (Photo-DSC). The objective was to compare the effectiveness of the two methods.
Methods: A novel experimental equipment based on a laser triangulation scheme was employed for monitoring linear polymerization shrinkage strain in dental restoratives. This method offers an important advantage, which is real-time monitoring without delay, over the conventional ones. The time at the maximum shrinkage rate (tmaxS) and maximum shrinkage rate (RmaxS) of the three materials were measured. The general reaction profile, maximum heat flow (RmaxH) and the time at the maximum heat flow (tmaxH) of the three materials were also obtained from the DSC curves.
The shrinkage rate and heat flow are related to the polymerization rate. Therefore, they can be utilized to evaluate the dynamic kinetics of photopolymerization of composite resins
Results: The two methods of measuring RmaxS and RmaxH, tmaxS and tmaxH, generated the same, statistically secured rankings for the three materials (Table 1).
Strong inverse relationships were observed between RmaxS and tmaxS, RmaxH and tmaxH.
Table 1. Comparison between the two methods
Composite | Photo-DSC(n=10) | Laser triangulation method(n=10) | ||
Maximum heat flow (mW) | Time at the maximum heat flow (s) | Maximum shrinkage rate(µm/s) | Time at the maximum shrinkage rate (s) | |
APX | 11.37(1.04) | 8.71(0.12) | 8.05(0.46) | 1.57(0.15) |
Solitaire2 | 16.85(1.28) | 7.59(0.22) | 8.80(0.51) | 1.41(0.16) |
CharmFil | 115.84(8.22) | 5.53(0.18) | 29.25(2.10) | 0.77(0.07) |
Conclusions: Laser triangulation method is suitable for measuring the dynamic polymerization shrinkage in real-time without delay. Therefore, it can be used to characterize the polymerization kinetics in a wide range of light-cured materials. It is possible to correlate the results of the two techniques.