Comparison between the dual-exponential and autocatalytic models to examine rapid photopolymerization kinetics of dental resins.

Objectives: 1) To investigate two empirical models used to characterize the polymerization kinetics of six resin-based composites (RBCs) and 2) the impact of the sampling rate on the time-varying degree of conversion (DC).

Methods: The DC of three sculptable and three flowable RBCs was recorded using attenuated total internal reflectance Fourier transform infrared spectroscopy at a collection rate of 13 DC/s. A multiple-diode light-curing unit delivered either an irradiance of 1.2 or 3 W/cm². The RBC specimens were either 0.2 mm or 4 mm thick and were photocured at 32 ºC. Sampling rates as low as 0.2 DC/s were simulated by numerically interpolating the measured DC(t). The DC(t) obtained at different sampling rates was fitted to the dual-exponential and autocatalytic models.

Results: For all six RBCs, the fit of the autocatalytic model to the data resulted in the smallest mean squared errors. The lower simulated sampling rates did not represent the highly time-resolved DC collected at an irradiance of 3 W/cm² and specimen thickness of 0.2 mm. For the DC simulated at a sampling rate of 0.2 DC/s using PowerFill and analyzed with the autocatalytic model, the maximum DC rate was 3.7 %/s, occurring at a time of 5 s after the start of photocuring. However, using a sampling rate of 13 DC/s, they were 64.5 %/s and 116 ms, respectively.

Significance: The autocatalytic model was found to better characterize the kinetics of RBC photopolymerization than the dual-exponential model. The data collection rate has a strong influence on the results.