Objectives: To determine the correlation between changes in light transmission through a commercial resin composite with changes in monomer conversion at the bottom surface in real-time.
Methods: Brass rings (2 mm high, 6 mm dia) were filled with a commercial resin composite paste (A3, Premise, Kerr), and used in one of two experimental methods. For light transmission change, the resin-filled rings were placed into the recessed detector well of a hand- held dental curing radiometer (Model 100, Demetron) The voltage drop across an internal, fixed resistor was digitized and recorded in real-time at 10 points-per-second. Millivoltage values were recorded and changes were compared to baseline values. The distal end of a light curing unit (LCU) (quartz-tungsten-halogen (Optilux 501); blue LED (LEDemetron 1); high intensity blue LED (DEMI)) was held 2 mm above the ring surface, and the disc was continuously exposed for 90 seconds. Other discs were placed over the diamond crystal of a horizontal total attenuated reflectance attachment in an infrared (IR) spectrometer. The same lights were held at 2-mm distance, and IR spectra were recorded at a rate of 1Hz at 2 cm-1 resolution. Changes in C=C absorbance peak heights were used to determine monomer conversion from processed spectra using standard methods. Five replications were performed for each test combination. Time-based plots were made for each parameter. Lin's coefficient of concordance (rL) measured the agreement between conversion and light-adjusted values at a 95% confidence level.
Results: A nearly perfect correlation existed between time-based changes in conversion and light transmission during the first 20 seconds of exposure: OP 501 rL0.994; LEDemetron rL0.996; DEMI rL0.998.
Conclusions: Real-time analysis of light transmission through polymerizing composite may be able to be used as an alternative for determining the curing kinetics of resin composite.