Evaluation of Polywave and Monowave Light Curing Units Efficiency on the Degree of Conversion and Microhardness of Resin Fissure Sealant

Objectives: The objective was to assess the polymerization efficiency of a polywave light-emitting-diode (LED) light-curing unit (LCU) by measuring the degree of conversion (DC) and Knoop microhardness (KHN) of a resin-based pit and fissure sealant at various light curing times and two distances compared to a monowave LED LCU.
Methods: Sixty disks of resin based pit and fissure sealant (Delton, DENTSPLY, York, PA) samples (6x1mm) were fabricated (n=5/LCU/group). Prepared samples were polymerized using 10, 20 and 40-second curing time at 2- or 4-mm curing distances. The irradiance and radiant exposure received on the top/bottom surfaces of the samples were measured using Managing Accurate Resin Curing-Resin Calibrator (MARC-RC) system. The samples were stored at 37°C for one hour. Then, the DC (n=3/surface) and KHN (n=5/surface) measurements were collected on the top and bottom surfaces using Attenuated Total Reflection-Fourier transform infrared spectroscopy (ATR-FTIR) and a microhardness tester (Instron) utilizing 25-gm at 10-seconds dwell time, respectively. Multiple-way ANOVA was performed followed by Tukey test (α=0.05).
Results: The irradiance from the polywave LED LCU was significantly higher than the Monowave LED LCU (1232.1 and 833.2 mW/cm²), respectively. Moreover, the polywave LED LCU displayed significantly higher DC (82.5%) and microhardness (26.2 KHN) compared to the monowave LED LCU (75.5% DC and 21.2 KHN) at specific locations; specially on the bottom surfaces, when curing samples at 2- and 4-mm curing distances assessed using 10, 20 and 40-second curing times. The 10 sec/4mm showed significantly lower DC and KHN values compared to the other groups.
Conclusions: The polywave LED LCU demonstrated significantly higher irradiance, DC and KHN at specific locations compared to the monowave LCU on a resin-based pit and fissure sealant at 2- and 4-mm curing distances and 10,20 and 40 second curing times. Therefore, the polywave LED LCU performed higher than the monowave LED LCU.