Efficiency of LED Polymerization of a Resin-modified Glass-ionomer Cement

The efficiency of polymerizing units equipped with light-emitting diodes (LED) and of mechanical tests to predict the degree of monomer conversion are the subject of many controversies. The monomer conversion of resin-modified glass ionomer cement (RMGIC) should be as high as possible to avoid side effects caused by HEMA Aim: The purpose of this study was to evaluate the curing efficiency through the degree of conversion (DC) and Knoop microhardness of RMGIC (Vitremer/3M ESPE) with two types of polymerization (halogen light, as control, or LED) in function of storage period. Material and methods: Forty-eight specimens were divided into Groups I and II (n=24) in which polymerization was carried out with halogen light or LED, respectively. In Control Group (n=3) no polymerization was done. In each Group, three speciments were tested at the experimental times of 6 hours, 1, 2, 3, 5, 7, 11 and 14 days and stored in dark conditions, at 37oC. All specimens were analyzed by FT-IR spectroscopy to measure the DC. Three specimens of each Group were tested for microhardness measurements, equipped with a Knoop indenter, 50g load for 30 seconds. Results: Two-way ANOVA and Tukey's (p<0.05) showed highest values of DC (97.63±0.66) and Knoop microhardness (81.63±2.3) with LED light-cured material. DC values increased with storage time while the Knoop microhardness achieved its highest values between 24-48 hours. Conclusion: RMGIC polymerized by LED achieved better values of DC. The Knoop microhardness test could not predict the DC.