Introduction: Besides the halogen curing lights, already accepted as standard equipment, diode and plasma-arc units for polymerization of filling materials have also been commercially available in Bulgaria in recent years. The present study was prompted by the lack of detailed scientific information about these novel light curing devices.
Aim: 1. To evaluate the quality of polymerization achieved by different light curing units by measuring the quantity of residual monomer in the test specimens. 2. To classify the units according to their convenience features and polymerization abilities.
Materials and methods: Five diode units from three different manufacturers, one plasma-arc unit and one halogen unit were used. The test specimens, made from the hybrid photopolymerizing material Illumine (Ortho Plus, France), Type II, radiopaque, color C1, were 2 mm high and 4 mm in diameter. They were cured for 40 seconds with the respective unit after which they were ground and 25 mg from each sample were immersed in 8 ml of 95% ethanol for extraction of the residual monomer. The quantity of the residual monomer was determined by the method of the standard straight line. Statistical analysis was performed with the analysis of variance and F-test. The comparisons in each group were made by the Tukey-Kramer test, the level of significance for the null hypothesis being P = 0.05. The complex evaluation of the units was made with the help of a scale, developed by us.
Results: The material polymerized by the halogen light demonstrated the smallest quantities of residual monomer of all the specimens. There was no statistically significant difference between the quantities of the residual monomer in the specimens polymerized by the plasma arc unit (PAC), OL2 and Elipar Free Light exp. Such a difference, however, existed when comparing the PAC unit and the 3M ESPE unit, working in a continuous irradiation mode, the former having more residual monomer. Polymerization by Elipar Free Light produced the smallest quantities of residual monomer of all other diode lights. The only exception was the comparison between OL2 and Elipar Free Light exp., where there was no difference. The diode light of 3M ESPE performed best of all units according to the criteria we used for evaluation of the light curing devices.
Conclusions: 1. The intensity of radiation of the light source and the duration of polymerization are of crucial importance for the complete conversion of the monomer into polymer. 2. Diode technology has not yet been able to reach any halogen equipment with respect to quality of polymerization, despite some of its unquestionable advantages. 3. When choosing a light curing unit, the quality of polymerization is more important than the price and the offered additional features.