We also investigated changes in surface hardness characteristics over time http://www.selleckchem.com/products/lapatinib.html for the different composite-LCU combinations. The first null hypothesis was only partially accepted. No significant effect of the LCU was demonstrated when hardness was evaluated at baseline or at 24 hours. Evaluation of the three-month values, however, revealed a significant effect of the LCU on microhardness, which resulted in partial rejection of the first null hypothesis. The second null hypothesis was rejected. A significant effect of the composite on microhardness was demonstrated at all testing periods, irrespective of the LCU. Significant interactions between the composite and LCU were also demonstrated both at baseline and after three months, indicating that the surface hardness of the composites was dependent on the type of LCU used for polymerization.
This was coincident with previous studies, which have demonstrated that the choice of composite affects the performance of LCUs.[2,13,23,24] However, a number of aspects play a role in the polymerization kinetics of composites, and thus, no definitive statements can be made as to the ability of the different composite-LCU combinations to polymerize. Effect of the light curing unit Evaluation of the hardness values immediately after polymerization and at 24 hours showed no significant differences between the specimens polymerized with LED and halogen, with only a few exceptions: Tetric EvoCeram and Premise at baseline and Filtek Supreme Plus at 24 hours demonstrated significantly higher hardness values when polymerized with halogen.
When the microhardness values were evaluated after three months, significantly higher values were seen for specimens polymerized with halogen, for all composites. The observed differences in hardness values at baseline and 24 hours revealed variations in the extent of polymerization, which might be the result of aspects relative to material composition and the amount of energy delivered during polymerization. Conversely, evaluation of the hardness values after three months incorporated the additional effect of aging conditions, such as water sorption and polymer swelling, which were expected to affect the specimens to various degrees depending on the extent of polymer network cross-linking achieved initially after photoactivation.
Less unreacted monomer, with the consequent greater hardness has previously been reported for composites polymerized with halogen compared to LED. However, the evidence in the subject remains inconclusive, with studies Cilengitide showing no difference in hardness values when polymerization was done with LED and conventional or high-intensity QTH, and studies showing greater extent of cure[27,28] and surface hardness for LED-polymerized composites. A number of aspects are known to affect the extent of polymerization of composite materials.