Effects Light-curing Procedures on Chemical-physical Characterics of Two Composite Materials

Objectives: Nowadays, nanohybrid and nanofilled composites are considered universal resin-based restorative materials suitable for the restoration of anterior and posterior teeth due to their excellent aesthetic properties. Nevertheless, their polymerization reaction can be inhibited during light-curing procedures due to the presence of oxygen. This latter acts as scavenger, which tends to convert radicals into hydroperoxides compounds able to alter the quality of the polymerization of the outer layer of resin composites. Thus, the aim of this study was to evaluate the effect of light-curing procedures on two modern resin composite using different air-inhibition coating strategies. This was accomplished by assessing the amount of monomer elution, surface microhardness and composite discoloration in different storage conditions.
Methods: A total of 120 specimens were prepared using Filtek Supreme XTE (3M ESPE, Seefeld, Germany) and CeramX Universal (Dentsply DeTrey, Konstanz, Germany). Specimens were light-cured in air (Group D) as per manufacturer’s instructions or in absence of oxygen. This latter condition was achieved using three different approaches: A) transparent polyester strip; B), glycerin; C) Argon gas. Specimens were assessed for release of monomers, Vickers hardness and discoloration after storage in different solutions. The results were analyzed with ANOVA one-way test
Results: The amount of monomers released from the tested specimens was very low in all conditions. The presence of oxygen induced no decrease in microhardness. The highest discoloration values, for both materials, were obtained after ageing in red wine (tab1).
Conclusions: In case finish and polish procedures are awkward to achieve in posteriors composite restoration, the application of a light-curing protocol performed in absence of oxygen may improve the chemico-physical properties. The use of glycerin or argon gas may be suitable for light-curing procedures of occlusal surface in posterior teeth, as well as in all those zones of the composite restoration that cannot be covered by a Mylar matrix.