Thermal and Mechanical Characteristics of Dual Cure Self-etching, Self-adhesive Resin Based Cement

One of the main objectives in research and development of resin based cements (RBCs) is to enhance their clinical longevity and ease of use. In spite of the undeniable technological advances introduced in the last few decades, the polymerization shrinkage i.e. strain that accompanies the chain-growth polymerization of dimethacrylate monomers remains one of the major concerns for the clinical performance of composite restorations. Also, RBCs can produce a considerable amount of heat, due to the light energy from the curing lights and exothermic reaction of polymerization. The purpose of this study was to determine the temperature changes during the photo-polymerization using thermocouples and to measure strain field of the self-etching, self-adhesive RBC, Maxcem Elite (Kerr, Orange, CA, USA) (empty set5 x 1 mm - Group I and empty set5 x 2 mm - Group II) using experimental technique, 3D Digital Image Correlation (DIC) method. Digital images were recorded immediately after photo-polymerization of the samples with a LED-curing unit for 20 s, according to manufacturer's recommendation. Vickers microhardness was determined after photo-polymerization and after 24 h. Temperature curves for both groups indicated similar patterns but the peak temperature of Group II was significantly higher compared to peak temperature of Group I. DIC showed that peripheral zone of the samples had the highest strain values in both groups. Group I indicated significantly higher values of hardness. All the results were material-dependent and probably correlated to the composition of each material, which is not fully disclosed by the manufacturers