Abstract

Objectives: An in vitro study of eleven polymeric adhesive systems, including etch-and-rinse (or conventional) and self-etch adhesive systems, was made to establish if clinical work conditions could improve their efficiency. It has been observed that self-etch adhesive systems have less thermal stability than conventional ones. As a consequence, early replacement of unsatisfactory aesthetic restorations is needed. To determine the thermal behavior of eleven polymeric adhesive systems under different rates of temperatures and a variety of conditions such as 100% humidity, presence of acidulated water (pH 3), environmental relative humidity and artificial saliva. Another aim was to establish if these factors are correlated with the adhesive systems composition. Methods: For each type of adhesive system, samples were prepared in small aluminum caps and polymerized with a LED lamp. All samples were analyzed with the Fourier-Transform Infrared Spectroscopy (FT-IR) method, which assigned absorption bands to organic functional groups of each compound corresponding to their chemical type. Subsequently, a thermogravimetric test was performed in a range temperature from room temperature to 500°C in order to establish the thermal behavior in an inert environment and after staying in acidulated water, 100% humidity, environmental humidity and artificial saliva. Thermograms were obtained to collect data about decomposition temperatures and loss of mass percentages. The FT-IR study results were correlated with the polymeric adhesive systems thermal behavior. Results: Thermogram images showed loss of mass, olymerization efficiency and residual mass amount. The different degradation dynamics were analyzed according to curve designs and baseline changes. Conclusions: Both groups of adhesive systems revealed high polymerization degrees. Nevertheless, the effect produced by the conditions in which they were subjected depends on the type of adhesive. Conventional adhesives, in contrast to self-etch adhesives, degraded in a minor extension as a result of their higher thermal stability.