[Risks and benefits of polymeric inlays]

Class I inlays were produced according to the direct method using six white light-cured composite, one inlay material and one veneer acrylic. They were subjected to extraoral heat treatment at 125 degrees C for 150 s. In addition, heat-cured inlays were produced according to the indirect method. In all cases heat treatment resulted in a considerable increase in transverse strength and modulus of elasticity as well as a material specific decrease in the specimen volume between 0.15% and 1.05%, and it facilitated finishing. With one exception heat-treated and heat-cured inlays could be inserted without open margins; even 5000 threshold load cycles of 500 N failed to cause marginal defects. However, these inlays also had no open margins when inserted without previous heat treatment. While in the case of four materials this resulted in no measurable reduction in fatigue strength, it reduced this value to a maximum of 100 N in three materials. Swelling of the polymeric inlays due to high water absorption resulted in extensive enamel cracks with one of the materials tested.