Effect of thickness of bonded composite resin on compressive strength

ObjectiveThe aim of this study was to investigate the compressive strength of composites with different physical properties bonded as a restoration to dentin in layers of varying thicknesses.MethodsFour types of direct composite materials: a midway-filled (Tetric EvoCeram); a compact-filled (Clearfil AP-X); a nano-filled (Filtek Supreme); and a micro-filled material (Heliomolar) were bonded in 0.5–3.0 mm thick layers onto bovine dentin. Each material group contained 25 samples, which were loaded until fracture.ResultsThe nano-filled and the compact filled material showed a significant association between layer thickness and compressive strength. The midway-filled composite was the most consistent material showing similar failure load over the complete thickness range.ConclusionA clear influence of layer thickness on compressive strength was found in some composite resin materials. When restorations are placed that are heavily loaded, such as in patients with severe wear due to bruxism it may be advisable to choose a material that is adequately strong in all thicknesses.