The effect of thermal cycling on the surface roughness of nanohybrid and high-viscosity bulk-fill resin-based composites

: The aim of this study was to investigate the effect of thermal cycling on the surface geometry of high-viscosity bulk-fill resin-based composites (RBCs) compared to conventional nanohybrid composites. : Four conventional nanohybrid composites (Tetric EvoCeram – TEC, GrandioSO – GD, Filtek Z550 – FZ, and Ceram·X Mono – CX) and 4 high-viscosity bulk-fill composites (Tetric EvoCeram Bulk Fill – TBF, X-tra fil – XF, Filtek Bulk Fill Posterior – FBF, and QuixFil – QF) were tested. After the 2-step polishing procedure, the samples were divided into 2 groups: control group (K) and thermal cycling group (TC). Samples from the TC were subjected to thermal cycling according to ISO 11405 (THE-1100, SD Mechatronik GmbH). Surface geometry was evaluated by profilometry (Turbowave v. 7.36, Hommel-Etamic) and scanning electron microscope – SEM (VEGA 3, Tescan Analytics). : The applied thermal cycles increased the surface roughness of conventional RBCs: TEC (p = 0.000007), GD (p = 0.04), and CX (p = 0.0005). A reduction in the surface roughness of bulk-fill composites was observed in the case of materials: XF (p = 0.000003) and QF (p = 0.0002). Thermal cycling was shown to alter the surface roughness of the TEC, CX, XF, and QF materials. : The application of thermal cycling in a water environment in accordance with the ISO 11405 standard causes the degradation of the organic matrix and the exposure of filler molecules on the surface of both conventional and high-viscosity bulk-fill composites. Some of the tested RBCs, especially those containing modern hydrophobic monomers, are less susceptible to these processes.