Randspaltvermeidungspotentiale unterschiedlicher Kompositrezepte in Klasse-II-Kavitäten

1.2.1 Aim of the study Aim of this in vitro study was to investigate marginal gap development of different resin composites (nanohybrid composite, low-shrinkage flowable special composite and two dual-curing resin composites) and to evaluate how these observations change when a bulk fill technique is applied. The resulting marginal gap widths should allow conclusions to be drawn about marginal gap avoidance potential of the different composites and moreover, the actual strength needed by the adhesive system. To exclude the influence of different adhesive systems and to allow for free shrinkage from bottom to top, cavities were only conditioned using the etch-and-rinse technique and not bonded. 1.2.2 Materials and methods Thirthy-six human third molars received mesial and distal standardized Class-II slot preparations with rounded boxes. The resulting 72 cavities were randomly assigned to nine groups (n=8). Cavities were etched with phosphoric acid but not bonded with any adhesive system. Depending on the experimental group, the different composites (Venus Diamond as control group, Venus Pearl, the experimental sample „low-shrink-flowable-special“, Rebilda DC and Visalys Core) were applied and cured in two different layer thicknesses (2mm-increments or bulk-fill with 4mm-layers). Subsequently, the placed fillings were polished and cleaned. After impression taking of the specimens an epoxy resin replica was made. These replicas were examined and evaluated under a scanning electron microscope (SEM) at 200x magnification to determine marginal gap width between dentin/cementum and restorative material. The data obtained were statistically evaluated using SPSS 17.0. 1.2.3 Results As provoked, all interfaces exhibited marginal gaps due to the lack of dentin adhesion. The increment thickness of the flowable composites (LSF, Rebilda DC and Visalys Core) had a significant influence on marginal gap widths (p<0,05). The 2mm increments performed better than the bulk-fill technique for all composites under investigation. Only with the nanohybrid composite Venus Pearl, the differences in marginal gap width were not significant (p<0.05) between the two layer thicknesses. A significant difference between the individual composites was also found. While Venus Pearl had the significantly smallest marginal gaps (p>0.05), the experimental sample, Visalys Core and Rebilda DC followed (p<0.05). 1.2.4 Conclusion The results of the study demonstrated, that the experimental material may be used in the same way as Venus Pearl and Diamond in the recommended increments of 2mm without negative influence on marginal quality. The marginal gaps are the result of non-established dentin adhesion, which is normally used in clinical applications. In order to compensate for the increased polymerization shrinkage of Rebilda and Visalys Core, particularly in the bulk fill technique, a sufficiently strong adhesive system is required. However, the polymerization is then more transferred to the surrounding tooth structure, which may cause crazing or fractures. For this reason, the dual-curing composites Visalys Core and Rebilda DC are indicated for core build-ups and the adhesive cementation of glass fiber posts in the root canal, since purely light-curing composites are disadvantageous in this area. Therefore, the indications of the different composites should be strictly checked and observed.