Einfluss der Adhäsivtechnik auf die marginale Adaptation siloranbasierter Komposite

Adhesive dentistry involving toothcolored resin-based composites as fundamental biomaterials have been considered as a vital part of dental occupation for many decades. For 20 years, these materials have also been successfully applied as stress-bearing restoration of posterior teeth. Since loss rates especially for posterior cavities are still considerable with secondary caries being a frequent failure mechanism, longlasting gap-free margins as well as permanent marginal integrity remain a demanding aim for contemporary resin composite restorations. Therefore it has been one of the thesis’ ambitions to evaluate the performance and efficiency of silorane-based composites and to provide a contrast to methacrylate-based systems. In addition, comparative investigations between etch-and-rinse adhesives and self-etch one-step adhesives have been conducted to give recommendations for the clinical situation. The present in vitro study included 64 human, caries- and filling-free molars, which received occlusal-distal Class II cavities carried out in a standardized manner. Teeth were randomly divided into eight experimental groups (n = 8). After the application of several one-step self-etch, two-step self-etch, three-step etch-and-rinse as well as four-step etch-and-rinse adhesives, cavities were restored using methacrylate- and silorane-based composites. Specimens were subjected to impression with an adder-cross-linked high-definition silicone, and epoxy replicas were manufactured. 10,000 thermocycles (+5 °C / +55 °C) were applied, followed by a second set of replicas. Using scanning electron microscopy, at 200x-, a semi-quantitative margin analysis was carried out and the percentages of perfect marginal adaptation were computed. The results confirm that etch-and-rinse adhesives are still superior to self-etch one-step adhesives with regard to enamel and dentin adhesion (p<0.05). Despite the development of the latest, more sophisticated products, bonding to dentin still remains the weak link in adhesive dentistry. After thermal loading, the marginal quality of both enamel and dentin dropped significantly (p<0.05). Hence two-step self-etch products accomplished a similar number of gap-free margins and resembling dentin bond strength in comparison with three-step and four-step etch-and-rinse systems. Furthermore silorane-based composites should only be applied in combination with the bonding system especially developed for them. “Pre-etching” by using 37 % phosphoric acid led to a better enamel but detrimental dentin bonding for this kind of composite. Silorane-based biomaterials do not only provide acceptable mechanical as well as physical qualities but also a very good esthetic performance which certainly make them appear as an alternative to conventional methacrylate-based composite systems. Yet they do not implement any change of previously known clinical algorithm regarding adhesive dentistry. Even with an optimal polymerization shrinkage of about 0.9 %, a permanently tight margin fit and the absence of secondary caries cannot be guaranteed. Moreover it is the dentist’s responsibility to know and consider the technique sensitivity and the challenges of every adhesive and composite system he applies and to adjust them to his clinical practice.