Randqualität unterschiedlicher Füllungsmaterialien bei Klasse-II-Kavitäten in vitro

Objectives: The aim of this in vitro study was to investigate the marginal quality of different restorative materials (composite, bulk-fill and glass ionomer cement) in enamel and dentin in Class II cavities after thermomechanical loading under the scanning electron microscope. In addition, the influence of the increment layer thickness as well as the combination of a bulk-fill composite with a universal composite on the bond strength was investigated. From the results, conclusions will be drawn as to which of the investigated groups exhibit the lowest marginal gaps. Material and methods: Under standardized conditions, 48 human and caries-free extracted molars were divided into 6 groups (n=8). A Class II cavity was placed in all specimens. All cavities were pretreated according to the manufacturer's instructions and included enamel and dentin etching using 36% phosphoric acid and the Syntac® Classic adhesive system. Subsequently, the specimens were filled with the various restorative materials according to the group classification. The grouping was as follows: Venus® Diamond 1 mm horizontal layering (Group 1), Venus® Diamond 2 mm horizontal layering (Group 2), SDR™ 4 mm horizontal layering with Venus® Diamond as the top layer (Group 3), CLEARFIL MAJESTY™ ES Flow High in one layer (Group 4), Ketac™ Fil Plus in one layer (Group 5) and Photac™ Fil Quick in one layer (Group 6). To simulate in vivo conditions, all specimens were subjected to artificial aging using thermomechanical loading. Thermal cycling (5°C/55°C) was performed in a thermocycler at 2500 cycles and mechanical loading in a masticatory simulator (50 N/0.5 Hz) at 100,000 cycles. A scanning electron microscopic examination was performed both before and after thermomechanical loading in order to evaluate the sample teeth with respect to the marginal gaps. Detailed images were taken at 200x magnification to check the marginal quality. Results: The results before thermomechanical loading show an adhesion quality in enamel for groups 1-4 of 100 %, and in dentin for groups 1-5 of 100 % and thus no marginal gap. A statistically significant worse adhesion in enamel is shown by the glass ionomer cements in group 5 (92.3 %, p<0.05) and group 6 (85.2 %, p<0.05). The significantly poorest adhesion in dentin before thermomechanical loading is shown by group 6 (95.0 %, p<0.05). After thermomechanical loading, all groups showed a reduction in the bond quality in both enamel and dentin. In terms of enamel bond strength, group 1 (89.3 %), group 2 (90.3 %) and group 3 (91.2 %) achieved the best results (all p>0.05). Group 4 (85.3 %, p<0.05), Group 5 (78.3 %, p<0.05) and Group 6 (73.4 %, p<0.05) performed significantly worse. Group 3 (62.1 %) and Group 1 (59.3 %, p>0.05) showed the best dentin adhesion. Group 2 (57.2 %), group 5 (56.0 %) and group 6 (54.9 %) showed significantly worse marginal gap behavior compared to group 3 (all p<0.05), but did not differ significantly from group 1 (all p>0.05). The filling material used in group 4 (49.3 %, p<0.05) showed the significantly highest loss of adhesion in the dentin. Conclusion: The combination of the bulk-fill composite SDR in 4 mm layering and the nanohybrid composite Venus Diamond as a top layer, as well as the sole use of Venus Diamond in a 1 mm layering, showed the best results and the lowest marginal gaps in Class II cavities. In addition, it could be shown that with increasing increment layer thickness, a negative influence on the bonding quality of composites is taken. The use of CLEARFIL MAJESTY ES Flow High in the bulk-fill method showed the highest loss of bonding quality in dentin and failed even in comparison to the glass ionomer cements. Class II cavities should therefore always be filled with composites according to the manufacturer's instructions, in small increments and taking the C-factor into account. If this recommendation is observed, composite restoratives show a lower incidence of marginal gaps in Class II cavities than glass ionomer cements.