Influence of deep margin elevation on marginal quality of root–filled molars restored with different onlays

Abstract Background This study evaluated the influence of deep margin elevation (DME) with composite resin when applied to deep margin defects in root–filled molars with mesiooccluso–distal (MOD) cavities, which were subsequently restored with computer-aided designed/computer-aided manufacturing (CAD/CAM) ceramic or composite onlays. Methods Forty–eight complete human third molars were removed and randomly distributed into 6 groups (n = 8). The MOD cavities were prepared with the distal gingival margin below the cementoenamel junction (CEJ) 2 mm and the mesial gingival margin above the CEJ 1 mm. All molars underwent endodontic treatment. The distal gingival margin was filled with 2 mm thick Filtek™ Z350 XT Flowable resin (FF) or Filtek™ Z350 XT Universal resin (FU) to the CEJ. Then, all molars were restored with onlays made by Vita MarkⅡ CAD (VC)/IPS e.max CAD (IC)/SHOFU ceramage (SC). Epoxy replicates were made before and after thermomechanical loading (5 ~ 55°C, 5000 cycles; 10 Hz at 360 N, 100000 cycles). Scanning electron microscopy (SEM) analysis was performed to analyze margin integrity. Statistical analysis was performed. Results All the interfaces exhibited a decrease in margin quality after thermomechanical loading(TML) ( P 0.05), and there were no significant differences among the FU/VC, FU/IC and FU/SC groups ( P > 0.05). After TML, FF/IC > FF/SC > FF/VC, and FU/IC > FU/SC > FU/VC, there was a significant differences among these groups ( P 0.05). At the resin‒dentin interface, before and after TML, the margin integrity of the dentin‒paste resin was greater than that of the dentin–flowable resin ( P < 0.05). Conclusions In this study, after TML, the best marginal integrity was obtained at resin–onlay interface with IPS e.max CAD material. However, DME with paste or flowable resin had no significant effect on the marginal integrity of the resin–onlay interface. At the dentin–resin interface, this study revealed that the marginal integrity of the flowable resin was lower than that of the paste resin, but both resulted in acceptable marginal quality for use as DME materials.