The influence of luting systems on the microtensile bond strength of dentin to indirect resin-based composite and ceramic restorations

Microtensile bond strength (microTBS) evaluation and fractographic analysis were used to compare four luting systems in the cementation of resin-based composite (RBC) and ceramic disks to dentin. Forty freshly-extracted molars were transversally sectioned to expose flat, deep dentin surfaces. Forty cylindrical specimens (5-mm diameter and 10-mm height), consisting of 20 RBC disks and 20 leucite-based glass ceramic disks, were produced. The RBC disks were sandblasted with 50-microm Al2O3. The ceramic disks were conditioned with 9.5% hydrofluoric acid gel and silane application. All the disks were then bonded to dentin surfaces according to the luting cements to be used: two etch-and-rinse luting agents (XP bond/CoreXFlow; Dentsply [XP]) (Enabond/EnaCem HF; Micerium [ENA]), a self-etch luting system (ED Primer II A+B/Panavia F2.0; Kuraray-Dental [PAN]) and a self-adhesive luting agent (RelyX Unicem; 3M ESPE [UNI]). The adhesive/luting cement systems were applied according to the manufacturers' instructions. The specimens were sectioned perpendicular to the adhesive interface to produce multiple beams, approximately 1 mm2 in area. All the specimen preparations were performed by the same operator. The beams were tested under tension at a crosshead speed of 0.5 mm/minute until failure. The microTBS data were analyzed by two different one-way-ANOVA and multiple comparison Tukey tests (alpha = 0.05). All the fractured beams were observed using a Scanning Electron Microscope (SEM) at 200x magnification for fracture mode determination. The mean bond strength in MPa (SD) for the RBC (Co) and ceramic (Ce) groups were: XP-Co = 31.39 (13.51), ENA-Co = 30.93 (10.17), PAN-Co = 18.29 (10.02), UNI-Co = 19.33 (7.91); XP-Ce = 4.83 (1.86), ENA-Ce = 5.15 (1.66), PAN-Ce = 4.36 (1.80), UNI-Ce = 7.16 (2.52). Statistical analysis showed that the bond strengths were significantly affected by the luting agent employed for both the RBC and ceramic groups (p<0.001). In particular, the XP-Co group and the ENA-Co group did not differ from each other (p > 0.05) and showed significantly higher bond strengths than the PAN-Co and UNI-Co groups (p < 0.05). On the contrary, the UNI-Ce group showed the highest bond strengths compared to the other ceramic experimental groups (p < 0.05). Regarding failure mode, differences were found between the RBC groups: for the etch-and-rinse luting systems (XP-Co and ENA-Co groups), most failures occurred cohesively in the luting agent, while the self-etch luting system (PAN-Co group) and self-adhesive luting system (UNI-Co group) failed predominantly adhesively at the luting agent-dentin interface. Little differences were found between the ceramic groups, where failure type was primarily adhesive between cement and ceramic.