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 0.05) 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