Shear bond strengths of primer-free and primer-based composite-cements to glass-ceramics and zirconia

OBJECTIVES: The aim of the present study was to investigate the extent to which the bond strengths of composite-cements depend on (i) the adherend (zirconia versus glass-ceramics) and (ii) the usage of primers on the adherend prior to cementation. METHODS: 280 zirconia-specimens were sandblasted with aluminum oxide (110 μm/1 bar [AL 110/1] or 50 μm/0.5 bar [AL50/0.5]). 280 surface treated steel cylinders (Rocatec-Plus, Solventum at 3.5 bar; = 20 steel cylinders per cement) were bonded to the zirconia specimens with 3 primer-free (PanaviaSA, Kuraray [PSA]; Nexus-Universal, Kerr [NexU]; Maxcem-Elite, Kerr [MAX]) and 3 primer-based (require a primer) cements (RelyX-Universal, Solventum [RelyX]; PanaviaV5, Kuraray [PV5]; Calibra-Universal, Dentsply-Sirona [CalU]) each applied according to the manufacturers´ instructions. 140 lithium-disilicate glass-ceramic specimens (IPS e.max CAD Ivoclar [EMAX]) and 140 zirconia-reinforced lithium-silicate-glass-ceramic specimens (Vita Suprinity, Vita [VITA]) were bonded to surface-treated steel cylinders (see above, 20 steel cylinders per cement) using 2 primer-free (PanaviaSA, Kuraray [PSA]; Nexus-Universal, Kerr [NexU]) and 5 primer-based cements (RelyX-Universal, Solventum [RelyX]; Variolink-Esthetic-DC, Ivoclar [VarE]; Nexus3, Kerr [Nex3]; Panavia-V5, Kuraray [PV5]; Calibra-Universal, Dentsply-Sirona [CalU]) each according to the manufacturers´ instructions. RESULTS: All failures were between ceramic and cement. The bond strengths of composite-cements were highest on VITA followed by ZIR50, EMAX and ZIR110 [p < 0.001]. Composite cements that required a primer and primer-free composite cements showed no significant difference in bond strength with ZIR50, EMAX and ZIR100; only for VITA the difference was significant [p < 0.001]. PanaviaSA had the highest bond strength on VITA, followed by RelyX-Universal and Nexus-Universal. On ZIR50 RelyX-Universal had the highest bond strength followed by Calibra-Universal and PanaviaSA. On EMAX the rank order was Calibra-Universal>PanaviaSA>RelyX-Universal, whereas on ZIR110 the rank order was RelyX-Universal>Calibra-Universal >PanaviaSA. SIGNIFICANCE: The bond strengths of the investigated composite cements were significantly higher on the zirconia-reinforced-lithium-silicate glass-ceramic (VITA) than on the lithium-disilicate glass-ceramic (EMAX) and on zirconia. Primer-free composite cements showed similar or higher shear strengths than composite cements that required a primer (primer-based). The authors propose the implementation of more standardized experimental protocols when determining bond strengths, to enable the inter-study comparison of results in line with the suggestions offered by the Academy of Dental Materials.