An investigation of atomic force microscopy, surface topography and adhesion of luting cements to zirconia: effect of silica coating, zirconia primer and laser

This study evaluated the effect various surface conditioning methods on the surface topography and adhesion of luting cements to zirconia. Zirconia blocks (N = 25) were randomly assigned to five groups according to the surface conditioning methods: (a) No conditioning, control (CON), (b) tribochemical silica coating (TSC), (c) MDP-based zirconia primer (ZRP), (d) coating with nano aluminum nitride (ALN) (e) etching with Er: YAG laser (LAS). The conditioned zirconia blocks were further divided into five subgroups to receive the luting cements: (a) MDP-based resin cement (Panavia F2.0) (PAN), (b) 4-META-based cement (Super Bond) (SUB), (c) UDMA-based (GCem) (GCE), (d) bis-GMA based (Bifix QM) (BIF) and (e) polycarboxylate cement (Poly-F) (POL). Cements were applied in polyethylene moulds (diameter: 3 mm; height: 2 mm). The bonded specimens were first thermocycled for 5500 cycles (5–55 °C) and then adhesive interface was loaded under shear (0.5 mm/min). The data (MPa) were analyzed using 2-way ANOVA, Tukey’s and Bonneferroni tests (alpha = 0.05). Regardless of the cement type, TSC resulted in significantly higher bond strength (p ˂ 0.05) (13.3 ± 4.35–25.3 ± 6.3) compared to other conditioning methods (2.96 ± 1.5–5.4 ± 5.47). Regardless of the surface conditioning method, no significant difference was found between MDP, 4-META and UDMA based cements (p > 0.05) being significantly higher than those of bis-GMA and polycarboxylate cements (p ˂ 0.05). Failure types were frequently adhesive in all groups. Tribochemical silica coating provided superior bond results compared to other conditioning methods tested on zirconia especially in conjunction with UDMA- and 4-META-based resin cements.