Bond strength of a multilayer graded zirconia to a self-adhesive resin cement

The latest generation of zirconia used in dental applications features a graded microstructure combining tetragonal and cubic grains to balance translucency and mechanical strength. However, limited evidence exists regarding the adhesion of its individual layers, particularly when simplified protocols such as self-adhesive cementation are used. This study evaluated the interfacial bond strength between different layers of a multilayer zirconia (3Y-TZP, transition zone, and 5Y-PSZ) and a self-adhesive resin cement, with or without a universal primer, at baseline and after aging. Thirty slabs of multilayer zirconia (IPS e.max ZirCAD Prime) were air-abraded and bonded with resin composite cylinders (Multilink Speed) applied with or without a universal primer (Monobond N) (n = 15 per group). Half of the specimens were tested after 24 h and the others after six months of water storage. Micro-shear bond strength was measured, and failure modes were classified. Three-way ANOVA revealed that primer application and aging significantly affected bond strength (p < 0.001), while zirconia layer had no effect (p > 0.05). Primer use improved initial adhesion but did not provide long-term benefits, as bond strength decreased after aging in primed groups, whereas non-primed groups showed stable bonding performance despite compositional gradients in the ceramic substrate.