Zirconium oxynitrate etchant improves dentin bonding performance of single-component adhesives: 5-year in-vitro evaluation

To evaluate, using microtensile bond strength (μTBS) testing and in situ zymography, the effects of an experimental zirconium oxynitrate-based etchant [ZrO(NO₃)₂; ZON] on dentin bonding performance and endogenous matrix metalloproteinases (MMPs) activity of two simplified adhesive systems after 5 years of artificial aging.

Deep coronal dentin surfaces (n = 8) were conditioned with either 37% phosphoric acid (PA, 15 s) or ZON (30 s). A single-component etch-and-rinse adhesive (ExciteF, Ivoclar - EF) or a universal adhesive (Adhese Universal, Ivoclar - AU) was then applied, followed by composite build-ups. μTBS, scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS) analyses were performed at baseline (T0) and after 5-years of artificial aging in artificial saliva at 37°C (T5). Additional teeth (n = 5) were used for in situ zymography to assess MMPs activity at T0 and T5. Data were statistically analyzed (α=0.05).

Etchant, adhesive system, and aging significantly affected bond strength and enzymatic activity (p < 0.05). ZON/AU exhibited the highest μTBS at both T0 and T5. At T0, ZON/EF showed higher μTBS than PA/EF, whereas this difference was no longer significant after aging. AU showed higher μTBS than EF with ZON at both time points, while under PA this difference emerged only after aging (p < 0.05). Aging reduced μTBS in all groups (p < 0.05). SEM revealed predominantly mixed failure modes. EDS detected Ca²⁺ deposits only in ZON-treated groups. ZON significantly reduced MMP activity compared with PA at both evaluation times (p < 0.05).

The experimental etchant improved immediate and long-term dentin bond strength while reducing collagen-degrading enzymatic activity. These effects were more pronounced when combined with a universal adhesive, suggesting enhanced bond durability through preservation of the hybrid layer and potential chemical interactions.