Post-opening storage temperature and its impact on zirconia bonding performance of a universal adhesive system

Universal adhesives have been widely combined with resin cements for bonding to zirconia. While the shelf life of unopened adhesive has been well documented, the post‑opening stability, specifically the interaction with ambient operatory temperature, remains unknown for zirconia bonding.

This in vitro study evaluated the influence of post‑opening storage conditions on the surface tension of a universal adhesive and its short‑term wettability on zirconia. Subsequently, the effects of these changes on the shear bond strength (SBS) to a universal resin cement were assessed.

A 1-bottle universal adhesive (Scotchbond Universal Plus) was stored for 0, 14, or 28 days at 25 or 35 °C before measurement of its surface tension. One hundred 3-mol% yttria‑stabilized tetragonal zirconia polycrystal specimens were treated with the universal adhesive under each storage condition and bonded with a dual‑polymerized universal resin cement (RelyX Universal). The contact angle was recorded to assess wettability, the SBS was measured, and the failure modes at the debonded interfaces were classified. Data were analyzed using 1-way analysis of variance, Pearson correlation, and linear regression (α=.05).

The surface tension (19.64 to 22.81 N/m) remained similar among storage conditions. In contrast, the contact angle increased with prolonged storage and higher temperatures, indicating reduced adhesive wettability. Accordingly, a decrease in SBS was also observed. The immediate‑use group showed the highest SBS (30.16 MPa), whereas specimens stored at 35 °C for 28 days exhibited the lowest SBS (18.81 MPa) and a higher proportion of adhesive failures at the zirconia-resin interface. The inverse relationship between contact angle and SBS suggests that reduced wettability compromises interfacial adhesion (r=-0.35, P=.013).

Immediate use of the universal adhesive after opening provided the greatest zirconia bond strength. Prolonged storage, particularly at elevated temperatures, reduced wettability and SBS.