Although universal adhesives have been widely used, the role of silane in their formulations, especially regarding its chemical stability and interaction with functional monomers like 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP), and how these factors affect zirconia bonding remains unclear.

The purpose of this in vitro study was to investigate the effect of universal adhesives (UAs) on the microshear bond strength (μSBS) and chemical interaction to zirconia immediately (IM) and after thermal aging (TC).

Zirconia polycrystals were sectioned into blocks (n=96), cut into segments, and sintered. The segments were randomly assigned to 7 experimental groups (n=10) according to the following independent variables: adhesive treatment, categorized by the presence of silane, as follows: silane-free adhesives: Ambar (AMB) and Adper Single Bond 2 (SB2); silane/MDP containing adhesives: Ambar Universal APS (AMU), Scotchbond Universal (SBU); Ambar Universal APS Plus (AMU+), and Scotchbond Universal Plus (SBU+); and time: immediate (24 hours) or after 10 000 TC. Alloy Primer, a 10-MDP containing zirconia primer, was used as the positive control group. Additionally, 26 zirconia slices were subjected to micro-Raman spectroscopy to assess the chemical interaction after bonding procedures. After surface treatment, cylindrical molds were filled with resin cement and polymerized. All specimens were tested for μSBS at a crosshead speed of 1.0 mm/minute. Data were analyzed using the Kruskal-Wallis and Mann-Whitney tests (α=.05).

At the immediate time, AMU, SBU, AMU+, and SBU+ exhibited μSBS values statistically comparable with those of Alloy Primer (P>.05), whereas AMB and SB2 showed significantly lower μSBS (P<.05). After TC, all groups demonstrated a significant decrease in μSBS (P<.001). Nevertheless, AMU, AMU+, SBU, and SBU+ preserved higher residual μSBS than the control group, while AMB and SB2 dropped to 0 MPa. Raman analysis confirmed chemical interaction between the adhesives (AMU, AMU+, SBU, and SBU+) and the zirconia surface.

The use of 10-MDP-containing universal adhesives was effective for zirconia bonding, enhancing the immediate performance and improving long-term durability. However, the inclusion of silane in these adhesives did not significantly influence the bond strength to zirconia.