Operator Experience Does Not Affect the Reliability of Universal Adhesives' Bond Strength; Adhesive Type Does

To determine the influence of operators' experience, dentin moisture condition (DMC), and adhesive type on shear bond strength, and evaluate the consistency of adhesive performance under these conditions to demonstrate clinical reliability.

Six hundred sound dentin surfaces were randomly divided by five dentists with at least 10 years of experience (n = 300/5 dentists) and five first-year dental students without dental experience (n = 300/5 students). Each operator applied universal (UA) (Adhese Universal, Ivoclar) and etch-and-rinse (ERA) (OptiBond FL, Kerr) adhesives (n = 60/adhesive type) before and after receiving demonstration on the manufacturers' recommended application techniques by the principal investigator (PI), on wet, moist, and dry dentin surfaces (n = 5/DMC). DMCs were obtained by the PI before the operators applied the adhesives. The PI applied composite restorations (Tetric EvoCeram Bulk Fill, Ivoclar) and polymerized for 20 s. Shear bond strength (SBS) test was conducted after 24 h storage at 37°C, in 100% humidity. Boxplot, Log Worth, and Tukey HSD were used for statistics.

The median SBS of ERA obtained by dentists was 17.79 MPa with an interquartile range (IQR) of 19.61, while students showed a lower median of 13.52 MPa with IQR of 15.81. The UA showed consistency in SBS and reduced variability across operators with median SBS by dentists and students (25.53 MPa and 24.96 MPa, respectively), with narrower IQRs of 10.6 and 7.3, respectively. SBS of UA was significantly higher than ERA (P 0.001). UA obtained 7.38 MPa ± 0.89 greater SBS than ERA. While no difference in SBS by operator was observed for UA, dentists obtained 1.65 MPa ± 0.73 greater SBS than students with ERA. Dry and moist dentin surface conditions yielded higher SBS values compared to wet surfaces (P 0.001 and P 0.002, respectively), with no significant differences observed between moist and dry surfaces.

The tested UA provided reliable outcomes regardless of operator and DMC.