Work of adhesion between resin composite cements and PEEK as a function of etching duration with sulfuric acid and its correlation with bond strength values

Objective: This study investigated the impact of sulfuric acid etching duration of PEEK on work of adhesion (WA) with resin composite cements, and compared additionally measured surface parameters to shear bond strength (SBS) results. Methods: PEEK specimens were fabricated and divided according to different etching times using 98% sulfuric acid (N=448/n= 54): 0, 5, 15, 30, 60, 90,120 or 300 s, respectively. The resin composite cements RelyX ARC, Variolink II and Clearfil SA Cement (N= 54/n=18) were smoothed on a glass plate. The sessile drop method was applied in all contact-angle measurements; distilled water and diiodomethane served as testing liquids. Overall 1350 single contact angle measurements were performed. Thereafter, surface free energy (SFE), WA, interfacial tension (IFT) and spreading coefficient (SC) of all combinations between etched PEEK and resin composite cements were calculated. Data were statistically analysed using Kolmogorov-Smirnov, Shapiro-Wilk tests, descriptive statistics and two-/one-way ANOVA with post-hoc Scheffe test (p < 0.05). Using Pearson correlation the association between SFE values and SBS results of a previous study was investigated. Results: Variolink II showed the lowest WA, followed by RelyX ARC and Clearfil SA Cement, respectively. Etching specimens for 60 s showed the lowest WA values while etching times between 0 s and 30s, and 300 s showed higher results. WA values for groups etched for 90 s and 120 s showed no differences when compared to the 60s groups. SFE and disperse percentage showed a positive correlation with SBS. A negative correlation was observed between SBS and polar percentage for etched PEEK, WA, IFT and SC. Conclusions: The WA values do not allow statements about the bond between two materials to be made; other parameters must be taken into account. A waiver of conventional bond test methods is not possible. (C) 2014 Elsevier Ltd. All rights reserved.