PICN Versus Dispersed Filler Materials Interfacial K_IC With Resin Cement

Objectives: The objective of this study was to evaluate adhesive interfacial fracture toughness (a-IFT) of resin cement with materials representatives of the two classes of CAD-CAM composites, Dispersed filler (DF) and Polymer Infiltrated Ceramic Network (PICN), after different surface treatments. The null hypotheses were that the material class and surface texture after treatment do not influence a-IFT.
Methods: Two DF, Cerasmart (CRT) and Lava Ultimate (LVA), two PICNs, Enamic (ENA) and experimental PICN (EXP), and e.Max CAD lithium disilicate glass-ceramic (EMX, control) were used to produce half prisms, which were bonded to their counterparts with Variolink DC resin cement either after hydrofluoric acid etching (HF) or sandblasting (SB) followed by silanization. All samples (n=30 per group) were thermocycled (10,000 cycles) and tested using the Notchless Triangular Prism (NTP) test in a water bath at 36°C. Moreover, etched and sandblasted rectangular samples of each material were examined for developed interfacial area ratio (Sdr) measurement by profilometry and SEM characterization.
Results: EXP-HF gave the highest a-IFT (1.85±0.39 MPa.m^1/2), followed by EMX-HF and ENA-HF, while CRT-HF gave the lowest (0.43±0.11 MPa.m^1/2). PICNs gave better results with HF, and DF with SB. Two-way ANOVA revealed significantly higher a-IFT and Sdr for PICNs than for DF. Weibull modulus of PICN a-IFT were higher than those of DF. A positive correlation (r²=0:901) was found between a-IFT and Sdr. SEM analysis highlighted the specific micro- and nanostructure of the surface of etched PICNs, with the presence of a retentive polymer-based honeycomb structure.
Conclusions: The null hypotheses were rejected. Etching of the typical double network microstructure of PICNs creates an original polymer-based surface characterized by an important increase of Sdr and a-IFT, while DF should be sandblasted and exhibited significantly lower Sdr and a-IFT. Results highlighted the importance of material class, microstructure and surface texture on bonding performance.