Effect of shear bond strenght of glass ceramic treated different primers after termal cycling

The aim of this study was to evaluate the effects of different surface treatment protocols applied to various lithium silicate-based CAD/CAM ceramics, which are commonly used in digital dentistry, on shear bond strength after thermal aging. In this study, three types of lithium silicate-based CAD/CAM glass ceramics (IPS e.max CAD, CEREC Tessera, and GC Initial LiSi) were sectioned using a slowspeed diamond-wafering blade (Isomet 1000 Precision) to obtain specimens with a thickness of 1.5 mm. IPS e.max CAD specimens were crystallized using a sintering furnace (Programat P310) according to the manufacturer's instructions. All ceramic bonding surfaces were etched with 5–9% hydrofluoric acid (IPS Ceramic Etching Gel) as recommended by the manufacturer. Following surface conditioning, specimens were divided into three treatment subgroups: (1) application of a universal adhesive containing MDP and HEMA (Scotchbond Universal Plus Adhesive), (2) application of silane followed by a universal adhesive containing MDP and HEMA (Bisco Porcelain Primer + Scotchbond Universal Plus Adhesive) and (3) application of silane only (Bisco Porcelain Primer). Combining these three surface treatments with the three different ceramic types resulted in nine experimental groups (N = 11). After surface treatment, all specimens were bonded using a light-cured resin cement (Calibra Veneer Esthetic Resin Cement). Subsequently, the specimens were subjected to thermal aging with 5,000 thermal cycles (Nova, Konya, Türkiye). To ensure standardization, all specimens were stored in distilled water for 24 hours prior to testing. Shear bond strength values were measured using a universal testing machine (TSTM 02500) at a crosshead speed of 1 mm/min. Failure modes were analyzed using a stereomicroscope (SZ-PT Olympus) at ×15 magnification and surface topography after surface treatments was evaluated by SEM analysis (Zeiss, Evo LS10). Data were statistically analyzed using two-way ANOVA, post-hoc Tukey HSD, and Levene's tests (IBM SPSS v21), with a significance level set at p < 0.05. It was found that, in addition to the type of ceramic and surface treatment, the interaction between these two factors significantly affected the shear bond strength values (p < 0.001). The highest mean bond strength was observed in the CEREC Tessera group treated with silane + MDP- and HEMA-containing adhesive (57,99 MPa). In contrast, the lowest bond strength was recorded in the IPS e.max CAD group treated with the silane (24,05 MPa). The combination of silane and universal adhesive application in CEREC Tessera specimens showed statistically higher bond strength compared to other treatments (p < 0.01). However, in the same ceramic group, there was no significant difference between the silane-only and MDP-containing adhesive-only groups. No significant difference was observed among surface treatments within the IPS e.max CAD group (p = 0.933). In the GC Initial LiSi group, the silane-only subgroup showed the significantly higher mean bond strength than MDP-containing adhesive group.