Evaluation of interface characterization and adhesion of glass ceramics to commercially pure titanium and gold alloy after thermal- and mechanical-loading

ObjectivesThis study evaluated the effect of thermal- and mechanical-cycling on the shear bond strength of three low-fusing glassy matrix dental ceramics to commercial pure titanium (cpTi) when compared to conventional feldspathic ceramic fused to gold alloy.MethodsMetallic frameworks (diameter: 5 mm, thickness: 4 mm) (N = 96, n = 12 per group) were cast in cpTi and gold alloy, airborne particle abraded with 150 μm aluminum oxide. Low-fusing glassy matrix ceramics and a conventional feldspathic ceramic were fired onto the alloys (thickness: 4 mm). Four experimental groups were formed; Gr1 (control group): Vita Omega 900–Au–Pd alloy; Gr2: Triceram–cpTi; Gr3: Super Porcelain Ti-22–cpTi and G4: Vita Titankeramik–cpTi. While half of the specimens from each ceramic–metal combination were randomly tested without aging (water storage at 37 °C for 24 h only), the other half were first thermocycled (6000 cycles, between 5 and 55 °C, dwell time: 13 s) and then mechanically loaded (20,000 cycles under 50 N load, immersion in distilled water at 37 °C). The ceramic–alloy interfaces were loaded under shear in a universal test machine (crosshead speed: 0.5 mm/min) until failure occurred. Failure types were noted and the interfaces of the representative fractured specimens from each group were examined with stereomicroscope and scanning electron microscope (SEM). In an additional study (N = 16, n = 2 per group), energy dispersive X-ray spectroscopy (EDS) analysis was performed from ceramic–alloy interfaces. Data were analyzed using ANOVA and Tukey's test.ResultsBoth ceramic–metal combinations (p < 0.001) and aging conditions (p < 0.001) significantly affected the mean bond strength values. Thermal- and mechanical-cycling decreased the bond strength (MPa) results significantly for Gr3 (33.4 ± 4.2) and Gr4 (32.1 ± 4.8) when compared to the non-aged groups (42.9 ± 8.9, 42.4 ± 5.2, respectively). Gr1 was not affected significantly from aging conditions (61.3 ± 8.4 for control, 60.7 ± 13.7 after aging) (p > 0.05). Stereomicroscope images showed exclusively adhesive failure types at the opaque ceramic–cpTi interfacial zone with no presence of ceramic on the substrate surface but with a visible dark titanium oxide layer in Groups 2–4 except Gr1 where remnants of bonder ceramic was visible. EDS analysis from the interfacial zone for cpTi–ceramic groups showed predominantly 34.5–85.1% O₂ followed by 1.1–36.7% Al and 0–36.3% Si except for Super Porcelain Ti-22 where a small quantity of Ba (1.4–8.3%), S (0.7%) and Sn (35.3%) was found. In the Au–Pd alloy–ceramic interface, 56.4–69.9% O₂ followed by 15.6–26.2% Si, 3.9–10.9% K, 2.8–6% Na, 4.4–9.6% Al and 0–0.04% Mg was observed.SignificanceAfter thermal-cycling for 6000 times and mechanical-cycling for 20,000 times, Triceram–cpTi combination presented the least decrease among other ceramic–alloy combinations when compared to the mean bond strength results with Au–Pd alloy–Vita Omega 900 combination.