Effect Of Different Physicochemical Surface Treatments On Bond Streagth Of Low-Fusing Porcelain To Commercially Pure Titanium

Objective:Fracture of porcelain between metal and porcelain is due to gold-internal stress or porcelain-porcelain interface stress concentration and cracking or produce porcelain layer recessive crack, which is a common cause of pure titanium failure of PFM restorations. So it is necessary to have a proper treatment of titanium surface before porcelain firing.The study aimed to find out the effects of different surface treatments on bond strength of low-fusing porcelain to commercially pure titanium (CP Ti).Materials and Methods:80 wrought CP Ti sheets were divided into 8 groups based on different surface treatments:Control group (C) was simply grinded; sandblasting (S) with 110 μm Al2O3; acid bath (H+) using 35% HNO3-5% HF; caustic bath (OH") using 50% NaOH-10% CuSO4·5H2O; sandblasting followed by acid bath (S+H+); sandblasting followed by caustic bath(S+OH-); acid bath followed by sandblasting (H++S) and caustic bath followed by sandblasting (OH-+S). Low-fusing porcelain was fused onto the titanium surfaces. Bond strength of the titanium-porcelain adhesion was measured by the three-point bending test. Microstructure of the bond interfaces, element distribution across interface and phase constitutions were determined by Scanning Electron Microscopy (SEM), Energy Dispersive Spectrometer (EDS) and X-Ray Diffraction (XRD), respectively. Data were analyzed using one-way ANOVA and Turkey’s test.Results:1. No significant differences of bond strength were found among group C, H+and OH- (P<0.05). Treatment with OH- alone or combination increases wettability.2. Significantly higher (P<0.01) bond strength values were found for the rest of the groups, and the OH-+S group showed the highest bond strength among all the groups (41.36±3.55MPa). Samples treated with the procedure of sandblasting commonly increases surface roughness and bond strength.3. The sequence of sandblasting and chemical treatment affects the bond strength(P<0.01); in samples treated with OH- the bond strength significantly increased initially. Compared to group S+OH" and OH-+S, proper surface roughness and wettability have a collaboration relationship to bond strength of Ti-porcelain.4. No significant linear correlation was found between the roughness and bond strength (P=0.128, R=+0.585). No significant correlation was found between wetting angles and bond strength (P=0.195, R=-0.511). While proper surface roughness and wettability have a collaboration relationship to bond strength of Ti-porcelain.5. Properly bonded interface without apparent cracks or narrow fissure was observed in group OH-+S. Oxide layer composed of Ti、Si and O was detected near the interface. Phase constitutions of the fracture surface were identified as oxides including TiO2、SiO2、TigO15etc.Conclusion:1. Acid or caustic bath treatment alone separately cannot improve the bond strength of CP Ti-porcelain.2. Combined treatment of caustic bath first, then sandblasting significantly improves the bond strength of CP Ti-porcelain.3. Proper surface roughness and wettability have a collaboration relationship to bond strength of Ti- porcelain.4. The main mechanism of Ti-porcelain bonding is mechanical interlocking and chemical wetting.