الفهرس 
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Abstract
This study was conducted to evaluate the effect of sandblasting, silica-coating and cold plasma surface treatments on the biaxial flexural strength, translucency, surface topography, as well as resin-zirconia bond strength and bond durability after hydrothermal aging. Also, the effect of these surface treatments on phase transformation and surface roughness was evaluated.
5Y-YSZ Katana UTML zirconia blank was used to obtain cylinders using a CAD/CAM machine. Disc-shaped specimens were then cut from these cylinders using a low speed saw. Specimens were then polished with SiC abrasive papers, ultra-sonically cleaned and sintered following the manufacturer’s instructions. A total of 317 specimens were used in this study and randomly divided into four experimental groups according to the surface treatment performed; group 1: sandblasting using alumina particles (n=83), group 2: tribochemical silica-coating using the Cojet system (n=83), group 3: cold plasma surface treatment using tabletop plasma generator (n=83), and group 4: untreated specimens as control (n=68).
Each surface treatment group was further subdivided into 6 subgroups according to the in vitro test used (except for the control group that was divided into 5 subgroups only where no translucency testing was performed). The relative translucency parameter (∆TP00) was evaluated with a spectrophotometer (n=15), phase transformation was evaluated using X-ray diffractometer (n=5), surface topography was assessed with a scanning electron microscope (SEM) (n=3), biaxial flexural strength (BFS) was tested using a universal testing machine (n=15) and the surface roughness for specimens of different surface treatments was assessed by image analysis of stereomicroscopic images (n=5). For microshear bond strength (μSBS) testing, 40 resin composite specimens (build-ups) were attached to 6 disks and tested with a universal testing machine; 20 specimens were tested after 24 hours, and 20 specimens after hydrothermal aging in a thermocycler.
The results of translucency testing showed significant difference among all groups; plasma surface treatment group had the lowest change in TP00 followed by silica-coating group, while sandblasting group showed the highest change in translucency parameter after surface treatment. XRD results revealed that plasma surface treatment resulted in significantly higher monoclinic volume fraction compared to all other groups.
Biaxial flexure strength test results showed that plasma surface treatment group had significantly higher value than other groups followed by the control group and silica-coating group with insignificant difference between them however, sandblasting group showed the lowest value.
SEM images of the control and plasma groups showed flat surfaces with shallow grooves and rounded elevations, while sandblasting group revealed irregular rough surface showing scratches and surface defects. The silica-coating group showed surface topography similar to sandblasting but with shallower and fewer defects. High magnifications of silica-coating group showed non-uniform silica coat across the surface.
The results of surface roughness testing showed that the highest value was shown by sandblasting group followed by silica-coating and then plasma treatment and control groups with insignificant difference between the two groups. Microshear bond strength results after 24 hours showed significant differences among all groups; sandblasting group showed the highest value followed by silica-coating then, plasma treatment group while, the control group showed the lowest value. After thermocycling, all groups showed significant decrease in their bond strength except for the sandblasting group.
Conclusions
Within the limitations of this in-vitro study, the following could be concluded:
1- Sandblasting is an effective method in improving bond strength and durability to ultra-translucent zirconia. However, it adversely affects strength and translucency.
2- Despite the lower bonding potential of tribochemical silica-coating compared to sandblasting, it has less deleterious effect on strength and translucency.
3- Non-thermal plasma treatment has a limited effect on improving bond strength to ultra-translucent zirconia compared to sandblasting and silica-coating, yet it improved its strength with minimal changes in translucency.