Effect of Surface Treatments and Cyclic Fatigue on Mechanical Properties and Shear Bond Strength to Zirconia

Abstract

Objectives: This project evaluated the effect of blasting or lasing zirconia surface with fluorapatite glass-ceramic (FGC) powder, compared to tribochemical silica-coated alumina particles, on mechanical properties and shear bond strength of repair materials to zirconia. Methods: IPS e.max ZirCAD blocks were sectioned, sintered, polished and embedded in epoxy resin. 240 blocks and 160 zirconia bars were used in the study. The first part of this project employed three surface treatments to 120 zirconia blocks (n=40) (a- Sandblasting with lab-prepared FGC powder or b- CoJet sand while the as polished specimens served as c-control group. Each group received one of four (n=10) primer/adhesives (Monobond plus, Calibra silane, Scotchbond Universal, and Futurabond M+). Precured resin composite (Tetric EvoCeram Bulk Fill) cylinders were luted to zirconia specimens with Multilink Automix resin cement. The second part of the project employed four surface treatments to 120 zirconia blocks (n=30). Besides the previous three surface treatments, one group of zirconia blocks was coated with FGC powder followed by Nd: YAG laser irradiation (FGC+Nd: YAG). Surface roughness, topography, silica content, and crystallinity were evaluated by surface roughness profilometer, scanning electron microscope, EDS and XRD analyses, respectively. Cylinders of feldspathic and lithiumdisilicate porcelain were bonded to treated zirconia specimens by Monobond Plus/ Multilink Automix resin cement (n= 10 each), while direct resin composite (Tetric EvoCeram Bulk Fill) was bonded to zirconia specimens by Monobond Plus/Adhese Universal (n=10). Bonded specimens in part 1 and 2 were thermocycled for 10,000 cycles, dry stored for 24 hrs then tested for shear bond strength (SBS) at speed of 0.5 mm/min till failure. Results were statistically analysed by one-way or two-way ANOVA. The third part of the study tested the effect of the previous four surface treatments on the flexural strength and fracture toughness of 160 zirconia bars (n=40). Half of the bars (n=20/group) were tested for initial flexural strength, while the rest of the bars underwent cyclic fatigue for 1,000,000 cycles before tested for residual flexural strength. Fracture toughness was calculated and fractographic analysis was done to the fractured segments under SEM. Statistical analysis was done using 1-way or 2-way ANOVA and Weibull modulus was compared among all groups. Results: Monobond Plus/Multilink automix showed the highest mean SBS values among all groups in the first part of the study. FGC groups reported the highest mean SBS in part 1 and 2 of the study followed by FGC+Nd: YAG and CoJet groups. Mixed adhesive/cohesive failure was a general finding in all groups except for the control group; a predominant adhesive failure was found. Highest surface roughness and monoclinic phase amount were found in the FGC+Nd: YAG group followed by FGC and CoJet groups, while the control group showed the lowest values. FGC+Nd: YAG approach was the most damaging to zirconia mechanical properties in the third part of study followed by CoJet, while FGC and control groups reported the highest flexural strength and fracture toughness values. Cyclic fatigue significantly reduced the flexural strength of all treated zirconia bars except for the FGC+Nd: YAG group. Conclusion: Sandblasting zirconia with FGC powder could be an effective mechanical surface treatment for zirconia repair.

Date of Award	1 Aug 2021
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Nick Silikas (Supervisor) & Xiaohui Chen (Supervisor)