Revolutionary Method for Repairing Zirconia Surface Scratches

Objectives: After occlusal adjustment or function in the oral cavity, monolithic zirconia crowns often leave some scratches on the occlusal surface. A novel way to mend the scratches by brushing the solution of photopolymerization adhesive bonding agent and ZrO₂ nanopowders to the zirconia was to find the proper proportion of the solution that can reduce the surface roughness of the specimen and sustain the durable test.
Methods: 108 zirconia discs (φ12.0 mm × 4.0 mm) with the same surface treatment smeared with mixing ZrO₂ nanopowders (TZ-3Y-E, Tosoh Corp., Japan) and adhesive (3M ESPE Single Bond Universal Adhesive, 91125C) according to 2:8, 5:5 and 0:10 (denoted as 2Z8A, 5Z5A, and 0Z10A) weight ratios, then light cure for 40 sec. The solubility test was carried out by soaking the specimen in 100 ml of deionized water and recording the flake situation and mass loss of the coating layer (1 week, 2 weeks, 1 month, 3 months, and 6 months). Another 27 zirconia specimens (2:8, 5:5, and 0:10 weight ratios) were implemented the abrasion test, which was soaking the specimens in the deionized water and conducted by an automatic abrasion tester (PAT-2012, PROES, Taiwan) under 200 gw and 60 times/min till 48000 times. The shear bond strength (SBS) test was conducted using a universal testing machine at a crosshead speed of 0.5 mm/min. The morphology and thickness of specimens were observed by the optical microscope (OM, Olympus BX51, Japan), and the roughness was measured by the surface roughness tester (SJ-301, Mitutoyo, Japan). All data were statistically analyzed by SPSS software.
Results: For abrasion and solubility tests, the weight loss of all specimens increased with longer immersion duration, and sample 2Z8A has a statistically significant difference for anti-wear and less weight loss than 5Z5A and 0Z10A. Moreover, the roughness of sample 2Z8A after abrasion test (0.48 ± 0.09 μm) was close to that of standardized-polished zirconia (0.42 ± 0.09 μm). SBS test showed that 2Z8A has the highest strength (5.49 ± 1.64 MPa), but no statistically significant differences between sample 2Z8A and 0Z10A.
Conclusions: From the abrasion test and solubility test, 2Z8A can get better adhesion, and the application in the oral cavity can be further explored in the future.