Surface modification of CAD-CAM Machined Zirconia using the 60 ?s, 700 ?s Er.Cr: YSGG laser pulse duration
Background: CAD-CAM milled zirconia surface treatment, for improving the resin cement bonding, by using Er,Cr:YSGG laser. Materials and Methods: 112 sintered zirconia disc specimens (VITA YZ HT) were prepared. They are divided into 16 groups, each group of seven samples. Control group (L): un treated samples. Laser groups are depending on laser power, irradiation time, and pulse duration, include 15 groups: group (A): 20 s, 50 Hz, 60 µs. Group (B): 30 s, 50 Hz, 60 µs. Group (C): 40 s, 50 Hz, 60 µs. Group (D): 20 s, 50 Hz, 700 µs. And group (E): 30 s, 50 Hz, 700 µs, and fractional Er,Cr:YSGG laser groups: Group f/A: 20 s, 25 Hz, 60 µs. Group f/B: 30 s, 25 Hz, 60 µs. Group f/C: 40 s, 25 Hz. 60 µs. Group f/D: 30 s, 50 Hz. 60 µs. Group f/E: 40 s, 50 Hz. 60 µs. Group f/a: 20 s, 25 Hz, 700 µs. Group f/b: 30 s, 25 Hz, 700 µs. Group f/c: 40 s, 25 Hz, 700 µs. Group f/d: 30s, 50 Hz, 700 µs. Group f/e: 40s, 50 Hz, 700 µs. All laser group specimens were applied for the different powers (1, 1.50, 2, 2.50, 3, 3.50, 4) W. Luting cement was bonded to treated zirconia surfaces and light-cured for 40 s. All samples were examined for determining the means for each specimen pulse depths. Shear bond strength was measured using a universal testing machine. then an average surface roughness was examined by an atomic force microscope. The obtained shear bond strength and laser pulse depth values were statistically analyzed. The bond failure modes were also examined. Results: There was a clear increment in zirconia surface laser pulse depth for the created micro holes especially in group E (30 s, 700 µs, 3.5 W) specimen, measuring (8.2 µm), accompanied by an enhanced average surface roughness, reaching (14.5nm) for the same group specimen. While the untreated specimen had the least examined average surface roughness value (3.05nm). The fractional laser applied parameters specimens showed no evident microscopically effect. Conclusion: It was showed that the shear bond strength was related to the depth of laser pulse and to the average surface roughness. The Er,Cr:YSGG laser pulse duration for a specific number of pulse repetition per second, are both important parameters for enhancing zirconia ceramic surface.