Examination the effect of Er:YAG laser treatment on flexural biaxial strength of CAD/CAM materials of different thicknesses

Removing all-ceramic restorations cemented with adhesive cements is extremely difficult due to strong restoration-resin cement-tooth bonding. Laser transmitted into the ceramic is used for debonding. This study is conducted to examine the changes on the biaxial flexural strength and on the surface of the material during debonding with Er: YAG laser. 6 different CAD/CAM ceramic blocks were used in this study. Disk shaped specimens from these blocks were fabricated with a diameter of 12 mm and a thickness of 0,5 and 1 mm (40 specimens from each group). A total of 80 specimens were randomly divided into 2 subgroups: control group and laser group. Control group was left untreated. All surfaces in the laser group were scanned with Er: YAG laser having the parameters set in 500 mJ – 2 Hz and 1000 µs (Very Long Pulse = VLP). In compliance with the standards of ISO 6872, biaxial flexural strength test (piston on three balls) was conducted on all specimens. 3 specimens of 2x2 mm of each ceramic group (Control, 0,5mm laser, 1mm laser) were prepared for X-Ray Photoelectron Spectroscopy (XPS) analysis. Obtained data were analysed by using the two-way variance (ANOVA) and LSD tests. The highest value was observed in 1mm control group of monolithic zirconium oxide ceramics as 979.27 ± 95.41 MPa while the lowest value was found in 0,5mm laser group of leucite-reinforced glass ceramics as 112.89 ± 20.37 MPa. It was concluded that laser treatment alone did not statistically affect the flexural strength; and that the effect of specimen thickness, type of ceramics and interaction on the flexural strength was statistically significant. (α=0.05). It was observed that Er: YAG laser ceramics surface treatment did change the surface chemistry but did not have any negative impact on the flexural strengths.