الفهرس 
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Abstract
This study was designed to show the proficiency of using Er,Cr:YSGG laser in debonding of laminate veneers of two types of glass ceramics (IPS EMAX and VITA MARK II), which were cemented using resin cements with different curing modes and its effect on the shear bond strength of rebonded ceramic discs.
Materials and methods: specimens were divided into two groups according to the glass ceramic material and then were further divided into two subgroups according to the cement-curing mode (light and dual cured resin) then finally each subgroup was finally subdivided into two subdivisions according to applied tests. The specimens were cut with dimension 10×10 mm and thickness 0.7 mm each using electric saw Isomet 4000 then were cemented on bovine teeth after surface preparation of both tooth and ceramic discs following manufacture instructions for bonding protocol, standardization of the tooth preparation was done by customized paralleling device, each bovine tooth was fixed in acrylic resin blocks which were color coded ; Pink acrylic for IPS Emax cemented by light cured resin cement and translucent for IPS Emax cemented by dual cured resin cement and green for VITA MARK II cemented by light cured resin cement and A2 shaded acrylic for VITA MARK II cemented by dual cured resin cement, After the cementation procedure, the specimens were stored in distilled water at 37 °C for 24 h to mimic intraoral situation. Then Laser beam was applied of wavelength 2780 nm using the following settings for each group: Power 4.5 W, repetition rate 20 Hz, Hand piece turbo (MX7), pulse duration (60µs) H mode Non-Contact mode 5 mm away, which has been established by a custom made stopper. Then, the specimens were evaluated with SEM 10,000x and 20,000x after being debonded and the mode of failure as well with SEM 500x.
The EDX spectrometer incorporated into a scanning electron microscope was used to identify compositional nanoparticles, Measurement of Surface roughness in this study was achieved by the contact Profilometer after the ceramic discs being lased then the ceramic discs were rebonded to start the shear test with crosshead speed of 1 mm/min.
Results showed that no damage or signs of ablation or ablation craters on the ceramic discs were detected proofed by SEM also the failure mode detected were adhesive failure along the “ceramic/resin” interface regardless the mode of curing of resin cement, where most of the resin remained on the tooth surface. The EDAX analysis showed that differences in the chemical composition compared with baseline groups and even variations were reported by changing the cement-curing mode. The shear bond strength of IPS Emax cemented using light curing resin showed no change from the control group, while group re-cemented using dual cured resin showed higher mean shear bond strength than control, VITA MARK II ceramic discs rebonded using light cured resin showed lower mean shear bond strength than control, Regarding VITA MARK II recemented using dual cured resin showed higher mean shear bond strength than control.
CONCLUSION
Within the limitation of this study the following conclusions may be drawn:
- Er,Cr:YSGG hydrokinetic laser system used for debonding a resin-bonded all-ceramic restoration is an effective clinical application. It can be said that the application of a laser for debonding ceramic restorations could serve as a practical and effective debonding method that eliminates the risk of restoration fractures.
- The laser irradiation had no effect on either IPS E.max or Vita MARK II; however, the most dramatic SBS decrease was observed for laser-treated Vita MARK II rebonded with light cured resin cement. The majority of failures in all groups were adhesive failures that occurred between the luting resin cement and the tooth surface.
- The presence of cement remnants after debonding demonstrated the thermal and ablative effects induced by irradiations only in the cement layer, implying that the protocols used may be suitable for future clinical application.
- The curing mode of resin cement have no effect on debonding efficiency of transmitted laser of wavelengths in the Erbium Family of Dental Lasers (using turbo hand piece).
RECOMMENDATIONS
Further studies are necessary to evaluate the bond strength changes after repeating the laser debonding and rebonding procedure more than once, and laser effect on different ceramics composition using different laser parameters.