الفهرس 
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Abstract
This in vitro study was designed to evaluate and compare the time of debonding of different types of ceramic ultra-thin occlusal veneers (lithium disilicate, highly condensed lithium disilicate, and zirconia) of 0.5 mm thickness as well as their state after debonding.
Twenty-four sound upper molars were collected and stored in saline. They were divided into three groups according to the material used to fabricate the occlusal veneers (n=8): Lithium disilicate (IPS Emax CAD), Highly condensed lithium disilicate (GC Initial® LiSi Block), and translucent zirconia (KATANA Zirconia STML).
The Extracted teeth were embedded in acrylic blocks for fixation and the occlusal surfaces were then flattened to receive the occlusal veneers.
IPS Emax CAD, GC Initial® LiSi, and KATANA Zirconia STML were milled using 5 axis milling machine to produce occlusal veneers with 0.5 mm thicknesses. The thickness was then verified using a digital caliper.
The suitable surface treatments for each material were performed. For the lithium disilicate and LiSi samples, the intaglio surface was etched with 9% Hydrofluoric acid to roughen the surface and accordingly increase the surface area for bonding then it was thoroughly washed, dried, and Silane coupling agent was applied to it for one minute.
As for the zirconia samples, the fitting surface of samples was sandblasted with 50 microns sized alumina (Al2O3) particles with a pressure of 3.5 bar press for 15 seconds at a distance of 10 mm. Zirconia primer was then applied to the fitting surface and air-dried for 5 seconds.
Cementation of the ceramic samples was performed to the prepared occlusal surface of the extracted teeth using BreezeTM self-adhesive resin cement using a loading device to standardize the seating load and the cement thickness. Short initial light curing or ”tack curing” for 5 seconds was used for easier excess material removal, then curing continued for 20 seconds at Rapid Mode.
Er;Cr:YSGG laser was applied perpendicular to the occlusal veneer surface at a distance of 2mm. The laser energy was applied by the scanning method through the surface for 15 seconds with horizontal movements.
The debonding time was measured in seconds and the de-bonded samples were examined under Olympus SZ 40 stereo microscope.
Numerical data were presented as mean with 95% confidence intervals (CI), standard deviation (SD), minimum (min.) and maximum (max.) values. Normality and variance homogeneity assumptions were confirmed using Shapiro-Wilk’s and Levene’s tests respectively. Data were normally distributed and were analyzed using one-way ANOVA followed by Tukey’s post hoc test. The significance level was set at p<0.05 within all tests. Statistical analysis was performed with R statistical analysis software version 4.3.2 for Windows.
Results showed that regarding debonding time of the occlusal veneers no significant difference is present between the debonding time of the three used materials.
Regarding the state of the debonded veneers, both lithium disilicate and zirconia samples were sound after debonding. As for the LiSi group, 40% of the samples were sound after debonding, 20% showed cracks under the microscope, and 40% fractured during debonding.