الفهرس 
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Abstract
One of the most important aims in aesthetic restorative dentistry is to produce restorations with optical qualities that are similar to natural teeth.
Translucent monolithic zirconia was employed to create multiunit anterior monolithic FDPs without increasing the danger of porcelain veneer fracture or reducing the core material’s cosmetic characteristics. This material was stated to offer good esthetic properties with load bearing capability in circumstances when the repair should resist increased stress.
Sandblasting, air abrasion, and Co2 laser surface treatment create microcracks on the zirconia surface, reducing bond strength and causing zirconia to phase transition. Because zirconia lacks a glassy phase, hydrofluoric acid etching is ineffective for surface treatment to boost bond strength.
Laser-controlled surface ablation, on the other hand, can create small microscales on the zirconia surface, roughening it and increasing micromechanical contact with the resin cement.
The wettability, translucency parameter, surface roughness, and shear bond strength of three kinds of translucent zirconia (translucent, high translucent, and ultra-translucent) were evaluated before and after Er:YAG laser surface treatment in this work.
A total of 120 CAD/CAM zirconia discs were divided into two equal groups n=60/gp based on surface treatment, according to the sample size calculation:
group A is the untreated (control) group.
group B is the laser-treated group.
Groups A and B were subsequently separated into three groups n=20/gp based on zirconia type into:
Translucent zirconia is in group I.
group II = High opacity zirconia
group III = zirconia ultra-translucent
Finally, the Wettability (CA), Translucency Parameter (TP), Surface Roughness (Ra), and Shear Bond Strength (SBS) tests were performed on each group.
Sirona software (version 19, USA) was used to create the zirconia specimens, which were then mixed into Zirconia discs (6mm diameter and 2mm thickness) using a Sirona milling machine. Discs were then sintered in a sintering furnace (inlab Profire for sintering Cercon) for 6 hours, with a 3°C/min gradual increase in temperature until reaching 1500 °C and holding this temperature for 2 hours, followed by a 5°C/min gradual decrease in temperature until complete cooling at 25°C.
Twenty prepared specimens of each zirconia type representing group (B) were exposed for 10 seconds to an Er:YAG laser (Fotona, Slovenia) with the following parameters: wavelength of 2940 nm, frequency of 10 Hz, energy of 200 mj, and power of 2W.
XRD and EDX were used to describe all zirconia disc specimens before and after laser treatment. After laser treatment, the XRD pattern of zirconia specimens revealed the emergence of a monoclinic phase.
For wettability testing, specimens were washed with dimethyl ketone, rinsed, and air dried before being sprayed with distilled water. A Goniometer was used to measure the developed angle. After laser surface treatment, all zirconia groups had a substantial reduction in contact angle (P-value 0.001).
In terms of the translucency parameter (TP) test, a spectrophotometer was used to calculate the color difference of the identical specimen against a white (W) and a black (B) backdrop. The average TP was computed, and the findings demonstrated a substantial decrease in TP following laser surface treatment in all zirconia groups (P-value0.001).
AFM was used to study surface roughness.For each specimen, the Control (untreated) specimens reflecting the baseline surface roughness (Ra) value were recorded. Following laser treatment, the identical surface of each specimen that had previously been tested for baseline surface roughness was reevaluated in the same manner as before. After laser treatment, the average surface roughness was determined, and the findings indicated a minor change in the average Ra in the Translucent zirconia group. However, following laser treatment, the mean Ra in the High Translucent Zirconia and Ultra Translucent Zirconia groups increased significantly (P-value0.001).
Control (untreated) had a non-uniform pattern with identifiable sharp projections dotted with pores, whereas after laser treatment had a rougher surface with higher and broader peaks and valleys than the untreated group.
For the shear bond strength (SBS) test, Zirconia specimens were inserted in a mold filled with auto-polymerizing acrylic resin (12mm in diameter and 3cm in height). Specimens were coated with an MDP primer before being packed in a Teflon mold 3mm in diameter and 4mm in height that was mounted on top of each zirconia disc using a specially manufactured SBS device and a steady pressure of 0.5 kg was applied for 1 minute over the eflon mold. All specimens were put on a Universal Testing Machine, and a beveled chisel of 1mm thickness attached to the testing machine’s upper moveable compartment was utilized to direct a parallel shearing force as near to the contact as feasible at a crosshead speed of 0.5 m/min.
The average SBS was computed, and the findings showed that the Ultra transparent group’s mean bond strength increased significantly following laser treatment (P-value0.001).
Conclusions:
Within the limitations of this study, the following conclusions could be drawn:
• Surface treatment with Er: YAG laser had a substantial impact on the wettability, translucency, surface roughness, and shear bond strength of ultra transparent zirconia.
• The Er:YAG Laser is a potential zirconia surface treatment.
• In addition to MDP primers, Er:YAG laser surface treatment plays an important role in enhancing the binding strength between zirconia discs and resin cement.
Recommendations
Based on the outcomes of this study, the following could be recommended for future research:
1. Additional study on Ultra-translucent zirconia, such as microleakage and flexural strength tests, should be conducted.
2. As a surface treatment for Translucent zirconia, several types of lasers with varied characteristics should be researched.
3. Additional in-vitro studies using transparent zirconia in thin and ultra-thin thicknesses.
4. In-vivo and clinical research examining the influence of laser surface treatment on several clinical transparent zirconia characteristics is necessary.