الفهرس 
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Abstract
This study was carried out to investigate the effect of laser and laser combined with other surface treatment on the shear bond strength of orthodontic stainless steel bracket bonded to porcelain surface.
A sample of 60 feldspathis porcelain tabs, divided into four groups fifteen for each. The treatment groups were sandblast (SB) with hydrofluoric acid (HF), laser, laser with sandblast, hydrofluoric acid with laser.
Super pulse 2 Watt carbon dioxide (CO₂) laser for 60 seconds was used for porcelain etching. 9% hydrofluoric acid used for porcelain acid etching and 50µm aluminum oxide powder under 4.5 bar air pressure for 5 seconds at 5 mm distance were used for intraoral sandblasting.
After different methods of surface treatment, one specimen from each group was selected and scanned using Scanning Electron Microscope (SEM) to evaluate the effect of the different methods of treatment on the porcelain surface. Moreover, the effect of different methods of treatment was assessed by naked eye examination of the porcelain surface after different methods of treatment.
Edge wise lower incisor orthodontic brackets were bonded to treated porcelain tabs with chemical cured adhesive. The specimens were stored in distilled water for 24 hours and then thermo cycled in water baths between 5°C and 55°C for 500 times.
Shear bond strength was determined in megapascals (Mpa) at 1 mm/minute crosshead speed and recorded by universal testing machine. Bond failure modes were observed under stereomicroscope to score Adhesive Remnant Index (ARI), as well as to show fracture incidence for each specimen.
Collected data were statistically analyzed for descriptive statistics as well as significance of difference between different groups using 1-way ANOVA and Tukey΄s test. Furthermore, comparing coefficient of variations between different treatment procedures were performed.