الفهرس 
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Abstract
Titanium alloys are most often used in the design of dental implant. The aim of the this study was to assess the effect of erbium chromium-doped yattrium-scandium-gallium-garnet (Er,Cr:YSGG 2780nm) laser surface treatment on the corrosion behavior of titanium alloy (Ti-6Al-4V)at different pH and to assess biocompatibility. Surface characteristics were examined by SEM to understand the impact of the laser and pH on the titanium alloy surface. Materials and Methods: A total of sixty discs (samples) were used. group I: Forty samples were used to assess the corrosion behavior of titanium alloy samples in Hank’s solution at room temperature at varies time intervals Subdivided into four subgroups ten samples for each: * IA: Ten untreated samples immersed in pH 5.2* IB: Ten untreated samples immersed in pH 7.4. * IC: Ten laser treated samples immersed in pH 5.2. * ID: Ten laser treated samples immersed in pH 7.4. group II: Twenty samples were used to assess the biocompatibility of titanium alloy samples in direct contact with (HFB4) fibroblast for 48 hours using the MTT cell viability assay. Subdivided into two subgroups ten samples each: * IIA: Ten untreated samples in direct contact with (HFB4) fibroblast (+ve control). * IIB: Ten laser treated samples in direct contact with (HFB4) fibroblast. * Considering cells not exposed to any material as (-ve control). Thirty discs were used as control (IA, IB, and IIA). Thirty discs (IC, ID, IIB) were irradiated with (Er,Cr:YSGG ) laser that was operating in a normal room atmosphere and temperature at power 2W. The corrosion behavior was investigated in simulated oral fluid at pH 7.40 and 5.20 at various time intervals upto 864hours using potentiodynamic polarization test and electrochemical impedance spectroscopy. Biocompatibility was investigated in-vitro via MTT assay. The surface characteristics of group I samples were recorded before and after the electrochemical assessment. Result: In group I Laser treatment significantly improves the corrosion behavior. Immersion time and pH also significantly affect the corrosion behavior. In group I surface analysis by SEM for laser treated samples showed no undesirable changes compared to untreated samples before the electrochemical assessment. The acidity yielded more aggressive changes on untreated titanium alloy samples compared to laser treated samples after the electrochemical assessment. In group II Laser treated samples showed superior cell viability compared to untreated samples. The Pearson product moment correlations matrix and Multivariable Scatter plot between the biocompatibility and corrosion behavior showed that the biocompatibility was inversely correlated with corrosion rate and corrosion current with weak correlation coefficient (-0.976, -0.0982) respectively, while it was directly correlated with polarization resistance with medium correlation coefficient (0.217). Conclusion: from the result of the present study we can conclude that: * All the factors in the present study had a significant contribution on the corrosion behavior of titanium alloy with the highest change attributed to laser treatment, followed by immersion time, and finally pH. * The application of non- contact Er,Cr:YSGG laser irradiation could improve the corrosion resistance of Ti–6Al–4V in the acidic and neutral medium. * The application of non- contact Er,Cr:YSGG laser safely could improve the biocompatibility of dental implant.