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Purpose: The aim of this in-vitro study will be directed to evaluating the effect of different hydrofluoric acid etching durations on the surface roughness of lithium silicate based glass ceramics obsidian and e-max, microstructure changes also color difference.Materials and methods: Eighty disc samples were grouped according to material type into two groups; obsidian group(n=40) and e-max group(n=40), each group was subdivided into four groups according the duration of hydrofluoric acid (HF) application into: Subgroup I (control) (n=10) without surface treatment. Subgroup II, (n=10) 20 seconds Subgroup III, (n=10): 40 seconds. Subgroup IV, (n=10): 60 seconds. All surface treated samples will be subjected to: Surface roughness examination, Surface topographic analysis using SEM and profilometer, and color differenceResults: the surface roughness test revealed that; the highest mean value was recorded in 60 second etch, followed by 40 sec etch then 20 second etch; with the least value recorded in control (no etch). ANOVA test revealed that the difference between etching subgroups was statistically significant (p<0.0001). Also higher mean value was recorded in E-max with statistically significant difference (p=0.014). Effect of etching time on color the highest mean value was recorded in 60 second etch, followed by 40 sec etch then 20 second etch,; with the least value recorded in control (no etch). ANOVA test revealed that the difference between etching time was statistically significant (p<0.0001).Also a higher mean value was recorded in E-max with statistically significant difference (p<0.0001),Conclusion E-max group showed higher means of surface roughness test and color difference rather than obsidian. Also 60 second etch showed the highest mean values of surface roughness test and color difference followed by 40 second etch followed by 40 second etch.

Effect of HF acid etching duration on surface roughness of newly introduced glass ceramic material