Femtosecond laser irradiation was found to be more effective than sandblasting or acid etching in increasing the surface roughness, and it was also the most effective surface treatment with silanization on the SBS of a resin cement to the ceramic-resin composites.
Yttrium-stabilized tetragonal zirconia polycrystalline (Y-TZP) ceramic is widely used as an all-ceramic core material because of its enhanced mechanical and aesthetic properties. The bond strength of Y-TZP restorations affects long-term success; hence, surface treatment is required on ceramic boundaries. This study evaluated the effect of different laser beam angles on Y-TZP-resin cement shear bond strength (SBS). Forty plates of Y-TZP ceramics were randomly assigned to four groups (n = 10). A femtosecond amplifier laser pulse was applied on Y-TZP surface with different incidence angles (90°, 75°, 60°, 45°). The resin cement was adhered onto the zirconia surfaces. The SBS of each sample was measured using universal testing machine at crosshead speed of 1 mm/min. The SBS was analyzed through one-way analysis of variance (ANOVA)/Tukey tests. The results showed that the degree of laser beam angle affects the SBS of resin cement to Y-TZP. The laser beam was applied to a surface with a 45° angle which resulted in significantly higher SBS (18.2 ± 1.43 MPa) than other groups (at 90° angulation (10.79 ± 1.8 MPa), at 75° (13.48 ± 1.2 MPa) and at 60° (15.85 ± 0.81 MPa); p < 0.001). This study shows that decreasing of the angle between the ceramic surface and the laser beam increased the SBS between the resin cement and the ceramic material, as well as the orifice.
Objective:The aim of the this study was to evaluate the perception of smile esthetics and alterations in cases of gingival plastic surgery for correction of a gummy smile, by means of alterations in smile photograph among dentistry degree students.Materials and Methods:A frontal smile photograph of a 40-year-old woman having normal occlusion was used with diverse compositions of gingival exposure level and crown length of maxillary teeth. The eight photographs were evaluated by 216 dentistry students in five class groups (1st, 2nd, 3rd, 4th and 5th classes).Results:The results revealed that almost all of the class’ students perceived differences between images, additionally, the highest percentage of students that answered “no difference” was 12% at 1st class’ students. 1st and 2nd class’ students most liked photograph which is 2.5 mm gingival display and 3rd class students liked two different photographs which are 2.5 mm gingival display and 2 mm gingival display whereas 4th class students preferred two different photographs which are 1.5 mm gingival display and 1 mm gingival display, 5th class students preferred photograph which is 1.5 mm gingival display as the most.Conclusion:Esthetic perception of smile improve as a student passes to higher study classes in terms of gingival exposure. The harmonious display of gingiva exhibits an important effect in the smile esthetics rather than reduced or excessive display.
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