ABSTRACT
Statement of the Problem: Surface roughness of zirconia is an important parameter that determines the success of zirconia restorations. When zirconia surfaces are left rough, higher susceptibility to hydrothermal aging, plaque accumulation and color changes would occur. Therefore, polish retention of these restorations is considered as a challenge. Purpose: The purpose of this in vitro study was to determine the effect of hydrothermal degradation, pH- cycling, and simulated tooth brushing on surface roughness, topography, and polish retention of an yttrium-stabilized monolithic zirconia. Materials and Method: In this experimental study, 64 specimens of yttria-stabilized tetragonal zirconium oxide (20×4×2mm) were prepared (ZirKonzahn, Steger, Ahrntal). The specimens were wet- polished (standard polishing), and divided into 8 groups (n=8). Four control groups were assessed in non-aged condition while in 4 experimental groups the artificially ageing was done. Different finishing and polishing procedures were performed in 8 groups. The surface roughness values including mean surface roughness (Ra) and mean height of surface roughness (Rz) was measured by a profilometer. The results were analyzed using two-way ANOVA and Tukey's HSD test (α=0.05). One representative specimen of each group was inspected under a scanning electron microscope (SEM) for assessment of surface topography. Results: The effects of surface treatments on Ra (p<.001) and Rz (p<.001) parameters were significant. Ageing had no significant effect on Ra (p=.086) and Rz (p=.067) values. Maximum Ra and Rz parameters were recorded following grinding (p<.001) and minimum values were recorded after glazing, which were significantly lower than the values in grinding group (p<.001). Polishing and glazing diminished the surface roughness (Ra) of ground zirconia similarly (p=.995). Conclusion: Aging had no significant effect on surface roughness of zirconia, irrespective of surface treatment type. Grinding yielded maximum surface roughness. Intra oral polishing yielded a surface roughness comparable to standard polishing and glazing.
ABSTRACT
OBJECTIVES: The degree of monomer conversion is crucial in determining the mechanical and clinical performance of dental resin composites. This study investigated the polymerization adequacy of two bulk-fill resin composites polymerized by Quartz-Tungsten-Halogen (QTH) and Light Emitting Diode (LED) light curing units at different depths. METHODS: Two bulk-fill resin composites (X-tra Fil; Voco and Tetric N-Ceram Bulk-fill; Ivoclar-Vivadent) with diameters of 7 mm and thicknesses of 1-4 mm were prepared and light-cured by LED or QTH. Then, the degree of conversion (DC) and microhardness of the two bulk-fill composites were evaluated. RESULTS: The microhardness of X-tra fill was significantly higher than that of Tetric N-Ceram polymerized by LED or QTH. The microhardness and DC of X-tra fil exhibited no significant difference among the increments regardless of type of light source. The DC, however, significantly decreased in deep increments for Tetric N-Ceram polymerized by QTH. CONCLUSIONS: The polymerization efficacies of the two bulk-fill composites were different in terms of the depth of cure and type of light source. The DC and microhardness of the X-tra fill bulk-fill composite polymerized by either QTH or LED did not decrease up to a thickness of 4 mm. Thus, new generations of LED light sources are better options for polymerizing the bulk-fill resin composites than QTH.
