Effect of Low-Temperature Degradation, Ph-Cycling and Simulated Tooth Brushing on Surface Roughness, Topography, and Polish Retention of Yttrium-Stabilized Tetragonal Zirconia.

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.

Effect of Chemical and Mechanical Degradation on Surface Roughness, Topography, Gloss, and Polish Retention of Three Composites Polished with Five Polishing Systems.

Objective: Finishing and polishing (F/P) of composites is a fundamental step influencing the clinical service of restorations. The aim of this study was to evaluate the effect of different F/P systems on surface roughness, gloss, and polish retention of composite resins. Materials and Methods: One-hundred and five disc-shaped specimens (4×4 mm) were made from nanofilled, microhybrid, and microfilled composites (n=35). The specimens were divided into five subgroups (n=7) for F/P with Sof-Lex (4-step), Shofu (4-step), Cosmedent (3-step), Diacomp Composite-Pro (2-step), and Opti1Step systems. The surface roughness values (Ra and Rz) were measured before and after pH-cycling and simulated toothbrushing. Surface topography was assessed by using a scanning electron microscope (SEM) at three magnifications. For assessment of surface gloss, 45 rectangular specimens (10×8×2 mm) were fabricated from three composites (n=15) and randomly allocated to five subgroups (n=3). Surface gloss was measured before and after aging. The mean values were calculated and analyzed by two-way ANOVA, Tukey, and t-test. Level of significance was set at 0.05. Results: The composite type had no significant effect on surface roughness (P>0.05); however, the type of F/P system significantly affected it (P<0.05). The pH-cycling and simulated toothbrushing had no significant effect on gloss or polish retention of the three composites (P>0.05). Conclusion: Type of F/P system had a greater effect on surface roughness and gloss of composite resins than the type of composite.

An In vitro Comparison of Apically Extruded Debris Using Reciproc, ProTaper Universal, Neolix and Hyflex in Curved Canals.

INTRODUCTION: As a consequence of root canal preparation, dentinal chips, irrigants and pulp remnants are extruded into preradicular space. This phenomenon may lead to post endodontic flare-ups. The purpose of this study was to compare the amount of extruded debris with four endodontic NiTi engine-driven systems. METHODS AND MATERIALS: Sixty mesiobuccal roots of maxillary molars with 15-30˚ curvature were divided randomly into four groups (n=15). Each group was instrumented up to apical size of 25 using Reciproc, ProTaper Universal, Neolix and Hyflex. Bidistilled water was used as irrigant and extruded debris was collected in pre-weighted Eppendorf tubes. Tubes were stored in incubator for drying the debris. Extruded debris were weighted in electronic microbalance with accuracy of 0.0001 g. The raw data was analyzed with one way analysis of variance (ANOVA) and Tukey's HSD post hoc test. Level of significance was set at 0.05. RESULTS: The debris extrusion with Reciproc files was significantly higher than the other groups (P<0.05). Hyflex significantly extruded less debris than other files (P<0.05). There was no significant difference between ProTaper Universal and Neolix regarding the amount of extruded debris (P=0.98). CONCLUSION: All systems extruded debris during the instrumentation. Reciproc system significantly extruded more debris. Caution should be taken when interpreting the results of this study and applying it to the real clinical situation.

Effect of coarse grinding, overglazing, and 2 polishing systems on the flexural strength, surface roughness, and phase transformation of yttrium-stabilized tetragonal zirconia.

STATEMENT OF PROBLEM: Limited information is available for the best polishing systems and methods to obtain minimally abrasive monolithic zirconia surfaces after contouring and occlusal adjustment. PURPOSE: The purpose of this in vitro study was to evaluate the effect of grinding and polishing procedures on the flexural strength, quality and quantity of surface roughness, topography, and phase transformation of a zirconia-based ceramic system. MATERIAL AND METHODS: Fifty bar-shaped yttrium-stabilized zirconium oxide specimens (20×4×2 mm) were cut from presintered zirconia blanks. The specimens were wet-polished and divided into 5 groups (n=10): standard polishing without any surface treatment (group SP); grinding with a diamond rotary instrument (group Gr); grinding with a diamond rotary instrument (DRI) and over-glazing (group Gl); grinding with a DRI and polishing with an intraoral zirconia polishing kit in a 2-step procedure (group BP); and grinding with a DRI and polishing with an intraoral polishing kit (group MP). The Ra and Rz surface roughness values (µm) were measured with a profilometer. One specimen of each group was subjected to x-ray diffraction (XRD) to estimate the monoclinic phase and evaluated using scanning electron microscopy (SEM) for surface topography. The 3-point flexural strength of the bars was measured in a universal testing machine at a crosshead speed of 0.5 mm/min. The mean flexural strength (MPa) and surface roughness values were calculated, and the results were analyzed using 1-way ANOVA and Tukey honest significant difference tests (α=.05). RESULTS: Statistically significant differences were noted among the experimental groups for Ra, Rz (P<.001), and flexural strength values (P<.001). The highest Ra and Rz values were found in group Gr (P<.001) and the lowest in group Gl, which were significantly lower than the values in group Gr (P<.001). The 2 polishing systems (BP and MP) were not significantly different in terms of Ra and Rz values (P=.755 for Ra and P=.319 for Rz). The highest flexural strength was found in group Gr (283.35 ±49.85 MPa) without significant differences from those of MP and BP (P=.958 for BP and P=.404 for MP). The lowest flexural strength was found in Gl, which had no significant differences from those of the control group (P=1.000). In XRD the monoclinic phase was observed in Gr (26%), BP (24%), and MP (23%) groups. However, groups Gl and SP did not have any monoclinic phase. SEM showed deep unidirectional scratches after grinding that were smoothened by glazing and polishing. CONCLUSIONS: Roughness increased significantly after grinding, but polishing and glazing similarly diminished it. Glazing after grinding significantly decreased the flexural strength values, but polishing did not.

In vitro evaluation of the effect of different laser irradiations on the enamel surfaces of teeth treated with home bleach procedure.

INTRODUCTION: The aim of this study was to evaluate the effect of dental surface treatment with Erbium-Doped Yttrium Aluminum Garnet(Er: YAG), Neodymium-Doped Yttrium Aluminium Garnet(Nd: YAG) and Carbon Dioxide Laser (CO2) lasers and sodium ascorbate to recently home bleached enamel by scanning electron microscope (SEM). METHODS: Thirty extracted human third molars were selected for this in vitro study. The teeth were randomly divided in two groups including home bleached group and control group (non-bleached). In group 1, the samples were bleached by home bleach technique. No bleaching procedure was done in second the group which served as control group.Then , the samples of two groups were divided to five subgroups as follow: Subgroup 1: treated using Nd:YAG laser with output power of 1 W, Subgroup 2: treated using Er:YAG laser with output power of 0.5 W, Subgroup 3: treated using CO2 laser with output power of 0.5 W, Subgroup 4: sodium ascorbate 10%, Subgroup 5: no treatment. After treatments, the surfaces were evaluated using Scanning Electron Microscope (SEM) analysis. RESULTS: The surfaces treated by Nd:YAG laser showed some melting and recrystallized areas and in some area droplet pattern was observed. But the surface treated by Er:YAG laser showed irregular and micro porous surface with flake pattern. CO2 laser treatment of home-bleached surfaces resulted in melting area and cracks. Sodium ascorbate did not change the home-bleached surface. CONCLUSION: Among different surface treatments used in this study, it seems that Er:YAG laser can best interact with home-bleached teeth.