Surface roughness and hardness of yttria stabilized zirconia (Y-TZP) after 10 years of simulated brushing

Abstract

Introduction: The Y-TZP zirconia used for prosthetic infrastructure, in some clinical situations, can be exposed to the oral environment. In these situations, a polished surface without changes is extremely important. Objective: The aim of this study was to evaluate the mean roughness (Ra) and Vickers hardness of Y-TZP zirconia (Lava™) after simulating ten years of brushing. Material and method: Thirty-six Y-TZP bar-shaped specimens (20mm X 4mm X 1.2mm) were divided into three groups: storage in distilled water (DW, n=12, control); brushing with distilled water (BDW, n=12) and brushing with distilled water and fluoride toothpaste (BFT, n=12). Brushing was performed using a brushing machine with a soft-bristled toothbrush, simulating 10 years of brushing (878.400 cycles, 100gf). The mean roughness (Ra in μm) and Vickers hardness (VHN) of all specimens were measured twice: before and after the experimental treatment, in profilometer and microhardness tester (500gf, 30 seconds), respectively. Data were analyzed using the two-way ANOVA test (α = 0.05). Result: The interaction between groups was not significant for roughness (p = 0.701) nor for hardness (p = 0.928). The final averages for Ra (μm) were equal to: DW - 0.63; BDW - 0.64; and, BFT - 0.68. The final averages for Vickers hardness (VHN) were: DW - 1301.16; BDW - 1316.60; and, BFT - 1299.58. Conclusion: It was concluded that the brushing with distilled or fluoridated toothpaste was not able to change the roughness and hardness of Y-TZP zirconia used in this study.

Effect of simulating tooth brushing on surface change of different ceramic materials

“…(26,27) Brushing effects on the surface properties of dental materials were evaluated in the study using simulated tooth brushing abrasion test, which is considered a typical model in the literature. (28,29) The load of brushing application in the present study was (300 g) that is near to the range of clinical application and consistent with other studies (200 g to 350 g). (30)(31)(32) The discussion regarding how much Ra values that considered clinically acceptable are controversial opinions in the literature, however, Ra values after brushing with conventional dentifrice in the present study is agreed with another study & were clinically acceptable where it presents within the Ra range from 0.25 um to 0.5um, which is undetectable clinically by the tongue.…”

“…(33) The Ra values obtained in this study disagree and differ from the values obtained in other studies in which the Ra values ranged from 0.18 to 0.98 um. (28,34) In the present study different kinds of ceramic blocks (Zirconia, e.max, Vita enamic & Lava ultimate) were used to include different classification of ceramics as possible. Roughness values (Ra) is different in all kinds of ceramics tested in the study resulting different wear pattern of each type of ceramics, that is closely influenced by microstructure and physical characteristics of ceramic type, specifically hardness, flexural strength and fracture toughness.…”

“…(44,45) On the other hand different results, such as unchanged roughness after brushing with conventional dentifrice and roughened ceramic surfaces after brushing with whitening dentifrice, have been published in other studies. (28,48) Although, homogenous and smooth wear patterns can be seen for lithium disilicate (e.max blocks) may be considerably attributed to smaller grain size of lithium disilicate crystals when compared with leucite crystals of glass based ceramics. (49,50) The null hypotheses of the study is partially rejected because surface roughness and wear of dental restorations occurred but with no significant differences.…”

Effects of whitening dentifrice on yttria-stabilized tetragonal zirconia polycrystal surfaces after simulating brushing

“…The Ra values obtained from the specimens used in this study agree with the values obtained in other studies in which the Ra values ranged from 0.18 to 0.98 mm. 15,25,37 No significant changes were found after immersion (control, SW group) and brushing with water (BW group). However, Ra values increased after brushing with conventional dentifrice (BD group), and there was a polishing effect on surfaces that were brushed with whitening dentifrice (BWD group).…”

“…The specimens were brushed using a linear brushing machine (Mavtec Comércio e Serviços) equipped with soft bristle toothbrush heads (#35, Oral-B Indicator; Procter & Gamble Brazil S/A) using distilled water (BW), conventional fluoride dentifrice slurry (BD), or whitening dentifrice slurry (BWD). The machine was set to brush at a rate of 60 reciprocal strokes per minute, with a vertical load of 0.98 N 32,37 for 244 hours. 27 Slurries of dentifrice were prepared by mixing 2 parts of distilled water (mL) and 1 part of dentifrice (g) 38 in a magnetic mixer for 10 minutes.…”