Comparison of different grinding procedures on the flexural strength of zirconia (original) (raw)
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Influence of grinding procedures on the flexural strength of zirconia ceramics
Brazilian Dental Journal, 2010
The surface of zirconia may be damaged during grinding, influencing the mechanical properties of the material. The purpose of this study was to compare the flexural strength of zirconia after different grinding procedures. Twenty bar-type zirconia specimens (21 x 5 x 2 mm) were divided into 4 groups and ground using a high-speed handpiece or a low-speed straight handpiece until the bars were reduced 1 mm using two different grinding times: continuous grinding and short-time grinding (n=5). Control specimens (n=5) were analyzed without grinding. The flexural strengths of the bars were determined by using 3-point bending test in a universal testing machine at a crosshead speed of 0.5 mm/min. The fracture load (N) was recorded, and the data were analyzed statistically by the Kruskal Wallis test at a significance level of 0.05. In the test groups, high-speed handpiece grinding for a short time had produced the highest mean flexural strength (878.5 ± 194.8 MPa), while micromotor continuo...
Effect of grinding and heat treatment on the mechanical behavior of zirconia ceramic
Brazilian oral research, 2016
The present study investigated the effect of grinding on roughness, flexural strength, and reliability of a zirconia ceramic before and after heat treatment. Seven groups were tested (n = 15): a control group (labeled CG, untreated), and six groups of samples ground with diamond discs, simulating diamond burs, with grits of 200 µm (G80); 160 µm (G120), and 25 µm (G600), either untreated or heat-treated at 1200°C for 2 h (labeled A). Yttria tetragonal zirconia polycrystal discs were manufactured, ground, and submitted to roughness and crystalline phase analyses before the biaxial flexural strength test. There was no correlation between roughness (Ra and Rz) and flexural strength. The reliability of the materials was not affected by grinding or heat treatment, but the characteristic strength was higher after abrasion with diamond discs, irrespective of grit size. The X-ray diffraction data showed that grinding leads to a higher monoclinic (m) phase content, whereas heat treatment prod...
The effects of dry and wet grinding on the strength of dental zirconia
The purpose of this study was to evaluate the effect of different dry and wet surface finishing on the mechanical strength and surface characters of a dental yttria-stablized zirconia ceramic (Y-TZP). Surface grinding treatments with a dental air turbine handpiece were performed with: coarse diamond (DC) and fine diamond (DF), tungsten carbide (Tc) and fine tungsten carbide (TcF) burs with or without water coolant. Air particle abrasion with 50 µm alumina (APA), combination of burs treatments or burs-abrasion, i.e. DC-TcF and DC-APA, were also performed with non-treatment group as control (C). Statistical analyses (α = 0.05) on results revealed that all surface treatments significantly increased the surface roughness (Ra) than control (p < 0.05), whilst decreased breaking force (BFN) and biaxial flexural strength (BFS). Tungsten carbide surface treatment could significantly lower (p < 0.05) BFS and BFN, but DC only significantly lowered BFN. DC and tungsten carbide treatments exhibited significantly lower BFS values in wet than dry. A positive correlation was found between the BFS and BFN with the number of fragments. Only tetragonal phase of ZrO2 was presented by XRD. Synchrotron XRD revealed the (101) peak exhibits a broadening effect in the tungsten carbide treated specimens (38 nm for Tc and 30 nm for TcF), i.e. grain sizes in these specimens were smaller than the control (60 nm for C). This study outcome suggested that tungsten carbide burs should be avoided for grinding Y-TZP because of significant reduction in the BFS. Water cooling during grinding did not consistently reduce the potential heat damaging effects expected with dry grinding.
Aim: The aim of the present study was to assess the change in physical properties (surface roughness, surface hardness and phase transformation) after surface grinding of zirconia by using three commercially available abrasives. Materials and Methods: Thirty sintered zirconia specimens were prepared and divided into three groups namely Group M (grinded using Mani Dia diamond bur standard grit), Group T (grinded using Tri Hawk diamond bur coarse grit) and Group P (grinded using Predator carbide bur). A customised assembly was used to follow a standardised protocol for surface grinding. The surface roughness, surface hardness and phase transformation was recorded before and after the grinding procedure. Statistical Analysis Used: ANOVA and Bonferroni post hoc test were used to assess the values obtained after the testing the surface roughness and surface hardness. Results: The results of the present study revealed the average values of change in surface roughness as Group M (0.44 µm) and Group T (1.235 µm) and Group P (-0.88 µm). The average values of change in surface hardness were Group T (19.578 HV), Group M (46.722 HV) and Group P (36.429 HV). The change in surface hardness was not statistically significant. There was no phase transformation seen after the grinding procedure. Clinical Significance: Carbide burs along with copious water irrigation when used to grind zirconia intra-orally produces has a polishing effect, minimal change in hardness & no phase transformation. The present study advocates the use of carbides for chair-side grinding of zirconia. Abstract Access this article online How to cite this article: Sandhu R, Kheur M, Kheur S. Effect of simulated chairside grinding procedures using commercially available abrasive agents on the surface properties of zirconia.
A Comparative Study on Simulated Chairside Grinding and Polishing of Monolithic Zirconia.
This study evaluated the effects of different simulated chairside grinding and polishing protocols on the physical and mechanical properties of surface roughness, hardness, and flexural strength of monolithic zirconia. Sintered monolithic zirconia specimens (15 mm × 3 mm × 3 mm) were abraded using three different burs: diamond bur, modified diamond bur (zirconia specified), and tungsten carbide bur, along with a group of unprepared specimens that served as a control group. The study was divided into two phases, Phase 1 and Phase 2. Surface roughness, surface hardness, and flexural strength were assessed before and after the grinding procedure to determine the 'best test group' in Phase 1. The best abrasive agent was selected for Phase 2 of the study. The specimens in Phase 2 underwent grinding with the best abrasive agent selected. Following the grinding, the specimens were then polished using commercially available diamond polishing paste, a porcelain polishing kit, and an indigenously developed low-temperature sintered zirconia slurry. The physical and mechanical properties were again assessed. Results were analyzed using one-way ANOVA test. Specimens were observed under scanning electron microscopy (SEM) and X-ray diffraction (XRD) for their microstructure and crystalline phases, respectively. Grinding with diamond burs did not weaken zirconia (p > 0.05) but produced rougher surfaces than the control group (p < 0.05). Tungsten carbide burs did not significantly roughen the zirconia surface. However, specimens ground by tungsten carbide burs had a significantly reduced mean flexural strength (p < 0.05) and SEM revealed fine surface cracks. Phase transformation was not detected by XRD. Polishing with commercially available polishing agents, however, restored the surface roughness levels to the control group. Dental monolithic zirconia ground with tungsten carbide burs had a significantly reduced flexural strength and a smooth but defective surface. However, grinding with diamond burs roughened the zirconia surface. These defects may be reduced by polishing with commercially available polishing agents. The use of tungsten carbide burs for grinding dental zirconia should not be advocated. Grinding with diamond abrasives does not weaken zirconia but requires further polishing with commercially available polishing agents.
Effect of grinding and polishing on roughness and strength of zirconia
The Journal of prosthetic dentistry, 2017
The clinical applications of high-translucency monolithic zirconia restorations have increased. Chairside and laboratory adjustments of these restorations are inevitable, which may lead to increased roughness and reduced strength. The influence of grinding and polishing on high-translucency zirconia has not been investigated. The purpose of this in vitro study was to compare the roughness averages (Ra) of ground and polished zirconia and investigate whether roughness influenced strength after aging. High-translucency zirconia disks were milled, sintered, and glazed according to the manufacturer's recommendations. Specimens were randomized to 4 equal groups. Group G received only grinding; groups GPB and GPK received grinding and polishing with different polishing systems; and group C was the (unground) control group. All specimens were subjected to hydrothermal aging in an autoclave at 134°C at 200 kPa for 3 hours. Roughness average was measured using a 3-dimensional (3D) optica...
Effect of post- processing heat treatment on flexural strength of zirconia for dental applications
Purpose: the purpose of this study was to evaluate the effect of annealing heat treatment on biaxial flexural strength and reliability of 3Y-TZP, sintered at various temperatures. Materials & methods: 3Y-TZP blanks were pre-sintered at 850ºC for 2 hours and sliced into discs (20x1.2mm). Specimens were randomly assigned to 5 groups and subsequently sintered at various temperatures ranging from 1350ºC to 1650ºC for 2 hours. For each sintering temperature, specimens were divided into three treatment groups. One group (n=20) was left as-sintered as control. One group was air-abraded with 50 micron aluminum oxide powder (n=20). The last group was air-abraded and heattreated at 1250ºC for 20 minutes (n=20). In addition, polished specimens (n=5 per sintering temperature) were prepared to study microstructure, grain size and indentation crack patterns. The mean density was measured by helium pycnometry. The percent porosity was calculated from measured and theoretical density. The mean grain size was determined by the linear intercept method on atomic force micrographs. Crystalline phases were analyzed by x-ray diffraction (XRD). Biaxial flexural strength (BFS) was tested according to ISO standard 6872 using a Universal Testing Machine. Polished specimens were thermally etched, gold coated and Vickers indentations were produced under a 98N load. Indentation crack patterns were analyzed by Scanning Electron Microscopy (SEM) on digital images. The length ratio of trans-granular to inter-granular fracture was determined. v Results were analyzed by Kruskal-Wallis test and Tukey's adjustment for multiple comparisons. A 0.05 level of significance was used. Reliability was evaluated by Weibull analysis. Results: There was an inverse relationship between density and sintering temperature (Spearman rank correlation r =-0.982, p<0.0001). Statistically significant differences were found between all the groups (p<0.0001, exact Kruskal-Wallis test). There was strong evidence of an increase in the percentage of porosity with increasing sintering temperature (Spearman rank correlation r=1.00, exact p = 0.017). The mean real grain size increased with sintering temperature. Analysis of XRD data showed that the monoclinic phase as well as ferro-elastic domain switching were present for all airabraded groups. A small amount of monoclinic phase was also present in groups sintered at 1600˚C and 1650˚C. In The mean BFS was higher for all air-abraded groups compared to as-sintered or air abraded and heat treated groups. Air-abraded groups sintered at 1350, 1450, 1550, and 1600˚C showed the highest mean BFS (1552.97±200.85, 1502.29±102.36, 1391.4±108.3, 1258.5±114.8 MPa), respectively. The highest Weibull moduli (reliability) were obtained with the heat-treated group sintered at 1550˚C (19.8), air-abraded group sintered at 1450˚C (17.6) and heat-treated group sintered at 1350˚C (15.4). The group sintered at 1650ºC was the least reliable, independently of treatment state. Based on the data analysis of both the biaxial flexural strength and Weibull modulus, it was found that, the optimal treatment combination was obtained for the airabraded group sintered at 1450˚C, followed by the air-abraded group sintered at 1550˚C. Crack patterns analyses showed that the proportion of trans-granular fracture increased with sintering temperature. vi Conclusions: Annealing heat treatment is not recommended after any adjustments, as it does not improves the reliability of the material. Crack patterns and flexural strength are strongly influenced by the crystalline phase composition of the material. Sintering at 1600ºC and 1650ºC is not recommended due to the corresponding decrease in mechanical properties independently of treatment state. Air-abrasion of zirconia sintered at 1450˚C or 1550˚C led to the best combination of high strength and reliability.
Egyptian Dental Journal
Statement of problem: The translucency of cubic zirconia is improved on the expense of its strength. The effect of grinding and finishing on its mechanical properties is still unclear. Purpose: The aim of this study was to evaluate the influence of glazing and polishing protocols on the surface roughness and flexural strength of monolithic cubic zirconia after dry and wet grinding. Materials and methods: Super translucent multilayer zirconia (STML) disks were cut, sintered, and glazed according to the manufacturer's recommendations. Samples were randomly divided into three groups according to surface grinding: Group (C): control (no grinding-as glazed), Group (D)grinding under dry condition and group (W) grinding under wet condition. Each group of (D)and(W) was subdivided into two subgroups according to surface finishing whether glazing or polishing. The roughness average (Ra) was measured using contact profilometer. Biaxial flexural strength test was done using a universal testing machine. Statistical analysis was performed. Results: The glazing showed a statistically significantly higher mean Ra (P<0.05) than polishing whether after wet or dry grinding. The dry ground groups showed a statistically significantly higher mean Ra (P<0.05) than wet ground groups. The glazing showed a statistically significantly lower mean biaxial flexural strength than Polishing (P<0.05) after dry grinding. While there was no statistically significant difference between glazing and polishing (P>0.05) after wet grinding. Conclusion: Adequate polishing can produce a smoother surface than reglazing. Dry grinding can increase the surface roughness to a degree that can affect the flexural strength of STML zirconia.