Michael G Botelho1, Sachin Dangay2, Kaimin Shih3, Walter Y H Lam4. 1. Prosthodontics, Faculty of Dentistry, The University of Hong Kong, Hong Kong, China. Electronic address: botelho@hku.hk. 2. Private Practice, New Delhi, India. 3. Department of Civil Engineering, Faculty of Engineering, The University of Hong Kong, Hong Kong, China. 4. Prosthodontics, Faculty of Dentistry, The University of Hong Kong, Hong Kong, China.
Abstract
OBJECTIVES: This study investigates the effect of selected surface finishing techniques on the biaxial flexural strength, surface roughness and phase transformation of a zirconia dental restorative material. MATERIALS AND METHODS: Fully-sintered zirconia discs (⌀19.5 mm × 0.85 mm) were treated on one side with a single or a combination of the following treatments: diamond and/or tungsten-carbide burs without water coolant in an air-turbine handpiece, air-particle abrasion, rubber-point polishing in a contra-angle handpiece, or no treatment (control). Biaxial flexural strength (BFS) (eleven groups, n = 10) was determined using a universal testing machine and surface roughness (thirteen groups, n = 6) was assessed using a profilometer. Results were analysed using one-way ANOVA and Student-Newman-Keuls Post-hoc test (α = 0.05) with Bonferroni correction. Specimens were observed under scanning electron microscopy (SEM) and x-ray diffraction (XRD) for their microstructure and crystalline phases respectively. RESULTS: Grinding with diamond burs did not weaken zirconia (p > 0.0045) but produced rougher surfaces than the control group (p < 0.0038). Tungsten-carbide burs smoothened diamond ground specimens (p < 0.0038) for both grits of diamond. Specimens ground by tungsten-carbide burs have significantly reduced mean BFS (p < 0.0045) by up to two-thirds and SEM revealed fine surface cracks. Air-particle abrasion restored the mean BFS of tungsten-carbide ground specimens to control levels (p > 0.0045) and surface cracks were not observed. Phase transformation was not detected by XRD. CONCLUSIONS: Dental zirconia ground dry with tungsten-carbide burs has a significantly reduced BFS and a smooth but defective surface. These defects may be removed and BFS restored by air-particle abrasion. CLINICAL SIGNIFICANCE: The use of tungsten-carbide burs for grinding dental zirconia should be cautioned. Diamond grinding does not weaken zirconia but requires further polishing.
OBJECTIVES: This study investigates the effect of selected surface finishing techniques on the biaxial flexural strength, surface roughness and phase transformation of a zirconia dental restorative material. MATERIALS AND METHODS: Fully-sintered zirconia discs (⌀19.5 mm × 0.85 mm) were treated on one side with a single or a combination of the following treatments: diamond and/or tungsten-carbide burs without water coolant in an air-turbine handpiece, air-particle abrasion, rubber-point polishing in a contra-angle handpiece, or no treatment (control). Biaxial flexural strength (BFS) (eleven groups, n = 10) was determined using a universal testing machine and surface roughness (thirteen groups, n = 6) was assessed using a profilometer. Results were analysed using one-way ANOVA and Student-Newman-Keuls Post-hoc test (α = 0.05) with Bonferroni correction. Specimens were observed under scanning electron microscopy (SEM) and x-ray diffraction (XRD) for their microstructure and crystalline phases respectively. RESULTS: Grinding with diamond burs did not weaken zirconia (p > 0.0045) but produced rougher surfaces than the control group (p < 0.0038). Tungsten-carbide burs smoothened diamond ground specimens (p < 0.0038) for both grits of diamond. Specimens ground by tungsten-carbide burs have significantly reduced mean BFS (p < 0.0045) by up to two-thirds and SEM revealed fine surface cracks. Air-particle abrasion restored the mean BFS of tungsten-carbide ground specimens to control levels (p > 0.0045) and surface cracks were not observed. Phase transformation was not detected by XRD. CONCLUSIONS:Dental zirconia ground dry with tungsten-carbide burs has a significantly reduced BFS and a smooth but defective surface. These defects may be removed and BFS restored by air-particle abrasion. CLINICAL SIGNIFICANCE: The use of tungsten-carbide burs for grinding dental zirconia should be cautioned. Diamond grinding does not weaken zirconia but requires further polishing.
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