OBJECTIVE: To study microstructure, friction and wear behaviors of silicon-lithium spray coating on the surface of zirconia ceramics and to preliminarily evaluate its esthetic so as to provide support and guidance for the clinical application. METHODS: Zirconia ceramic specimens were randomly divided into three groups: coating group (two subgroups), polishing group (two subgroups), and glazing group (four subgroups), with 10 samples in each subgroup. The two subgroups of coating group were the zirconia ceramics with the untreated and preliminary polishing surfaces sprayed with silicon-lithium coating, respectively. The two subgroups of polishing group were preliminary polishing and fine polishing of zirconia ceramics, respectively. The four subgroups of glazing group were preliminarily polished zirconia ceramics glazed with Biomic and Stain/Glaze products, respectively; and untreated zirconia ceramics glazed with Biomic and Stain/Glaze products, respectively. The above 8 subgroups of zirconia ceramic specimens were used as friction pairs with 80 steatite ceramics for 50 000 chewing cycles under 50 N vertical load and artificial saliva lubrication using chewing simulation. Scanning electron microscope was used to observe the microstructure of the surface and section of the coating group, and the thickness of the coating and glazing were measured. The linear roughness of the coating and polishing groups was mea-sured using a laser confocal scanning microscope. Vickers hardness was measured using a microhardness tester and the esthetic of zirconia ceramic full crown sprayed with silicon-lithium coating was preliminarily evaluated. White light interferometer was used to measure the width, the maximum depth and the volume of the wear scars of each group, and the wear depth of steatite ceramics and wear rate of zirconia ceramic specimens were calculated. Kruskal-Wallis nonparametric test and Dunn's multiple comparisons test were used to analyze the wear depth of each group (α=0.05). RESULTS: The microstructures of the silica-lithium spray coatings on the untreated and preliminarily polished zirconia ceramic surfaces showed the protruding defects, and the line roughness of coating group was larger than that of the polishing group. The median thickness of the silica-lithium spray coating on the preliminarily polished zirconia ceramic was 13.0 μm (interquartile range, IQR: 11.6, 17.9), while that of the silica-lithium spray coating on the untreated zirconia ceramic was 4.4 μm (IQR: 4.1, 4.7). The Vickers hardness and wear rate of the coating group were between the polishing group and the glazing group. The wear depths of the wear scars of steatite ceramics were the glazing group, coating group, and polishing group in descending order, and there was statistically significant difference between glazing and polishing groups (P < 0.05). With the increase of polishing procedure, the wear depth of steatite ceramics decreased in each subgroups. The orders of maximum depth and volume of wear scars of zirconia ceramic were the glazing group, coating group, and polishing group in descending order, and there was statistically significant difference in the maximum depth of wear scars between glazing and polishing groups (P < 0.05). CONCLUSION The silica-lithium spray coating on the zirconia ceramic, can be used as a new method for zirconia ceramic surface treatment, because it can increase the esthetic of zirconia ceramics compared with polishing and reduce the wear of steatite ceramics compared with glazing.
Humans ; Silicon ; Materials Testing ; Friction ; Lithium ; Cicatrix ; Surface Properties ; Silicon Dioxide ; Zirconium/chemistry* ; Ceramics ; Dental Porcelain

Zirconia is widely used in the field of dentistry because of its superior mechanical and esthetic characteristics. However, the tetragonal zirconia polycrystal restorations commonly used in clinics will degrade at low temperatures in the oral environment, resulting in increased surface roughness, microcracks, and decreased mechanical properties. Low-temperature degradation of zirconia can be affected by grain size, stress, stabilizer content and type, surface treatment, sintering conditions, and other factors. Through a literature review and analysis, this review summarizes the research progress on the low-temperature degradation of zirconia in prosthetic dentistry to provide references for the improvement of zirconia in clinical and research applications.
Ceramics ; Dental Materials ; Esthetics, Dental ; Materials Testing ; Prosthodontics ; Surface Properties ; Temperature ; Yttrium/chemistry* ; Zirconium

Objective: To evaluate the effects of pre-sintering heating rate and powder size on dental recycled zirconia. Methods: Recycled zirconia powders were sieved to obtain the large (50 μm With the same particle size, the recycled zirconia pre-sintered at different heating rates showed no significant differences in the relative densities, and the open porosities (P>0.05). When the pre-sintering heating rates were 2 ℃/min, 5 ℃/min, and 8 ℃/min, the flexural strengths of the large-particle recycled zirconia were (421.2±54.7), (444.2±70.1) and (427.5±68.4) MPa, the flexural strengths of the small-particle recycled zirconia were (750.1±74.1), (777.2±95.5) and (746.7±73.0) MPa, respectively. The flexural strength of commercial zirconia was (988.4±129.8) MPa. The flexural strengths of the recycled zirconia were significantly lower than that of the commercial zirconia (P<0.05). At the same pre-sintering heating rate, the flexural strengths of the small-particle recycled zirconia were significantly higher than that of the large-particle recycled zirconia (P<0.05). Conclusions: Compared with the large particles, small-particle recycled zirconia powders can effectively improve the properties of recycled zirconia, while the pre-sintering heating rate has no effect on the properties of the recycled zirconia.
Ceramics ; Dental Materials/chemistry* ; Heating ; Materials Testing ; Powders ; Surface Properties ; Yttrium ; Zirconium

Objective: To evaluate the effect of shear bond strength between resin cement and zirconia using SiO₂-ZrO₂ slurry coating. Methods: One hundred and forty pre-sintered zirconia discs were randomly divided into seven groups (n=20) according to the surface treatments: AS (as-sintered), SB (sand blasting with Al₂O₃), 2SiO₂-1ZrO₂ (2∶1 mole ratio SiO₂-ZrO₂ coating), 1SiO₂-1ZrO₂ (mole ratio 1∶1 SiO₂-ZrO₂ coating), 1SiO₂-2ZrO₂ (mole ratio 1∶2 SiO₂-ZrO₂ coating), 1SiO₂-3ZrO₂ (mole ratio 1∶3 SiO₂-ZrO₂ coating), 1SiO₂-4ZrO₂ (mole ratio 1∶4 SiO₂-ZrO₂ coating). Each zirconia disc was bonded to composite resin cylinder using resin cement. All specimens were stored in distilled water (37 ℃, 24 h). Each group was divided into two subgroups in which half specimens were tested using universal testing machine and another half specimens accepted artificial aging of 5 000 times thermocycling then tested. Scaning electron microscopy (SEM) was used to observe the micro-morphology of coating surface etched by hydrofluoric acid,then the coating thickness was measured. Results: Before artificial aging, 1SiO₂-1ZrO₂ showed a higher shear bond strength [(41.69±6.28) MPa] than all the other group (P<0.05). 1SiO₂-2ZrO₂ gained a higher strength than AS, SB, 1SiO₂-3ZrO₂ and 1SiO₂-4ZrO₂ (P<0.05). However, 1SiO₂-2ZrO₂ did not get a significant higher shear bond strength than 2SiO₂-1ZrO₂ (P>0.05). No significant differences were found among SB, 2SiO₂-1ZrO₂ and 1SiO₂-3ZrO₂ (P>0.05). After artificial aging, shear bond strength of all groups were decreased significantly besides 2SiO₂-1ZrO₂. 2SiO₂-1ZrO₂, 1SiO₂-1ZrO₂ and 1SiO₂-2ZrO₂ [(24.13±5.50), (22.28±4.40), (23.11±4.80) MPa] showed higher shear bond strength than SB and 1SiO₂-3ZrO₂ (P<0.05),no intergroup differences were observed (P>0.05). Shear bond strength of AS and 1SiO₂-4ZrO₂ fell to 0 MPa approximately. The SEM images of etched coating surface showed contraction fissure due to different thermal expansion coefficient between SiO₂ and ZrO₂ and intercrystal pores of zirconia. The thickness of coating was measured to be less than 30 μm. Conclusions: Mole ratio 1∶1 SiO₂-1ZrO₂ slurry coating showed the highest shear bond strength of resin cement to zirconia.
Dental Bonding ; Materials Testing ; Resin Cements/chemistry* ; Silicon Dioxide ; Surface Properties ; Zirconium

Sub-gingival anaerobic pathogens can colonize an implant surface to compromise osseointegration of dental implants once the soft tissue seal around the neck of an implant is broken. In vitro evaluations of implant materials are usually done in monoculture studies involving either tissue integration or bacterial colonization. Co-culture models, in which tissue cells and bacteria battle simultaneously for estate on an implant surface, have been demonstrated to provide a better in vitro mimic of the clinical situation. Here we aim to compare the surface coverage by U2OS osteoblasts cells prior to and after challenge by two anaerobic sub-gingival pathogens in a co-culture model on differently modified titanium (Ti), titanium-zirconium (TiZr) alloys and zirconia surfaces. Monoculture studies with either U2OS osteoblasts or bacteria were also carried out and indicated significant differences in biofilm formation between the implant materials, but interactions with U2OS osteoblasts were favourable on all materials. Adhering U2OS osteoblasts cells, however, were significantly more displaced from differently modified Ti surfaces by challenging sub-gingival pathogens than from TiZr alloys and zirconia variants. Combined with previous work employing a co-culture model consisting of human gingival fibroblasts and supra-gingival oral bacteria, results point to a different material selection to stimulate the formation of a soft tissue seal as compared to preservation of osseointegration under the unsterile conditions of the oral cavity.
Acid Etching, Dental ; methods ; Alloys ; chemistry ; Bacterial Adhesion ; physiology ; Bacteriological Techniques ; Biofilms ; Cell Adhesion ; physiology ; Cell Culture Techniques ; Cell Line, Tumor ; Cell Movement ; physiology ; Ceramics ; chemistry ; Coculture Techniques ; Dental Alloys ; chemistry ; Dental Etching ; methods ; Dental Implants ; microbiology ; Dental Materials ; chemistry ; Dental Polishing ; methods ; Humans ; Osseointegration ; physiology ; Osteoblasts ; physiology ; Porphyromonas gingivalis ; physiology ; Prevotella intermedia ; physiology ; Surface Properties ; Titanium ; chemistry ; Yttrium ; chemistry ; Zirconium ; chemistry

The aim of this study was to determine if accelerated aging of porcelain veneering had an effect on the surface properties specific to a tetragonal-to-monoclinic transformation (TMT) of zirconia restorations. Thirty-six zirconia samples were milled and sintered to simulate core fabrication followed by exposure to various combinations of surface treatments including as-received (control), hydrofluoric acid (HF), application of liner plus firings, application of porcelain by manual layering and pressing with firing, plus accelerated aging. The quantity of transformed tetragonal to monoclinic phases was analyzed utilized an X-ray diffractometer and one-way analysis of variance was used to analyze data. The control samples as provided from the dental laboratory after milling and sintering process had no TMT (Xm = 0). There was an effect on zirconia samples of HF application with TMT (Xm = 0.8%) and liner plus HF application with TMT (Xm = 8.7%). There was an effect of aging on zirconia samples (no veneering) with significant TMT (Xm = 70.25%). Both manual and pressing techniques of porcelain applications reduced the TMT (manual, Xm = 4.41%, pressing, Xm = 11.57%), although there was no statistical difference between them. It can be concluded that simulated applications of porcelain demonstrated the ability to protect zirconia from TMT after aging with no effect of a liner between different porcelain applications. The HF treatment also caused TMT.
Dental Porcelain ; chemistry ; Surface Properties ; X-Ray Diffraction ; methods ; Zirconium ; chemistry

OBJECTIVETo evaluate the effect of microwave sintering on the translucency of zirconia and to compare these effect with those of conventional sintering. The relationship between the microstructure of specimens and translucency was investigated.

METHODSA total of 10 disc-shaped specimens were fabricated from 2 commercial brands of zirconia, namely, Zenostar and Lava. Each group included 5 discs. Conventional sintering was performed according to the manufacturers' specifications. The maximum temperature for Zenostar was 1,490 °C, whereas that for Lava was 1,500 °C. The dwelling time was 2 h. The sintering temperature for microwave sintering was 1,420 °C, heating rate was 15 °C · min⁻¹, and dwelling time was 30 min. After sintering, the translucency parameter (TP) of the specimens were measured with ShadeEye NCC. The sintered density of the specimens was determined by Archimedes' method. The grain size and microstructure of the specimens were investigated by scanning electron microscopy.

RESULTSDensity and translucency slightly increased by microwave sintering, but no significant difference was found between microwave and conventional sintering (P > 0.05). Small and uniform microstructure were obtained from microwave sintering. The mean TP of Lava was significantly higher than that of Zenostar (P < 0.001).

CONCLUSIONThe translucency of zirconia sintered by microwave sintering is similar to that of the zirconia sintered by conventional sintering.

Ceramics ; chemistry ; Dental Prosthesis Design ; methods ; Heating ; Materials Testing ; Microscopy, Electron, Scanning ; Microwaves ; Surface Properties ; Technology, Dental ; methods ; Zirconium ; chemistry

OBJECTIVEThe effect of sandblasting on the bond strength between 3mol% yttrium-stabilized tetragonal zirconium polycrystal (3Y-TZP) zirconia framework and veneering porcelain was evaluated.

METHODSA total of 21 specimens [(25 ± 1) mm x (3 ± 0.1) mmx (0.5 ± 0.05) mm] were prepared according to ISO 9693. The specimens were then randomly divided into 3 groups. Sandblasting was performed on 2 meshes of Al₂O₃ particles: group A with mesh 110 and group B with mesh 80. Group C, which was not sandblasted, was the control group. The surface roughness of the zirconia framework, as well as the bond strength between 3Y-TZP zirconia framework and veneering porcelain, was measured. The interface microstructure was observed by scanning electron microscope (SEM), and elemental distribution was detected by energy dispersive spectroscopy (EDS).

RESULTSSurface roughness values were (1.272 ± 0.149) μm for group A, (0.622 ± 0.113) μm for group B, and (0.221 ± 0.065) μm for group C. Statistical significance were found among groups (P < 0.05). The bond strength values were (28.21 ± 1.52) MPa for group A, (27.71 ± 1.27) MPa for group B, and (24.87 ± 3.84) MPa for group C. Statistical significance was found between group A and group C (P < 0.05), whereas the other groups had no statistical significance (P > 0.05). Interface adhesion failure was the primary performance. SEM images showed the close interface bonding, and EDS showed that the interface had no obvious element penetration.

CONCLUSIONAl₂O₃ sandblasting can slightly enhance the bond strength between zirconia framework and veneering porcelain.

Aluminum Oxide ; chemistry ; Dental Bonding ; Dental Porcelain ; chemistry ; Dental Stress Analysis ; Dental Veneers ; Materials Testing ; Microscopy, Electron, Scanning ; Shear Strength ; Surface Properties ; Yttrium ; chemistry ; Zirconium ; chemistry

OBJECTIVETo evaluate the effect of Fe2O3 and CeO2 as colorants on yttria stabilized tetragonal zirconia poly-crystals (Y-TZP) powder.

METHODSThe spray granulation slurry of colored zirconia was prepared with different concentrations of Fe2O3 (0.15%) and CeO2 (4%), which were added in Y-TZP. Zirconia powder was made by spray granulation. The powder specimens were divided into three groups: uncolored zirconia, Fe2O3 (0.15%) zirconia, and CeO2 (4%) zirconia. The particle morphologies of the powder specimens were measured with a laser particle size analyzer and an optical microscope.

RESULTSThe differences in D50 among the three groups were statistically significant (P<0.05). Group Fe2O3 showed a significant difference from groups CeO2 and uncolored zirconia (P<0.05). Group uncolored zirconia showed no significant difference from group CeO2 (P>0.05). Mostly spherical powder was observed in the three groups.

CONCLUSIONFe2O3 as a colorant can affect particles, whereas CeO2 has no effect.

Color ; Dental Stress Analysis ; Ferric Compounds ; Humans ; Materials Testing ; Yttrium ; chemistry ; Zirconium ; chemistry

The aim of this study was to evaluate the effect of controlled intraoral grinding and polishing on the roughness of full-contour zirconia compared to classical veneered zirconia. Thirty bar-shaped zirconia specimens were fabricated and divided into two groups (n=15). Fifteen specimens (group 1) were glazed and 15 specimens (group 2) were veneered with feldspathic ceramic and then glazed. Prior to grinding, maximum roughness depth (Rmax) values were measured using a profilometer, 5 times per specimen. Simulated clinical grinding and polishing were performed on the specimens under water coolant for 15 s and 2 N pressure. For grinding, NTI diamonds burs with grain sizes of 20 µm, 10 µm, and 7.5 µm were used sequentially. The ground surfaces were polished using NTI kits with coarse, medium and fine polishers. After each step, Rmax values were determined. Differences between groups were examined using one-way analysis of variance (ANOVA). The roughness of group 1 was significantly lower than that of group 2. The roughness increased significantly after coarse grinding in both groups. The results after glazing were similar to those obtained after fine grinding for non-veneered zirconia. However, fine-ground veneered zirconia had significantly higher roughness than venerred, glazed zirconia. No significant difference was found between fine-polished and glazed zirconia, but after the fine polishing of veneered zirconia, the roughness was significantly higher than after glazing. It can be concluded that for full-contour zirconia, fewer defects and lower roughness values resulted after grinding and polishing compared to veneered zirconia. After polishing zirconia, lower roughness values were achieved compared to glazing; more interesting was that the grinding of glazed zirconia using the NTI three-step system could deliver smooth surfaces comparable to untreated glazed zirconia surfaces.
Aluminum Silicates ; chemistry ; Ceramics ; chemistry ; Crowns ; Dental Materials ; chemistry ; Dental Polishing ; instrumentation ; methods ; Dental Prosthesis Design ; Dental Veneers ; Diamond ; chemistry ; Humans ; Materials Testing ; Microscopy, Electron, Scanning ; Particle Size ; Potassium Compounds ; chemistry ; Pressure ; Surface Properties ; Time Factors ; Water ; chemistry ; Yttrium ; chemistry ; Zirconium ; chemistry