Microstructure and mechanical properties of fully sintered zirconia glazed with an experimental glass

Borosilicate glass as a surface finishing alternative for improving the mechanical properties of third-generation zirconia

OBJECTIVE

This study evaluated the effect of an experimental borosilicate glass on the mechanical and optical behavior of 5Y-PSZ zirconia and comparing it to commercial glaze and as-sintered.

METHODS

Disc-shaped specimens of a 5Y-PSZ (Zpex Smile) were prepared and sintered (1550 °C, 2 h). The zirconia discs were randomly divided according to the surface treatment: as-sintered (C), commercial glaze (G), and experimental borosilicate glass (SL). Glaze and experimental glass powders were mixed with building liquids and applied to zirconia with a brush. G specimens were fired at 950 °C and SL at 1200 °C. An extended dwell time of 20 min was applied to both groups. Biaxial flexural strength, roughness (Ra and Rz), translucency (TP00), color alteration (ΔE00), Vickers hardness, fracture toughness, residual stresses, and x-ray diffraction analyses were conducted. Statistical analyses were performed with Weibull statistics, Kruskal-Wallis, or ANOVA tests (α = 5%).

RESULTS

SL yielded the highest flexural strength (799.35 MPa), followed by G (662.34 MPa), and C (485.38 MPa). The fracture origin of SL specimens was in the bulk zirconia, while G and C showed fractures starting at the surface. As-sintered reached the highest fracture toughness and hardness. Glaze and borosilicate glass provided surface compressive stresses. Borosilicate glass application led to phase transformation (t→m). SL and G showed the lowest roughness. TP00 and ΔE00 were similar among groups.

SIGNIFICANCE

Borosilicate glass improved strength without harming the optical properties of third-generation zirconia. Toughness and roughness provided by the experimental glass were similar to those from commercial glaze.

Minimally processed recycled yttria-stabilized tetragonal zirconia for dental applications: Effect of sintering temperature on glass infiltration

This study aimed to develop a recycling process for the remnants of milled 3Y-TZP and enhance their properties using glass infiltration. 3Y-TZP powder was gathered from the vacuum system of CAD-CAM milling equipment, calcined and sieved (x < 75 μm). One hundred twenty discs were fabricated and pre-sintered at 1000 °C/h. These specimens were then divided into four groups, categorized by glass infiltration (non-infiltrated [Zr] or glass-infiltrated [Zr-G]) and sintering temperature (1450 °C [Zr-1450] or 1550 °C [Zr-1550]/2h). After sintering, the specimens were characterized by X-Ray Diffraction (XRD), relative density measurement, and scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS). The biaxial flexural strength test was performed according to the ISO 6872 and followed by fractographic analysis. Subsequent results were analyzed using Weibull statistics. Relative density values of the sintered specimens from Zr-1450 and Zr-1550 groups were 86.7 ± 1.5% and 92.2 ± 1.7%, respectively. Particle size distribution revealed particles within the range of 0.1-100 μm. XRD analysis highlighted the presence of the ZrO2-tetragonal in both the Zr-1450 and Zr-1550 groups. Glass infiltration, however, led to the formation of the ZrO2-monoclinic of 9.84% (Zr-1450-G) and 18.34% (Zr-1550-G). SEM micrographs demonstrated similar microstructural characteristics for Zr-1450 and Zr-1550, whereas the glass-infiltrated groups exhibited comparable infiltration patterns. The highest characteristic strength was observed in the glass-infiltrated groups. Fractographic analyses suggested that fracture origins were related to defects on the tensile side, which propagated to the compression side of the samples. Both the sintering temperature and glass infiltration significantly influenced the mechanical properties of the 3Y-TZP recycled.

Boron-containing coating yields enhanced antimicrobial and mechanical effects on translucent zirconia

OBJECTIVES

To evaluate the mechanical and antimicrobial properties of boron-containing coating on translucent zirconia (5Y-PSZ).

METHODS

5Y-PSZ discs (Control) were coated with a glaze (Glaze), silver- (AgCoat), or boron-containing (BCoat) glasses. The coatings' antimicrobial potential was characterized using S. mutans biofilms after 48 h via viable colony-forming units (CFU), metabolic activity (CV) assays, and quantification of extracellular polysaccharide matrix (EPS). Biofilm architectures were imaged under scanning electron and confocal laser scanning microscopies (SEM and CLSM). The cytocompatibility was determined at 24 h via WST-1 and LIVE&DEAD assays using periodontal ligament stem cells (PDLSCs). The coatings' effects on properties were characterized by Vickers hardness, biaxial bending tests, and fractography analysis. Statistical analyses were performed via one-way ANOVA, Tukey's tests, Weibull analysis, and Pearson's correlation analysis.

RESULTS

BCoat significantly decreased biofilm formation, having the lowest CFU and metabolic activity compared with the other groups. BCoat and AgCoat presented the lowest EPS, followed by Glaze and Control. SEM and CLSM images revealed that the biofilms on BCoat were thin and sparse, with lower biovolume. In contrast, the other groups yielded robust biofilms with higher biovolume. The cytocompatibility was similar in all groups. BCoat, AgCoat, and Glaze also presented similar hardness and were significantly lower than Control. BCoat had the highest flexural strength, characteristic strength and Weibull parameters (σF: 625 MPa; σ0: 620 MPa; m = 11.5), followed by AgCoat (σF: 464 MPa; σ0: 478 MPa; m = 5.3).

SIGNIFICANCE

BCoat is a cytocompatible coating with promising antimicrobial properties that can improve the mechanical properties and reliability of 5Y-PSZ.

Effect of Finishing Protocols on the Surface Roughness and Fatigue Strength of a High-Translucent Zirconia

Purpose

In case of need for esthetical improvement of zirconia restorations, an individualization using extrinsic staining can be applied. This study aimed to evaluate the surface roughness and fatigue strength (survival) of high-translucency zirconia (3Y-TZP, YZ®HT, Vita Zanhfabrik) with extrinsic characterization and/or glaze.

Methods

Sixty (60) zirconia discs (12 × 1.2 mm) were obtained, sintered, and randomly distributed among three groups (n = 20) according to the surface finishing protocol: C (control), C + G (extrinsic characterization followed by a glaze layer), and G (glaze layer). The surface roughness (Ra) was analyzed with a contact profilometer. Subsequently, the specimens were subjected to a fatigue load profile starting at 120 N during 20,000 cycles at 4 Hz frequency, with a 5% increase at each step until failure. The failed specimens were evaluated under a stereomicroscope. Surface roughness analysis was evaluated by using one-way ANOVA and post hoc Tukey tests (95%); while fatigue survival probability was analyzed with Kaplan-Meier and Mantel-Cox (log- rank, 95%).

Results

One-way ANOVA revealed that surface roughness was affected by the finishing protocol, where C + G showed the highest mean value (0.46 ± 0.18 µm)A followed by G (0.30 ± 0.10 µm)B, and C (0.19 ± 0.02 µm)C. While for fatigue strength, the G protocol presented a higher mean value (243.00, and 222.36-263.63)A, followed by C + G (192.75 and 186.61-198.88)B and C (172.50 and 159.43-185.56)C.

Conclusion

Surface finishing protocols modify the surface roughness and fatigue strength of high-translucent zirconia. Regardless of the surface roughness, both glazing protocols improved the ceramic fatigue strength, favoring the restoration's long-term survival.

Effect of surface treatments on wear and surface properties of different CAD-CAM materials and their enamel antagonists

STATEMENT OF PROBLEM

Which surface treatment provides optimal surface roughness, microhardness, and wear behavior for computer-aided design and computer-aided manufacturing (CAD-CAM) materials and their enamel antagonists is unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of surface treatment on the surface roughness, microhardness, and 2-body wear of different CAD-CAM materials and their enamel antagonists.

MATERIAL AND METHODS

Monolithic zirconia, polymer-infiltrated ceramic network, lithium disilicate, leucite-reinforced ceramic, zirconia-reinforced lithium silicate, and feldspathic ceramic specimens were sliced into 2-mm-thick rectangular plates and divided into polished or glazed subgroups (n=6). After surface roughness and microhardness measurements, the specimens were loaded at 49 N for 250 000 cycles and simultaneously thermocycled (5 °C and 55 °C). All specimens were scanned before and after the wear test by using a scanner. The volumetric loss and wear depth of the materials and the volumetric and height loss of the enamel were calculated, and scanning electron microscope images of the specimens were made. Multiple 2-way ANOVAs and Tukey honestly significant difference tests were used to assess the effect of material and surface treatment on surface roughness, microhardness, and wear behavior of materials and enamel (α=.05).

RESULTS

Material and surface treatment interactions affected the surface roughness (P<.001), microhardness (P<.001), volumetric loss of materials (P=.044), and height loss of enamel (P<.001).

CONCLUSIONS

Polishing resulted in higher surface roughness and microhardness than glazing. Volumetric loss depended on the material, which affected the height loss of the antagonists. Glazing and polishing had similar effects on the volumetric loss of materials and antagonists. No correlation was found between the wear of materials and the antagonists, nor between the surface roughness of materials and the volumetric loss of materials or antagonists.

Evaluation of the Tooth Surface after Irradiation with Diode Laser Applied for Removal of Dental Microorganisms from Teeth of Patients with Gingivitis, Using X-ray Photoelectron (XPS) and Optical Profilometry (OP)

Gingivitis is accompanied by microorganisms, including pathogens, which must be eliminated to speed up the treatment of inflammation. Laser irradiation may be one of the safe methods for reducing tissue contamination on the tooth surface. The aim of the study was the assessment of the tooth surface in patients with gingivitis after the use of a diode laser to eliminate microorganisms living there. In the first stage of the research, microorganisms were isolated (Candida albicans, C. guilliermondii, Escherichia coli, Haemophilus parainfluenzae, Klebsiella oxytoca, Neisseria subflava, Rothia dentocariosa, Rothia mucilaginosa, Streptococcus pneumoniae) from three patients with gingivitis, their identification confirmed using the MALDI-TOF MS technique (matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry). Then, the irradiation process with a diode laser was optimized to a wavelength of 810 nm ± 10 nm in five variants to reduce microorganisms on the tooth. The tooth surface was analyzed by X-ray photoelectron spectroscopy (XPS) and optical profilometry (OP) before and after irradiation. 103 to 106 CFU were detected on a 0.4 cm² tooth area. Nine types of bacteria and two types of fungi dominated among the microorganisms. The laser at the most effective biocidal dose of 25 W/15.000 Hz/10 µs, average = 3.84 W, with three uses after 15 s, increased the reduction of fungi from 57.97% to 93.80%, and bacteria from 30.67% to 100%. This dose also caused a decrease in the degree of oxidation and in the effect of smoothing on the treated surfaces.

The Use of a Diode Laser for Removal of Microorganisms from the Surfaces of Zirconia and Porcelain Applied to Superstructure Dental Implants

The aim of this paper was to study the effectiveness of a diode laser (LD) for removal of microorganisms isolated from porcelain and zirconia crown surfaces used in implantoprosthetics in order to minimize infections around dental implants. In order to optimize biocidal efficacy of the process (at the same time, avoiding increasing the surface roughness during decontamination) the effects of diode laser doses were investigated. The irradiation was performed with a diode laser at the wavelength of λ = 810 nm in three variants with a different number of repetitions (1 × 15 s, 2 × 15 s, 3 × 15 s). The quantitative microbial contamination of the surface of teeth, porcelain and zirconia crowns assessment was made using the culture-dependent method. The identification of microorganisms took place using the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and next-generation sequencing (NGS) methods. The studies of the surface morphology and roughness were carried out by means of the optical profilometry, scanning electron microscopy (SEM) and optical microscopy with the C1 confocal attachment. The most important conclusion from the research is the fact that the laser operation, regardless of the exposure time, effectively eliminates the microorganisms from the surfaces used for dental implant rebuilding and does not have a destructive effect on the tested material.