Zirconia Hybrid Research Articles

Metal-free implant-supported single-tooth restorations. Part I: Abutments and cemented crowns.

In many areas of restorative dentistry, metal-free materials offer an alternative to metal-based restorations while ensuring high levels of biocompatibility and esthetics. Rapidly evolving CAD/CAM technology has significantly expanded the range of materials available, providing access to materials classes and their combinations not previously available within conventional manufacturing, such as zirconia ceramics and hybrid ceramics. In addition, digital methods offer previously unavailable options in diagnostics, greater planning reliability, better material quality through standardization of the manufacturing process, and reproducibility - significant benefits that can be used to advantage, especially in oral implantology. Even though technological progress in the field of metal-free materials has given rise to considerable improvements in their mechanical properties over the decades, their clinical long-term success is still very much dependent on an appropriate indication and proper material selection, on the knowledge and skills of the dental practitioner and dental technician, and on an adequate occlusion concept. The high rate of innovation - both with regard to the materials themselves and to CAD/CAM technology - therefore requires an adequate level of prior knowledge to sensibly and successfully implement the wide range of possibilities now open. It is becoming more and more puzzling for users to find their way around the many different new techniques and materials. This review article provides an up-to-date overview of the possibilities and limitations of metal-free implant-supported single-tooth restorations. This first part discusses abutments and cemented crowns. Resultant treatment concepts are presented and evaluated based on clinical examples.

Fracture resistance and survival of implant-supported, zirconia-based hybrid-abutment crowns: Influence of aging andcrown structure.

The aim of the present study was to investigate fracture resistance of implant-supported zirconia-based crowns (monolayer vs bilayer) cemented to hybrid abutments. Monolayer and bilayer zirconia crowns were constructed and cemented to zirconia hybrid abutments. Crowns were divided into two subgroups: (a) untreated control group; and (b) experimental group, which underwent thermal-cycling mechanical loading in a chewing simulator. Up to 1.2 million stress cycles with simultaneous thermocycling (5 and 55°C) were applied. Samples were finally subjected to static load to fracture. Data were analyzed using one-way analysis of variance and t test. Fractured surfaces were observed using scanning electron microscopy. Monolayer zirconia crowns had a 100% survival rate upon completion of the thermal mechanical loading, whereas bilayer zirconia crowns had a 50% survival rate. The fracture load of monolayer zirconia crowns was significantly higher than that of bilayer crowns. Moreover, the fracture load was significantly reduced in monolayer zirconia crowns after aging. Monolayer zirconia crowns showed bulk fracture within the monolayer, while bilayer crowns exhibited cohesive fracture within the veneering porcelain only. Monolayer implant-supported hybrid-abutment crowns exhibit significantly higher fracture resistance compared to bilayer crowns, making them better suited to handle higher masticatory loads encountered in the posterior region of the mouth.

Marginal and Internal Adaptation of Hybrid Abutment Assemblies After Central and Local Manufacturing, Respectively.

Central manufacturing of two-piece computer-aided design/computer-aided manufacture (CAD/CAM) zirconia abutments may provide a higher accuracy of internal and external adaptation at the expense of delayed restoration delivery. The aim of this study was to compare the fit of two-part zirconia abutments that were either fabricated centrally with the DEDICAM system or at a local laboratory. The field of interest was the marginal, external, and internal luting gap between the titanium insert and CAD/CAM zirconia coping. Two groups of nine two-piece CAD/CAM zirconia hybrid abutments were subjected to scanning electron microscopy (SEM) to evaluate the precision of fit and thickness of the adhesive joint. Control specimens were fabricated with the CAMLOG DEDICAM system at the manufacturer's site; the test specimens were produced in a local laboratory. After embedding all samples (n = 18) in resin, they were sectioned, and the external, marginal, and internal luting gaps between the titanium base and zirconia coping were measured with SEM. Welch's t test was used for statistical analysis of the obtained data. The overall range of measured gaps between the components of two-piece CAD/CAM zirconia abutments was 0 to 115.5 μm; the mean overall gap size and standard deviation was 45.61 ± 5.88 μm and showed no appreciable difference between the test and control groups. The mean sizes of the marginal/external and internal gaps showed only negligible differences. The internal gap size was generally larger and showed a higher variability than the marginal/external gaps, albeit on a very low level. None of the reported differences between the test and control specimens were statistically significant. Luting-gap sizes of CAMLOG DEDICAM- and locally fabricated CAD/CAM zirconia hybrid abutments showed no appreciable difference. Both configurations of two-piece abutments provided a highly precise fit of hybrid components, overmatching the high-quality standards in CAD/CAM implant-based prosthetic dentistry.

Continuous flow catalytic partial hydrogenation of hydrocarbons and alcohols over hybrid Pd/ZrO2/PVA wall reactors

• Wall reactors comprising Pd nanoparticles into an hybrid zirconia / polyvinyl alcohol layer are prepared. • Wall reactors are used in the catalytic partial hydrogenation reaction of unsaturated hydrocarbons in the liquid phase. • Monoenes are obtained with excellent selectivity for dienes and alkynes, respectively, under continuous flow conditions. • Minimal amounts of catalyst and mild reaction conditions are required in hydrophilic solvents. • Neither metal leaching nor need of additives is observed. Catalytic hydrogenation reactions of functionalized hydrocarbons are of utmost interest in the fine-chemicals industry. Current hurdles relate to catalyst selectivity and stability, which often require use of sophisticated catalysts and/or the use of considerable amount of toxic additives. For practical applications, processes intensification would also be needed in terms of reagents/catalyst separation, improved space-time-yield productivity. We have shown that catalytic wall reactors comprising a zirconia/polyvinyl alcohol/Pd hybrids layered onto an inert solid support can be easily engineered and used in the liquid phase continuous flow partial hydrogenation reaction of alkenes and alkynes. Films of typical 0.5–1.5 nm thickness and containing ca. 10% wt palladium nanoparticles of 3.6 ± 0.9 nm size (TEM) provided good conversion and selectivity (88–99%) in the partial hydrogenation of 1,5- cyclooctadiene and 3-hexyn-1-ol over ca. 1 mg hybrid catalyst, under very mild flow conditions, i.e. residence times 150–180 s and room temperature. The catalysts showed remarkable resistance over prolonged time on stream, with neither metal leaching detected nor additives or regeneration steps required for use in hydrophilic solvents.

Enantiomer Separation of Acidic Chiral Compounds on a Clarithromycin‐Zirconia Hybrid Monolith by Capillary Electrochromatography

A carbamoylated clarithromycin‐incorporated zirconia hybrid monolith (CLA‐ZHM) was prepared in a fused silica capillary via an in situ sol–gel process. The CLA‐ZHM capillary column was employed for enantiomer separation of acidic chiral compounds by capillary electrochromatography in eluents consisting of acetonitrile, methanol, and acetic acid and triethylamine as electrolytes. Influences of the composition of eluent and applied voltage on enantiomer separation were investigated. Baseline resolutions were achieved for 10 acidic compounds in an eluent consisting of 70/30 acetonitrile/methanol with 255 mM acetic acid and 17.4 mM triethylamine at an applied voltage of −10 kV and capillary temperature of 25 °C. Relative standard deviation values in resolution parameters for column to column and batch to batch repeatability were less than 2.7% (for n = 3) under the optimal separation settings, indicating that stability of the ZHM columns and reproducibility of the column preparation method are acceptable.

Fracture Resistance of Titanium-Based Lithium Disilicate and Zirconia Implant Restorations.

To evaluate the fracture resistance of a newer lithium disilicate abutment material. A premolar-shaped implant crown was designed using CAD/CAM software, and four groups of implant and crown combinations were milled: (1) lithium-disilicate hybrid-abutment crown; (2) "screwmentable" lithium-disilicate hybrid abutment/lithium-disilicate crown with screw channel; (3) lithium-disilicate hybrid abutment/lithium-disilicate crown; and (4) zirconia hybrid abutment/lithium-disilicate crown (control). The specimens were cemented to a titanium-base implant system, subjected to thermocycling and cyclic loading, and fractured in a material testing device. The lithium-disilicate hybrid-abutment crown had significantly greater fracture load than all the other groups, which were not significantly different from each other. Based on fracture load, the new lithium-disilicate hybrid-abutment material may serve as a viable alternative to the use of zirconia as a hybrid-abutment material.

Compressive and flexural properties of novel polylactic acid/hydroxyapatite/yttria-stabilized zirconia hybrid nanocomposite scaffold

ABSTRACTThe mechanical property is a crucial factor in the design of bone tissue engineering scaffolds. In the current study, novel PLLA (Poly-L-lactic acid)–Hydroxyapatite (HA)–yttria-stabilized zirconia (YSZ) nanocomposite scaffold with various compositions was prepared and characterized. The effect of HA and YSZ contents on the mechanical behavior of the resultant composites was investigated. TEM micrograph revealed that HA particles are needle-like in shape and nano in size. Scanning electron microscopy (SEM) micrograph also showed that YSZ powder is in granule form and submicron size. SEM disclosed that all scaffolds had a highly interconnected porous structure and X-ray diffractometry revealed that there were some molecular interactions between PLA (Polylactic acid), HA, and YSZ in the composites. The results depicted that introducing YSZ to the nanocomposite leads to a significant increase in compressive strength, modulus, and densification strain. In addition, flexural strength and modulus showed an upward trend by adding YSZ particles to scaffolds. It should be noted that PLA–20%HA–20%YSZ indicates the highest strength and modulus in both compression and bending tests, though, it did not demonstrate the proper strain compared to other scaffolds. Thus, PLA–15%HA–15%YSZ has been reported as the best candidate due to appropriate strength and strain. Also, energy absorption in nanocomposites showed an upward trend by increasing the amount of YSZ particles. It was found that the strength of samples was declined after being soaked in simulated body fluid. However, scaffolds with HA underwent more decrease in strength compared to samples containing YSZ.

In Vitro Microbiological Analysis of Bacterial Seal in Hybrid Zirconia Abutment Tapered Connection.

The aim of this study was to evaluate the bacterial seal at the implant-hybrid zirconia abutment interface and Morse taper-type connections through in vitro microbiological analysis. Sixteen implants and their respective abutments were divided into 3 groups: test (10 sets), positive control (3 sets), and negative control (3 sets). In the test group, 10 implants were contaminated with Escherichia coli using a sterile inoculating loop to the inner portion of the implants, followed by torque application to the abutment (30 N·cm). The positive controls were also contaminated, but no torque was applied to the abutment screw. The negative control consisted of uncontaminated sets. All specimens were immersed in test tubes containing 5 mL brain heart infusion (BHI) broth, maintained in a microbiological incubator for 14 days at 37°C under aerobic conditions, and monitored every 24 hours for evidence of bacterial growth. During the 14 days of incubation, no significant increase in the number of cloudy culture media was observed in the test group (P = 0.448). No significant difference in broth turbidity ratio was observed (P > 0.05). Hybrid zirconia abutments can create an effective seal at the tapered abutment-implant interface with a 30-N·cm installation torque.

Study of Ethylurea Doped Hybrid Zirconia Nanoparticle Based Sol–Gel Coating for the Corrosion Protection of Aluminum

Study of Ethylurea Doped Hybrid Zirconia Nanoparticle Based Sol–Gel Coating for the Corrosion Protection of Aluminum

Preparation and optical properties of functionalized zirconia–silica xerogels displaying a multicolor emission at UV excitation

A simple procedure for the functionalization of europium-doped zirconia–silica sol–gel composites with 1,10-phenanthroline is demonstrated. The functionalized materials display a multicolor emission at UV excitation, containing two components: a red component coming from Eu(phen)2(NO3)3 and a blue component from Zr(IV)-1, 10-phenanthroline complexes. Room-temperature diffuse reflectance spectra and excitation/luminescence spectra are used to describe the optical properties of the hybrid zirconia–silica composites. The functionalized samples are characterized by X-ray diffraction, electron microscopy and IR-spectroscopy. Excitation spectra prove an efficient energy transfer between 1,10-phenanthroline and the Eu3+ ion. A simple procedure for functionalization of europium-doped zirconia–silica sol–gel composites with 1,10-phenanthroline is demonstrated. The functionalized materials display a multicolor emission at UV excitation. Luminescence spectra of inorganic and hybrid gels at 330 nm excitation are presented. The Eu3+ 5 D 0 → 7 F 0,1,2,3,4 f–f electronic transitions are denoted as 0–0, 0–1, 0–2, 0–3 and 0–4.

Fitting accuracy and fracture resistance of crowns using a hybrid zirconia frame made of both porous and dense zirconia.

The purpose of this study is to evaluate the fitting accuracy and fracture resistance of crowns using a hybrid zirconia frame made of both porous and dense zirconia. Commercial semi-sintered zirconia, sintered dense zirconia and sintered hybrid zirconia were used. Sintered zirconia was milled using the CAD/CAM system, and semi-sintered zirconia was milled and sintered to fabricate molar crown frames. Completed frames were veneered with tooth-colored porcelain. The marginal and internal gaps between frames/crowns and abutments were measured. Each crown specimen was subjected to a fracture test. There were no significant differences in marginal and internal gap among all the frames and crowns. The crown with the hybrid zirconia frame had a 31-35% greater fracture load than that with the commercial or dense zirconia frame (p<0.01). This suggests that the all-ceramic crowns with a hybrid zirconia frame have a high fracture resistance.

Development of functional hybrid cotton fabrics by coating with SiO2and ZrO2/SiO2composites

The silica (SiO2) sol and hybrid zirconia (ZrO2)/SiO2 sol were used to coat cotton fabrics using the pad-dry-cure method to improve their physical and functional properties. The physical properties of coated and uncoated fabrics, such as tensile strength, tear strength, crease recovery angle, air permeability and whiteness index, were tested as per the standard test methods. The wash durability of the coating on the fabric was also analysed after five and 10 wash cycles. The observed results show that the ZrO2/SiO2-coated fabric has better physical properties than SiO2-coated and uncoated fabrics. In addition, an antibacterial activity test confirms that the SiO2-coated fabric possesses higher antibacterial properties against Escherichia coli and Staphylococcus aureus than the ZrO2/SiO2-coated fabrics.

Machinability of poly(methyl methacrylate) infiltrated zirconia hybrid composites

A new poly(methyl methacrylate) (PMMA) infiltrated zirconia hybrid composite (PZC) has been demonstrated to exhibit improved fracture toughness; however, its machinability remains unknown. The objective of this research is to characterize and correlate the machinability of PZC with its microstructure and mechanical properties. The results suggest that the composite exhibits an excellent machinability that is similar to that of resin composite and better than that of glasses and ceramics. This PZC hybrid composite may enable new opportunities for the use of PZC with the dental CAD/CAM technique.

Investigations on coatings generated from silica–zirconia hybrid sols synthesized through hydrolytic/non-hydrolytic wet chemical routes on PMMA substrates

Organic–inorganic silica–zirconia hybrid sols were synthesized by a wet chemical process using an organically modified silane (methacryloxypropyltrimethoxysilane) and zirconium-n-propoxide. One sol was synthesized through a hydrolytic route using isopropanol as the solvent, whereas another was synthesized through a non-hydrolytic route using tetrahydrofuran as the solvent. These sols were independently dip coated on flat polymethylmethacrylate (PMMA) substrates. The coated substrates were subjected to ultraviolet curing followed by thermal curing at 80°C for 6h. The cured coatings were characterized and tested for their optical (UV–vis transmittance, haze), mechanical (abrasion resistance) and weather resistance properties according to ASTM standard testing methods. The FTIR spectra were also acquired and analyzed to study the bonding characteristics under the two synthesis conditions. The properties of the coatings obtained from the hybrid sols synthesized through hydrolytic/non-hydrolytic routes were compared.

Functionalization of Sol-Gel Zirconia Composites with Europium Complexes

Different sol-gel strategies based on functionalization of ZrO2:Eu microparticles with 1,10- phenanthroline (phen) and incorporation of colloidal Eu(phen)2(NO3)3 into zirconia have been used to obtain hybrid sol-gel composites with controlled optical properties. The process leads to materials with quantum yields of about 48% monitoring the 615 nm emission line at 350 nm excitation. Excitation/ luminescence spectroscopy, diffuse reflectance spectroscopy and X-ray diffraction have been used to characterize the hybrid zirconia composites.

Adopting the principles of collagen biomineralization for intrafibrillar infiltration of yttria-stabilized zirconia into three-dimensional collagen scaffolds.

In this paper, we report a process for generating collagen-yttria-stabilized amorphous zirconia hybrid scaffolds by introducing acetylacetone-inhibited zirconia precursor nanodroplets into a poly(allylamine)-coated collagen matrix. This polyelectrolyte coating triggers intrafibrillar condensation of the precursors into amorphous zirconia, which is subsequently transformed into tetragonal yttria-stabilized zirconia after calcination. Our findings represent a new paradigm in the synthesis of non-naturally occurring collagen-based hybrid scaffolds under alcoholic mineralizing conditions.

Effect of addition of surface modified nanosilica into silica–zirconia hybrid sol–gel matrix

An organic–inorganic hybrid sol (MZ) comprising a methacrylate functionalized silane matrix (M) and zirconium-n-propoxide (Z) was prepared using sol–gel technique. Two methodologies were adopted to modify the hybrid sol for generating nanocomposite coatings viz., (a) addition of acrylic surface modified silica nanoparticles (N) of diameter ∼20 nm to the sol to enhance their compatibility with the hybrid sol–gel matrix and (b) in-situ formation of a three dimensional silica network by addition of tetraethoxy silane (T) to the sol MZ. In the first methodology, the sols were prepared with six different weight ratios of the nanoparticles to the sol, i.e. 0, 0.01, 0.05, 0.1, 0.25 and 1 which were labelled as MZ+N x where x =0, 1, 2, 3, 4 and 5 respectively. The prepared sols were dip coated on 100 mm×100 mm polycarbonate substrates followed by thermal curing at 130 °C. The coatings were characterized for their mechanical properties like pencil scratch hardness, scratch resistance using scratch tester, nanoindentation hardness, and abrasion resistance as well as visible light transmittance. FT-IR studies were also carried out on heat-treated gels derived from the sols. A maximum pencil scratch hardness of 3H was obtained for the MZ+T coatings and these coatings withstood a critical load of 4.3±0.7 N before failure during scratch test. The maximum nanoindentation hardness of 3.8±0.01 GPa was obtained for the MZ+N5 coatings. The abrasion resistance of MZ+T coatings was higher when compared to MZ+N0 and MZ+N5 coatings. The scratch and nanoindentation hardness were seen to be better for an in-situ formed –Si–O–Si– network in the hybrid sol when compared to those obtained from coatings generated by external addition of acrylic surface modified silica nanoparticles. The difference in properties was attributed to the level of interaction between the nanoparticles and hybrid sol–gel matrix.

Poly(vinyl butyral)-zirconia hybrid films formed by sol-gel process

A sol-gel process has been successfully utilized to form hybrid materials of poly(vinyl butyral) (PVB) and zirconium dioxide (zirconia). The gelation occurred due to the interaction between remaining hydroxyl group of PVB and zirconia. The hybrids showed good optical transparency and significant improvement in Young's modulus, dynamic mechanical property, abrasion resistance and impact resistance. The glass transition temperature of PVB shifted to higher temperatures by hybridization of PVB and zirconia.

Two-dimensional DFB laser fabricated on dye-doped hybrid zirconia f ilm by soft lithography

A two-dimensional (2D) distributed feedback (DFB) structure is fabricated on dye-doped sol-gel derived hybrid zirconia films by soft lithography. The Q-switched Nd:YAG laser (\lambda = 532 nm) is used to pump these structures. The lasing emissions of the gain medium doped with Rhodamine 6G (Rh6G) in two perpendicular directions are shown, and the threshold pump energy is measured.

Fabrication of cellulose acetate–zirconia hybrid membranes for ultrafiltration applications: Performance, structure and fouling analysis

Organic–inorganic hybrid membranes were fabricated by solution casting using different ratios of cellulose acetate (CA) and zirconia (ZrO 2) in N,N′-dimethylformamide (DMF). The addition of ZrO 2 microparticles in the CA matrix was varied from 0 to 7 wt.%. The developed membranes were characterized for ultrafiltration (UF) performance, mechanical stability, morphology and fouling-resistant ability. It is found that the pure water flux increases from 15.6 to 46.7 lm −2 h −1 while the tensile strength decreases from 2 to 1.4 N/mm 2 with addition of zirconia from 0 to 7 wt.% to pure CA, respectively. Morphological studies indicate that the CA:ZrO 2 hybrid membranes possess asymmetric structure with ultra scale pores. From the pore statistics analysis, it was seen that the CA:ZrO 2 (6:4 ratio) hybrid membranes have an average pore radius of 47.52 Å compared to 26.88 Å of pure CA membrane. It was found that the hybrid CA:ZrO 2 membranes exhibit higher permeate flux for the separation of different molecular weight proteins compared to pure CA membrane. It has been demonstrated that the fouling-resistant ability and the recycling property of CA:ZrO 2 hybrid membranes are enhanced due to the high flux recovery ratio with the addition of ZrO 2 in the casting solution.