Improving wettability,antibacterial and tribological behaviors of zirconia ceramics through surface texturing

3 mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) ceramics are promising restorative materials being extensively used for fabricating dental prosthodontics. However, peri-implant inflammation and the severe abrasive wear on occlusive natural teeth are two critical problems in the clinical application of zirconia dentures. The paper aims to improve the antibacterial and tribological performance of 3Y-TZP ceramics through laser surface texturing. Three types of surface textures, including micro-honeycombs, micro-composite grids, and micro-grooves, were fabricated onto the zirconia specimens. The effects of different microtextures on the surface behaviors, including wettability, bacteria adhesion, and wear behavior, of 3Y-TZP ceramics were rigorously studied. The results indicate that the introduction of microtextures can change the solid-liquid contact of the zirconia surface, thus affecting its wettability. Wettability is a decisive factor that determinines the antibacterial behavior of textured zirconia ceramics. A hydrophobic surface is more conducive to inhibiting the adhesion, extension, reproduction of bacteria and thus achieves a superior antibacterial performance. The examined microtextures yield the improvement of wear resistance for the zirconia ceramics, but their performances depend on the texture density and the structural strength. The results obtained can provide technical guidance for the design and application of microtextures in the restorative dental fields.     

Synergistic reinforcement of surface modification on improving the bonding of veneering ceramics to zirconia

Veneering ceramics should be strongly bonded to zirconia core in order to achieve successfully long-term clinical practice. Indeed, to pursue the high zirconia core–veneering ceramic bonding is still a concerned issue. In this regard, this study was to treat zirconia surface using a 3?wt% Si₃N₄ solution in 4?M NaOH and to investigate the effect of soaking time (5, 10, and 20 days) on the surface properties of zirconia and shear bond strength between zirconia and veneering ceramics. The residual veneering ceramics on zirconia surfaces and failure modes were also examined after fracture. The results showed that the phase composition of zirconia before and after surface modification was not changed. The elemental mapping and depth profiling consistently revealed the soaking-time-dependent Si content on the zirconia surface. The surface roughness of zirconia was significantly (P?<?0.05) increased with the increasing soaking time. When zirconia was treated for 10 days, the shear bond strength value of 27.4?MPa was significantly (P?<?0.05) higher than the control (18.6?MPa), associated with greater remaining amounts of veneering ceramics on the zirconia surface. The failure mode of the treated zirconia was almost the mixed failure. On the basis of the data, surface modification using Si₃N₄ in NaOH solution for zirconia core could be a simple and effective method for enhancing the veneering ceramic–zirconia bonding.     

Effect of surface finishing and thickness on the translucency of zirconia dental ceramics

The effects of different surface finishing procedures on the translucency of yttria stabilized zirconia ceramics (ZrO₂) were evaluated. ZrO₂-3mol.%Y₂O₃ (designed Zr3) or ZrO₂-5mol.%Y₂O₃(Zr5) specimens with thickness varying between 0.5 and 1.5 mm were obtained by sintering at 1500 °C for 2 h. Surface finishing of the sintered specimens was done in three distinct manners: polishing with diamond pastes, blasting with Al₂O₃ particles and blasting with Al₂O₃–SiO₂ particles, according to the preparation protocol for dental prostheses. These sample groups were characterized by X-Ray diffraction analysis, scanning electron microscopy, surface roughness and spectrophotometry. The sintered ceramics exhibited relative densities higher than 99% and were composed of 68.5% and 31.5%of tetragonal (t)-ZrO₂ and cubic(c)-ZrO₂ for composition Zr3 and 25.2% and 74.8% for composition Zr5, respectively. Furthermore, 1.5 to 1.8% of monoclinic (m)-ZrO₂, has been found in the blasted surfaces. The average grain size varied from 0.5 μm for Zr3 to 1.45 μm for the Zr5 samples. After polishing, all samples presented a surface roughness R_aof about 0.05 μm, while blasting resulted in an increased roughness ranging between 1.24 μm and 1.49 μm.Samples rich in (c)-ZrO₂ phase (Zr5) are more translucent than samples rich in (t)-ZrO₂ (Zr3) because of their larger grain size and because the cubic phase is less anisotropic than (t)-ZrO₂. Furthermore, the translucency of thinner samples is more affected by abrasive blasting because they also present the highly anisotropic monoclinic(m)-ZrO₂ phase and, therefore, the reduction of translucency is more pronounced. Parameters such as grain size, crystalline phase composition, porosity and grain boundary density are used to explain the phenomena involved in the differences of translucency of these materials.     

Effect of airborne-particle abrasion of yttria-containing zirconia dental ceramics on mechanical properties before and after regeneration firing

The zirconia-resin adhesion, crucial in fixed dental prostheses, may be mechanically enhanced by airborne-particle abrasion (APA) induced surface roughening. APA may substantially increase the strength of 3Y-TZP, which is associated with (sub)surface compressive residual stresses through t-m phase transformation. In this work, the effects of APA and regeneration firing (RF) (1000 °C, 15 min) of various zirconia dental ceramics containing 3–5 mol.% of yttria were investigated. The phase composition, (sub)surface microstructural changes, and biaxial flexural strengths coupled with Weibull statistics and fractography were analysed and compared. The results show a significant increase in strength for 3Y and 4Y specimens after APA, ascribed to the t-m transformation toughening. However, APA substantially decreased the strength of 5Y variant. After RF, the ferroelastic domain switching phenomenon was presumably the persisting mechanism to withstand the propagation of APA-induced cracks in 3Y and 4Y zirconias, not being inferior to strength values of the as-sintered counterparts.     

Extrusion-based 3D printing of fully dense zirconia ceramics for dental restorations

Extrusion-based 3D printing using zirconia ceramics shows promising results in biomedical applications, but the challenges in deployment are still significant. In this study, we developed an optimized extrusion-based 3D printing method for fabrication of intricate, fully dense ceramics based on gelled zirconia suspensions. The viscoelastic properties of the suspensions were tailored to facilitate smooth flow through a 150–250 µm nozzle at high solid volume fraction (52%) and produce self-supporting features. Because of the minimal organic content, the as-dried zirconia specimens could be directly sintered without binder-removal steps. The maximum relative density, flexural strength, and hardness of the sintered zirconia ceramics were 99.3%, 1010 MPa, and 15.9 GPa, respectively. Zirconia dental restorations were fabricated, and the occlusal details were preserved by co-printing a novel polyacrylate supporting material which can be removed by cooling owing to its temperature-dependent rheological behavior.     

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.     

Bonding of novel self-glazed zirconia dental ceramics

ABSTRACT

Bonding behaviours of a novel self-glazed zirconia dental material were investigated. The effect of a preformed porous nanoceramic bonding surface and the different cleansing methods on saliva-contaminated bonding surfaces was assessed in this in vitro study. Cleaning procedures commonly used in dental offices were tested. All specimens demonstrated adhesive fracture patterns except for airborne particle abrasion group, which resulted in mixed-type fracture pattern and the highest bonding force values. No statistically significant differences in bonding force values were found between self-glazed zirconia with and without a preformed porous nanoceramic bonding surface when bonded with the self-adhesive resin cement (RelyX? Unicem 2). Scanning electron micrographs revealed no interaction between the bonding surface and the resin cement after priming. Mechanical retention is the predominant bonding mechanism between the bonding surface and the luting resin cement.     

Effect of laser surface texturing on primary stability and surface properties of zirconia implants

The aim of this study was to investigate the influence of different laser surface texturing parameters on static and dynamic coefficient of friction values of Yttria-tetragonal zirconia polycrystals (3Y-TZP) against bone to assess the primary stability of implants. The ability of the textures to promote osseointegration, as measured by wettability, and eventual changes in roughness, due to possible aging during sterilization, were also assessed. 3Y-TZP disks were divided into four groups: as sintered sample, sandblasting and etching treatment, laser irradiation using two output power of 0.9 and 1.8 W. The friction tests were carried out by using a pin-on-plate configuration, being the pins the 3Y-TZP disks and the plates the bone. The surfaces were inspected by SEM/EDS and by surface roughness profilometer. Wettability characteristics were also evaluated by drop contact angle, and aging was assessed, after laser treatments, by XRD analysis. Results demonstrate that with laser surface texturing of zirconia it is possible to combine better wettability, better aging performance, and better primary stability, as compared to traditional - Sand blasting and Etching treatments. Thus, it is shown that the laser irradiation technique is a promising alternative to conventional sandblasting and etching procedures.     

Femtosecond laser microstructuring of alumina toughened zirconia for surface functionalization of dental implants

The continuous need for high-performance implants that can withstand mechanical loads while promoting implant integration into bone has focused recent research on the surface modification of hard ceramics. Their properties of biocompatibility, high mechanical and fatigue resistance and aesthetic color have contributed to its succefull applications in dentistry. Alumina toughened Zirconia (ATZ) has been gaining attention as a material for dental implants applications due to its advanced mechanical properties and minimal degradation at body temperature. Still, in order to improve tissue response to this bioinert material, additional modifications are desirable. Improving the surface functionality of this ceramic could lead to enhanced implant-tissue interaction and subsequently, a successful implant integration.In this work, microtopographies were developed on the surface of Alumina toughened Zirconia using an ultrafast laser methodology, aiming at improving the cellular response to this ceramic. Microscale grooves and grid-like geometries were produced on ATZ ceramics by femtosecond laser ablation, with a pulse width of 150 fs, wavelength of 800 nm and repetition rate of 1 kHz. The variation of surface topography, roughness, chemistry and wettability with different laser processing parameters was examined.Cell-surface interactions were evaluated for 7 days on both microstructured surfaces and a non-treated control with pre-osteoblasts, MC3T3-E1 cells. Both surface topographies showed to improve cell response, with increased metabolic activity when compared to the untreated control and modulating cell morphology up to 7 days.The obtained results suggest that femtosecond laser texturing may be a suitable non-contact methodology for creating tunable micro-scale surface topography on ATZ ceramics to enhance the biological response.     

Comparative investigation of tribological behavior of hybrid dental restorative composite materials

Dental restorative composite materials require appropriate tribological characteristics to bear different stresses in the oral environment. This study inspects the tribological aspects of micro-nano parttticulate filled dental restorative composite materials. Nano-hydroxyapatite (nHA) (0, 2, 4, 6, and 8 wt%), alumina (20 wt%), and titanium oxide (20 wt%) were reinforced in the form of hybrid into the dental resin matrix. The dental resin matrix was fabricated from a base monomer, diluents, initiator, and accelerator. Two body sliding wear tests were conducted by rubbing the prepared nano-composites against a Carbon steel-EN 31 counter plate. ANOVA was used to find significant statistical factors. Besides, the wear mechanisms were clarified via scanning electron microscopy. EDS (energy dispersive spectroscopy) analysis was also done to identify the organic and inorganic groups incorporated in the dental composite samples. The results showed that incorporating high amounts of nHA nanoparticles can improve the wear properties of dental composites. The results of specific wear rate were found significant as per literature.     

Effects of solid lubricant and laser surface texturing on tribological behaviors of atmospheric plasma sprayed Al2O3-ZrO2 composite coatings

Atmospheric plasma-sprayed (APS), low-friction Al₂O₃-ZrO₂ coatings were deposited with solid lubricants, and their effects on the laser surface texturing (LST) under a lubricated condition (commercial engine oil, 5W30) were evaluated. All specimens showed a 19.6% dimple density, and the contact angle of the APS coatings after LST processing decreased by ∼19–50%. The hydrophilicity of the APS coatings improved after LST processing, and the tribological behaviors of the APS coating containing different solid lubricants were mainly observed in the abrasive grooves, spalling, microcracks, residual pores and trapped wear debris on the worn surface. The coefficient of friction for the APS coatings was affected by the solid lubricants and the LST processing. The coefficient of friction for the APS coatings (except for h-BN) when adding solid lubricants and LST processing decreased to 3.7–7.9% and 2.3–9.5%, respectively.     

The mechanical behavior of the material-tissue and material-material interface in dental reconstructions

In dental and craniofacial sciences, frequently the goal is to replace lost or damaged natural tissue with synthetic materials. For ideal function, these replacement materials must strongly bond to the existing tissue, but they also must form a hermetic seal that eliminates the passage of microorganisms and fluids that would lead to further tissue destruction or weakening of the interface or the individual materials, compromising the final outcome. Therefore, the study of interfaces is crucial, and the manner in which they can be tested to predict the likelihood of success is of great interest to the field.Because a variety of materials and material combinations are used for the repair or replacement of oral and craniofacial tissues, numerous types of material interfaces exist. A complete discussion of this important topic requires an examination of all of them. In this review article, the three different types of interfaces are treated separately. First, the interface between the tooth tissue and restorative material is explored, specifically by considering resin-based materials such as dental adhesives and composite, and the manner in which they interact with dentin and enamel. Second, the interaction between these same resin-based materials and other structures, such as oxide ceramic dental crowns, are explored, because these tooth replacement materials are typically fixed to the remaining tooth structure through the use of resin-based adhesives and cements, or repaired intraorally with similar materials. Finally, the interface between different synthetic materials, such as metals and ceramics, with dental porcelain used as an esthetic veneering material is addressed.     

Effects of glass-ceramic spray deposition manipulation on the surface characteristics of zirconia dental restorations

A novel glass-ceramic spray deposition (GCSD) method was developed to modify the yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) surface and to enhance the bond strength between Y-TZP and resin cement. Five different experimental groups were characterized, non-treatment (NT), airborne particle abrasion (AB), GCSD without etching (GS), GCSD with 5% HF etching (GSE5), and GCSD with 9.5% HF etching (GSE9), to determine the optimal method for improving the bond strength. Scanning electron microscopy and an argon ion milling system were used to investigate the surface and cross-sectional microstructures. The changes in the surface characteristics of Y-TZP were analyzed via contact angle analysis, atomic force microscopy, X-ray diffraction, and energy-dispersive X-ray spectrometry. The bond strengths were determined using shear bond strength test. The results revealed that GCSD could produce a dense and uniform lithium disilicate glass-ceramic coating layer and infiltrate the Y-TZP surface. This coating resulted in superior micromechanical interlocking and increased hydrophilicity, thereby enhancing the bond strength between Y-TZP and resin cement (P < 0.05). The study findings indicated that GCSD accompanied by 5% HF etching for 100 s is optimal for strengthening the Y-TZP/resin cement bond, thereby providing a novel solution for dental bonding systems.     

Wear behavior of silica-infiltrated monolithic zirconia: Effects on the mechanical properties and surface characterization

The objective of this study was to assess the wear behavior and its effects on the flexural strength of silica-infiltrated zirconia compared to glaze and polishing finishing treatments. To do so, disc-shaped samples of a second-generation zirconia were prepared and divided into three groups: silica infiltration, glazing, or polishing. Half of the samples of each finishing were subjected to sliding wear testing using a steatite antagonist. The discs and antagonists had their volume loss measured. The wear-tested and the other half of samples were subjected to biaxial flexural strength testing and the following characterization analyses were also performed: roughness, hardness, X-ray diffraction, profilometry, and scanning electron microscopy (SEM). Data were evaluated with ANOVA and Weibull analyses. Glazing caused greater antagonist volume loss, followed by silica infiltration, and polishing. Silica-infiltrated zirconia surface was similarly worn to polished, which was lower than that for glazed zirconia. Polished zirconia presented the highest flexural strength. However,the strength decreased and became similar in all worn groups. Silica infiltration showed slightly lower characteristic strength after sliding wear. The highest roughness and hardness values were observed on glazed zirconia. These values decreased after wear testing and became similar to the other groups. SEM evidenced an irregular surface for glazing. No phase transformation occurred after sliding wear. Despite producing some volume loss on zirconia and antagonist surfaces, silica infiltration is a promising alternative for finishing monolithic restorations. Moreover, the damage caused by sliding wear leads to decreasing the strength of zirconia regardless of the surface finishing.     

Nanosecond laser induced microstructure features and effects thereof on the wettability in zirconia

Zirconia are widely employed as a bone-substitute material for surgical implants due to its biocompatible and mechanical properties. However, implants introduced into the human undergo detachment from the host tissue due to poor biological performance. The laser-texturing can enhance the biological performance of the surface by altering surface properties and maintaining the bulk properties of the zirconia. In this work, laser-texturing microstructure features on zirconia are carried out to modify surface characteristics. Wettability are evaluated through water contact angles (WCAs) measurements. To characterize the influence of laser-texturing on pattern morphology, the produced surfaces are measured by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Micro cracks with melted material flowing along the scanning tracks in the untreated areas were observed from SEM. XRD results, in turn, show that the tetragonal → monoclinic phase transformation leads to many tiny cracks around the transformed particles. Wettability can be attributed to the modifications of the surface's microstructure depending on laser parameters and chemical composition. The stability tests prove that the super-hydrophobic surfaces produced by laser-texturing possess good abrasion resistance. This work may provide a simple method for producing zirconia surfaces with controlled wettability with the proper choice of laser parameter for extremely extensive industrial applications.     

Femtosecond laser micro-milling dental glass ceramics: An experimental analysis and COMSOL finite element simulation

Dental glass ceramic materials are widely used in all-ceramic restoration technology. In order to effectively solve the problems existing in the process of traditional diamond cutter milling dental glass ceramic materials, such as severe needle loss, large tool wear and general milling efficiency, a new method of ultrafast laser milling dental glass ceramics is proposed. In this paper, 1030 nm femtosecond laser with pulse width of 600fs was used to micro-mill dental glass ceramics. Confocal laser microscopy was used to measure the milling depth and surface roughness of single-layer milling under selected laser processing parameters. The pre-layered milling software was developed to control the z-axis lifting and to compensate the focal length synchronously. Scanning electron microscope (SEM), Raman spectrometer and Vickers micro-hardness tester were used to characterize the dental glass ceramics after femtosecond laser milling. The results showed that under the specific laser processing parameters, the infrared femtosecond laser milling system can achieve a good processing morphology without changing the surface composition and surface hardness of dental glass ceramics. This new dental glass ceramics processing method based on ultrafast laser technique indicated a new direction for further chair processing of dental all-ceramic restoration technology.     

Evaluation of the effect of high-speed sintering on the mechanical and crystallographic properties of dental zirconia sintered bodies

There are only a few reports investigating the effects of high-speed sintering on the properties of dental zirconia. In this study, we investigated the effects of high-speed sintering on the crystal phase, mechanical properties, microstructure, and LTD resistance of 3 mol. % and 4 mol. % Y₂O₃ stabilized zirconia (3Y and 4Y zirconia). In both 3Y and 4Y zirconia, yttria distribution in the zirconia sintered body was suppressed and the LTD resistance was improved by high-speed sintering. High-speed sintering slightly reduced the mechanical properties of 3Y and 4Y zirconia, but they showed clinically sufficient mechanical properties. From the above results, it was concluded that high-speed sintered 3Y and 4Y zirconia are sufficiently clinically acceptable.     

Wettability modification of zirconia by laser surface texturing and silanization

This paper presents the modification of wettability by nanosecond laser surface textured followed by silanization to fabricate the superhydrophobic zirconia surface. Surface modification by varying the pitch between channels leads to micro-channel and micro-grid pattern with different surface roughness. The generated morphological and metallurgical modifications of the surface are measured by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Numerous micro-pits and cracks in the laser-treated areas can be observed from SEM, which indicates crack propagation dominating the process of laser ablation of zirconia. The surface is superhydrophilic with laser-texturing instantly, whose wettability is modified over time. By analyzing the XPS, carbon content, especially C-C (H) groups, is important for the time-dependent wettability. The hydrophobicity of all laser-textured surfaces is improved after silanization. Laser texturing with smaller pitch (50 μm and 70 μm) leads to superhydrophobic surfaces after silanization, which may be due to the modification of physicochemical properties of substrate by very rapid local heating and cooling on the thick surface layer. Overall, the investigations indicate that wettability modifications can be attributed to the surface's microstructure, which depend on laser processing parameters, and chemical composition, especially in terms of −CF₃, −CF₂, and C-C (H).     

The preparation and surface characterization of zirconia polymorphs

Zirconium hydroxides were obtained by precipitation of zirconium chloride with aqueous ammonia at constant pH followed by hydrothermal treatment The effect of thermal activation of the zirconium hydroxide on physical properties, and the effect of crystalline phase on the surface properties of zirconia were studied. The pressure during the hydrothermal treatment of zirconium hydroxide affected the surface area, particle growth, and phase transformation of the zirconia product. Hydrothermally treated zirconia under atmospheric pressure (LP) shows higher surface area than that under high pressure (HP) and untreated (UT). HP zirconia shows a mixture of tetragonal and monoclinic phase after hydrothermal treatment due to the higher solubility and reprecipitation rate, whereas LP sample shows a tetragonal crystal structure from 600 to 1,050 ℴC. Monoclinic phase zirconia shows greater CO₂ and NH₃ surface adsorption than amorphous and tetragonal phase zirconia. This suggests that the crystal structure of zirconia strongly affects the amount and strength of the surface adsorption site.     

In vitro cyclic fatigue and hydrothermal aging lifetime assessment of yttria-stabilized zirconia dental ceramics

The in vitro lifetime assessment of dental zirconia has been the focus of researchers. This work mainly studied the cyclic fatigue lifetime in saliva and aging lifetime of three commercial zirconia dental materials: two kinds of 3 mol%-yttria stabilized zirconia ST(super-translucence) and MT(medium-translucence), in which MT contains a small amount of alumina; a 5 mol%-yttria stabilized zirconia TT(tooth-translucency). ST and MT materials have higher initial mechanical strength (flexural strength) and initial crack propagation threshold than TT materials, thus they have longer cycle fatigue lifetime, but TT has best aging resistance(no aging) in existing aging procedures. MT has a higher initial mechanical strength and better aging resistance than ST samples due to the influence of alumina at grain boundary, but has lower strength reliability. Finally the service lifetime of the three materials was evaluated, and some guidance for their use is provided.