Zirconia

Boron doped and undoped Poly(vinyl) alcohol/Zirconium-yttrium acetate (PVA/Zr-Y) nanofibers were prepared by electrospinning using PVA as a precursor. The effect of boron doping was investigated in terms of solution properties, morphological changes and thermal properties. The effect of boron doping on calcined yttria stabilized zirconia (YSZ) fibers were evaluated by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy analysis. XRD
analysis revealed varying amounts of monoclinic and tetragonal zirconia present in the undoped fibers calcined at 800oC. The average crystallite sizes of the undoped YSZ were increased from 9.28 to 22.79 nm with calcining temperature increasing from 250 to 800 °C. The crystallite size was enhanced with boron doping. The systematic evolution of morphological features in the spun and the processed fibers were employed by scanning electron microscopy.

The conditions for preparation of high surface area zirconia were studied. Samples were prepared by precipitation from aqueous solutions of zirconium chloride with ammonium hydroxide. The order of addition of the reactants was found to affect the surface area. Digestion of the hydrous zirconia is the key to high surface area zirconia without the necessity of adding other oxides or dopants. Both the temperature and the time of digestion are important parameters. Zirconia with surface area in excess of 220 m2/g after calcination at 500°C have been obtained. The materials maintained a surface area of >90 m2/g even after heat treatment at 900°C for 12 h. In addition, digestion led to the formation of the tetragonal allotrope of zirconia. Samples which had been digested for long times at 100°C are tetragonal and maintain this phase up to 1000°C. The effects of digestion seems to be related to a phase transformation of the hydrous precursor at around 80°C. A mechanism based on defect density is postulated to explain the phase stability.

The ceramic shells were fabricated with ceramic slurry containing zirconia as filler material and colloidal silica binder to cast Zr-alloy 705. The investment shell mould characteristics in terms of hot bending strength, thermal expansion and metal-mould reaction were measured. On account of phase transformation (confirmed by Raman spectra) of zirconia at high temperatures the hot bending strength zirconia shells decreases with increasing temperature. A hard ZrO2 case layer was noticed beneath the surface of the casting.

Objectives

The aim of the present study was to evaluate the effect of novel silane system coatings on zirconia and titanium implant surfaces and the attachment of the fungal pathogen Candida albicans.
Materials and methods

Titanium and zirconia specimens were silica-coated and silanized either with a commercial silane primer (RelyX Ceramic Primer™, 3M ESPE) or a novel silane system primer. The novel silane system primer was a blend of 1.0 vol% 3-acryloxypropyltrimethoxysilane and 0.3 vol% bis-1,2-(triethoxysilyl)ethane diluted in acidified ethanol-water solvent. The surface roughness (Ra), the surface free energy and the chemical composition of substrate surfaces after treatments were evaluated. C. albcans biofilms were developed on silica-coated + silanized surfaces during 48 h of incubation time. Colony forming units (CFU) and real-time PCR (RT-PCR) quantified the cells on the material surfaces. Statistical analyses were carried out by 1-way ANOVA, Tukey post hoc and Games Howell post hoc test at 5% significance level (p).
Results

On zirconia and titanium surfaces, the Ra and the chemical composition of the specimens were equal (P < 0.05). The surface free energy was decreased on titanium specimens and increased on zirconia specimen after silanization. CFU of C. albicans was significantly lower on zirconia coated with RelyX Ceramic Primer™, (P < 0.001) and on titanium coated with both silanes (P = 0.002). RT-PCR revealed no differences between the mean quantities of C. albicans (P ≥ 0.067).
Conclusion

Silica-coating and silanization had modified the titanium and zirconia surfaces significantly. Both the control and experimental silane primers might inhibit the biofilm formation of C. albicans.

OBJECTIVE: To assess clinical and radiological performance of novel digital workflow integrating dynamic guided surgery, to streamline execution of implant placement, soft and bone tissue sculpturing, and immediate delivery of navigation guided complete-arch prosthesis.
MATERIALS AND METHODS: This proof of concept prospective single cohort study investigated 10 consecutive patients (three males, seven females; mean age 62.5 ± 8.9 years; range, 48-75) requiring at least one complete-arch fixed dental prostheses (FDP) in both jaws, treated between January and August 2019. Primary outcomes were implant and prosthetic success rates, surgical and prosthetic complications. Secondary outcomes were marginal bone loss (MBL), implant stability quotient (ISQ), periodontal parameters (plaque and bleeding indexes).
RESULTS: Sixty implants (32 NobelParallel TiUltra and 28 NobelActive TiUltra, Nobel Biocare) were placed and 14 complete-arch FDPs immediately loaded (mean follow-up 16.2 ± 1.7 months, 14-18). One implant failed and was immediately replaced. No other surgical or biological complications occurred, accounting for a cumulative success rate of 98.3%. No prosthetic complication occurred, leading to 100% prosthetic success rate. Mean ISQ at implant placement was 71 ± 2.8 (65-78). The mean MBL was -0.53 ± 0.28 mm (-0.22 to -1.12 mm). Plaque and bleeding scores were 14.4 ± 8.18 and 7.15 ± 4.4, respectively.
CONCLUSION: Within the limitations of this proof-of-concept dynamic navigation was effective to deliver in the planned coordinates both implants and prosthesis and guide bone and soft tissue sculpturing. Immediate loading of digitally prefabricated esthetically driven complete-arch FDP was facilitated, resulting in high implant and prosthetic success rates.
CLINICAL SIGNIFICANCE: The investigated digital workflow integrating dynamic navigation may overcome the difficulties related to immediate positioning and loading of digitally prefabricated complete-arch FDP. The navigation guided soft and bone tissues sculpturing, associated to xenogeneic collagen matrix grafting, represented a predictable technique to achieve the digitally planned interface, reestablishing the mucosal dimension required for the protection of underlying bone while maintaining tissue health.

In this study, the potentiality of Bangladesh zircon as a raw material for zirconia and zircon brick production was examined. Decomposition of zircon (ZrSiO4) into zirconia (ZrO2) was attempted by using caustic soda (NaOH) as the decomposition agent. 5-10 μm size zircon, 5-30 wt.% NaOH, and decomposition temperatures ranging from 1300 to 1500°C were investigated. X-ray diffraction method using Mo Kα radiation was used in order to find out the extent of decomposition of zircon into zirconia. Zircon bricks of 0.06 mm× 0.06 mm× 0.025 mm shaped were made under a pressure of 15 MPa. Carboxi methyal cellulose (CMC) and Fe2O 3 were used as a binder. With increasing temperature and percentage of NaOH, decomposition of zircon increases. Crushing strengths and density of these bricks could be found as high as 53.36 MPa and 3210 kg/m3, respectively. Bangladesh zircon can be used successfully for preparation of refractory bricks for high temperature use.

http://www.sciencedirect.com/science/article/pii/S092401360500909X

Zirconia is widely used for load-bearing functional structures in medicine and dentistry. The quality of engineered zirconia surfaces determines not only the fracture and fatigue behaviour but also the low temperature degradation (ageing sensitivity), bacterial colonization and bonding strength of zirconia devices. This paper reviews the current manufacturing techniques for fabrication of zirconia surfaces in biomedical applications, particularly, in tooth and joint replacements, and influences of the zirconia surface quality on their functional behaviours. It discusses emerging manufacturing techniques and challenges for fabrication of zirconia surfaces in biomedical applications.

Due to an increasing interest in esthetics and concerns about toxic and allergic reactions to certain alloys, zirconia was proposed as a new ceramic material in the later part of 20th century. It has become a popular alternative to alumina as biomaterial and is being used in dental applications for fabricating endodontic posts, crown and bridge restorations and implant abutments. It has also been applied for the fabrication of esthetic orthodontic brackets. This article presents a brief history, dental applications and new methods for fabrication of zirconia improving its mechanical properties. Additionally, the bonding between zirconia and resin cements as well as conventional cementation has been discussed. The methods of the improvement of the bonding strength have also been highlighted.

The interest of dental research in metal-free restorations has been rising in the last 20 years following the introduction of innovative all-ceramic materials in the daily practice. In particular, high strength ceramics and related CAD/CAM techniques have widely increased the clinical indications of metal-free prostheses, showing more favourable mechanical characteristics compared to the early ceramic materials.The purpose of the present paper is providing a brief review on the all-ceramic dental materials, evaluating pros and cons in the light of the most recent scientific results and of the authors’ clinical experience.A structured review of the literature was given on the basis of medical and engineering papers published in the last decades on the use of dental ceramics and zirconia in particular. The experimental and clinical findings of the most relevant researches were reported.Zirconia is one of the most promising restorative materials, because it yields very favourable mechanical properties and reasonable esthetic. Several in vitro and in vivo investigations reported suitable strength and mechanical performances of zirconia, compatible with clinical serviceability as a framework material for both single crowns and short-span fixed partial dentures. However, clinical results are not comparable, at the moment, with conventional metal–ceramic restorations, neither is there sufficient long-term data for validating the clinical potential of zirconia in the long run.The use of zirconia frameworks for long-span fixed partial dentures or for implant-supported restorations is currently under evaluation and further in vivo, long-term clinical studies will be needed to provide scientific evidence for drawing solid guidelines.

Purpose: To seek a simple solution that can recycle and regenerate dental CAD/CAM zirconia green blanks from its waste residuals. Methods: Waste residuals (3M® Lava™ Plus HT) were pulverized after dry milling and cutting, and subsequently sieved before pickling in a 0.5 M nitric acid. These powders were then dry-pressed and pre-sintered into blocks at seven different temperatures in the range 800−1100 °C. New zirconia blocks flagged with the same batch numbers were used as control. These blocks were cut into bars before subjected them to manufacturer-recommended sintering at 1450 °C. Crystalline phases (by XRD), elemental compositions (by EDX), surface morphologies (by SEM), machinability, linear shrinkage rate, relative density, and Knoop microhardness were evaluated before and after sintering, and four-point flexural strengths were also evaluated for the sintered zirconia bars. Results: Only tetragonal phases were found in both pre-and fully-sintered recycled zirconia blocks. SEM results showed that pre-sintered samples at 950 °C had smooth and flat surfaces with evenly distributed particles. Recycled and control zirconia blocks had similar elemental compositions. Results from machined surface, linear shrinkage rate, relative density, and Knoop microhardness established that 950 °C and 1000 °C were suitable pre-sintering temperatures for recycling zirconia. Pre-sintered recycled zirconia had no significant differences in flexural strengths, however, samples pre-sintered at 1000 °C exhibited the closest value (897 MPa) compared to that of the control (904 MPa). Conclusions: Dental CAD/CAM zirconia can be recycled and reused from its waste residuals by adopting a simple method that requires a pre-sintering at 950 or 1000 °C.

Alumina has received considerable attention and has been historically well-accepted as biomaterials for dental and medical applications. This article reviews the applications of this material in dentistry. It presents a brief history, dental applications and methods for improving the mechanical properties of alumina-based materials. It also offers perspectives on recent research aimed at the further development of alumina for clinical uses, at their evaluation and selection, and very importantly, their clinical performance. This article also stated about the Functionally Graded Materials (FGMs) which has been conceived as a new material design approach to improve performance compared to traditional homogeneous and uniform materials. This technique allows the production of a material with very different characteristics within the same material at various interfaces. The importance of the FGM concept in biological applications and functions was highlighted. Fundamentally, the combination of mechanical properties and biocompatibility are very important factors in application of any biomaterial to medical or dental fields. The characteristics of the surface govern the biocompatibility of the material, and the mechanical strength is determined by the average mechanical strength of the materials. However, the fabrication of FGMs is most often hindered by the variation of elastic, plastic, thermal, chemical, and kinetic properties within the composite. Across a material interface, these discontinuities in material properties lead to the formation of residual stresses. Despite these challenges, compositional gradient structures offer significant benefits. Notable research literature is highlighted regarding (1) applications of alumina in various fields in dentistry; (2) improvement of the mechanical properties of alumina by microstructural manipulation, FGM as well as composite formulations involving metallic, intermetallic elements and bioceramics.

The following article is a review of the dental literature available, which is aiming to provide the clinician the up-to-date information about the ceramic metal-free dental materials available in Latin-America. Some clinical aspects are mentioned, as well as, classification, indications, contraindications, advantages and disadvantages of the materials specifically selected for single complete crowns. During the literature search, the articles of clinical research were selected, as well as, the articles dedicated to publish the results in vitro research.
This article is intended to be a guide in order to select a metal-free system for complete crowns based on physical properties and according to the specific esthetic and functional needs of each patient.

Key words: Metal-free, full-porcelain, allceramic, crown, ceramic, porcelain, aesthetic.

Palabras clave: Libre de metal, corona, cerámica, porcelana, estética.

Calcium phosphate materials are similar to bone in composition and in having bioactive and osteoconductive properties. Calcium phosphate materials in different forms, as cements, composites, and coatings, are used in many medical and dental applications. This paper reviews the applications of these materials in dentistry. It presents a brief history, dental applications, and methods for improving their mechanical properties. Notable research is highlighted regarding (1) application of calcium phosphate into various fields in dentistry; (2) improving mechanical properties of calcium phosphate; (3) biomimetic process and functionally graded materials. This paper deals with most common types of the calcium phosphate materials such as hydroxyapatite and tricalcium phosphate which are currently used in dental and medical fields.

Purpose: To compare the fracture resistance of implant-supported milled zirconia, milled lithium disilicate, and additively manufactured zirconia crowns. Materials and Methods: Maxillary cast with a dental implant replacing right second bicuspid was obtained. Custom abutments and full-contour crowns for milled zirconia, milled lithium disilicate, and additively manufactured zirconia crowns (n = 10/group) were digitally designed and fabricated. The crowns were cemented to implant-supported zirconia abutments and mounted onto polyurethane blocks. Fracture resistance was determined by vertical force application using a universal testing machine at a crosshead speed of 2 mm/minute. Kruskal-Wallis test was used to analyze data and failure mode was determined for all the groups. Results: Milled zirconia crowns demonstrated the highest median fracture resistance (1292 ± 189 N), followed by milled lithium disilicate (1289 ± 142 N) and additively manufactured zirconia (1243.5 ± 265.5 N) crowns. Statistical analysis showed no significant differences in fracture resistance between the groups (p = 0.4). All specimens fractured at the implant-abutment interface. Conclusion: Additively manufactured zirconia crowns demonstrated similar fracture resistance to milled ceramic crowns, when cemented to implant supported zirconia abutments. The results of this in vitro study signify the promising potential of additive manufacturing for the fabrication of all ceramic zirconia crowns.

In this study, boron doped and undoped poly(vinyl) alcohol/zirconium-barium acetate (PVA/Zr-Ba) nanofibers were prepared using an electrospinning technique then calcinated at three different temperatures; 250 oC, 500 oC, 800 oC for 2 h. The
originality of this study is the addition of boron to metal acetates. The fibers were characterized by FT-IR, DSC, XRD and SEM. The addition of boron did not only increase the thermal stability of the fibers, but also increased their diameters, which gave stronger fibers. The FT-IR spectra of the fibers were in good accordance with literature data. The DSC results indicate that the glass transition (Tg) and melting temperatures (Tm) showed a change with the addition of boron. Also, boron doped fibers were observed to degrade at higher temperatures. XRD analyses showed that after further heat treatment at 800 oC, zirconia exists in two phases of tetragonal and monoclinic modifications. The systematic evolution of morphological features in the spun and the processed fibers were studied by scanning electron microscopy. The SEM appearance of the fibers showed
that the addition of boron resulted in the formation of cross linked bright surfaced fibers.

Micro-laminates and nanocomposites of Al2O3 and ZrO2 can potentially exhibit higher hardness and fracture toughness and lower thermal conductivity than alumina or zirconia alone. The potential of these improvements for abrasion protection and thermal barrier coatings is generating considerable interest in developing techniques for producing these functional coatings with optimized microstructures. Al2O3-ZrO2 composite coatings were deposited by suspension thermal spraying (APS and HVOF) of submicron feedstock powders. The liquid carrier employed in this approach allows for controlled injection of much finer particles than in conventional thermal spraying, leading to unique and novel fine-scaled microstructures. The suspensions were injected internally using a Mettech Axial III plasma torch and a Sulzer-Metco DJ-2700 HVOF gun. The different spray processes induced a variety of structures ranging from finely segregated ceramic laminates to highly alloyed amorphous composites. Mechanisms leading to these structures are related to the feedstock size and in-flight particle states upon their impact. Mechanical and thermal transport properties of the coatings were compared. Compositionally segregated crystalline coatings, obtained by plasma spraying, showed the highest hardness of up to 1125 VHN3 N, as well as the highest abrasion wear resistance (following ASTM G65). The HVOF coating exhibited the highest erosion wear resistance (following ASTM G75), which was related to the toughening effect of small dispersed zirconia particles in the alumina-zirconia-alloyed matrix. This microstructure also exhibited the lowest thermal diffusivity, which is explained by the amorphous phase content and limited particle bonding, generating local thermal resistances within the structure.

The scale-up of nanoparticle synthesis by a versatile flame aerosol technology (flame spray pyrolysis) is investigated numerically and experimentally for production of ZrO2. A three-dimensional computational fluid dynamics model is developed accounting for combustion and particle dynamics by an Eulerian continuum approach coupled with Lagrangian description of multicomponent spray droplet atomization, transport, and evaporation. The model allows the extraction of the high-temperature particle residence time (HTPRT) that is governed by the dispersion gas to precursor liquid mass flow ratio as well as the flame enthalpy content. The HTPRT is shown to control the primary particle and agglomerate size, morphology, and even ZrO2 crystallinity in agreement with experimental data. When the HTPRT is kept constant, the production rate for ZrO2
nanoparticles could be scaled up from ∼100 to 500 g/h without significantly affecting product particle properties, revealing the HTPRT as a key design parameter for flame aerosol processes.