Ageing assessment of zirconia implant prostheses by three different quantitative assessment techniques

PURPOSE: To evaluate the influence of cyclic loading on phase transformation of zirconia abutments and to compare the effectiveness of three different quantitative ageing assessment techniques. MATERIALS AND METHODS: Thirty two Y-TZP prostheses fabricated from two brands, InCoris ZI and Ceramill ZI, were cemented to titanium bases and equally divided into two subgroups (n=8): control group without any treatment and aged group with cyclic loading between 20 N and 98 N for 100,000 cycles at 4 Hz in distilled water at 37℃. The tetragonal-to-monoclinic phase transformation was assessed by (i) conventional x-ray diffraction (XRD), (ii) micro x-ray diffraction (µXRD), and (iii) micro-Raman spectroscopy. The monoclinic-phase fractions (M%) were compared by two-way ANOVA. RESULTS: InCoris Zi presented significantly higher M% than Ceramill Zi in both control and aged groups (P<.001). Both materials exhibited significant phase transformation with monoclinicphase of 1 to 3% more in aged groups than controls for all thre e assessment techniques. The comparable M% was quantified by both µXRD and XRD. The highest M% was assessed with micro-Raman. CONCLUSION: Cyclic loading produced significant phase transformation in tested Y-TZP prostheses. The micro-Raman spectroscopy could be used as an alternative to XRD and µXRD.

The effects of surface grinding and polishing on the phase transformation and flexural strength of zirconia

PURPOSE: The purpose of this in vitro study was to evaluate the effect of surface grinding and polishing procedures using high speed zirconia diamond burs with different grit sizes on the phase transformation and flexural strength of zirconia.

The effect of various polishing systems on surface roughness and phase transformation of monolithic zirconia

PURPOSE: The purpose of this study was to evaluate and compare three polishing systems on the surface roughness and phase transformation of monolithic zirconia. MATERIALS AND METHODS: 100 disk shaped specimens (10 mm diameter, 3 mm thickness) were fabricated from monolithic zirconia blocks. 20 specimens were left as a control group and remaining specimens were grinded by diamond bur to simulate the occlusal adjustments. Grinded specimens were randomly divided into 4 groups: group G (no polishing), group M (Meisinger, zirconia polishing kit), group E (EVE Diacera, zirconia polishing kit), and group P (EVE Diapol, porcelain polishing kit). Surface roughness was measured with profilometer and surface topography was observed with SEM. XRD analysis was performed to investigate the phase transformation. Statistical analysis was performed with one-way ANOVA and Tukey's post hoc tests at a significance level of P=.05. RESULTS: All polishing groups showed a smoother surface than group G. Among 3 polishing systems, group M and group E exhibited a smoother surface than the group P. However, no significant differences were observed between group M and group E (P>.05). Grinding and polishing did not cause phase transformations in zirconia specimens. CONCLUSION: Zirconia polishing systems created a smoother surface on zirconia than the porcelain polishing system. Phase transformation did not occur during the polishing procedure.

Extraction and Separation of Boron in Anhydrite and Gypsum Minerals and Its Isotopic Measurement by Thermal Ionization Mass Spectrometry / 分析化学

The anhydrite and gypsum are the main sulfate minerals during evaporation of seawater or lake.They record the information about relative hydrogeology and the composition of mother liquor.Boron is diffluent element, and often occurs in all kinds of evaporites.Presently, the boron isotope has been applied widely in mineral deposits forming, geochemistry and palaeoenvironment.However, there is little research about characteristic of boron isotope in anhydrite and gypsum minerals, because of the low content of boron and micro-solubility in water and hydrochloric acid.This study developed a method of extracting and purifying boron in anhydrite and gypsum by phase transformation and ion-exchange.Firstly, the samples were mixed with ammonium hydrogen carbonate to transform the calcium sulfate to calcium carbonate.And diluted hydrochloric acid (1 mol/L) was added to resolve calcium carbonate.The percent conversion was about 85%in the first stage, and up to complete resolution by repeating this process.Secondly, boron specific ion-exchange resin ( Amberlite IRA 743 ) was used to gather the boron ions fully and further refined the samples with more than 1 μg of boron by anionic and cationic resin mixed by Ion Exchange Ⅱ and Dowex 50 W × 8.Finally, according to the modified method by He, the values of boron isotope were determined by TIMS.The boron content is analytically pure gypsum was 3.501 ± 0.128 μg/g ( n=12 , RSD=3.6%) and the average recovery was 100.47%.Besides, the δ11B value of analytically pure gypsum added with NIST SRM 951 was 17.98‰±0.21‰ (n=3, RSD=1.2%).This method has good repeatability and can meet the requirements of boron isotopic measurement of anhydrite and gypsum.

Efecto de un tratamiento experimental de una superficie sobre la resistencia flexural en una zirconia Y-TZP / Effect of an experimental surface treatment on Y-TZP zirconia flexural strength

RESUMEN Objetivo: Analizar el efecto del microgranallado superficial como tratamiento experimental de regeneración, en la resistencia flexural y esfuerzos residuales de una Zirconia Y-TZP, una vez ha sido alterada con otros tratamientos mecánicos como microarenado y fresado. Métodos: Un total de 75 probetas de Zirconia Y-TZP fueron divididas en cinco grupos n=15 y sometidas a tratamientos de superficie así: fresado y microarenado (Grupos 2 y 4) microarenado + microgranallado y fresado + microgranallado (Grupos 3 y 5), y comparadas con un grupo control (Grupo 1), mediante Difracción de Rayos X (DRX), Microscopía electrónica de barrido (SEM), Microscopía confocal (CLSM) y sometida a falla en máquina universal de ensayos. Resultados: Los grupos de microgranallado y microarenado presentaron un aumento significativo de la resistencia flexural p=0.0082 con relación al grupo de fresado. Las mediciones mediante DRX no mostraron relación estadística con los cambios en la resistencia flexural. Significancia: Es posible que el microgranallado se considere un tratamiento para regenerar las propiedades mecánicas reducidas por fresado o arenado en la Zirconia Y-TZP.

ABSTRACT Objective: To analyze the effect of surface micro shot peening as an experimental regeneration treatment on the flexural strength and residual stresses of a Y-TZP Zirconia, once it has been altered with other mechanical treatments such as micro sandblasting and milling. Methods: A total of 75 Zirconia Y-TZP specimens were divided into five n = 15 groups and subjected to surface treatments such as: milling and micro sandblasting (Groups 2 and 4) micro sandblasting + micro shot peening; and milling + micro shot peening (Groups 3 and 5), compared to a control group (Group 1), by X-ray diffraction (XRD), scanning electron microscopy (SEM), confocal microscopy (CLSM) and subjected to failure in a universal testing machine. All the results were compared to find a statistical relationship between them using a mixed linear model and Tuckey. Results: The groups of micro shot peening and micro sandblasting presented a significant increase of the flexural strength p = 0.0082 vs the milling group. The XRD technique is not related to flexural strength measurements. Significance: It is possible that the micro shot peening be considered a treatment to regenerate the mechanical properties reduced by milling or sandblasting in Zirconia Y-TZP.

Caracterização do estado sólido de ganciclovir / Solid state characterization of ganciclovir

O presente trabalho teve como objetivo o estudo do estado sólido do ganciclovir (GCV) e suas diferentes formas polimórficas. O GCV é um fármaco antiviral útil no tratamento de infecções por citomegalovírus (CMV). Embora seja um fármaco amplamente usado, poucos estudos têm sido realizados sobre seu estado sólido. Atualmente, o GCV é conhecido por apresentar quatro formas cristalinas, duas anidras (Forma I e II) e duas hidratas (III e IV). Neste trabalho, nós reportamos a solução da estrutura cristalográfica da Forma I do GCV, que foi encontrado durante o screening de cristalização do fármaco, em que nove ensaios de cristalização (GCV-1, GCV-A, GCV-B, GCV-C, GCV-D, GCV-E, GCV-F, GCV-G e GCV-H) foram realizados e os materiais resultantes foram caracterizados por Difratometria de raios X (DRX), análise térmica (DTA/TG) e Hot Stage Microscopy. De todas as cristalizações realizadas foram obtidas quatro formas sólidas, denominadas como Forma I (GCV-1, GCV-B e GCV-H), Forma III (GCV-C, GCV-D, GCV-F e GCV-G), Forma IV (GCV-A) e Forma V (GCV-E). Esta última está sendo descrita pela primeira vez na literatura e indica a presença de outra forma hidratada de GCV. As Formas I, III e IV corresponderam a forma anidra e as duas formas hidratadas do fármaco, respectivamente. Além disso, foi evidenciado por experimentos de conversão de slurry e análise térmica que o cristalizado de GCV-1 (Forma I) foi o mais estável entre os materiais obtidos, e este deu origem ao monocristal da Forma I de GCV, estrutura cristalina anidra do fármaco. Neste trabalho, pela primeira vez, a estrutura cristalina deste composto foi definida por cristalografia de raios X de monocristal. A análise estrutural mostrou que a Forma I do fármaco cristaliza no grupo espacial monoclínico P21/c e está composta por quatro moléculas de GCV na sua unidade assimétrica. Cada molécula está unida intermolecularmente por ligações de hidrogênio, que dão lugar à formação de cadeias infinitas e estas por sua vez se arranjam de maneira a formar uma estrutura tridimensional.

This presented work aims to study the solid state of ganciclovir (GCV) and its different polymorphic forms. GCV is an antiviral drug useful in the treatment of cytomegalovirus (CMV) infections. Although it is a widely-used drug, few studies have been conducted on its solid state. Currently, GCV is known to have four crystalline forms, two anhydrous (Form I and II) and two hydrates (III and IV). In this investigation, we report a successful preparation of GCV Form I and its crystallographic structure, which was found during the crystallization of the drug, in which nine crystallization tests (GCV-1, GCV-A, GCV-B, GCV- D, GCV-E, GCV-F, GCV-G and GCV-H) were performed and the resulting materials were characterized by X-ray diffractometry (XRD), thermal analysis (DTA/TG) and Hot Stage Microscopy. Of all the crystallizations performed, four solid forms were obtained, denoted as Form I (GCV-1, GCV-B and GCV- H), Form III (GCV-C, GCV-D, GCV-F and GCV-G), Form IV (GCV-A) and Form V (GCV-E). The latter is being described for the first time in the literature and indicates the presence of another hydrated form of GCV. Forms I, III and IV corresponded to the anhydrous form and the two hydrated forms of the drug, respectively. In addition, it was evident by both the slurry conversion and the thermal analysis methods that the GCV-1 crystallized (Form I) was indeed the most stable amongst the materials obtained. This gave rise to GCV Form I monocrystal, anhydrous crystalline structure of the drug. The compound was characterized by monocrystal X-ray crystallography. The structural analysis showed that Form I of the drug crystallized in the monoclinic system space group P21/c is composed of four molecules of GCV in its asymmetric unit. Each molecule is linked intermolecularly by hydrogen bonds, which give rise to the formation of infinite chains arranged in a way that form a three-dimensional structure.

Mechanical behavior of yttria-stabilized tetragonal zirconia polycrystal: Effects of different aging regimens

Abstract This study aimed to characterize and compare the effect of different aging regimens on surface characteristic (topography and roughness), structural stability (phase transformation) and mechanical performance (Weibull analysis) of a Y-TZP ceramic. Discs (15 × 1.2 mm; VITA In-Ceram YZ) were prepared according to ISO 6872-2015 for biaxial flexural strength testing and randomly assigned into five groups (n = 30): as-sintered, no aging treatment (CTRL); 20 h in autoclave at 134°C, 2 bar pressure (AUT); intermittent mechanical loading at 20 Hz/106 load pulses (MechLoad); AUT followed by MechLoad (AUT+MechLoad); and storage in distilled water at 37°C, for 1 year (STO). The following analyses were performed: roughness (n = 30), surface topography (n = 2), phase transformation (n = 2) and biaxial flexure strength (n = 30). Phase transformation (increase of m-phase content) was shown to be a spontaneous, unavoidable and time-dependent process, occurring even under ambient conditions (dry storage after 1 year = 6.0% increase), and is considerably accelerated in the presence of moisture (STO = 17.6%; AUT= 63.1%; and AUT+MechLoad = 59.9%). For roughness parameters, only Ra was affected by aging, and the highest values were observed for AUT+MechLoad (0.25 ± 0.07 µm). For Weibull analysis, structural reliability (Weibull moduli) and characteristic strength were not impaired after aging, and some aging conditions led to increased values (highest weibull moduli in AUT, and highest characteristic strength in STO). Phase transformation proves to be a time-dependent spontaneous mechanism that is accelerated in the presence of different stimuli. However, none of the aging regimens had a negative effect on the characteristic strength and structural reliability of Y-TZP ceramic.

Effects of different surface modifications on micro-structure and adhesion of zirconia ceramic: an in vitro study / 华西口腔医学杂志

<p><b>OBJECTIVE</b>This study evaluated the effect of different mechanical-chemical surface treatments on the characteristics, microstructure, and composition of zirconia ceramics and on the zirconia-dentin adhesion.</p><p><b>METHODS</b>The sintered commercial zirconia blocks (IPS e.max ZirCAD) were sectioned into 126 beams (6 mm×6 mm×5 mm) and randomly assigned to seven experimental groups (n=18). The zirconia block specimens were further treated as follows: (A) untreated, as control; (B) sandblasted with 50 μm Al2O3; (C) sandblasted with 50 μm Al2O3+30 μm silica powder; (D) sandblasted with 50 μm Al2O3+30% silica-sol coating; (E) sandblasted with 110 μm Al2O3; (F) sandblasted with 110 μm Al2O3+30 μm silica powder; and (G) sandblasted with 110 μm Al2O3+30% silica-sol coating. The surface roughness (Ra) of zirconia ceramics using X-ray diffraction (XRD), field emission scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX) after seven surface treatments was analyzed. Seventy specimens of dentin surfaces were prepared. A dual-cure resin cement was applied into zirconia surfaces with its corresponding adhesive components to dentin. Shear bond strength (SBS) of each sample was measured using a universal testing machine. The data were analyzed by ANOVA using SPSS 17.0 software.</p><p><b>RESULTS</b>Ra of zirconia were significantly different compared with the control group (P<0.05). The crystalline transformation from tetragonal phase to monoclinic phase was observed after surface modification. Monoclinic volume content of the heat-treated group was highest than that in other groups. The content of element Si in the heat-treated group was higher than that in other treatment groups accompanied by a decrease in elements Zr, Y, and Hf after being treated by two silica-coating methods. Air abrasion significantly increased the micro-cracks in the ceramic surface and caused the grain boundaries to disappear. A serious shrinkage of the thin silica film can be observed after sintering procedure. This process induced cracks and the film to strip away slightly from the surfaces of Y-TZP substrate. The SBS values from large to small were F and G groups, C and D groups, B and E groups (P<0.05), and control group (P<0.05).</p><p><b>CONCLUSIONS</b>Alumina sandblasting, silica powder abrasion, and silica-sol coating affect the surface morphology, structure, and composition of the tooth. This effect can also achieve the improved micro-mechanical interlocking or chemical bonding and finally increase the bond strength between zirconia and tooth. Alumina sandblasting followed by silica coating is an effective technique to increase the bonding strength between the zirconia ceramic and dentin.
.</p>

Importancia clínica del punto austenítico final en la selección de las aleaciones de níquel-titanio para su aplicación en arcos utilizados en Ortodoncia / Clinical importance of austenitic final point in the selection of nickel-titanium alloys for application in orthodontic-use arches

Resumen: Existe en el mercado una gran cantidad de alambres de aleaciones de níquel-titanio; sin embargo, no todos poseen las características ideales de memoria de forma y superelasticidad para ser utilizados en ortodoncia. El objetivo de este estudio fue encontrar la temperatura austenitica final de estos arcos con la finalidad de determinar la fase de transformación para su mejor uso clínico en Ortodoncia. Métodos: Se estudiaron once alambres de níquel-titanio más utilizados en Ortodoncia y se evaluó la fase de transformación utilizando la prueba de calorimetría de barrido diferencial. Conclusiones: Este estudio muestra cómo algunos arcos de NiTi en Ortodoncia presentan resultados contrarios a los que promocionan.

Abstract: There are many nickel-titanium alloy wires available in the market. Nevertheless not all of them possess the ideal characteristics of shape memory and super-elasticity to be used in orthodontic treatment. The aim of the present study was to find austenitic final temperature of these archwires so as to determine the transformation phase in order to better use them in orthodontics. Methods: Eleven nickel-titanium orthodontic wires were selected. Transformation phase was assessed using differential scanning calorimetry method. Conclusions: The present study illustrates how some orthodontic Ni-Ti wires elicit results contrary to those advertised.

Effect of different grinding burs on the physical properties of zirconia

PURPOSE: Grinding with less stress on 3Y-TZP through proper selection of methods and instruments can lead to a long-term success of prosthesis. The purpose of this study was to compare the phase transformation and physical properties after zirconia surface grinding with 3 different grinding burs. MATERIALS AND METHODS: Forty disc-shaped zirconia specimens were fabricated. Each Ten specimens were ground with AllCeramic SuperMax (NTI, Kahla, Germany), Dura-Green DIA (Shofu Inc., Kyoto, Japan), and Dura-Green (Shofu Inc., Kyoto, Japan). Ten specimens were not ground and used as a control group. After the specimen grinding, XRD analysis, surface roughness test, FE-SEM imaging, and biaxial flexural strength test were performed. RESULTS: After surface grinding, small amount of monoclinic phase in all experimental groups was observed. The phase change was higher in specimens, which were ground with Dura-Green DIA and AllCeramic SuperMax burs. The roughness of surfaces increased in specimens, which were ground with Dura-Green DIA and AllCeramic SuperMax burs than control groups and ground with Dura-Green. All experimental groups showed lower flexural strength than control group, but there was no statistically significant difference between control group and ground with Dura-Green DIA and AllCeramic SuperMax burs. The specimens, which were ground with Dura- Green showed the lowest strength. CONCLUSION: The use of dedicated zirconia-specific grinding burs such as Dura-Green DIA and AllCeramic SuperMax burs decreases the grinding time and did not significantly affect the flexural strength of zirconia, and therefore, they may be recommended. However, a fine polishing process should be accompanied to reduce the surface roughness after grinding.

Corrosion and microstructural characterization of martensitic stainless steels submitted to industrial thermal processes for use in surgical tools

INTRODUCTION: The mechanical properties and corrosion resistance of a material are dependent on its microstructure and can be modified by phase transformation. When a phase transformation occurs in a material it usually forms at least one new phase, with physical-chemical characteristics that differ from the original phase. Moreover, most phase transformations do not occur instantly. This paper presents an evaluation of the phase transformation of martensitic stainless steels ASTM 420A and ASTM 440C when submitted to different thermal processes. METHODS: Dilatometry tests were performed with several continuous heating and cooling rates in order to obtain the profiles of the continuous heating transformation (CHT) and continuous cooling transformation (CCT) diagrams for these two types of steel. Also, the temperature ranges for the formation of the different phases (ferrite and carbides; ferrite; austenite and carbides; non-homogeneous and homogeneous austenite phases) were identified. Rockwell hardness (HRC) tests were performed on all thermally treated steels. Anodic and cathodic potential dynamic polarization measurements were carried out through immersion in enzymatic detergent as an electrolyte for different samples submitted to the thermal processes in order to select the best routes for the heat treatment and to recommend steels for the manufacture of surgical tools. RESULTS: The martensitic transformation temperature tends to increase with increasing temperature for the initiation of cooling. The 440C steel had a higher hardness value than the 420A steel at the austenitizing temperature of 1100 °C. Above the austenitizing temperature of 1100 °C, the material does not form martensite at the cooling rate used, which explains the sharp decline in the hardness values. CONCLUSION: The study reported herein achieved its proposed objectives, successfully investigating the issues and indicating solutions to the industrial problems addressed, which are frequently encountered in the manufacture of surgical instruments.

Biaxial flexural strength and phase transformation of Ce-TZP/Al2O3 and Y-TZP core materials after thermocycling and mechanical loading

PURPOSE: The purpose of the present study was to evaluate the effect of thermocycling and mechanical loading on the biaxial flexural strength and the phase transformation of one Ce-TZP/Al2O3 and two Y-TZP core materials. MATERIALS AND METHODS: Thirty disc-shaped specimens were obtained from each material. The specimens were randomly divided into three groups (control, thermocycled, and mechanically loaded). Thermocycling was subjected in distilled water for 10000 cycles. Mechanical loading was subjected with 200 N loads at a frequency of 2 Hz for 100000 times. The mean biaxial flexural strength and phase transformation of the specimens were tested. The Weibull modulus, characteristic strength, 10%, 5% and 1% probabilities of failure were calculated using the biaxial flexural strength data. RESULTS: The characteristic strengths of Ce-TZP/Al2O3 specimens were significantly higher in all groups compared with the other tested materials (P<.001). Statistical results of X-ray diffraction showed that thermocycling and mechanical loading did not affect the monoclinic phase content of the materials. According to Raman spectroscopy results, at the same point and the same material, mechanical loading significantly affected the phase fraction of all materials (P<.05). CONCLUSION: It was concluded that thermocycling and mechanical loading did not show negative effect on the mean biaxial strength of the tested materials.

Mathematical modeling of dilatometric behavior of 420A and 440C martensitic stainless steels used in surgical tools / Modelamento matemático de ensaio dilatométrico em aços inoxidáveis martensíticos 420A e 440C utilizados em ferramental cirúrgico

This research consisted of implementing and evaluating an empirical mathematical model to reproduce analytically the dilatometric behavior of ASTM 420A and ASTM 440C martensitic stainless steels, widely used for manufacturing surgical tools. Martensitic stainless steels can be subdivided into three subgroups: low-carbon, medium-carbon and high-carbon steels. The microstructure of each group is also characteristic as needlelike martensitic; very fine martensitic; and ultra-fine martensitic containing carbides. The proposed method was based on experimental data obtained from the dilatometric testing of the steel samples applying low heating rates. It was possible to determine the formation of phase fields near the equilibrium conditions. The method, being based on empirical data, ensured a greater approximation to the experimental values, verifying that it can be applied as a useful tool in the evaluation of industrial heat treatments for surgical tools.

O presente trabalho consistiu em implementar e avaliar um modelo matemático empírico que reproduz analiticamente o comportamento dilatométrico dos aços inoxidáveis martensíticos ASTM 420A e ASTM 440C, utilizados em ferramental cirúrgico. Aços inoxidáveis martensíticos podem ser subdivididos em três subgrupos, ou seja, baixo carbono; médio carbono e alto carbono. A microestrutura de cada grupo é caracterizada por martensita em forma de agulha; martensita fina e martensita ultra-fina contendo carbetos. A elaboração do método matemático se baseou em dados extraídos de ensaios dilatométricos sob baixas taxas de aquecimento. Foi possível determinar a formação dos campos de fase próximos às condições de equilíbrio. Os resultados obtidos garantiram boa aproximação com os valores experimentais, evidenciando que o modelo aplicado é um instrumento útil na avaliação dos tratamentos térmicos industriais para ferramental cirúrgico.

Comparison of transition temperature range and phase transformation behavior of nickel-titanium wires / 대한치과교정학회지

OBJECTIVE: The aim of this research was to evaluate the mechanical properties (MP) and degree of the phase transformation (PT) of martensitic (M-NiTi), austenitic (A-NiTi) and thermodynamic nickel-titanium wire (T-NiTi). METHODS: The samples consisted of 0.016 x 0.022 inch M-NiTi (Nitinol Classic, NC), A-NiTi (Optimalloy, OPTI) and T-NiTi (Neo-Sentalloy, NEO). Differential scanning calorimetry (DSC), three-point bending test, X-ray diffraction (XRD), and microstructure examination were used. Statistical evaluation was undertaken using ANOVA test. RESULTS: In DSC analysis, OPTI and NEO showed two peaks in the heating curves and one peak in the cooling curves. However, NC revealed one single broad and weak peak in the heating and cooling curves. Austenite finishing (Af) temperatures were 19.7degrees C for OPTI, 24.6degrees C for NEO and 52.4degrees C for NC. In the three-point bending test, residual deflection was observed for NC, OPTI and NEO. The load ranges of NC and OPTI were broader and higher than NEO. XRD and microstructure analyses showed that OPTI and NEO had a mixture of martensite and austenite at temperatures below Martensite finishing (Mf). NEO and OPTI showed improved MP and PT behavior than NC. CONCLUSIONS: The mechanical and thermal behaviors of NiTi wire cannot be completely explained by the expected degree of PT because of complicated martensite variants and independent PT induced by heat and stress.

The effect of low temperature aging on the mechanical property & phase stability of Y-TZP ceramics

STATEMENT OF PROBLEM: Recently Yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP) has been introduced due to superior flexural strength and fracture toughness compared to other dental ceramic systems. Although zirconia has outstanding mechanical properties, the phenomenon of decrease in the life-time of zirconia resulted from degradation in flexural strength after low temperature aging has been reported. PURPOSE: The objective of this study was to investigate degradation of flexural strength of Y-TZP ceramics after various low temperature aging treatments and to evaluate the phase stability and micro-structural change after aging by using X-ray diffraction analysis and a scanning electron microscope (SEM). MATERIAL AND METHODS: Y-TZP blocks of Vita In-Ceram YZ (Vita Zahnfabrik, Bad Sackingen, Germany) were prepared in 40 mm (length) x 4 mm (width) x 3 mm (height) samples. Specimens were artificially aged in distilled water by heat-treatment at a temperature of 75, 100, 125, 150, 175, 200, and 225degrees C for 10 hours, in order to induce the phase transformation at the surface. To measure the mechanical property, the specimens were subjected to a four-point bending test using a universal testing machine (Instron model 3365; Instron, Canton, Mass, USA). In addition, X-ray diffraction analysis (DMAX 2500; Rigaku, Tokyo, Japan) and SEM (Hitachi s4700; Jeol Ltd, Tokyo, Japan) were performed to estimate the phase transformation. The statistical analysis was done using SAS 9.1.3 (SAS institute, USA). The flexural strength data of the experimental groups were analyzed by one-way analysis of variance and to detect statistically significant differences (alpha= .05). RESULTS: The mean flexural strength of sintered Vita In-Ceram YZ without autoclaving was 798 MPa. When applied aging temperature at below 125degrees C for 10 hours, the flexural strength of Vita In-Ceram YZ increased up to 1,161 MPa. However, at above 150degrees C, the flexural strength started to decrease. Although low temperature aging caused the tetragonal-to-monoclinic phase transformation related to temperature, the minimum flexural strength was above 700 MPa. CONCLUSION: The monoclinic phase started to appear after aging treatment above 100degrees C. With the higher aging temperature, the fraction of monoclinic phase increased. The ratio of monoclinic/tetragonal + monoclinic phase reached a plateau value, circa 75% above 175degrees C. The point of monoclinic concentration at which the flexural strength begins to decrease was between 12% and 54%.

The Degradation of Metallurgical Structure of Ti-6A1-4V Alloy after TKA in the Human

PURPOSE: To investigate the causes of structural degradation in Ti-6A1-4V alloy. MATERIALS AND METHODS: We prepared 20 metal specimens by cutting the fringe of 4 screw holes of tibial components taken from 5 cases of MG TKS(unused: 1, 3 years used: 2, 6 years used: 2). The structure and composition of specimens were analyzed by Scanning electron microscope(SEM), Energy dispersive spectrometer(EDS), and hardness tester. RESULTS: In soft tissue, titanium contained giant cells were observed by H-E stain, and Ti and Va peaks were detected by EDS. SEM showed that the unused specimens had normal metal fiber mesh texture, and the texture began to disappear from the surface of specimens after 3 years later. There were no metal fiber mesh, but black deposits were detected in specimens of 6 years. EDS revealed that Ti, Va, and Al peaks were appeared in the unused specimens, whereas 0 and C peaks in specimens of 3 years a#od 0, C, P, S, Ca and Cl peaks in specimens of 6 years were obtained. The hardness was decreased with the used period. CONCLUSION: It seemed that various molecular components of human body including carbon, hydrogen and oxygen influenced the metal elements of alloy to degrade in their structure.