Low Temperature Degradation of Alumina-toughened Zirconia in Artificial Saliva

The long-term aging behavior of an alumina-toughened zirconia （ATZ） ceramic in artificial saliva hydrothermal atmosphere was determined and compared with that of tetragonal zirconia polycrystals doped with 3mo1% Y203 （3Y-TZP）. The specimens of 3Y-TZP and ATZ were aged in distilled water and artificial salivary respectively at 134 ~C. Monoclinic phase content was evaluated by X-ray diffraction （XRD） analysis. Specimen strength was determined by a biaxial bending test. Surface screening was done using an atomic force microscope （AFM）. No statistically significant influence of any treatment on strength was demonstrated for either material. However, XRD measurements revealed ATZ＇s anti-aging properties were much better than TZP after the aging treatment. Therefore, ATZ can be applied to the field of dentistry. Artificial saliva in ceramic surface sediments may be useful for stren^heninl ceramics.

In vitro Degradation of Pure Mg for Esophageal Stent in Artificial Saliva

Magnesium and its alloys as biodegradable implant materials can be potentially used in cardiovascular and orthopedic devices. However, few studies have focused on its application in esophageal stents. In this paper, time-lapse degradation characteristics of pure Mg were analyzed by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, hydrogen evolution, pH and electrochemical measurements after immersion in artificial saliva for different times. Results revealed that a dense degradation product film formed on samples, which mainly consisted of two kinds of layers： one was calcium phosphate compounds with different structures; the other was thin magnesium hydrate layer close to the substrate. Less pH increase and low degradation rate were ob- served in the first 5 days of immersion, which can be ascribed to the formation of a thicker and denser layer on the sample surface with increasing immersion time. And then there was an increase in degradation rate and pH values; the deposition layer remained almost intact after immersion for 6 and 8 days. After 10 days of immersion, the degradation rate and pH value remained stable, and the calcium phosphate layer was delaminated and the inner magnesium hydrate layer was exposed. This study indicated that pure Mg exhibited desirable degradation resistance in artificial saliva, which provided magnesiumbased materials with the potential to be used as esophageal stents.

Influence of Fluoride Content of Artificial Saliva on Metal Release from 17-4 PH Stainless Steel Foam for Dental Implant Applications

Highly porous 17-4 PH stainless steel foam for implant applications was produced by space holder technique. Metal release and weight loss from 17-4 PH stainless steel foams were investigated in fluoride added artificial saliva environment by static immersion test. An inductively coupled plasma-mass spectrometer was employed to measure the concentrations of various metal ions. Effects of fluoride content of artificial saliva on metal release and weight loss from the steel foams were investigated. Effects of immersion time, pH value and process parameters on the weight loss and metal release were determined. Pore morphology, pore size and mechanical properties of the 17-4 PH stainless steel foams were also characterized.

Corrosion and passive film characteristics of 3D-printed NiTi shape memory alloys in artificial saliva

Electrochemical tests and surface analysis were applied to study the corrosion behavior and passive film characteristics of three-dimensional-printed NiTi shape memory alloys fabricated by laser-powder bed fusion(LPBF) in artificial saliva at 37.C. The passivity of L-PBF NiTi shows to be influenced by the process parameters and resulting morphological and physicochemical surface properties. The results show that the defects at the surface of L-PBF Ni Ti can promote the passivation rate in the early stages of exposure but a slowly formed passive film shows the best corrosion protection. The thickness of the passive film is positively correlated with its corrosion protective performance. The L-PBF NiTi alloy prepared at a linear energy density of 0.2 J·m^(-1) and volumetric energy density of 56 J·mm^(-3) shows the least defects and best corrosion protection. An outer Ti-rich and inner Ni-rich dense passive film could be also obtained showing higher corrosion resistance.

Acid Elution of Aluminum and Calcium from Human Deciduous Enamel in Relation to Dental Caries

Although aluminum itself was reported to prevent dental caries, previous in vitro studies reported that the aluminum level in the whole saliva of children was independent of caries prevalence. Purposes of this study were to compare the elution levels of aluminum and calcium from deciduous enamel into acidic artificial saliva, and determine whether the degree of aluminum elution reflects individual caries risk. One hundred and eleven extracted human deciduous teeth were collected. Concentrations of aluminum and calcium eluted from sound regions of enamel into artificial saliva (pH 6.2 or 5.5) were determined using atomic absorption spectrophotometry. One hundred and four and 108 available data samples were obtained for aluminum and calcium evaluation, respectively, and were compared based on the sex, tooth type, caries history, and the number of the donor’s carious teeth at each pH. Calcium elution was not affected by the sex;however, more aluminum was eluted from boys’ than from girls’ teeth at pH 5.5. The aluminum release depended on the tooth type, and was significantly higher in incisors than in molars at a pH of 5.5. In relation to the caries history, aluminum (at pH 5.5) and calcium (at pH 6.2) dissolved more from sound regions of the enamel of caries-experienced teeth than from the enamel of teeth without caries experience. Moreover, aluminum markedly dissolved from enamel in artificial saliva at both pH 6.2 and 5.5 when the donor had more carious teeth, regardless of the presence or absence of caries experience in the sampled teeth. There is a possibility that the rate of aluminum elution from enamel into acidic fluid reflects individual caries sensitivity.

A Comparative Study on the Corrosion Performance of Ni_(47)Ti_(49)Co_4 and Ni_(51)Ti_(49) Shape Memory Alloys in Simulated Saliva Solution for Dental Applications

In this study, the corrosion behavior of Ni47Ti49Co4 shape memory alloy（SMA） was investigated in simulated saliva solution with the binary alloy Ni（51）Ti49 as a reference. The surface morphology and the chemical composition of the oxide films were characterized by scanning electron microscopy and X-ray photoelectron spectroscopy before and after immersion in the test solutions, respectively. The results showed that the ternary alloy was less affected by the test solution,owning to the formation of passive layer composed mainly of the oxides of titanium and cobalt in several oxidation states.Cyclic voltammetry, electrochemical impedance spectroscopy and potentiodynamic polarization measurements affirmed that the passive oxide film significantly improved the corrosion resistance of Ni47Ti49Co4 SMAs as demonstrated by the smaller corrosion current density, larger resistance and smaller capacitance. Consequently, alloying with cobalt, which has paramount importance in enhancing the passive layer, expands the use of Ni47Ti49Co4 SMAs in dental work as new nitinol alloys with high corrosion resistances.

Effect of Rolling Temperature on the Mechanical Properties and Corrosion Behavior of Mg-Zn-Y-Nd Alloy Thin Sheets

There is a growing demand for degradable membranes with sufficient mechanical properties to guide tissue regeneration in dental surgery.In the present work,a two-stage rolling process in which the first rolling stage(FRS)adopted a reduction rate of 30%for six passes at various temperatures,while the second rolling stage was rolling at 200℃for two passes,was employed to prepare a 150μm-grade Mg-2.0Zn-0.5Y-0.5Nd(ZE21B)Mg alloy sheets for guided tissue regeneration membrane.The microstructure of the thin sheets was gradually refined with increasing rolling passes,and the thin sheets that were rolled at different FRS temperatures exhibit an ellipse texture.The thin sheets rolled at 350℃for FRS show low elongation due to premature fracture caused by the coarse second phase particles.On account of uniform and fine grains,the thin sheets rolled at 400℃for the FRS have proper mechanical properties:yield strength of 214.6±8.5 MPa,ultimate tensile strength(UTS)of 246.8±10.3 MPa and elongation to failure of 28.3±1.2%.When rolling at 450℃for FRS,proper ductility of the thin sheets has been acquired,followed by a decline in UTS since a bimodal structure with fine and coarse grain was developed.Immersion tests demonstrated the FRS temperature had no significant effect on the corrosion behavior and corrosion rate of Mg alloy sheets after 7 days’immersion in artificial saliva solution.This research has great significance for the production of degradable Mg sheets for guided tissue regeneration membrane.

Corrosion resistance and antibacterial activity of different zones in TA2 weldment by TIG welding

The corrosion resistance behavior of TA2 pure titanium processed by tungsten inert gas(TIG)welding was investigated in artificial saliva solution at 37℃.By metallographic examination,electrochemical measurement technology,and electrochemical impedance spectroscopy(EIS),the corrosion resistance of the base metal(BM),heat-affected zone(HAZ),and weld metal(WM)were investigated.Metallographic examination experiments show that welding process would cause the growth of grain size.In addition,phase change happens in the HAZ and WM.The change of grain size and phase would influence the generation of the original passive film.The electrochemical tests show that the BM,HAZ,and WM are all equipped with good corrosion resistance.The welded joint shows a better corrosion resistance than the original TA2.It is shown that the BM with the lowest corrosion potential and the biggest corrosion current has a worse corrosion resistance than WM as well as HAZ.Silver(Ag)nanoparticles can be distributed on the WM zone of Ti uniformly.The WM zone of Ti with Ag coating considerably enhances the antibacterial activity of Ti implants.