Jiro Hasegawa

Morphological regulation and crystal growth of hydrothermal-electrochemically deposited apatite.

Apatite was deposited on commercially pure titanium plates using a hydrothermal-electrochemical method in an electrolyte containing calcium and phosphate ions. Needle-like apatites were synthesized in 43 kinds of condition with different electrolyte temperatures (90-200 degrees C), current densities (5.0-25.0 mA/cm2), and current loading times (10-120 min). The length of one side of the hexagonal apatite and longitudinal length of them were determined through field-emission-type scanning electron microscopic photographs. The size of needle-like apatites remarkably increased with the electrolyte temperature and current loading time, and slightly changed with current density. Multivariate analysis revealed that both size and shape of apatite needle on titanium substrate can be regulated accurately by systematic control of the electrolyte temperature, current density, and current loading time. These results revealed that hydrothermal-electrochemical deposition of apatite consists of two processes: nucleation and crystal growth, which strongly depend on the electrolyte temperature and current density.

Effect of electrochemically deposited apatite coating on bonding of bone to the HA-G-Ti composite and titanium

The surfaces of hydroxyapatite-glass-titanium (HA-G-Ti) functionally gradient composite and titanium bars were treated with electrochemical apatite deposition, and a cathodic current was applied at 62 degrees C in a solution containing calcium and phosphate ions. Specimens with and without the electrochemical surface treatment were implanted in the femurs of Japanese white rabbits. The rabbits were sacrificed at 3, 6, and 9 weeks after implantation, and the bonding strengths of bone to these specimens were determined by a pull-out method. At 3 and 6 weeks after implantation the specimens with the electrochemical surface treatment showed larger values for the Weibull modulus and characteristic strengths than those of untreated specimens, whereas there was no remarkable difference in the results at 9 weeks. Especially the pull-out strengths of surface-treated specimens were significantly larger than the untreated ones at 3 weeks after implantation. Scanning electron microscopy and Fourier transform infrared absorption spectroscopy of the specimen surface after implantation demonstrated that formation of new bone was enhanced by the electrochemical surface treatment. It can be concluded that the electrochemical surface treatment undoubtedly contributes to the early stage fixation between bone and implant.

Osteoinductive activity of composites of bone morphogenetic protein and pure titanium

Titanium sponges were infused with bone morphogenetic protein (BMP-Ti), and the osteoinductivity of the resultant composite was measured. New bone formation occurred three weeks after implantation and was identified by soft x-ray analysis. Quantitative analysis showed no significant difference between BMP-Ti composites and control samples (BMP only). Consequently, pure titanium neither inhibited nor promoted BMP activity. Chondrocytes and new bone formation occurred in direct contact with the surfaces of the titanium. X-ray microanalysis demonstrated new bone formation inside the pores of the titanium sponges. The BMP-Ti composite has interesting properties as an osteoinductive implant and has potential practical clinical applications.

Alloying titanium and tantalum by cold crucible levitation melting (CCLM) furnace

Abstract Recently, titanium alloys have been studied as implant materials for dental and orthopedic surgery. Titanium alloys have distinguished characteristics of biocompatibility, corrosion resistance and mechanical properties. Having non-poisonous character to a living body, Ta, Zr and Nb have been used for addition to titanium alloys, which are free of vanadium and aluminum. It is well-known that titanium and tantalum are difficult metals to alloy in usual furnaces as these are very reactive metals, having great differences in melting point and specific gravity. To produce an alloy of titanium and tantalum, cold crucible levitation melting (CCLM) is effective in obtaining a uniform composition. Notable features of CCLM are that it can (1) melt metals with a high melting point, (2) create an alloy of uniform composition with a strong stirring effect by an electromagnetic force and (3) allow metals to be melted without contamination. We have melted 850 g of titanium and 150 g of tantalum by a CCLM furnace and have successfully made 1.0 kg of uniform composite Ti–15wt.% Ta alloy. It is noteworthy that the alloy was produced from pure base metals which were not alloyed beforehand and was made by a single melting (no re-melting) process.

Release of mercury from dental amalgam fillings in pregnant rats and distribution of mercury in maternal and fetal tissues.

Mercury vapor released from a single amalgam restoration in pregnant rats and mercury concentrations in maternal and fetal rat tissues were studied. Dental treatment was given on day 2 of pregnancy. Mercury concentration in air sample drawn from the metabolism chamber with the rat was measured serially for 24 h on days 2, 8 and 15 of pregnancy. An average mercury concentration in the air samples from the rats given amalgam restorations was 678.6+/-167.5 ng/day on day 2. The average mercury concentration in the air samples tended to decline as time elapsed but a marked amount (423.2+/-121.5 ng/day) was observed even on day 15. The amount of mercury in the air samples increased 7--20-fold after chewing. The placement of the single amalgam restoration (3.8--5.5 mg in weight) increased the levels of mercury approximately three to 6 times in the maternal brain, liver, lung, placenta and 20 times in the kidneys. The highest mercury concentration among fetal organs was found in the liver, followed by the kidneys and brain. Mercury concentrations in maternal organs and fetal liver were significantly higher than those of the controls, and concentrations in maternal whole blood, erythrocytes and plasma, and in fetal whole blood were also significantly higher. Mercury concentrations in the fetal brain, liver, kidneys and whole blood were lower than those of the maternal tissues.

Effect of loading conditions on bi-axial flexure strength of dental cements

A ball-on-three-ball bi-axial flexure test was used to evaluate the flexure strengths of five kinds of dental cements (zinc phosphate, polycarboxylate, glass ionomer, silicate, and zinc oxide-eugenol cements). The bi-axial flexure strengths of zinc phosphate cement discs of variable dimensions were also measured to determine the size effects of test specimens. Finite element stress analyses were performed on disc specimens which were subjected to both a concentrated load and a uniformly distributed load. The observed values were compared with the theoretical value calculated by the finite element method. A ball-on-three-ball bi-axial flexure test could not be used for thicker specimens, since the fracture origin of these specimens is more likely to occur on the loaded side.

Electrochemical corrosion behaviour of hydroxyapatite-glass-titanium composite.

To determine whether hydroxyapatite(HA)-containing glass would exhibit the desired stability and activity under in vivo conditions, electrochemical corrosion behaviour of HA-glass-titanium composites was estimated by anodic polarization measurement in a simulated body fluid, 0.001 N HCl solution, 0.1 M NaCl solution, 0.1% albumin solution, and 0.1% fibrinogen solution. Potentiostatic anodic polarization measurements were made from each rest potential to +2 V versus s.c.e. with an increasing rate of 1 mV/s. Anodic polarization curves for pure titanium provided typical passive corrosion behaviour in HCl solution. The breakdown potentials were +1.4 V in HCl solution and +1.2 V in other solutions. The glass-coated specimens showed extremely low current density, less than 0.001 microA/cm2, from rest potential to about +1.8 V, and showed a slight increase in current density over +1.8 V. The polarization curves for the HA-glass-Ti composites were quite different from those for Ti and the glass-coated specimens. The current density for 50-90% HA -glass-Ti composites increased drastically from less than 0.001 to 10 microA/cm2 around rest potential (about -0.5 V), and continued to rise slightly up to +2 V. Addition of protein in NaCl solution exhibited little effect on anodic polarization curves for Ti and HA-glass-Ti composites.

Effect of electrochemical deposition of calcium phosphate on bonding of the HA-G-Ti composite and titanium to bone

ABSTRACT Calcium phosphates were deposited on the hydroxyapatite-glass-titanium (HA-G-Ti) functionally gradient composite bars as well as pure titanium bars by electrochemical process. After implantation in femur of rabbits, the bonding strengths of the four groups of the specimens to the bone were determined by the pull-out method. At 3 weeks after implantation, the bonding strengths of the composite and of the titanium with the electrochemical calcium phosphate coating were significantly higher than those without it, respectively (p 0.05). These results demonstrate that the electrochemical calcium phosphate coating increases the bonding strength of the implant to bone in the early stages of implantation.

Dissolution of metallic mercury in artificial saliva and eleven other solutions

Dissolution of metallic mercury immersed in various solutions for one, three, seven, and 14 days was investigated by flameless atomic absorption spectrophotometry. Solutions used in this study were artificial saliva, compounds of the four groups forming the artificial saliva (inorganic salts, amino acids, vitamins, other organic compounds) wholly or in part, 0.9% NaCl solution (saline solution), Ringers solution, and distilled water. Artificial saliva showed a level of mercury dissolution seven times higher than that of saline or Ringers solution. A large amount of dissolution, similar to that in artificial saliva, was found in the solution of the other organic compounds (containing glutathione) and in a solution containing only glutathione. Mercury dissolution in the solution of vitamins was small. There was a similarity in dissolution amounts between the solution of inorganic salts and that of amino acids. Glutathione played a major role in the dissolution of mercury.

Effect of Etching Condition on the Formation of Bioactive Surface of Hydroxyapatite-Glass-Titanium Composite

X-ray diffraction study shows that an etching solution of 3% HF and 5% HNO3 is the most suitable solution for preparing a bioactive surface layer of HA-glass-titanium composite, since the glass is removed, a great number of HA particles are exposed, and little CaF2 is produced by the etching. Anodic polarization measurement demonstrates that the 3-min etching gives an electrochemically active surface of the composites. These results and SEM observations suggest that this solution provides an adequate surface of the composite for the dental and medical implants.