Search

In order to obtain early and good osteointegration after implantation of a titanium implant in the human body, the surface modified treatments using NaOH or H2O2 etc. were reported. In this study, titanium was hydrothermally treated with CaCl2 solutions at 200 ∘C for 24hr (CaCl2-HT). Scanning electron microscope (SEM) observation clearly showed apatite deposition on the surface of CaCl2 HT treated titanium faster than other chemical treated titanium immersion in simulated body fluid. X-ray photoelectron spectroscopy (XPS) analysis demonstrated that Ti–O–Ca bonding was formed on titanium surface by hydrothermal treatment with CaCl2 solution. And it was revealed that thickness of TiO2, which was known to play important roles for the formation of bone-like apatite, became approximately three times thicker than as-polished titanium. The amount of initial attached MC3T3-E1 cells on as-polished and NaOH, H2O2 and this CaCl2 HT treated titanium were almost the same values. After 5 days incubation, the growth rate of MC3T3-E1 cells on CaCl2-HT treated titanium was significantly higher than that on other chemical treated titanium. The hydrothermal treatment with 10–20 mmol/L CaCl2 solution at 200 ∘C was an effective method for the fabrication of titanium implant with good bioactivity and osteoconductivity.

Apatite cement (AC) can be injected through syringe and forms apatite mass. Therefore, AC is very useful for a minimally invasive surgical operation aimed for the reconstruction of bone defects. However, injectability of current AC is not satisfactory for its clinical use. In this investigation, therefore, spherical tetracalcium phosphate (s-TTCP) was prepared with plasma melting method and its effect on injectability were evaluated as well as other basic properties of AC. We found much better handling property and injectability when we used s-TTCP as a component of AC (s-AC). For example, cement spread area used as an index of consistency of the s-AC paste was 512 mm2whereas that of ordinary AC with irregular TTCP (i-AC) was 158 mm2when powder to liquid mixing ratio was 2.5. However, diametral tensile strength of set s-AC (1.4 MPa) was significantly lower than that of set i-AC (10.7 MPa) when the powder to liquid ratio was 4.0. X-ray powder diffraction analysis revealed limited formation of apatite in the case of s-AC. Although there are some drawbacks, we feel the use of spherical particle is very useful to improve the injectability of AC. Therefore, it is important to find suitable method to prepare spherical powder as the component of AC.

2,2,6,6-Tetramethylpiperidinyloxy (TEMPO)-substituted β-cyclodextrin (β-CyD), 1, was synthesized as the initiator for the nitroxide-mediated living radical polymerization. Styrene (St) was polymerized with 1 using a molar ratio of St and 1 in a feed ([St]/[1]) of 200 at 120 °C for 6 h. The size exclusion chromatography (SEC) trace of the product exhibited a symmetrical peak with a weight-average molecular weight (Mw,SEC) of 11 400 and a polydispersity (Mw/Mn) of 1.13. In the ¹H NMR spectrum of the product, the signals due to polystyrene (PSt) appeared along with the characteristic signals due to the 1 unit. Thus, the product was assignable to the end-functionalized PSt with acetylated β-CyD, 2. The introduction of acetylated β-CyD into 2 was found to occur in a quantitative fashion, which was confirmed by thin-layer chromatography equipped with a flame ionization detector (TLC-FID). For the [St]/[1] of 600 at 120 °C, the St/1 system proceeded in a controlled manner to afford 2 with polymerization times of 1.5−9 h with yields of 5−40% and Mw,SEC's of 7500−26 000. On the other hand, the St/1 system for 15 and 20 h afforded polymers with 54 and 75% though an unexpected side reaction occurred. Polymer 2 with Mw,SEC's of 7500−26 000 was modified by deacetylation using sodium methoxide in dry THF into end-functionalized PSt with β-CyD, 3. Particle formation was observed during dynamic laser light scattering measurements of 3 in benzene, indicating that 3 was stably suspended in a good solvent for PSt by forming aggregates with β-CyD as a core. The average aggregation numbers (NA) of the aggregates were found to range from 42 to 125, which were determined by static laser light scattering measurement.

The effect of fluoride on the hydrolysis of tetracalcium phosphate (TTCP; Ca4(PO4)2O) in 0.1 mol/l KH2PO4containing 62–83 mmol/l KF was studied with the help of X-ray fluorescence measurements. Fluorine X-ray emission and absorption spectra of the final product of hydrolysis and reference samples (CaF2and Ca5(PO4)3F) were measured at Beamline BL-2C of Photon Factory (PF, Tsukuba). Based on these measurements we concluded that hydrolysis of TTCP in the presence of KF converts it into fluorapatite. Formation of CaF2, which is often found in the hydrolysis of hydroxyapatite at high fluoride concentration, was not observed.

The nucleation and crystallization behavior of a series of glasses based on 4.5SiO2- 3Al2O3-YP2O5-3CaO-1.51CaF2was studied. The parameter Y was varied to give calcium to phosphate ratios between one and two. All of the glasses studied crystallized firstly to fluorapatite (Ca5(PO4)3F). The glass with a calcium to phosphate ratio of 1.67, corresponding to apatite, bulk nucleated to give fluorapatite (FAP). The glasses with calcium : phosphate ratios either less than that of apatite, or greater than that of apatite all exhibited surface nucleation of FAP. However, following a nucleation hold of one hour at approximately 50 K above the glass transition temperature these glasses exhibited bulk nucleation of FAP. © 2001 Kluwer Academic Publishers

The reaction of Ca(PO4)2O (TTCP) and CaHPO4(DCPA) in an aqueous solution has been shown to be responsible for the hardening of a calcium phosphate cement. This reaction was investigated by monitoring pH changes and composition of solid phases. In the first set of experiments (no attempt to control pH), 2.5 g each of mixtures of TTCP/DCPA, molar ratio from 0.25 to 2, was placed in 12.5 mL of 0.15 mol/L KCl solution, at initial pH about 7, and the pH was allowed to drift for 24 h. Results show that at any time up to 24 h, the pHs were higher for slurries with higher TTCP/DCPA molar ratios. For the slurries with TTCP/DCPA molar ratio of ≥ 0.83, the 24 h pHs of the slurries were 9 to 11, whereas for those with TTCP/DCPA of ≤ 0.67, the pHs were between 5.3 and 7. The slurries with TTCP/DCPA molar ratios between 0.5 and 1 (Ca/P molar ratio=1.5 to 1.67) reacted completely within 24 h to form hydroxyapatite(OHAp), Ca5(PO4)3OH. In the second set of experiments, 2 g of an equimolar TTCP and DCPA mixture was placed in 20 mL of 0.15 mol/L KCl solution. The pH values were kept constant (6, 8 or 10) by using H3PO4and Ca(OH)2or HCl and KOH as titrant solutions. At pH 8, DCPA and TTCP dissolved at about the same rate, whereas at pH 10, DCPA was consumed more rapidly than TTCP. At both pHs, OHAp was the only product formed. However, at pH 6, the composition of reaction products depended on the types of the titrants used. Specifically when H3PO4and Ca(OH)2were used, hydrolysis of TTCP was the predominant reaction and both octacalcium phosphate and OHAp were formed. But, when HCl and KOH were used, only OHAp was formed. In this case hydrolysis of TTCP and DCPA appeared to proceed independently with TTCP hydrolysis beginning immediately and progressing slowly through 48 h while the DCPA hydrolysis began several hours after the reaction started but was completed in 24 h. ©2000 Kluwer Academic Publishers

The activity product of tetracalcium phosphate (TTCP, Ca4(PO4)2O), was determined at 37°C, and the hydrolysis of TTCP was investigated in 0.01–0.1 mol l−1H3PO4and KH2PO4solutions by means of calcium and phosphorus analyses, X-ray diffraction and infrared analysis. The activity product, defined as Ksp=(Ca2+)4(PO43−)2(OH−)2, was 37.36 as pKsp, which was smaller than that previously reported (42.4). TTCP easily hydrolysed to form calcium-deficient apatite (Ca-def OHAp, Ca5−x(HPO4)x(PO4)3−x(OH)1−x), or dicalcium phosphate dihydrate (DCPD, CaHPO42H2O), depending on the initial phosphate concentration. With 0.1 mol l−1H3PO4, TTCP hydrolysed to form DCPD within several minutes. In 0.025 mol l−1H3PO4and 0.1 mol l−1KH2PO4, TTCP hydrolysed to form Ca-def OHAp through DCPD. In the latter solution, a small amount of octacalcium phosphate (OCP, Ca8(H2PO4)2(PO4)45H2O), was detected as an intermediate product. In 0.025 mol l−1KH2PO4, TTCP hydrolysed directly to form Ca-def OHAp. In 0.01 mol l−1H3PO4, hydrolysis of TTCP was not completed, although Ca-def OHAp was only a product. Thus the final product and the degree of hydrolysis depended on the pH and the overall Ca/P ratio in the reaction system. The rate of Ca-def OHAp formation seemed to be controlled by the dissolution rate of TTCP rather than the crystallization rate of the OHAp.

Shape restoration effects associated with order–disorder transformation in equiatomic AuCu and Au0.47Cu0.47Ga0.06alloys were examined by means of surface roughness measurements of sheet specimens and the change in the distance between tips of U-shaped specimens. The specimen surface became irregular and a macroscopic shape change occurred after an ageing heat treatment. The shape change was attributed to the heterogeneity in the deformation which arose from the stress release by twinning at the free surface. After disordering of the age-hardened specimen, they regained completely to its original shape. When the specimen was aged without any constraint, spontaneous deformation occurred and did not result in any given shape. However, when the external stress was applied during ordering heat treatment, a given shape was obtained by the formation of favorably oriented ordered domains and twin lamellae. It is suggested that once the direction of deformation was decided, growth of the existing variants continued.

Computer simulation experiments were performed for the anodic dissolution process of Cu0.7Au0.3-xPdx (x=0–0.3) alloys. Dissolution probabilities of constituents which represented the dissolution rate were defined by considering the standard electrode potential of the dissolution reaction and atomic interaction between Cu and the other atoms. The simulation results qualitatively reproduced the experimental results of anodic potentiostatic polarization tests regarding the dependence of the anodic dissolution behaviour on the polarization potential and the alloy composition, and the atomic concentration depth profile of the constituents after anodic polarization. Atomic interaction among the constituents of an alloy was found to be one of the important factors which control the anodic dissolution features of the alloys.

The effect of microstructure on the corrosion behaviour of Au-Cu-11 at % Pd, Au-Cu-11 at % Ag and (Au-Cu-11 at % Ag)-5 at % Pd alloys was studied by anodic potentiodynamic and potentiostatic polarization tests. The single-phase Au-Cu-11 at % Pd alloys had high corrosion resistance and their potentiodynamic polarization curves were simple. The high-nobility Au-Cu-11 at % Ag alloy displayed high corrosion resistance regardless of its microstructure. The two-phase Au-Cu-11 at % Ag and (Au-Cu-11 at % Ag)-5 at % Pd alloys had lowered corrosion resistance compared with the single-phase alloys. Anodic potentiodynamic polarization curves of the two-phase alloys were complex, but they were explained by superimposing the curves of each phase using the principle of additivity. The potential at which the current density sharply increased corresponded with that of each phase, and the value of current density was calculated as the sum of the current density of each phase and taking account of their volume fractions. In the anodic potentiodynamic polarization, there was little galvanic effect between the two phases.

Tarnishing tests were carried out on Au-Cu-Ag and Au-Cu-Pd alloys. This study focused on the individual and combined effects of nobility, palladium content and microstructure. Tarnish resistance was almost perfect for the alloys with nobility higher than 50 at%, but it seemed to relate to the palladium : gold atomic ratio for the alloys with low nobility. Palladium inclusion reduced the tarnish susceptibility up to about 10 at%. This decrease in the degree of tarnishing was attributed to the decrease in the diffusion rate of S2 ion which resulted in a decrease in the growth rate of sulphide layer. Tarnishing of the alloy with low nobility was very sensitive to its microstructure. The tarnishing susceptibility of dual-phase Au-Cu-Ag alloy was twice as high as that of the single-phase alloy. However, palladium-bearing alloy showed no increase in the degree of tarnishing by phase separation. This may be attributed to the enrichment of palladium in the copper-rich phase.

The effect of fluoride on the hydrolysis of tetracalcium phosphate (TTCP; Ca4(PO4)2O) was investigated in 0.1 mol l−1KH2PO4 containing 0–83 mol l−1 KF. Characterization of the final apatite phase formed by the hydrolysis was made with X-ray diffraction and SEM. The initial pH was between 4.5 and 5.4, depending on the solutions, and the pH rapidly increased and was kept constant between 7.3 and 6.5. An increase in KF concentration tended to lower the pH in the final stage of hydrolysis. The calcium concentration was considerably lower than the phosphorus concentration throughout the reaction. The fluoride concentration decreased shortly after the start of hydrolysis. The hydrolysis of TTCP in 0.1 mol l−1 KH2PO4 proceeded to form hydroxyapatite via DCPD when the KF concentration was low. The hydrolysis product was a calcium-deficient non-stoichiometric hydroxyapatite with a Ca/P ratio of about 1.5. With an increase in the KF concentration in the 0.1 mol l−1 KH2PO4 solution, TTCP directly transformed into hydroxyapatite containing F- ions or fluorapatite and with improved crystallinity. The addition of fluoride in the solution initially accelerated the formation of apatite. However, the layer of newly formed apatite adhering to the TTCP particles retarded TTCP dissolution; as a result, hydrolysis was delayed. IR analysis showed that the apatite phase contained HPO2−4 ions in the structure. The formula for the hydrolysis product of TTCP in the presence of fluoride can be expressed as follows: Ca10−x(HPO4)x(PO4)10−x(OH)2−x−yFy. © 1998 Chapman & Hall.

Objectives. The purpose of this study was to assess the feasibility of forming polymeric calcium phosphate cements from a mixed powder of dicalcium phosphate/tetracalcium phosphate or only tetracalcium phosphate and poly(methyl vinyl ether-maleic acid) (PMVE-Ma), and to study their setting reaction. Methods. The setting reaction process of the polymeric cements was evaluated by mechanical strength tests, infrared spectroscopy and x-ray diffraction analysis and compared with that of a water-setting calcium phosphate cement. The mechanical strength data were analyzed using ANOVA and Scheffe's multiple comparisons test. Results. Cements prepared from the mixed powder and 25-30 wt% aqueous solutions of PMVE-Ma had high mechanical strength after 24 h storage in distilled water at 37^oC. The hardening mechanism dependended on an acid-base reaction between the carboxyl groups of PMVE-Ma and the mixed powder, especially its tetracalcium phosphate component. The formation of hydroxyapatite in the polymeric calcium phosphate cement was not detected and is apparently inhibited as a result of the competing reaction of PMVE-Ma with the mixed powder. Significance. The cement-forming reaction was significantly faster than that of a water-setting calcium phosphate cement and slower than that observed with the mixed powder and polyacids such as poly(acrylic acid). The characteristics of the polymeric cements suggest that the materials may be useful in cavity lining or endodontic sealing.

Dental gold alloys with age-hardenability at intraoral temperature were developed. Either 3 or 6 at% Ga, Al, Zn, In, Ni or Pd were added to an equiatomic AuCu alloy and the effect of additives on the low-temperature age-hardenability was examined. Alloys containing Ga, Al or Zn exhibited excellent low-temperature age-hardenability. The hardness of an alloy containing 6 at% Ga or 6 at% Al was doubled in one to ten days by ageing at 37 °C. Pronounced hardening was not demonstrated in an as-cast alloy, but solution treatment for only a few minutes provided enough age-hardenability. The age-hardening rate at low temperature related closely with the melting temperature of the alloy. Experimental gold alloys exhibited electrochemical behaviour similar to that of a commercial Type IV gold alloy. It is therefore concluded that AuCu alloy with added Ga, Al or Zn is expected to have enough age-hardenability and corrosion resistance for clinical use in the oral environment.