Effect of heat treatment on apatite-forming ability of Ti metal induced by alkali treatmentKIM , H.; MIYAJI , F; KOKUBO , T; NAKAMURA , T
doi: 10.1023/A:1018524731409pmid: 15348733
The present authors previously showed that titanium metal forms a bone-like apatite layer on its surface in a simulated body fluid (SBF), when it has been treated with a NaOH solution to form a sodium titanate hydrogel layer on its surface. This indicates that the NaOH-treated Ti metal bonds to living bone. The gel layer as-formed is, however, mechanically unstable. In the present study, the NaOH-treated Ti metal was heat treated at various temperatures in order to convert the gel layer into a more mechanically stable layer. The gel layer was dehydrated and transformed into an amorphous sodium titanate layer at 400–500°C, fairly densified at 600°C and converted into crystalline sodium titanate and rutile above 700°C. The induction period for the apatite formation on the NaOH-treated Ti metal in SBF increased with the transformation of the surface gel layer by the heat treatment. Ti metal heat treated at 600°C, however, showed a fairly short induction period as well as high mechanical stability, since it was covered with a fairly densified amorphous layer.
Glass-ionomer dental restorative: Part I: a structural studyMILNE , K.; CALOS , N.; O’DONNELL , J.; KENNARD , C.; VEGA , S; MARKS , D
doi: 10.1023/A:1018576715479pmid: 15348734
A structural study of glass-ionomer cement (GIC) dental restoratives has been completed. Transmission electron microscopy, selected area electron diffraction, and X-ray diffraction studies indicate domain-like microstructure in a new experimental material, whereas a featureless amorphous gel-like microstructure exists in the conventional GIC. Nuclear magnetic resonance studies were also conducted. The new experimental GIC contains domains of (i) bonelike material (apatite), (ii) mesoporous material and (iii) other framework structures (aluminium phosphate in the high cristobalite structure), with its setting chemistry a restructuring of the aluminosilicate glass around the template of poly(acrylic acid). Conventional glass-ionomer cement may set by a similar but slower process. Leaching properties of glass-ionomer cements are also explained.
Corrosion of gallium alloys in vivoHERØ , H; OKABE , T; WIE , H
doi: 10.1023/A:1018528832317pmid: 15348735
The aim of this work was to study the corrosion of gallium alloys in vivo. Three gallium alloys were tested: GF alloy, Galloy and an experimental GaIn alloy. An amalgam was applied as a control. After ageing for a minimum of two weeks, one disc of each of these alloys was mounted with the polished side up in the buccal surfaces of 17 acrylic dentures. Eight sets of the specimens were retrieved after exposure to the oral cavity for 2–4 months, and another seven were retrieved after 6–9 months. Corrosion of the polished cross-sections of the specimens was studied using scanning electron microscopy (SEM). Only the CuGa2 phase was found to corrode substantially in all three of the alloys investigated, leaving behind holes up to 20 μm deep. This is consistent with the corrosion reported after immersion tests in a solution of 0.1 mol lactic acid and 0.1 mol NaCl for 7 days. Such in vitro tests are also reported to cause distinct corrosion of the Sn phase in the gallium alloys. However, a salient feature of the corrosion in vivo was the lack of detectable dissolution of this phase. Thus, for gallium alloys, the accelerated in vitro immersion method produced results which did not agree with clinical observations. Large variations in the corrosion of the CuGa2 were observed from patient to patient. The amount of corrosion on the Galloy specimens appeared to be less and on a finer scale than on specimens of the two other alloys. The depth of corrosion was thus shallower than for this alloy. This finding indicates that there is room for further improvement of the corrosion resistance by modifying the microstructures. Less overall corrosion was found for the amalgam control than for the gallium alloys.
Preparation and mechanical properties of calcium phosphate/copoly-L-lactide compositesKIKUCHI , M; SUETSUGU , Y; TANAKA , J; AKAO , M
doi: 10.1023/A:1018580816388pmid: 15348736
New artificial bone materials were prepared using calcium phosphates, hydroxyapatite and β-tricalicum phosphate, and copoly-L-lactide, CPLA. Calcium phosphate powder and CPLA were mixed at 453 K for 10 min with various mixing ratios. Scanning electron microscope observations indicated that the composites of β-tricalicum phosphate and CPLA were homogeneously dispersed and highly adhesive. Young’s modulus of the composites was the same as bone, and bending strength was over half that of bone. The improvement of Young’s modulus compared to the original two materials was due to a composite effect. The composites are expected to be usable as artificial bone materials.
Morphology and ultrastructure of the interface between hydroxyapatite-polyhydroxybutyrate composite implant and boneLUKLINSKA , Z.; BONFIELD , W
doi: 10.1023/A:1018589018205pmid: 15348740
A composite of polyhydroxybutyrate (PHB) polymer, reinforced with synthetic hydroxyapatite (HA) particles, with potential as a bone-analogue material, was examined microscopically using scanning electron microscopy and transmission electron microscopy. These imaging techniques provide the means of understanding and monitoring the morphological and structural behaviour of retrieved implants. Scanning electron microscopy was used to assess the overall mechanism of new bone formation at the implant interface after up to 6 months implantation. This procedure was followed by a detailed ultrastructural examination at lattice plane resolution level, using high resolution electron microscopy and selected area diffraction of the regions showing bone apposition. Fine hydroxyapatite crystallites were found to form at the interface after in vivo implantation into cortical bone.