Effect of investment composition ratio for pure titanium crown and bridge on some mechanical properties of mould / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To determine the optimal composition of a self-developing investment material by measuring physical and mechanical properties of mould.</p><p><b>METHODS</b>L(9) (3(4)) orthogonal design was adopted. One hundred and fifty specimens with the size of 80 mm × 20 mm × 20 mm were prepared to measure the atmospheric temperature bending strength, high temperature bending strength and residual bending strength. Nine specimens with the size of 5 mm diameter 25 mm heigh were prepared to survey the thermal expansion curve from ambient temperature to 1150°C.</p><p><b>RESULTS</b>Strengths were greatly affected by fine powder proportion in refractory and water/powder ratio. When the content of fine powder was 35% and water/powder ratio was 1:7.5, adequate atmospheric temperature strength and high temperature strength could be achieved. Moreover, the residual strength was moderate. The thermal extension curves of specimens in experiment group were almost similar. And the average linear expansion coefficient was (4 ∼ 5) × 10(-6)/°C.</p><p><b>CONCLUSIONS</b>The three kinds of bending strength of self-developing investment material are compared with commercialized investment material for titanium casting when water/powder ratio and the content of fine powder are carefully controlled.</p>

Effect of investment for titanium crown and bridge on reactive layer of castings / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the effect of self-developing investment (FUS-invest) on the reactive layer of titanium castings.</p><p><b>METHODS</b>Three 10 mm x 10 mm x 1 mm pure titanium castings were founded using FUS-invest. Metallographical structure of reactive layer was observed. X-ray diffraction (XRD) and scanning electron microscope with energy-dispersive spectrum (EDS) were used to analyze the status of composition of the casting surface. Micro-Vickers hardness was measured.</p><p><b>RESULTS</b>The metallograph indicated that the reactive layer was composed of coarse flake-shaped alpha phase of grains. The value of micro-Vickers hardness with the range 243 to 314 MPa had not significantly difference under the depth of 105 microm beneath the surface. The XRD pattern clearly showed the peaks of ZrO2, SiO2, Mg2TiO4 and TiO2. EDS analysis demonstrated that the main elements were Al, Si, Zr and Cl.</p><p><b>CONCLUSION</b>FUS-invest is suited for pure titanium casting because of the thin reactive layer and less change to metallographical structure.</p>

Effects of the improved FUS-invest investment for zirconium-oxide titanium crown and bridge on the reaction layer / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the effects of the improved FUS-invest investment for zirconium-oxide titanium crown and bridge on the reaction layer.</p><p><b>METHODS</b>10 mm x 10 mm x 1 mm titanium castings were invested. Spectrum analysis was done to its reaction layer, the metallographic examination was observed and Vickers hardness was measured.</p><p><b>RESULTS</b>The reaction layer was not obvious by the metallographic examination. The layer with plenty of Si was hardly detectable. The needle crystal layer diffused distribution on the surface of the titanium matrix. The depth was about 55 microm. Spectrum analysis showed that the contents of Si and Zr decreased as the depth increased. The microhardness, which obviously decreased from the surface to the matrix, tended to be equal with the hardness of the matrix after the depth reached 75 microm from the surface.</p><p><b>CONCLUSION</b>The thickness of the reaction layer of the improved FUS-invest investment for zirconium-oxide titanium crown and bridge was decreased to 55 microm from 85 microm, which was the thickness before improvement.</p>

The effect of casting techniques on the accuracy of titanium crown and bridge / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the method of enhancing the accuracy of titanium crowns by improving the casting method.</p><p><b>METHODS</b>A self-assembled die was used to fabricate 48 standardized wax crowns. The dies were averagely divided into two groups. 21 crowns were successfully fabricated from one group according to the improved techniques. 18 crowns were fabricated by traditional method. A reference mark was scribed 90 degrees apart at four sites on the margin of each wax pattern and respective die. The distance between the margins of the wax pattern and the die was measured under a stereomicroscope. Similar method was also applied to measure the margin of castings. The castings were longitudinally split through midline. The distance between the 4 points(B',C',D',E') selected in the inner part of the crown and the die was respectively examined.</p><p><b>RESULTS</b>Castings acquired by the improved method were more complete and had smoother surface. Marginal discrepancy value had significant difference between the two groups. Value in experimental group was smaller. Distance from B',E' to die between the two groups had no significant difference, but the distance from C',D' to the die was significantly different. The experimental group was smaller.</p><p><b>CONCLUSION</b>Standardized crowns fabricated by the improved titanium casting technique were more accurate, but special investment for titanium crowns and bridges should be developed to compensate the casting shrinkage of metal.</p>