Corrosion resistance of casted titanium by compound treatments in the artificial saliva with different fluoride concentrations / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To study the corrosion resistance of casted titanium by plasma nitriding and TiN-coated compound treatments in the artificial saliva with different fluoride concentrations and to investigate whether compound treatments can increase the corrosion resistance of casted titanium.</p><p><b>METHODS</b>Potentiodynamic polarization technique was used to depict polarization curve and to measured the current density of corrosion (Icorr) and the electric potential of corrosion (Ecorr) of casted titanium (Group A) and casted titanium by compound treatments (Group B) in the artificial saliva with different fluoride concentrations. After electrochemical experiment, the microstructure was observed by scanning electron microscope (SEM).</p><p><b>RESULTS</b>The Icorrs of Group A and B in the artificial saliva of different fluoride concentrations were (1530.23 ± 340.12), (2290.36 ± 320.10), (4130.52 ± 230.17) nA and (2.62 ± 0.64), (7.37 ± 3.59), (10.76 ± 6.05) nA, respectively. The Ecorrs were (-0.93 ± 0.10), (-0.89 ± 0.21), (-0.57 ± 0.09) V and (-0.21 ± 0.04), (-0.17 ± 0.03), (-0.22 ± 0.03) V, respectively.The Icorrs of Group B were significantly lower (P < 0.01)than that of Group A. The Icorrs increased significantly with the increasing of fluoride concentrations (P < 0.01). The Ecorrs of Group B were significantly higher than that of Group A (P < 0.01). The SEM confirmed the microstructure in the casted titanium was much severely than that in Group B, the microstructure in Group A and B corroded more and more heavily with increasing of fluoride concentrations.</p><p><b>CONCLUSIONS</b>The increase of fluoride concentrations influence the corrosion resistance of both treated and untreated casted titanium negatively, but plasma nitriding and TiN-coated compound treatments can significantly increase the corrosion resistance of casted titanium.</p>

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>

Study of the bonding strength of pure titanium and light-cured hard crown and bridge composite after filming by TiSiN / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To evaluated the bonding strength between pure titanium and Solidex after deposition by magnetron sputtering TiSiN with different content of Si (9%, 19%) and analyzed the surface component by electron probe micro-analysis (EPMA).</p><p><b>METHODS</b>All pure titanium samples divided into 3 groups according to different surface treatment, then bonded with Solidex light-cured composite. Material test machine was used to measure bonding strength and the surface was analyzed by EPMA.</p><p><b>RESULTS</b>The bonding strength of deposition with TiSiN groups were higher than unfilming group, increasing the content of Si could enhance the bonding strength between pure titanium and Solidex in TiSiN groups (P < 0.05). EPMA showed amorphous materials like TiN, SiN gathered on the surface in TiSiN groups. There were obvious interspaces between unfilming pure titanium and Solidex, contrary no interspaces was observed in TiSiN groups.</p><p><b>CONCLUSION</b>The bonding strength of filming groups was higher than unfilming group, amorphous material like TiN, SiN gathering on the surface may prevent the microleakage and stop metal ion leaking.</p>

Cr-Ti-Al-N complex coating on titanium to strengthen Ti/porcelain bonding / 南方医科大学学报

<p><b>OBJECTIVE</b>To study the feasibility of magnetron sputtering Cr-Ti-Al-N complex coating as an interlayer on titanium to enhance the titanium-ceramic binding strength.</p><p><b>METHODS</b>With a three-point bending test according to ISO 9693, the binding strength of Duceratin (Degussa) to titanium substrate prepared with 4 different surface treatments (polishing, polishing and megnetron sputtering Cr, Ti, Al, and N complex coating, sandblasting, sandblasting and coating) was evaluated. Ti/porcelain interface and fractured Ti surface were examined using scanning electron microscopy with energy-dispersive spectrometry (EDS).</p><p><b>RESULTS</b>The binding strength of polished and coated titanium/Duceratin was significantly higher than polished titanium group (P<0.05). The binding strength of sandblasted and coated titanium/Duceratin did not differ significantly from that of sandblasted titanium group (P>0.05), and the strength in the two sandblasted titanium groups was significantly higher than that in polished and coated titanium group (P<0.05).</p><p><b>CONCLUSION</b>Megnetron sputtering Cr-Ti-Al-N complex on polished titanium can increase the titanium/porcelain binding strength. Megnetron sputtering coating is a promising Ti/porcelain interlayer.</p>

A study of mandible chewing movement in patients with developmental lateral jaw deformity / 中华口腔医学杂志

<p><b>OBJECTIVE</b>The purpose of the present study was to investigate effects of developmental lateral jaw deformity (DLJD) on masticatory movement.</p><p><b>METHODS</b>Three coordinates of mandibular movement signals were recorded in 35 young healthy adults with normal occlusion and 28 patients with DLJD by means of a Sirognathography System during gum chewing movement. Paired and unpaired t-tests were used to compare significant difference of intra-group and inter-groups in displacement and speed. P < 0.05 was chosen as significance level.</p><p><b>RESULTS</b>(1) The rhythm and directional sequence of chewing trajectory in both frontal and sagittal planes were normal in control group, while anomalies of rhythm and distribution (n = 9) and reversed sequencing (n = 7) were found in DLJD group. (2) The maximum magnitude of jaw retrusion and average speed were significant higher in DLJD group than those in control group (P < 0.01). The spatial displacement and average speed in horizontal plane and in chewing phase were also higher in DLJD group compared with control group (P < 0.05).</p><p><b>CONCLUSIONS</b>DLJD patients showed anomalies in chewing pattern as well as chewing speed and displacement in horizontal plane.</p>

Effect of mold temperature on mechanical properties of Ti-Zr alloy castings / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the influence of mold temperature on the mechanical properties of Ti-Zr alloy castings.</p><p><b>METHODS</b>Ti-Zr alloy was cast into a mold which was made of a zircon (ZrO2.SiO2) investment with a casting machine (China) designed as vacuum, pressure and centrifuge. At three mold temperatures (room temperature, 300 degrees C, 600 degrees C) the Ti-Zr alloy was cast separately. The ultimate tensile strength (sigmab), 0.2% offset yield point strength (sigma0.2), and elongation to fracture (delta) were determined by a universal testing machine with 15 mm pre-marked gauge interval. The surface micro-structures of Ti-Zr alloy castings at three mold temperatures were observed by optical microscope.</p><p><b>RESULTS</b>At a higher mold temperature during casting, the tensile strength and yield strength of Ti-Zr alloy were significantly increased, while the elongations were significantly decreased. The micro-structure of the surface was different from the inner part. There was a reacted layer in the outermost surface. The thickness of reacted layers at the three mold temperatures was about 35.5 man (room temperature), 55.0 microm (300 degrees C) and 65.5 microm (600 degrees C), respectively. The inner part of microstructure composed of main a phases within the prior alpha grain boundaries.</p><p><b>CONCLUSION</b>The mold temperature is one of the major factors influencing Ti-Zr alloy mechanical properties. Comparing with Ti6Al4V alloy and Co-Cr alloy castings, Ti-Zr alloy is more suitable for denture frame.</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>

The bonding characteristic of titanium and RG experiment porcelain / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To study the bonding characteristic of Titanium and RG experiment porcelain.</p><p><b>METHODS</b>5 specimens with a size of 10 mm x 5 mm x 1.4 mm were cast from pure titanium. Then 1 mm of RG experiment opaque and body porcelain were fused on the surface of the titanium specimens. The interface of titanium and porcelain was analyzed with a scanning electron microscope with energy-despersive spectrometry; 6 metal specimens with the size of 25 mm x 3 mm x 0.5 mm were cast from Ni-Cr alloy and a uniform thickness of 1 mm of VMK 99 porcelain was veneered on the central area of 8 mm x 3 mm 18 metal specimens as the same size were cast from pure titanium. The uniform thickness of 1 mm of VITA TITANKERAMIK porcelain, of Noritake super porcelain Ti-22 and of RG experiment porcelain were veneered on every 6 specimens respectively in the central area of 8 mm x 3 mm. The specimens were subjected to a three-point bending test on a load-test machine with a span of 20 mm, then the failure loads were recorded and statistically analysised. The RG porcelain/titanium crown was fabricated by fusing RG opaque porcelain and body porcelain to cast titanium substrate crown.</p><p><b>RESULTS</b>The SEM results show no porosity and crackle were found in the interface. The energy-dispersive spectrometry show that there are Si, Ti and O in the 1 micro m layer between porcelain and titanium, which suggesting titanium and experiment porcelain bonding well. The three point test showed the fracture force for the combinations of titanium/VITA TITANKERAMIK porcelain, titanium/Noritake super porcelain Ti-22 and titanium/RG experiment porcelain were (7.233 +/- 2.539) N, (5.533 +/- 1.199) N and (6.316 +/- 1.433) N respectively. There were not statistically significant differences among them (t test, P < 0.01). The fracture force for the Ni-Cr alloy/VMK99 porcelain combination (12.733 +/- 3.297) N was significantly greater than those of the cast titanium/porcelain (t test, P > 0.05). The crown was translucent with no crack.</p><p><b>CONCLUSION</b>RG porcelain is well compatible with titanium.</p>