Comparative study on torsional strength, ductility and fracture characteristics of laser-welded alpha+beta Ti-6Al-7Nb alloy, CP Titanium and Co-Cr alloy dental castings.

OBJECTIVES: The purpose of this study was to compare torsional strength, ductility and fracture behaviors of Ti-6Al-7Nb, CP Ti and Co-Cr alloy castings after laser welding. METHODS: Dumbbell-shaped castings of three metal alloys (Ti-6Al-7Nb alloy, CP Ti, Co-Cr alloy) were cut in half and laser welded with a Nd:YAG pulse laser-welding machine at either 220V or 260V of laser voltage. After being laser welded, all cast specimens were tested with a multi-axial hydraulic testing machine (MTS 858 Mini Bionix) using a torsional test. The fracture surfaces were investigated with a scanning electron microscope. RESULTS: None of the laser-welded Ti-6Al-7Nb alloy and CP Ti castings was broken within the welded joint, showing torsional strength as high as the unwelded castings. Unlike the other groups, the laser-welded Co-Cr alloy castings exhibited brittle fracture appearance and provided substantially less torsional strength. SIGNIFICANCE: The torsional strength of the laser-welded Ti-6Al-7Nb alloy and CP Ti castings was as high as that of the unwelded castings while this finding could not apply to the Co-Cr alloy castings. This indicates that the mechanical strength of the laser-welded Ti-6Al-7Nb alloy dental casting is sufficient for clinical applications.     

Mechanical strength and microstructure of laser-welded Ti-6Al-7Nb alloy castings

Mechanical properties of laser-welded castings of Ti-6Al-7Nb alloy, CP Ti, and Co-Cr alloy were investigated and compared to the unwelded castings using a tensile test. Dumbbell-shaped specimens were cut at the center, and two halves of the specimens were welded with an Nd:YAG laser welding machine at 220 or 260 V of laser voltage. The mechanical strength of 260 V groups was higher than that of 220 V groups for Ti-6Al-7Nb and Co-Cr alloys except for CP Ti. All 260 V laser-welded castings of Ti-6Al-7Nb alloy and CP Ti, which fractured outside the welded joints, exhibited ductile characteristics, while all laser-welded Co-Cr alloy castings, which fractured within the welded joints, showed brittle characteristics. This study proved that the mechanical strength of laser-welded Ti-6Al-7Nb alloy and CP Ti castings was as high as that of unwelded castings, while the mechanical properties of laser-welded alloy joints were influenced by microstructural changes.     

Laser Welding of Cast Titanium and Dental Alloys Using Argon Shielding

PURPOSE: This study investigated the effect of argon gas shielding on the strengths of laser-welded cast Ti and Ti-6Al-7Nb and compared the results to those of two dental casting alloys. MATERIALS AND METHODS: Cast plates of Ti, Ti-6Al-7Nb, gold, and Co-Cr alloy were prepared. After polishing the surfaces to be welded, two plates were abutted and welded using Nd:YAG laser at a pulse duration of 10 ms, spot diameter of 1 mm, and voltage of 200 V. Five specimens were prepared for each metal by bilaterally welding them with three or five spots either with or without argon shielding. The failure load and percent elongation were measured at a crosshead speed of 1.0 mm/min. RESULTS: The factor of argon shielding significantly affected the failure load and elongation of the laser-welded specimens. The failure loads of argon-shielded laser-welded CP Ti and Ti-6Al-7Nb were greater compared with the failure loads of specimens welded without argon shielding for both three- and five-spot welding. Regardless of argon shielding, the failure loads of the laser-welded gold alloy were approximately half that of the control specimens. In contrast, the failure loads of the nonshielded laser-welded Co-Cr alloy were greater. The percent elongations positively correlated with the failure loads. CONCLUSIONS: The use of argon shielding is necessary for effective laser-welding of CP Ti and Ti-6Al-7Nb but not for gold and Co-Cr alloy.     

Attractive force of castable iron-platinum magnetic alloys.

OBJECTIVE: The objective of this study was to examine the attractive force of cast Fe-Pt alloys of varying compositions to dental iron-neodymium-boron magnets. METHODS: Ingots of Fe-40 at%Pt, Fe-38 at%Pt, Fe-37 at%Pt and Fe-36 at%Pt alloys were cast in pattern molds for dental magnetic attachment keepers. The attractive forces of the cast Fe-Pt alloy keepers and magnetic stainless steel keepers to dental Fe(14)Nd(2)B magnets (MAGFIT and HICOREX) were measured and statistically evaluated. The saturation magnetization of each Fe-Pt alloy was determined by recording the hysteresis loop using a vibrating sample magnetometer under a magnetic field of 1.6 MA/m. RESULTS: Decreasing the Pt percentage increased the saturation magnetization value and resulted in an increase of the attractive force to each magnet. There was no statistical difference (p>0.05) in attractive force between the Fe-36 at%Pt alloy specimens and the stainless steel keepers for both magnets. A definite correlation between Pt percentage and the value of saturation magnetization was also found (r(2)=-1.000). SIGNIFICANCE: The Fe-Pt alloys with less than Fe-39.5 at%Pt produced high saturation magnetization values and great attractive force to the magnet, and thus, they have the potential to serve as magnetic attachment keepers. Of the Fe-Pt alloys tested, Fe-36 at%Pt seemed to be the best composition for making magnetic attachment keepers.     

Use of metal conditioners to improve bond strengths of autopolymerizing denture base resin to cast Ti-6Al-7Nb and Co-Cr

OBJECTIVE: The shear bond strengths of an autopolymerizing denture base resin to cast Ti-6Al-7Nb and Co-Cr alloys using three metal conditioners were investigated. METHODS: Ti-6Al-7Nb alloy and Co-Cr alloy discs were cast. The disc surfaces were air-abraded with 50 microm alumina particles and treated with three metal conditioners (Alloy Primer; Cesead II Opaque Primer; Metal Primer II). An autopolymerizing denture base resin was applied on the discs within a hole punched in a piece of sticky tape and a Teflon ring to define the bonding area. All specimens were immersed in 37 degrees C water for 24 h. Half of the specimens were thermocycled up to 20,000 cycles. The shear bond strengths were determined at a crosshead speed of 1.0 mm/min. RESULTS: Specimens treated with the three metal conditioners had significantly (p<0.05) improved shear bond strengths of the autopolymerizing denture base resin to both Ti-6Al-7Nb and Co-Cr. Although the bond strengths of the bonded Ti-6Al-7Nb specimens were higher than those of the Co-Cr alloy before thermocycling, the decrease in the bond strength of Ti-6Al-7Nb was considerably greater than that of the Co-Cr after thermocycling. CONCLUSION: Significant improvements in bond strength of the autopolymerizing denture base resin to cast Ti-6Al-7Nb alloy and Co-Cr alloy were achieved through the application of Alloy Primer, Cesead II Opaque Primer and Metal Primer II. The bond durability to Ti-6Al-7Nb alloy was inferior to that to Co-Cr.     

The development of Ti alloys for dental implant with high corrosion resistance and mechanical strength

The corrosion behaviors of Ti and Ti-6Al-4V, Ti-6Al-7Nb, Ti-0.5Pt, Ti-6Al-4V-0.5Pt, and Ti-6Al-7Nb-0.5Pt alloys were examined using an electrochemical analyzer in artificial saliva containing 0.1 and 0.2% NaF at a pH of 4.0. The SEM observations revealed that the surfaces of the alloys containing 0.5 wt% Pt were not affected in fluoride-containing environments, whereas the surfaces of Ti, Ti-6A1-4V, and Ti-6Al-7Nb alloys were markedly rough. In artificial saliva containing 0.1% NaF at a pH of 4.0, the amounts of Ti dissolved from the Ti, Ti-6Al-4V, and Ti-6Al-7Nb alloys were about 50 times larger than those of the alloys containing 0.5 wt% Pt. The tensile strengths of the alloys containing 0.5 wt% Pt were equal to or higher than those of pure Ti or the alloys without Pt. The Ti-0.5Pt, Ti-6Al-4V-0.5Pt, and Ti-6Al-7Nb-0.5 alloys are expected to be useful in clinical dentistry as new Ti alloys with high corrosion resistance and mechanical strength.     

Mechanical properties and microstructures of cast Ti-Cu alloys.

OBJECTIVES: This study evaluated the mechanical properties of cast Ti-Cu alloys with the hope of developing an alloy for dental casting with better mechanical properties than unalloyed titanium. METHODS: Ti-Cu alloys with five concentrations of copper (0.5, 1.0, 2.0, 5.0 and 10.0 mass%) were made in an argon-arc melting furnace. The alloys were cast into magnesia-based molds using a centrifugal casting machine. The microstructure, microhardness profile of the specimen cross section, tensile strength, yield strength, and elongation were determined for the castings. Scanning electron microscope fractography was undertaken for the fractured surfaces after tensile testing. XRD was performed on the polished specimens. Results were analyzed using one-way ANOVA and the Student-Newman-Keuls tests. RESULTS: The mean tensile strengths of all the cast Ti-Cu alloys were significantly (p<0.05) higher than for cast commercially pure titanium (CP Ti). Of the Ti-Cu alloys tested, the 5 and 10% Cu alloys had significantly higher strength than the rest. The 10% Cu alloy exhibited the lowest mean elongation. CP Ti and the 0.5 and 1% Cu alloys showed higher ductility. The bulk hardness of all the cast Ti-Cu alloys, except for the 10% Cu alloy, and CP Ti was approximately the same. SIGNIFICANCE: By alloying with copper, the cast titanium became stronger. Increases in the tensile strength (30%) and yield strength (40%) over CP Ti were obtained for the 5% Cu alloy. Elongation was approximately 3%, which was similar to cast Ti-6Al-4V. Ti-Cu alloys, such as the 5% Cu alloy, could be used for prosthetic dental applications if other properties necessary for dental castings are obtained.     

Mechanical properties of cast Ti-6Al-4V-XCu alloys

The mechanical properties of Ti-6Al-4V-XCu (1, 4 and 10 wt% Cu) alloys were examined. The castings for each alloy were made in a centrifugal titanium casting machine. Two shapes of specimens were used: a dumbbell (20 mm gauge length x 2.8 mm diameter) for mechanical property studies, and a flat slab (2 mm x 10 mm x 10 mm) for metallography, microhardness determination and X-ray diffractometry. Tensile strength, yield strength, modulus of elasticity, elongation and microhardness were evaluated. After tensile testing, the fracture surfaces were observed using scanning electron microscopy. The tensile strengths of the quaternary alloys decreased from 1016 MPa for the 1% Cu alloy to 387 MPa for the 10% Cu alloy. Elongation decreased with an increase in the copper content. The 1% Cu alloy exhibited elongation similar to Ti-6Al-4V without copper (3.0%). The results also indicated that the copper additions increased the bulk hardness of the quaternary alloy. In particular, the 10% Cu alloy had the highest hardness and underwent the most brittle fracture. The mechanical properties of cast Ti-6Al-4V alloy with 1 and 4% Cu were well within the values for existing dental casting non-precious alloys.     

Joint properties of cast Fe-Pt magnetic alloy laser-welded to Co-Cr alloy

This study investigated the joint properties of Fe-Pt alloy laser-welded to Co-Cr alloy. Cast plates (0.5 x 3.0 x 10 mm) were prepared with Fe-Pt and Co-Cr alloys. Fe-Pt plates were butted against Co-Cr plates and laser-welded using Nd:YAG laser. Control and homogeneously welded specimens were also prepared. Laser welding was performed with and without argon shielding. Tensile testing was conducted, and both fracture force (Ff: N) and elongation (El: %) were recorded. There were no differences in the Ff value between the specimens with and without argon shielding for the welded Fe-Pt/Co-Cr. Lower Ff value of the welded specimen was obtained in the order of Fe-Pt alloy < Fe-Pt/Co-Cr < Co-Cr alloy. The results indicated that Fe-Pt welded to Co-Cr had Ff values between the values of homogeneously welded Fe-Pt and Co-Cr alloys. Argon shielding, on the other hand, had no effect on the weld strength between Fe-Pt and Co-Cr alloys.     

Castability of Ti-6Al-7Nb alloy for dental casting

Castability of Ti-6Al-7Nb alloy, CP Ti, and Co-Cr alloy was examined for mesh type and plate type specimens. The casting was carried out with a pressure type casting machine and commercial molding material. The castability of the mesh type specimen was evaluated in terms of the number of cast segments (castability index), and that of the plate type was evaluated by the area of the specimen (casting rate). X-ray images processed by a digital imaging technique were used to identify the casting porosity. The casting rate of the specimens increased with increasing thickness of the specimens. It was concluded that the castability index and the casting rate of Ti-6Al-7Nb alloy was slightly lower than that of CP Ti, and higher than that of Co-Cr alloy, were as Ti-6Al-7Nb alloy showed fewer casting porosities than CP Ti and smaller ones than Co-Cr alloy, which was advantageous for increasing the reliability of the casting properties.     

Infrared Gold Alloy Brazing on Titanium and Ti-6Al-4V Alloy Surfaces and its Application to Removable Prosthodontics

PURPOSE: This study investigated the area size of the flow of a gold braze alloy on commercially pure titanium and Ti-6Al-4V alloy plates, and elemental composition at the interface was determined. In the second part of this study, the tensile strengths of titanium plates brazed using a gold alloy were investigated. MATERIALS AND METHODS: Chips of Type IV gold alloy and silver braze alloys were melted onto commercially pure titanium and Ti-6Al-4V surfaces in a dental infrared radiation unit. Flow area of each braze alloy was measured using a digital image analyzer. Tensile specimens (n = 5) were also prepared by infrared brazing using the braze alloys. Five specimens for each combination of the two titanium plates and the two braze alloys were subjected to tensile loading using a Universal testing machine. Electronprobe microanalysis of x-rays at cross-section of the brazed joints to determine elemental composition across the interface, as well as scanning electron microscopic observation at the fracture surfaces, were also conducted. RESULTS: The braze alloys flowed well and spread over the Ti and Ti-6Al-4V plates. Braze alloy type significantly influenced flow, and the gold alloy flowed less on the titanium materials. The mean tensile strengths of Ti and Ti-6Al-4V plates brazed using the gold braze alloy were 219 MPa and 417 MPa, respectively. The fracture surfaces of Ti-6Al-4V specimens with the gold braze alloy exhibited typical ductile behavior. Ti with the same braze alloy showed brittle surfaces. A greater concentration of Cu was found at the Ti with gold braze interface. CONCLUSION: The flow and the tensile strength of the gold alloy coating on titanium surface by means of an infrared brazing is adequate for dental use.     

Effect of surface reaction layer on grindability of cast titanium alloys.

OBJECTIVE: The purpose of this study was to investigate the effect of the cast surface reaction layer on the grindability of titanium alloys, including free-machining titanium alloy (DT2F), and to compare the results with the grindability of two dental casting alloys (gold and Co-Cr). METHODS: All titanium specimens (pure Ti, Ti-6Al-4V and DT2F) were cast using a centrifugal casting machine in magnesia-based investment molds. Two specimen sizes were used to cast the titanium metals so that the larger castings would be the same size as the smaller gold and Co-Cr alloy specimens after removal of the surface reaction layer (alpha-case). Grindability was measured as volume loss ground from a specimen for 1 min using a handpiece engine with a SiC abrasive wheel at 0.1 kgf and four circumferential wheel speeds. RESULTS: For the titanium and gold alloys, grindability increased as the rotational speed increased. There was no statistical difference (p>0.05) in grindability for all titanium specimens either with or without the alpha-case. Of the titanium metals tested, Ti-6 Al-4V had the greatest grindability at higher speeds, followed by DT2F and CP Ti. The grindability of the gold alloy was similar to that of Ti-6 Al-4V, whereas the Co-Cr alloy had the lowest grindability. SIGNIFICANCE: The results of this study indicated that the alpha-case did not significantly affect the grindability of the titanium alloys. The free-machining titanium alloy had improved grindability compared to CP Ti.     

In vitro corrosion behavior of cast iron-platinum magnetic alloys.

OBJECTIVE: The objective of this study was to investigate the corrosion resistance of cast Fe-Pt alloys of varying compositions for use as attachment keepers and to make a comparison with the corrosion resistance of magnetic stainless steel. METHODS: The corrosion behavior of cast Fe-Pt alloy keepers (Fe-40 at%Pt, Fe-38 at%Pt, Fe-37 at%Pt and Fe-36 at%Pt) was evaluated by means of an immersion test and an anodic polarization test. The solutions used were a 1.0% lactic acid aqueous solution (pH=2.3) (10 ml) and 0.9% NaCl solution (pH=7.3) (10 ml). As a control, the corrosion resistance of a magnetic stainless steel keeper (SUS 447J1: HICOREX) was also measured. RESULTS: Chromium and platinum ions were not detected in either the 1.0% lactic acid or 0.9% NaCl solutions. The only released ions detected were the Fe ions in the 1.0% lactic acid solution. The amounts of Fe ions released from the Fe-40 at%Pt and Fe-38 at%Pt alloys were significantly (p<0.05) lower than from the Fe-37at%Pt, Fe-36 at%Pt and SUS 447J1 alloys. In the anodic polarization test, the potentials at the beginning of passivation for the four Fe-Pt alloys were higher than for the SUS 447J1 alloy in both solutions. SIGNIFICANCE: The Fe-Pt alloys, especially the alloys with higher Pt percentages (Fe-40 and 38 at%Pt), indicated a high corrosion resistance compared to the magnetic stainless steel keeper. A reduction in the Pt percentage may decrease the corrosion resistance in the oral environment.     

Pre-overloading to extend fatigue life of cast clasps

Permanent deformation in bending is associated with the development of residual stresses. The objective of this study was to characterize those residual stresses and test whether they can be manipulated to extend the fatigue lives of cast clasps. Simulations with validated non-linear finite element models were used to characterize the residual stresses in clasps cast from Ti-6Al-7Nb, Co-Cr, and Type IV gold alloys. In addition, two groups of as-cast and pre-overloaded (subjected to a load that produced 20 microm of permanent deformation) Ti-6Al-7Nb clasps (10 specimens each) were subjected to cyclic 0.5-mm deflections at 5 Hz until fatigue. Pre-overloaded specimens demonstrated significantly longer fatigue lives (32,200 +/- 17,300 cycles) than did those tested in the as-cast condition (17,900 +/- 7600 cycles), consistent with the maximum tensile stress values revealed by finite element analysis.     

Grindability of Cast Ti-6Al-4V Alloyed with Copper

Purpose: This study investigated the grindability of cast Ti-6Al-4V alloyed with copper.
Materials and Methods: The metals tested were commercially pure titanium (CP Ti), Ti-6Al-4V, experimental Ti-6Al-4V-Cu (1, 4, and 10 wt% Cu), and Co-Cr alloy. Each metal was cast into five blocks (3.0 × 8.0 × 30.0 mm³). The 3.0-mm wide surface of each block was ground using a hand-piece engine with an SiC wheel at four circumferential speeds (500, 750, 1000, and 1250 m/min) at a grinding force of 100 g. The grindability index (G-index) was determined as volume loss (mm³) calculated from the weight loss after 1 minute of grinding and the density of each metal. The ratio of the metal volume loss and the wheel volume loss was also calculated (G-ratio, %). Data (n = 5) were statistically analyzed using ANOVA (α= 0.05).
Results: Ti-6Al-4V and the experimental Ti-6Al-4V-Cu alloys exhibited significantly ( p < 0.05) higher G-indexes compared with CP Ti and Co-Cr at any rotational speed except for the lowest speed (500 m/min). At 500 m/min, the G-index of Ti-6Al-4V-Cu increased as the amount of alloyed copper increased. The 4% Cu and 10% Cu alloys had significantly greater G-indexes than did 1% Cu and Ti-6Al-4V at the highest rotational speed (1250 m/min). Increasing the percentage of alloyed copper and the circumferential speed also increased the G-ratio.
Conclusions: A slight reduction in ductility due to alloying Ti-6Al-4V with copper improved the grindability of some of the resultant Ti-6Al-4V-Cu alloys.     

Magnetic retention for complete and partial overdentures. Part I

Magnets have been used as aids to denture retention for many years with some success. The development of new cobalt and rare earth magnet alloys has greatly extended the potential application of magnetic retention in removable partial dentures, complete overdentures, fixed partial dentures, and sectional dentures.Effects of magnetic fields on tissues have been investigated extensively, with conflicting results, but reports describing dental applications for magnets claim no damaging tissue effects. The closed-field magnetic retention system described avoids any possibility of magnetic field effects on tissues by using paired magnets and a fixed and detachable keeper in a modified horseshoe arrangement. The detachable keeper is cemented or screwed to a decoronated, root-treated tooth. The denture-retention element, consisting of paired magnets and a fixed keeper, abuts the keeper in the tooth root and holds the denture in place by magnetic attraction. When in position, there is no external field surrounding the denture or tooth root. This arrangement also doubles the available retention.The shape, size, and configuration of the two magnets and fixed and removable keepers were chosen to provide maximum retention in a magnetic denture retention unit of a size convenient for most applications. The retention provided is approximately 300 gm per unit.The magnet alloy, Co₅Sm, is very hard but brittle, and it can corrode in the mouth. To prevent this from occurring in service, end plates protect the exposed magnet faces. The plates, of the same stainless steel alloy as the keepers, prevent magnet corrosion and reduce wear at the denture-retention keeper-element interface in service.     

Effects of fluoride and dissolved oxygen concentrations on the corrosion behavior of pure titanium and titanium alloys

The effects of dissolved-oxygen concentration and fluoride concentration on the corrosion behaviors of commercial pure titanium, Ti-6Al-4V and Ti-6Al-7Nb alloys and experimentally produced Ti-0.2Pd and Ti-0.5Pt alloys were examined using the corrosion potential measurements. The amount of dissolved Ti was analyzed by inductively coupled plasma mass spectroscopy. A decrease in the dissolved-oxygen concentration tended to reduce the corrosion resistance of Ti and Ti alloys. If there was no fluoride, however, corrosion did not occur. Under low dissolved-oxygen conditions, the corrosion of pure Ti and Ti-6Al-4V and Ti-6Al-7Nb alloys might easily take place in the presence of small amounts of fluoride. They were corroded by half or less of the fluoride concentrations in commercial dentifrices. The Ti-0.2Pd and Ti-0.5Pt alloys did not corrode more, even under the low dissolved-oxygen conditions and a fluoride-containing environment, than pure Ti and Ti-6Al-4V and Ti-6Al-7Nb alloys. These alloys are expected to be useful as new Ti alloys with high corrosion resistance in dental use.     

Cutting efficiency of air-turbine burs on cast titanium and dental casting alloys

OBJECTIVE: The purpose of this study was to investigate the cutting efficiency of air-turbine burs on cast free-machining titanium alloy (DT2F) and to compare the results with those for cast commercially pure (CP) Ti, Ti-6Al-4V alloy, and dental casting alloys. METHODS: The cast metal (DT2F, CP Ti, Ti-6Al-4V, Type IV gold alloy and Co-Cr alloy) specimens were cut with air-turbine burs (carbide burs and diamond points) at air pressures of 138 or 207 kPa and a cutting force of 0.784 N. The cutting efficiency of each bur was evaluated as volume loss calculated from the weight loss cut for 5 s and the density of each metal. The bulk microhardness was measured to correlate the machinability and the hardness of each metal. RESULTS: The amounts of DT2F cut with the carbide burs were significantly (p < 0.05) greater than for the other titanium specimens at either 138 or 207 kPa. The diamond points exhibited similar machining efficiency among all metals except for Type IV gold alloy. The increase in the volume loss of Co-Cr alloy (Vitallium) cut with the diamond points showed a negative value (-29%) with an increase in air pressure from 138 to 207 kPa. There was a negative correlation between the amounts of metal removed (volume loss) and the hardness (r2 = 0.689) when the carbide burs were used. SIGNIFICANCE: The results of this study indicated that a free-machining titanium alloy (DT2F) exhibited better machinability compared to CP Ti and Ti-6Al-4V alloy when using carbide fissure burs. When machining cast CP Ti and its alloys, carbide fissure burs possessed a greater machining efficiency than the diamond points and are recommended for titanium dental prostheses.     

Deformation properties of Ti-6A1-7Nb alloy castings for removable partial denture frameworks

Ti-6Al-7Nb alloy was cast into three differently designed, removable partial denture frameworks: Palatal strap (PS), Anterior-posterior bar (AP), and Horseshoe-shaped bar (HS). The vertical displacement and local strain of Ti-6Al-7Nb alloy frameworks were investigated to compare against those of Co-Cr alloy frameworks. Vertical loading force of 19.6 N was applied at two locations, 10 and 20 mm, from the distal end of the framework. Although higher vertical displacement and local strain were observed for Ti-6Al-7Nb alloy frameworks than those for Co-Cr alloy frameworks, the PS framework appeared to show the least deformation. In addition, the strain at 10-mm location was higher than that at 20-mm location for AP and HS frameworks. This study thus proved that design had a significant influence on the deformation properties of denture frameworks. The PS design was evaluated to be a suitable design for the removable denture framework with Ti-6Al-7Nb alloy.     

Corrosion behavior of pure titanium and titanium alloys in fluoride-containing solutions

The effects of fluoride concentrations and pH on the corrosion behavior of pure titanium, Ti-6Al-4V, Ti-6Al-7Nb alloys and a new Ti alloy adding palladium, which is expected to promote a repassivation of Ti were examined by anodic polarization and corrosion potential measurements. The amount of dissolved Ti was analyzed by inductively coupled plasma mass spectroscopy. The surface of the specimen was analyzed by X-ray photoelectron spectroscopy before and after the measurement. Pure Ti, Ti-6Al-4V and Ti-6Al-7Nb alloys were easily corroded even in a low fluoride concentration in an acidic environment. The corrosion resistance of Ti-0.2Pd alloy was greater than those of pure Ti, Ti-6Al-4V and Ti-6Al-7Nb alloys in the wide range of pH and fluoride concentrations. The high corrosion resistance of Ti-0.2Pd alloy was caused by the surface enrichment of Pd promoting a repassivation of Ti. The Ti-0.2Pd alloy is expected to be useful as a new Ti alloy with high corrosion resistance in dental use.