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To increase the transmission efficiency of incoming and outgoing light on the side of a transparent resin light guide, such as an acrylic plate, we created a machined surface that does not become cloudy and transmits visible light well by cutting it with a single crystal diamond tool. When light is guided to this mirror-finished acrylic plate using an LED light source, its uneven brightness or illuminance distribution may be noticeable, depending on the application. To suppress the uneven distribution, attempts have made the luminance distribution uniform by a decorative cut on the acrylic plates for a fine pattern shape. Our research is developing a light environment design support system using an acrylic light-guiding plate with a decorative cut surface. This system consists of a rapid decoration pattern design technique with optical simulation, a decorative cutting technique to satisfy the demanded optical characteristics, and a technique to maintain machining quality. We implemented decorative cutting tests for various stripe patterns by adjusting the cutting conditions for the acrylic plates. Estimation of the decorative shapes was based on the shape of the tool cutting edge and its trajectory. We controlled the decoration shape and dimensions. The tendency of luminance distributions estimated by optical simulation were corresponded with the actual distributions.

Following the introduction of additive manufacturing technology, there have been several reports describing its efficacy for fabricating medical and dental devices. Although minimizing biofilms is important clinically, few studies have compared biofilm accumulation on additive manufactured devices with that on alloys fabricated by other methods. Streptococcus mutans ATCC 25175 biofilm accumulation on additive manufactured Ti–6Al–4V ELI was compared with that on conventional dental alloys fabricated by lost-wax casting (Commercially pure titanium, Ti–6Al–4V ELI alloy, Au–Cu–Ag alloy, Pd–Ag–Cu–Au alloy, Ag–Sn–Zn alloy, and Co–Cr alloy). Teflon® disks served as controls. Biofilm accumulation on each alloy (n = 3) was conducted at 37 °C under anaerobic conditions. After 4 h, the number of metabolically active S. mutans adhering to each alloy was determined using a bioluminescence assay. Although the surfaces of the additive manufactured Ti–6Al–4V ELI alloy were rougher than those of cast alloys, this roughness, unexpectedly, did not increase the biofilm accumulation. Apparently, alloy composition minimizes biofilm accumulation even when the surface is rough.

Additive layer deposition techniques such as electron beam melting (EBM) and laser beam melting (LBM) have been utilized to fabricate rectangular plates of Ti-6Al-4V with extra low interstitial (ELI) contents. The layer-by-layer deposition techniques resulted in plates that have different surface finishes which can impact significantly on the fatigue life by providing potential sites for fatigue cracks to initiate. The fatigue life of Ti-6Al-4V ELI alloys fabricated by EBM and LBM deposition techniques was investigated by three-point testing of rectangular beams of as-fabricated and electro-discharge machined surfaces under stress-controlled conditions at 10 Hz until complete fracture. Fatigue life tests were also performed on rolled plates of Ti-6Al-4V ELI, regular Ti-6Al-4V, and CP Ti as controls. Fatigue surfaces were characterized by scanning electron microscopy to identify the crack initiation site in the various types of specimen surfaces. The fatigue life data were analyzed statistically using both analysis of variance techniques and the Kaplan-Meier survival analysis method with the Gehan-Breslow test. The results indicate that the LBM Ti-6Al-4V ELI material exhibits a longer fatigue life than the EBM counterpart and CP Ti, but a shorter fatigue life compared to rolled Ti-6Al-4V ELI. The difference in the fatigue life behavior may be largely attributed to the presence of rough surface features that act as fatigue crack initiation sites in the EBM material.

Customized one-component dental implants have been fabricated using Electron Beam Melting(®) (EBM(®)), which is a rapid prototyping and manufacturing technique. The goal of our study was to determine the effect of electron beam orientation on the fatigue resistance of EBM Ti-6Al-4V ELI alloy. EBM technique was used to fabricate Ti-6Al-4V ELI alloy blocks, which were cut into rectangular beam specimens with dimensions of 25 × 4 × 3 mm, such that electron beam orientation was either parallel (group A) or perpendicular (group B) to the long axis of the specimens. The specimens were subjected to cyclic fatigue (R = 0.1) in four-point flexure under ambient conditions using various stress amplitudes below the yield stress. The fatigue lifetime data were fit to an inverse power law-Weibull model to predict the peak stress corresponding to failure probabilities of 5 and 63% at 2M cycles (σ(max, 5%) and σ(max, 63%)). Groups A and B did not have significantly different Weibull modulus, m (p > 0.05). The specimens with parallel orientation showed significantly higher σ(max, 63%) (p ≤ 0.05), but there was no significant difference in the σ(max, 5%) (p > 0.05). Thus, it can be concluded that the fatigue resistance of the material was greatest when the electron beam orientation was perpendicular to the direction of crack propagation.

The objective of the study was to evaluate the hypothesis that the mechanical properties and fatigue behavior of removable partial dentures (RPD) made from cast titanium alloys can be improved by alloying with low-cost, low-melting elements such as Cu, Al, and Fe using commercially pure Ti (CP-Ti) and Ti-6Al-4V as controls. RPD specimens in the form of rest-shaped, clasp, rectangular-shaped specimens and round-bar tensile specimens were cast using an experimental Ti-5Al-5Cu alloy, Ti-5Al-1Fe, and Ti-1Fe in an Al2O3-based investment with a centrifugal-casting machine. The mechanical properties of the alloys were determined by performing tensile tests under a controlled displacement rate. The fatigue life of the RPD specimens was tested by the three-point bending in an MTS testing machine under a cyclic displacement of 0.5 mm. Fatigue tests were performed at 10 Hz at ambient temperature until the specimens failed into two pieces. The tensile data were statistically analyzed using one-way ANOVA (α = 0.05) and the fatigue life data were analyzed using the Kaplan-Meier survival analysis (α = 0.05). The experimental Ti-5Al-5Cu alloy showed a significantly higher average fatigue life than that of either CP-Ti or Ti-5Al-1Fe alloy (p

Although pure titanium is known to have good biocompatibility, a titanium alloy with better strength is needed for fabricating clinically acceptable, partial removable dental prosthesis (RDP) frameworks.The mechanical properties of an experimental Ti-5Al-5Cu alloy cast with a 2-step investment technique were examined for RDP framework applications.Patterns for tests for various properties and denture frameworks for a preliminary trial casting were invested with a 2-step coating method using 2 types of mold materials: a less reactive spinel compound (Al(2)O(3)·MgO) and a less expensive SiO(2)-based material. The yield and tensile strength (n=5), modulus of elasticity (n=5), elongation (n=5), and hardness (n=8) of the cast Ti-5Al-5Cu alloy were determined. The external appearance and internal porosities of the preliminary trial castings of denture frameworks (n=2) were examined with a conventional dental radiographic unit. Cast Ti-6Al-4V alloy and commercially pure titanium (CP Ti) were used as controls. The data for the mechanical properties were statistically analyzed with 1-way ANOVA (α=.05).The yield strength of the cast Ti-5Al-5Cu alloy was 851 MPa and the hardness was 356 HV. These properties were comparable to those of the cast Ti-6Al-4V and were higher than those of CP Ti (P.05). One of the acrylic resin-retention areas of the Ti-5Al-5Cu frameworks was found to have been incompletely cast.The cast biocompatible experimental Ti-5Al-5Cu alloy exhibited high strength when cast with a 2-step coating method. With a dedicated study to determine the effect of sprue design on the quality of castings, biocompatible Ti-5Al-5Cu RDP frameworks for a clinical trial can be produced.

This study characterized properties of Ti-6Al-4V ELI (extra low interstitial, ASTM grade 23) specimens fabricated by a laser beam melting (LBM) and an electron beam melting (EBM) system for dental applications. Titanium alloy specimens were made into required size and shape for each standard test using fabrication methods. The LBM specimens were made by an LBM machine utilizing 20 µm of Ti-6Al-4V ELI powder. Ti-6Al-4V ELI specimens were also fabricated by an EBM using 40 µm of Ti-6Al-4V ELI powder (average diameter, 40 µm: Arcam AB®) in a vacuum. As a control, cast Ti-6Al-4V ELI specimens (Cast) were made using a centrifugal casting machine in an MgO-based mold. Also, a wrought form of Ti-6Al-4V ELI (Wrought) was used as a control. The mechanical properties, corrosion properties and grindability (wear properties) were evaluated and data was analyzed using ANOVA and a non-parametric method (α = 0.05). The strength of the LBM and wrought specimens were similar, whereas the EBM specimens were slightly lower than those two specimens. The hardness of both the LBM and EBM specimens was similar and slightly higher than that of the cast and wrought alloys. For the higher grindability speed at 1,250 m/min, the volume loss of Ti64 LBM and EBM showed no significant differences among all the fabrication methods. LBM and EBM exhibited favorable results in fabricating dental appliances with excellent properties as found for specimens made by other fabricating methods.

In recently advanced rapid prototyping and manufacturing methods, one additional process is to use an electron beam to fabricate metal objects by the layer by layer sintering and/or melting metal powder. This method is often called electron beam melting (EBM). This study examined the mechanical properties, the grindability and corrosion resistance of Ti–6Al–4V ELI (extra low interstitial) specimens which were fabricated by the electron beam melting (EBM) process. Dumbbell-shaped specimens and two kinds of plate specimens were prepared using the Ti–6Al–4V ELI powder in the EBM system. The yield strength, tensile strength, modulus of elasticity and percent elongation at a crosshead speed of 0.25 mm/min were tested. The Vickers hardness in interior structures was determined. Grindability was evaluated as volume loss (mm 3 ) when the specimen was abraded using a SiC wheel at 1250 m/min for 1 min. Lastly, corrosion behavior was examined using the dynamic potentiostatic polarization technique in an artificial saliva at 37 °C. As controls, cast and commercial wrought alloys of Ti–6Al–4V ELI and commercially pure titanium (CP Ti) were evaluated. Cast specimens were prepared in a centrifugal casting machine using a MgO based mold. For the cast specimens, all the mechanical properties, grindability and corrosion characteristics were tested. On the other hand, for wrought specimens, only grindability and corrosion properties were tested. The yield and tensile strength of the as-fabricated Ti–6Al–4V ELI specimens without any additional metallurgical treatments were found to be 735 MPa and 775 MPa, respectively. The elongation was 2.3%. These values are well within many of precious and non-precious dental casting alloys.

This study examined the effects of the speed and force in centrifugal casting on the wedge castability of Ti–5 mass%Cu (Ti–5Cu) alloy and commercially pure titanium (CP-Ti). The Ti–5Cu alloy was prepared by argon-arc melting. Whole wedge-shaped acrylic patterns were prepared with either 15° or 30° angles and invested with a MgO-based material. The wedge specimens were cast using a centrifugal casting machine at rotational speeds of 600, 1000, 1250, 1500 and 3000 rpm. Mold filling, an index for a measure of castability, was determined as the missing length between the edge of the cast wedge and the theoretical acute tip of the triangle. CP-Ti was used as a control. An analytical model was developed to relate the mold-filling index to the surface energy and rotational speed. The experimental results indicate that the means of the mold-filling index of the 30° wedge angle were lower than those of the 15° wedge angle when compared for each corresponding metal and rotational speed. In each angle for CP-Ti, the means tended to reduce with increase in the rotational speed. The mold-filling index of 5% Cu titanium was found to be similar to that of CP-Ti, even for 15° wedge when the rotational speed was higher than 1250 rpm. The results suggest that dental prosthesis, which has narrow cross sections containing very narrow regions (for example, clasps of a denture), can be cast successfully by utilizing high rotational speed during centrifugal casting. The complex dependence of mold-filling index on wedge angle and rotational speed is explained on the basis of the analytical model and the dependence of the apparent surface energy on rotation speed.

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.

Titanium (Ti) castings generally contain a hard surface layer of alpha-case (α-case) that is enriched of oxygen. For dental Ti prostheses, the hard and brittle α-case can be a significant fraction of the thickness of the entire work piece and must be controlled properly to ensure minimum properties. The objective of this article is to present a theoretical framework for predicting α-case formation in dental Ti castings as a function of cooling rate and the influence of α-case on the tensile ductility and wear resistance. First, a diffusion analysis is presented to describe the oxygen profile and microhardness distribution within the α-case in Ti castings of CP-Ti and Ti-6Al-4V. The reduction in tensile ductility by the α-case is then predicted using an existing tensile ductility model. Furthermore, the improvement in wear resistance by the α-case is predicted using a recent wear model. These results are then used to assess the feasibility of controlling the α-case thickness to optimize both tensile ductility and wear resistance in Ti castings.

Scale analyses indicate that three distinct contaminant mass-transfer processes, occurring on distinct time scales, underlie formation of the alpha case on small titanium castings. High rates of mold-to-liquid metal mass transfer occur during an extremely short induction period, the length of which is determined by the time required for heterogeneously nucleated solidification fronts to cover mold surface asperities. Following the induction period, but prior to complete cast solidification, mold contaminants diffuse through a rapidly growing solidification layer, where the solid-phase mass-diffusion boundary layer grows at a rate approximately an order of magnitude slower than the solidification front. Finally, following complete solidification and until the part is removed from the mold, contaminant mass transfer continues via solid diffusion. Based on the scale analyses, an analytical model that incorporates an empirical relation between titanium solid phase oxygen concentration and titanium microhardness is developed and compared against representative experimental near-surface microhardness measurements.

The wear behavior of Ti-based alloys was analyzed by considering the elastic-plastic fracture of individual alloys in response to the relevant contact stress field. Using the contact stresses as the process driving force, wear was computed as the wear rate or volume loss as a function of hardness and tensile ductility for Ti-based cast alloys containing an alpha, alpha+beta or beta microstructure with or without the intermetallic precipitates. Model predictions indicated that wear of Ti alloys increases with increasing hardness but with decreasing fracture toughness or tensile ductility. The theoretical results are compared with experimental data to elucidate the roles of microstructure in wear and contrasted against those in grindability.

The grindability of Ti-based alloys was analyzed by considering the fracture behavior of individual alloys in response to the stress field of a grinding wheel. First, the stress field under a grinding wheel was computed by treating the grinding wheel as a cylindrical disk with a flat region acting on a flat substrate. The initiation and propagation of microcracks in the substrate was then examined on the basis of the contact stress field and one of two fracture criteria: (1) a critical stress criterion for the onset of cleavage crack initiation, and (2) a critical stress intensity factor criterion for the initiation and propagation of shear cracks. Grindability was computed as a function of grinding speed and microstructure for several Ti-based cast alloys containing α, α + β, or β microstructure with or without the intermetallic precipitates. Model predictions indicated that the grindability of Ti alloys increases with decreasing fracture toughness or tensile ductility. The theoretical results are compared against experimental data in the literature to elucidate the roles of microstructure in grindability. The comparison revealed that alloying addition that leads to the formation of brittle intermetallics enhances grindability by reducing fracture toughness, tensile ductility, and the resistance to crack initiation and propagation.

As part of our systematic studies characterizing the properties of titanium alloys, we investigated the grindability of a series of cast Ti-Hf alloys. Alloy buttons with hafnium concentrations up to 40 mass% were made using an argon-arc melting furnace. Each button was cast into a magnesia-based mold using a dental titanium casting machine; three specimens were made for each metal. Prior to testing, the hardened surface layer was removed. The specimens were ground at five different speeds for 1 min at 0.98 N using a carborundum wheel on an electric dental handpiece. Grindability was evaluated as the volume of metal removed per minute (grinding rate) and the volume ratio of metal removed compared to the wheel material lost (grinding ratio). The data were analyzed using ANOVA. A trend of increasing grindability was found with increasing amounts of hafnium, although there was no statistical difference in the grindability with increasing hafnium contents. We also found that hafnium may be used to harden or strengthen titanium without deteriorating the grindability.

Anodic polarization tests were performed in 0.9% NaCl and 1% lactic acid solutions to characterize the relationship between the corrosion behavior and the microstructures of cast Ti-Ag (5-40% Ag) alloys. The anodic polarization curves for the Ti-Ag alloys up to 17.5% Ag were similar to those for pure titanium in both solutions. On the other hand, an abrupt increase in the current density was observed for the alloys with more than 20% Ag in the NaCl solution and with more than 27.5% Ag in the lactic acid solution. The microstructures of the corroded alloy surfaces indicated the deterioration of precipitated intermetallic compounds along the grain boundaries. The Ti-Ag alloys up to 17.5% Ag had excellent corrosion resistance similar to that of pure titanium. The alloys with 20-25% Ag may be also used as dental alloys, since they passivated again immediately after preferential dissolution in the NaCl solution.

This study examined the characteristics of as-cast Ti-Cr(7–19%)-Cu(3–7%) (all percentages in this article are mass%) alloys to evaluate their suitability for dental applications; studies on the alloy structures and mechanical properties, grindability, and corrosion behavior were included in the investigation. The alloys were centrifugally cast and bench-cooled in investment molds. The x-ray diffractometry of the as-cast alloys bench-cooled in the molds indicated the following phases: α+β+ω in the 7% Cr and 7% Cr+3% Cu; β+ω in the 13%Cr; and β in the 13%Cr+3% Cu through the 19%Cr+3% Cu alloys. The strengths of the binary β Ti-Cr and ternary β Ti-Cr-Cu alloys with 13 and 19% Cr were approximately two times higher than those of CP Ti. The alloy ductility was dependent on the chemical composition and thus, the microstructure. The 7% Cr alloys were extremely brittle and hard due to the ω phase, but the ductility was restored in the 13 and 19% Cr alloys. The hardness (HV) of the cast 13 and 19% Cr alloys was approximately 300–350 compared with a value of 200 for CP Ti. The grindability of the cast alloys was examined using a rotating SiC wheel at speeds (circumferential) of 500 and 1250 m/min. At the higher speed, the grindability of the 13 and 19% Cr alloys increased with the Cu content. The grindability of the 13% Cr alloy with 7% Cu was similar to that of CP Ti. Evaluation of the corrosion behavior in an artificial saliva revealed that the alloys are like many other titanium alloys within the normal intraoral oxidation potential. The wear resistance testing of these alloys also showed favorable results.

Good mechanical properties, biocompatibility and corrosion resistance make titanium an excellent material for biomedical applications. However, when better mechanical properties than those offered by commercially pure titanium (CPTi) are needed, Ti–6Al–4V is sometimes a good alternative. Some new titanium alloys, developed as industrial structural materials, aim at an intermediate range of strength between that of CP Ti and Ti–6Al–4V. Two of these alloys are Super-TIX800™ (Ti–1% Fe–0.35% O–0.01% N) and Super-TIX800N™ (Ti–1% Fe–0.3% O–0.04% N) (both produced by Nippon Steel Corp., Japan). Besides being stronger than CP Ti, the cost of manufacturing these alloys is reportedly lower than for Ti–6Al–4V since they do not contain any expensive elements. In addition, they are not composed of elements such as aluminum or vanadium, which have caused biocompatibility concerns in medical and dental appliances. To evaluate these alloys as candidates for dental use, it is helpful to compare them to CP Ti (ASTM Grade 2) and Ti–6Al–4V (ASTM Grade 5), which have already been employed in dentistry. We evaluated the tensile properties, mold filling capacity, corrosion characteristics and grindability of these industrial alloys prepared by investment casting. Compared to the strengths of cast CPTi, the yield strength and tensile strength of these cast alloys were more than 20% and approximately 30% higher, respectively. On the other hand, both of these properties were 30% lower than for Ti–6Al–4V. Better grindability and wear resistance were additional benefits of these new alloys for dental applications.

This study characterized the electrochemical behavior of Ti-Hf binary alloys in a simulated oral environment. Ti-Hf alloys (10, 20, 25, 30, 35 and 40 mass% Hf) were prepared by arc-melting titanium sponge and hafnium sponge. Specimens of each alloy (n = 4) were prepared using a dental titanium casting system with a MgO-based investment. Specimens were inspected with X-ray radiography to ensure minimal internal porosity. Castings (n = 4) made from pure titanium and commercially pure titanium were used as controls. The ground flat surface (10 mm x 10 mm) on each specimen where approximately 30 microm was removed was used for the characterization. Sixteen-hour open-circuit potential (OCP) measurement, linear polarization and potentiodynamic cathodic polarization were performed sequentially in aerated (air + 10% CO2) MTZ synthetic saliva at 37 degrees C. Potentiodynamic anodic polarization was conducted in the same medium but deaerated (N2 + 10% CO2) 2 h before and during testing. Polarization resistance (R(P)) and Tafel slopes were determined, as were corrosion current density (I(CORR)) and passive current density (I(PASS)). Results were subjected to nonparametric statistical analysis (alpha = 0.05). The OCP stabilized (mean values -229 mV to -470 mV vs. SCE) for all specimens after the 16-h immersion. Similar passivation was observed for all the metals on their anodic polarization diagrams. The Kruskal-Wallis test showed significant differences in OCP among the test groups (p = 0.006). No significant differences were found in R(P), I(CORR) or I(PASS) among all the metals (p>0.3). Results indicate that the electrochemical behavior of the Ti-Hf alloys examined resembles that of pure titanium.

summary 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 × 2·8 mm diameter) for mechanical property studies, and a flat slab (2 mm × 10 mm × 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.

This study examined the Hg evaporation during setting from experimental Ag-Sn-Cu alloy powders with and without Pd. Four series of alloy powders were fabricated to examine the effect on the Hg evaporation of the alloy compositions (all percentages in this report are weight percents): Pd (0-1.5), Cu (9.0-14.0), Ag (57.0-63.7), and Sn (24.9-29.5). These variations in composition produced alloy powders with gamma-Ag3Sn to beta-AgSn ratios varying from 0.0 to 23.9. The total amounts of Hg released from 10 min after trituration were measured from cylindrical specimens (4 x 8mm; n = 4 ) at 37 degrees C using a Hg vapor analyzer. The results were compared to those from commercial alloys (one high-Cu and one low-Cu alloy). All amalgams made from alloys containing 1.5% Pd exhibited lower Hg vapor release than any other amalgams, with the exception of the low-Cu amalgam. The results clearly showed that the alloy formulation affected the mercury evaporation behavior during setting of the resultant amalgams. A small addition of Pd to the alloy can produce amalgams with 50-60% less Hg vapor release during setting than a leading commercial high-Cu amalgam, Tytin.

Anodic polarization was performed in 0.9% NaCl and 1% lactic acid solutions to characterize the relationship between the corrosion behavior and microstructures of cast Ti-Au (5-40%) alloys. An abrupt increase in the current density occurred at approximately 0.6 V vs. SCE for the 30% and 40% Au alloys in the 0.9% NaCl solution. The microstructures after corrosion testing indicated that this breakdown may have been caused by the preferential dissolution of the Ti3Au. However, the potential for preferential dissolution was higher than the breakdown potential of stainless steel or Co-Cr alloy, which meant that the corrosion resistance of the Ti-Au alloys was superior. In 1% lactic acid solution, the corrosion resistance of the Ti-Au alloys was excellent, with no breakdown at any composition. In the present test solutions, the Ti-Au alloys up to 20% Au had good corrosion resistance comparable to that for pure titanium.

This study characterized the corrosion behavior of cast CP titanium made with a face-coating method. Wax patterns were coated with oxide slurry of Y 2 O 3 or ZrO 2 before investing with a MgO-based investment. Three surface preparations were tested: ground, sandblasted, and as-cast. Uncoated castings served as controls. Sixteen-hour open circuit potential (OCP) measurement, linear polarization and potentiodynamic cathodic polarization were performed in an aerated modified Tani-Zucchi synthetic saliva at 37°C. Anodic polarization was conducted in the same deaerated medium. Polarization resistance ( R p ) and Tafel slopes were determined. Corrosion current density was calculated for each specimen. Results ( n =4) were subjected to nonparametric statistical analysis ( α =0.05). Cross sections of cast specimens were examined by optical microscopy. Energy dispersive spectroscopy (EDS) spot analysis was performed at various depths below the surface. The OCP stabilized within several hours for all the specimens. Apparent differences in anodic polarization behavior were observed among the different surfaces. A distinctive wide passive region followed by breakdown was seen on specimens with ground and sandblasted surfaces. There were no significant differences in the corrosion resistance among the control and the two face-coating groups for each group. The Mann–Whitney test showed significantly lower OCP and higher R p values for ground surfaces. The surface condition significantly affected the corrosion behavior more than the face coating methods. In most cases, specimens with as-cast surfaces exhibited the least corrosion resistance during the potentiodynamic anodic polarization.

Objectives. The purpose of the present study was to evaluate the grindability of a series of cast Ti–Cu alloys in order to develop a titanium alloy with better grindability than commercially pure titanium (CP Ti), which is considered to be one of the most difficult metals to machine. Methods. Experimental Ti–Cu alloys (0.5, 1.0, 2.0, 5.0, and 10.0 mass% Cu) were made in an argon-arc melting furnace. Each alloy was cast into a magnesia mold using a centrifugal casting machine. Cast alloy slabs (3.5 mm×8.5 mm×30.5 mm), from which the hardened surface layer (250 μm) was removed, were ground using a SiC abrasive wheel on an electric handpiece at four circumferential speeds (500, 750, 1000, or 1250 m/min) at 0.98 N (100 gf). Grindability was evaluated by measuring the amount of metal volume removed after grinding for 1 min. Data were compared to those for CP Ti and Ti–6Al–4V. Results. For all speeds, Ti–10% Cu alloy exhibited the highest grindability. For the Ti–Cu alloys with a Cu content of 2% or less, the highest grindability corresponded to an intermediate speed. It was observed that the grindability increased with an increase in the Cu concentration compared to CP Ti, particularly for the 5 or 10% Cu alloys at a circumferential speed of 1000 m/min or above. Significance. By alloying with copper, the cast titanium exhibited better grindability at high speed. The continuous precipitation of Ti2Cu among the α-matrix grains made this material less ductile and facilitated more effective grinding because small broken segments more readily formed.

Experimental Ti-Ag alloys (5, 10, and 20 mass% Ag) and Ti-Cu alloys (2, 5, and 10 mass% Cu) were cast into magnesia molds using a dental casting machine, and their grindability was investigated. At the lowest grinding speed (500 m min(-1)), there were no statistical differences among the grindability values of the titanium and titanium alloys. The grindability of the alloys increased as the grinding speed increased. At the highest grinding speed (1500 m x min(-1)), the grindability of the 20% Ag, 5% Cu, and 10% Cu alloys was significantly higher than that of titanium. It was found that alloying with silver or copper improved the grindability of titanium, particularly at a high speed. It appeared that the decrease in elongation caused by the precipitation of small amounts of intermetallic compounds primarily contributed to the favorable grindability of the experimental alloys.

A reaction layer forms on cast titanium alloy surfaces due to the reaction of the molten metal with the investment. This surface layer may affect the corrosion of the alloy in the oral environment. The objective of this study was to characterize the in vitro corrosion behavior of cast titanium alloys. ASTM Grade 2 CP titanium, Ti-6Al-4V, Ti-6Al-7Nb and Ti-13Nb-13Zr alloys were cast into a MgO-based investment. Experiments were performed on castings (N=4) with three surface conditions: (A) as-cast surface after sandblasting, (B) polished surface after removal of the reaction layer, and (C) sandblasted surface after removal of the reaction layer. Open-circuit potential (OCP) measurement, linear polarization, and potentiodynamic cathodic polarization were performed in aerated (air+10% CO(2)) modified Tani-Zucchi synthetic saliva at 37 degrees C. Potentiodynamic anodic polarization was subsequently conducted in the same medium deaerated with N(2)+10% CO(2) gas 2 h before and during the experiment. Polarization resistance (R(P)) and corrosion rate (I(CORR)) were calculated. Numerical results were subjected to nonparametric statistical analysis at alpha=0.05. The OCP stabilized for all the specimens after 6 x 10(4)s. Apparent differences in anodic polarization were observed among the different surfaces for all the metals. A passivation region followed by breakdown and repassivation were seen on specimens with surfaces A and C. An extensive passive region was observed on all the metals with surface B. The Kruskal-Wallis test showed no significant differences in OCP, R(p), I(CORR) or break down potential for each of the three surfaces among all the metals. The Mann-Whitney test showed significantly lower R(P) and higher I(CORR) values for surface C compared to the other surfaces. Results indicate that the surface condition has more effect on corrosion of these alloys than the surface reaction layer. Within the oxidation potential range of the oral cavity, all the metal/surface combinations examined showed excellent corrosion resistance.

PURPOSE Wear of commercially pure (CP) titanium prosthetic teeth has frequently been observed. The greatest wear has been found when the same grades of CP titanium are used for both maxillary and mandibular teeth. This study examined the wear behavior of teeth made with cast titanium alloy and compared these results with those for CP titanium and gold alloy teeth. MATERIALS AND METHODS All tooth specimens were cast with grade 3 alpha titanium, 3 metastable beta alloys [Ti-15Mo-2.8Nb-0.2Si (Timetal 21 SRx), Ti-13Nb-13Zr, and Ti-15V-3Cr-3Sn-3Al], and 2 alpha+beta alloys (Ti-6Al-7Nb and Ti-6Al-4V). As a control, Type IV gold alloy was also cast conventionally. All teeth (both maxillary and mandibular) were secured in an in vitro 2-body wear testing apparatus that simulated chewing function (60 strokes/min; grinding distance, 2 mm under flowing water). Wear resistance was assessed as volume loss (mm(3)) at 5 kgf (grinding force) after 50,000 strokes. The results (n = 5) were analyzed using analysis of variance or Fisher's exact test (alpha = 0.05). RESULTS Of the titanium teeth, the wear of 2 of the metastable beta alloys (Timetal 21 SRx and Ti-15V-3Cr-3Sn-3Al) was found to be significantly (p

Pure titanium and titanium alloys are potential materials for the fabrication of cast dental appliances. One important factor in producing sound castings is the capacity of the metal to fill the mold. This study used a wedge-shaped mold to compare the mold filling of titanium with that of conventional dental casting alloys. The metals used were CP Ti, Ti-6Al-7Nb, Ti-6Al-4V, Ti with 1 and 4wt% Cu and ADA Type III gold alloy and an Ni-Cr alloy. The castings were cut into four pieces parallel to the triangular surface. Mold filling was evaluated as the distance between the tip of the cast wedge and theoretical tip of the triangle. The mold filling of the gold alloy was superior compared to all the metals tested, while the mold filling of the Ni-Cr alloy was the worst. There were no statistical differences at the 30 degrees marginal angle for all the cast titanium metals. At the sharper 15 degrees angle, CP Ti and Ti-6Al-7Nb was superior to both the Ti-Cu alloys. Although the mold filling of titanium was inferior compared to the gold alloy, the data justify the use of titanium for the production of dental appliances.

OBJECTIVES: A reaction layer forms on cast titanium surfaces due to the reaction of the molten titanium with the investment material. Such a layer prevents strong adhesion between titanium and porcelain. This study characterized the effects of surface modifications on cast titanium surfaces and titanium-ceramic adhesion. METHODS: ASTM grade II CP titanium was cast into an MgO-based mold. Castings were devested by sandblasting with alumina particles, and subjected to surface modification by immersion in one of the following solutions: (1) 35% HNO3-5% HF at room temperature for 1min; (2) 50% NaOH-10% CuSO4 x 5H2O at 105 degreesC for 10min; (3) the NaOH-CuSO4 solution followed by the HNO3-HF solution; (4) 50% NaOH-10% NaSO4 at 105 degreesC for 10 min; (5) the NaOH-NaSO4 solution followed by the HNO3-HF solution; and (6) 50% NaOH solution at 105 degreesC for 10min. Surfaces only sandblasted with alumina were used as controls. Specimen surfaces were characterized by XRD and SEM/EDS, and hardness-depth profiles were determined. All specimens were sandblasted with 110 microm alumina particles before porcelain firing. An ultra-low-fusing porcelain (Vita Titankeramik) was fused on the titanium surfaces. The titanium-ceramic adhesion was characterized by a biaxial flexure test, and area fraction of adherent porcelain (AFAP) was determined by X-ray spectroscopy. RESULTS: EDS analyses revealed a substantial amount (13-17 wt%) of Al on the control, and specimens modified with Methods 2, 4, and 6. XRD revealed residual stress in the titanium surfaces and corundum on the control, and Methods 2, 4, and 6 specimens. A new Ti(Cu, Al)2 phase was identified on the titanium surfaces modified by immersion in 50% NaOH-10% CuSO4 x 5H2O aqueous solution. Reduced residual stress was observed on Method 1, 3, and 5 specimens. No corundum peaks were detected on these specimens. Compared to the control, significantly lower (P < 0.05) hardness values were found for Methods 1-3 and Method 5 specimens at 20 microm below the surfaces and for Method 1-5 specimens at 50 microm below the surfaces. Significantly higher (P < 0.05) AFAP values were found for surfaces modified with Methods 2-6 compared to the control and Method 1, and no significant differences were found among Methods 1-6, and between control and Method 1. SIGNIFICANCE: Based on the results from the present study, porcelain adherence to cast CP titanium can be improved by the caustic baths used in the study.

X-ray diffraction (XRD) was employed to study dental alloy-ceramic interfaces. A Au-Pd-In alloy, which requires oxidation before porcelain firing, and a Au-Pt-Pd-In alloy, which does not require oxidation before porcelain firing, were selected in this study. Alloy specimens were centrifugally cast. Specimen surfaces were metallographically polished through 0.05 μm Al2,O3} slurries. A thin layer (

Titanium, once considered to be difficult to cast because of its relatively high melting point \(\left( {1670 \pm 50^\circ {\text{C}}} \right)\) and strong chemical affinity, can now be acceptably cast using newly developed casting apparatus. The objectives of this study were to examine the castability of commercially pure (CP) titanium using an ultra high-speed centrifugal casting machine and a pressure difference-type casting unit and to compare the castability of titanium with that of conventional dental casting alloys. To determine castability, two types of patterns were used: a mesh pattern of 22 × 24 mm cut polyether thread sieve, and a saucer pattern (24 mm diameter) perforated to create four T-shaped ends. The casting equipment significantly affected the mold filling of both patterns \(\left( {p < 0.001} \right)\). The castability indices obtained from both patterns of CP titanium cast in the centrifugal casting machine were significantly \(\left( {p < 0.05} \right)\) better than the indices of the castings produced in the pressure-difference casting unit. The radiographs of the saucer pattern cast in the centrifugal casting machine showed some pores that were fewer and smaller in size than the pores found in castings made in the pressure-difference unit. When the ultra high-speed centrifugal casting machine was used with the manufacturer’s recommended mold material, the castability of titanium was similar to that of gold alloy or Ni-Cr alloy cast by conventional means.

Objective: The aim of this study was to determine if Hg vaporization during setting and after abrasion of amalgams could be reduced by adding indium to Hg prior to trituration. Methods and materials: Hg–In alloys (0,5,10,15 wt% In) were triturated with commercial amalgam alloys (Tytin, Kerr; Artalloy, Degussa; Sybraloy, Kerr) and condensed into cylinders (4×8 mm). In one experiment, Hg release during setting was measured in air (37°C) with a Jerome 431 Hg analyzer (n=4). In a second experiment, amalgams aged two months were uniformly abraded on wet #600 SiC, blotted dry, and Hg release was measured in air (22°C) for 30 min with a Jerome 411 Hg analyzer (n=6). Total Hg was determined by integration (ng/mm2). Results were compared by ANOVA and Tukey's test (α=0.05). Results: Indium reduced Hg release from amalgams during setting. Amalgams ceased Hg release within 5 h. Indium did not reduce Hg release from abraded, set amalgams except Artalloy w/15% In. Significance: Coupled with our previous studies, this work shows that 5–15 wt% indium can be added to effectively reduce Hg release during setting, but not after abrasion of set amalgams.

Statement of problem. There is little information regarding bond strengths of resin cements to cast titanium surfaces contaminated by investment material. Purpose. This study examined the effect of surface contamination on the shear bond strength of resin cements to cast titanium and Ti-6Al-4V alloy. Material and methods. Two types of disks were cast from commercially pure titanium (CP-Ti) and Ti-6Al-4V alloy ingots using an argon-arc pressure casting unit and a phosphate-bonded Al 2 O 3 /LiAlSiO 6 investment. After casting, disks were subjected to 3 surface treatments: (1) cast surface sandblasted (50 μm-sized Al 2 O 3 ) for 30 seconds; (2) metal surface sanded with silicon-carbide paper (600 grit) after grinding the contaminated cast surface (approximately 200 μm in thickness); and (3) metal surface sandblasted for 30 seconds after treatment 2. Surface structures were examined after each treatment with SEM and optical microscopy. Each type of disk was then bonded with 2 types of luting materials. Bonded specimens were subjected to thermocycling for up to 50,000 cycles, and shear bond strengths were determined after 0 (baseline) and 50,000 thermocycles. Results were statistically analyzed with 3-way ANOVA ( P Results. Microscopic observation of cast CP-Ti and Ti-6Al-4V exhibited noticeable structures on the cast surfaces apparently contaminated with investment material. However, there were no statistical differences ( P >.05) in the bond strengths of both cements between contaminated (treatment 1) and uncontaminated surfaces (treatment 3) for both metals at baseline and after 50,000 thermocycles. The bond strength of specimens sanded with silicon-carbide paper (treatment 2) deteriorated dramatically after 50,000 thermocycles. Conclusions. Contamination of the cast metal surfaces by elements of the investment during casting did not affect bond strengths of the luting materials to CP-Ti and Ti-6Al-4V. (J Prosthet Dent 1999;81:270-6.)

The corrosion of cast or milled ASTM Grade II CP titanium with different surface conditions was studied by potentiodynamic anodic polarization and immersion testing. Specimens were fabricated using three dental titanium casting systems and from machined titanium. Three surface conditions were tested: (1) sandblasted with surface reaction layers remaining; (2) polished surface without surface reaction layers; and (3) sandblasted surface without surface reaction layers. An acidic saline solution (0.1 M lactic acid/0.1 M NaC1 [pH = 2]) and an artificial saliva were used as the corrosion media. Anodic polarization was performed starting at 50 mV below the rest potential and terminating at +2250 mV vs Ag/AgCl. Two surface conditions (sandblasted with the surface reaction layers and polished without such layers) were examined in the immersion test. Specimens were immersed in the corrosion media at 37 degrees C for six months. The recovered solution was analyzed by an atomic absorption spectrophotometer for titanium dissolution. A distinctive passive region on the polarization diagram, ranging from approximately 0 to approximately +1300 mV, was observed for all specimens in both media. Great similarity was observed for all the sandblasted specimens which had larger primary passive current densities and passive regions compared to the polished ones. A current density peak at approximately +1600 mV seen for all the specimens with sandblasted surfaces was less well defined for the polished specimens. Immersion testing in the acidic saline solution revealed no significant differences among the polished specimens. A significant increase (P < 0.05) in titanium dissolution was found for the sandblasted specimens with surface reaction layers remaining on the surfaces made with phosphate-bonded SiO2/Al2O3 investment compared to the polished ones. Significant differences were also found between sandblasted specimens with the surface reaction layers resulting from different investment materials and different casting methods. Measurable amounts of titanium were not found for all specimens in the artificial saliva after six months. It is evident that the corrosion behavior of cast CP titanium is similar to that of machined titanium. The surface roughness appears to be a more prominent factor than do the surface reaction layers on the polarization behavior of the CP titanium under the present experimental conditions. Surface roughness and the presence of the surface reaction layers both affect the dissolution of titanium.

Experimentation in all aspects of titanium casting at universities and industries throughout the world for the last 20 years has made titanium and titanium-alloy casting nearly feasible for fabricating sound cast dental prostheses, including crowns, inlays, and partial and complete dentures. Titanium casting in dentistry has now almost reached the stage where it can seriously be considered as a new method to compete with dental casting using conventional noble and base-metal alloys. More than anything else, the strength of titanium’s appeal lies in its excellent biocompatibility, coupled with its comparatively low price and abundant supply. Research efforts to overcome some problems associated with this method, including studies on the development of new titanium alloys suitable for dental use, will continue at many research sites internationally.

Mercury vapor release from amalgams during setting significantly decreases when the amalgams are prepared with binary Hg-In liquid alloys. The objective of this study was to compare the cytotoxicity of amalgams made with experimental Hg-In alloys with that of amalgam without In and a commercial In-containing amalgam.Amalgam specimens were prepared by triturating a high-Cu alloy powder (Tytin, Kerr) with pure Hg or Hg-In liquid alloy containing 5, 20 or 50% In and also by triturating an In-containing high-copper alloy powder (Indiloy, Shofu) with pure Hg. After the specimens were aged for 2 wk, a cylindrical specimen of each amalgam was immersed consecutively in cell culture medium for 0-8, 8-48 and 48-72 h. The cytotoxicity of the extracts was determined by placing them in contact with Balb/c 3T3 mouse fibroblasts for 24 h, after which the succinic dehydrogenase (SDH) activity was measured and expressed as a percentage of the Teflon negative controls. The results were statistically compared using ANOVA and Tukey's test (alpha = 0.05). The concentration of elements released into the extracts was determined by atomic absorption spectrophotometry and evaluated by Kruskal-Wallis and nonparametric multiple comparisons.For the 0-8 h and 8-48 h intervals, the 20% In amalgam was significantly (p0.05) less toxic than the other amalgams, and not different from the Teflon control. Results for the other amalgams were only slightly depressed compared to the Teflon control. For the 48-72 h interval, all amalgams were essentially no different from the control. Copper was the element dominantly released into the medium from all the amalgams tested.For amalgam tested after aging, alloying indium to mercury did not deleteriously affect the cytotoxicity of the resultant amalgam compared to the amalgam without indium.

Objectives: Aluminum ions interfere with fluoride determination when an ion-selective electrode (ISE) method is used. This study examined the effect of the presence of aluminum ions on the determination of fluoride ions released from glass ionomers. Methods: Disk-shaped specimens of five different commercial glass ionomers were immersed in deionized distilled water at 37 °C for one day or up to seven weeks. The amounts of released aluminum were determined by atomic absorption spectrophotometry, whereas the released fluoride was quantitated using a fluoride ISE with TISAB plus two different decomplexing agents for aluminum (CDTA or sodium citrate-potassium nitrate) or TISAB only. Results: Released amounts of aluminum and fluoride ions were found to be significantly different among the five different glass ionomers tested. Based on preliminary examination of the effect of the amount of aluminum ions on the measured value of fluoride, it was found at the end of one day for some of the glass ionomers that the fluoride concentrations measured without decomplexing agents were significantly lower than those measured with decomplexing agents, depending on the amounts of aluminum in the solution. However, since all the glass ionomers tested leached out most of the aluminum ions by seven days, the measured fluoride concentrations were not affected by a small amount of released aluminum from the glass ionomers immersed longer than seven days. Conclusions: When fluoride release from the glass ionomer is determined using ISE, care must be taken with the experimental design and analytical procedures to eliminate the interference by aluminum ions.

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 microm 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.

Titanium has received a great deal of attention from dental researchers and clinicians. In the United States, the history of the application of titanium as a biomaterial started as early as 1940 when experiments with titanium implants were done using laboratory animals. It appears that in 1959, two American researchers were the first to suggest casting titanium to fabricate implant posts. The use of cast titanium for dental prostheses in the U.S. was first reported in 1977. The present survey revealed that during the last decade, the number of research projects on the applications of titanium to dentistry that were presented at annual IADR/AADR meetings has steadily increased. The majority of these presentations have been made by American researchers, and 59% of these were related to dental implantology. The numbers of reports on casting and prosthodontic applications have steadily increased, but they are still more limited. The purpose of this review was to provide information on the development and the current status of research on titanium in dentistry in the U.S.

To optimize the properties of titanium for use in dentistry, alloying is necessary. This study reports on the characterization of some titanium alloys for grindability, wear, and corrosion resistance. Improvements in grindability and wear seemed to occur with the presence of the eutectoid in the alloy.

The fact that mercury is released from dental amalgam restorations after abrasion provides a source of continued controversy over the safe use of this material. Studies have shown that the amount and rate of mercury release vary for different amalgam products. The objective of this study was to determine how alloy composition affects mercury vaporization from experimental amalgams with similar alloy particle size and shape and percent residual mercury. An hypothesis to be tested was that mercury release is dependent upon the concentration of tin in the silver-mercury matrix phase of the amalgam. Seven spherical amalgam alloys (two low-copper and five high-copper) were made by a dental manufacturer (Tokuriki Honten, Japan). Trituration conditions were adjusted so that all set amalgams had the same residual Hg (47.3%). ADAtype amalgam cylinders were aged for 14 days at 37°C, then lightly wet-abraded on #600 silicon carbide, dried, and placed into a tube through which air was blown at a rate of 750 mL/min. Mercury vaporization was monitored with a gold film analyzer (Jerome 411) for 30 min. Total Hg release was determined by integration. We analyzed polished specimens via electron microprobe to determine composition, volume fraction of silver-mercury matrix (γ 1), and amount of tin in the γ1. The results showed a strong negative correlation (r2 = 0.941) between the log of total mercury released and the amount of tin in the γ1. The effect of alloy composition, specifically the presence or absence of zinc in the amalgam, could not be definitively determined. It is concluded that the tin content in the γ1 matrix is the primary determinant of Hg vaporization from amalgam.

This study was conducted to determine the effect of zinc in amalgam on the static mechanical properties and resistance to fatigue-crack propagation of amalgams.Fatigue, creep, compressive and flexure tests were performed on high-Cu Dispersalloy (Johnson and Johnson Dental Products Co., East Windsor, NJ, USA) and low-Cu Velvalloy (S.S. White Dental Products Int., Philadelphia, PA, USA) in both Zn-containing and Zn-free formulations. Linear Elastic Fracture Mechanics principles were used to characterize the fatigue behavior (crack lengths were monitored).The incorporation of Zn into these amalgams significantly improved their fatigue and creep resistance, while the effect of Zn on the static compressive and flexure strengths was not consistent. Zn significantly increased (p0.05) the resistance to fatigue crack propagation during Stage II crack growth for both amalgams, and increased the variations in crack velocity for a given stress intensity difference, without visibly altering the path or nature of the fatigue cracks. Possible influences on fatigue behavior were the mixed microstructure (particles and matrix), the nature of the crack tip, and creep.The superior resistance to tensile fatigue crack propagation of amalgams containing small amounts of Zn (approximately 1 wt%) in vitro compared with amalgams with no Zn correlated with the superior resistance to marginal breakdown in vivo of Zn-containing amalgams. The range of stress intensities over which stable cracks could propagate was small, while the large variations observed in fatigue crack growth rates for individual materials invalidate predicting a unique fatigue life from the empirical equations obtained.

An in vitro screening test was used to compare the cytotoxicity and elemental release from mercury- and gallium-based dental restorative materials.The test employed three sequential extractions of the samples into cell-culture medium which were then used to evaluate the cytotoxicity of the samples and the release of elements from the samples. Cytotoxicity was measured by placing the extract in contact with Balb/c mouse fibroblasts for 24 h and measuring the succinic dehydrogenase activity of the cells. The release of elements was measured by means of atomic absorption spectrophotometry.Samples of Tytin (Kerr) showed no cytotoxicity compared to Teflon controls. Dispersalloy (Johnson and Johnson) was severely cytotoxic initially when Zn release was greatest, but was less toxic between 48 and 72 h as Zn release decreased. Gallium Alloy GF (Tokuriki Honten) was moderately cytotoxic after 8 h, and increased in cytotoxicity thereafter, which correlated with a substantial and persistent release of Ga from this material.The results of the current study concurred with in vivo assessments of these materials, and the use of sequential extractions was useful in determining trends in the cytotoxicity and elemental release from these materials.

The handling characteristics of a gallium alloy (Gallium Alloy GF) were compared to those of a spherical high-copper amalgam (Tytin). Ten dentists each restored four identical MO preparations in acrylic typodont teeth (no. 30), two with amalgam and two with gallium alloy. Each restoration was evaluated immediately following completion by the operator for six clinically relevant criteria. Each criterion was scored between 1 and 5, where 1 = very poor, 2 = poor, 3 = fair, 4 = good, and 5 = very good. Three two-sided Mann-Whitney tests were used to compare the median scores for significant differences (P < 0.05). The first test indicated no significant difference between scores for the first- and second-placed restorations, within criteria and within alloy type (n = 10). The second test indicated a significant difference between amalgam and gallium alloy, within criteria and within restoration sequence (n = 10), for each criterion except resistance to fracture during removal of the matrix band. The third test indicated a significant difference between amalgam and gallium alloy, within each criteria, combining scores for first- and second-placed restorations (n = 20). During simulated clinical placement, amalgam was rated significantly higher than gallium alloy in each handling characteristic evaluated.

The hardened alpha-case (alpha-case) layer inevitably forms on the surface of titanium castings when prepared by investment casting. Because the hardness of the alpha-case is incomparable to that of the interior structure, the perception exists that the alpha-case is difficult to remove during cutting, grinding and polishing. Grindability (ease of grinding) of cast cpTi and cast Ti-6Al-4V was evaluated by grinding cast specimens incrementally using a SiC abrasive wheel. The present study revealed that the presence of the brittle alpha-case with lower fracture toughness is beneficial in grinding titanium. The alpha-case on the ductile cpTi can be ground much easier than its bulk interior structure. In less ductile Ti-6Al-4V, the grinding rate is much higher than that of cpTi, and the alpha-case and its interior structure are at similar levels since the fracture toughness of its alpha-case and the bulk material is not large enough.

An object of this study was to examine the mold filling capacity of some Ti-Hf alloys. Regardless of the edge angle, the Ti-Hf alloys behaved similar to commercially pure (CP) Ti due to their isomorphous nature of solidifying congruently over the ranges of the alloys examined.

The dynamic mechanical properties of two high-copper amalgams (Tytin and Dispersalloy) and two traditional amalgams (Aristalloy and Aristalloy with Zn) were measured over a temperature range of 0-70 degrees C and at frequencies of 0.1, 1, and 10 Hz by means of a DuPont DMA. Values of storage modulus (E') for the amalgams were equivalent to the Young's modulus (E) measured from static mechanical test methods, with Dispersalloy demonstrating the highest moduli. Values of E' decreased with increased temperature. E' of traditional amalgams decreased more rapidly than did those of the Cu-rich amalgams. Values of loss modulus (E") for Tytin were smaller than those of Dispersalloy and the two types of Aristalloy. High values of E" for the traditional amalgams correspond to a greater viscous behavior. Marked differences between the magnitude of tan delta and its temperature coefficients for traditional and high-copper amalgams were observed, which is indicative of differences in visco-elastic behavior between these two amalgam systems.

This study investigated the interfacial microstructure between gold-coated titanium and low-fusing porcelain. The square surfaces of cast titanium split rods were sputter-coated with gold using a sputter coater at 40 mA for 1,000 seconds. Specimens were prepared for transmission electron microscopy (TEM) by cutting and polishing two pieces of the gold-coated split-rod specimens, which were glued and embedded in Cu tubes with an epoxy adhesive. TEM observation was also conducted for the gold-coated specimens after degassing and porcelain fusing. Due to the gold coating, intermetallic compounds of Au-Ti formed under the sputtered gold layer after degassing and porcelain fusing. Ti3Au and Ti3Al layers were also observed beneath the Au-Ti intermetallic compound layer. There was good adhesion of porcelain to the Au-Ti compound and Ti oxides without any gaps or formation of a Ti-deficient intermediate layer, which is normally observed at the titanium-porcelain interface. The results of this TEM study suggested that gold-sputter-coating the cast titanium surface produced a Ti-Au intermetallic compound and suppressed the formation of a Ti-deficient intermediate layer, resulting in improved adherence between porcelain and titanium.

We assessed the biological response to several novel titanium alloys that have promising physical properties for biomedical applications. Four commercial titanium alloys [Super-TIX(R) 800, Super-TIX(R) 51AF, TIMETAL(R) 21SRx, and Ti-6Al-4V (ASTM grade 5)] and three experimental titanium alloys [Ti-13Cr-3Cu, Ti-1.5Si and Ti-1.5Si-5Cu] were tested. Specimens (n = 6; 5.0 x 5.0 x 3.0 mm(3)) were cast in a centrifugal casting machine using a MgO-based investment and polished to 600 grit, removing 250 mum from each surface. Commercially pure titanium (CP Ti: ASTM grade 2) and Teflon (polytetrafluoroethylene) were used as positive controls. The specimens were cleaned and disinfected, and then each cleaned specimen was placed in direct contact with Balb/c 3T3 fibroblasts for 72 h. The cytotoxicity [succinic dehydrogenase (SDH) activity] of the extracts was assessed using the MTT method. Cytotoxicity of the metals tested was not statistically different compared to the CP Ti and Teflon controls (p > 0.05). These novel titanium alloys pose cytotoxic risks no greater than many other commonly used alloys, including commercially pure titanium. The promising short-term biocompatibility of these Ti alloys is probably due to their excellent corrosion resistance under static conditions, even in biological environments.