Mechanical Properties of Ti-Nb-Cu Alloys for Dental Machining Applications.

Titanium has excellent biocompatibility and good corrosion resistance and is extensively used in dental implants and denture bases. However, pure titanium lacks the strength for use in dental prostheses that require relatively high strength. We developed 15 different types of Ti-Nb-Cu alloys and investigated their alloy phases and mechanical properties, including tensile and yield strength, elongation after fracture, and Vickers hardness. The alloy phases of Ti-8%Nb-2%Cu and Ti-13%Nb-2%Cu were α + ß, while those of Ti-5%Nb-5%Cu and Ti-10%Nb-5%Cu were α + Ti2Cu. The tensile strength and hardness of these alloys were significantly higher than those of titanium; however, their elongation was less. In particular, the yield strength of these alloys was more than twice that of titanium. These differences in mechanical properties are attributable to solid-solution strengthening and precipitation strengthening. Other compositions with an alloy phase of α + ß + Ti2Cu or ß + Ti2Cu had high hardness but not high strength. These results suggest that the Ti-8%Nb-2%Cu, Ti-5%Nb-5%Cu, Ti-13%Nb-2%Cu, and Ti-10%Nb-5%Cu alloys can be applied to dental prostheses, which are subject to very high forces from accessories such as long-span bridges, clasps, implant-retained superstructures, and narrow-diameter implants.

Development of Ternary Ti-Ag-Cu Alloys with Excellent Mechanical Properties and Antibiofilm Activity.

Titanium-20 mass% Silver (Ti-20%Ag) alloy can suppress biofilm formation on the surface. Unlike bactericidal agents, it does not kill bacteria; therefore, the healthy oral microflora remains undisturbed. To utilize the unique functions of this alloy and enable its use in the fabrication of dental prostheses that require relatively high strength, we added copper (Cu) as an alloying element to improve strength. This study aimed to develop ternary Ti-Ag-Cu alloys with excellent mechanical properties and antibiofilm activity. As a result of investigating the mechanical properties of several experimental alloys, the tensile strength, yield strength, and hardness of Ti-20%Ag-1%Cu and Ti-20%Ag-2%Cu alloys were improved by the solid-solution strengthening or hardening of the αTi phase. In addition, these alloys had the same ability to suppress biofilm formation as the Ti-20Ag alloy. Thus, Ti-20%Ag-1-2%Cu alloys can be used for fabrication of narrow-diameter dental implants and prostheses subjected to extremely high force, and these prostheses are useful in preventing post-treatment oral diseases.

Ideal set-up angle between a pair of oval dental magnetic attachments for suppression of the loss in retentive force associated with horizontal displacement.

Two oval sandwich type magnetic attachments set up in various angulations and spacing, then the pattern of retentive force against horizontal displacement studied. A measuring device and methodology that matches ISO 13017 was used. A pair of magnetic attachments fixed on the same plane at a specific distance on the measuring device and set in various angulations. Retentive force readings of magnetic attachments in various setup positions against the horizontal displacement along the major or minor axis directions were taken. The pattern of decline in retentive force as horizontal displacement increased was different across the various set-ups. It was found that the decrease in retentive forces associated with horizontal displacement can be suppressed when the angle between the major axis and the direction of movement is as small as possible. Formation of a 90° angle between major axes of any pair of magnetic attachments led to nullification of the decline in retentive forces associated with displacement in any direction. Therefore, 90° is the practical, ideal set-up angle between any pair of dental magnetic attachments critical for suppression of the loss in retentive force associated with horizontal gap.

Usefulness of conventional glass ionomer cements in an environment of insufficient moisture exclusion.

PURPOSE: Moisture exclusion while treating dental caries can be challenging, and the glass ionomer cements (GICs) used for these procedures are susceptible to water. Few studies have examined the effects of the powder/liquid ratio (PLR) on the physical properties of GICs exposed to water. In this study, the hardness and thickness of the water-susceptible surface layer of three GICs were evaluated. METHODS: Three conventional GICs were mixed in increasing PLRs, and hardness over time was measured under conditions of no water exposure, distilled water exposure, and saliva exposure. Furthermore, the thickness of the water-susceptible layer for each GIC was determined. RESULTS: A water-susceptible layer of approximately 250 µm was evident for all GICs, and the thickness decreased with increasing PLR. GIC hardness increased with increasing PLR in conditions without water for all GIC types. Furthermore, the removal of the water-susceptible layer restored the physical properties of each GIC. CONCLUSION: Overall, the results indicate that conventional GIC restoration with the removal of the water-susceptible surface layer is a feasible strategy for treating dental caries in individuals for whom exclusion of moisture can be difficult.

Osteogenic response under the periosteum by magnesium implantation in rat tibia.

This study was designed to examine osteoconductive effects of Mg in rats tibia. The animals were sacrificed after 1, 2, and 8 weeks. The elemental analysis was performed using SEM/EDX at week 1. Following X-ray micrography at weeks 2 and 8, samples were embedded in paraffin. The expression of osteocalcin was observed by immunohistochemical staining. The element concentrations of fibrous capsules around the specimens were also measured by ICP-MS. The concentrations of Ca and P on the surface of the Mg specimen increased in SEM/EDX. The tissue specimen showed new bone formation on the bone surface near the implanted area. The concentrations of Mg, Ca, and P were high in the fibrous capsules surrounding Mg. Implantation induced differentiation of osteoblasts, and this process was considered to be associated with new bone formation. Induction of cell differentiation may be influenced by corrosion products in addition to corroding magnesium.

Mechanical properties and microstructures of cast dental Ti-Fe alloys.

Binary Ti-Fe alloys of varying concentrations of Fe between 5-25% were made, and their castings evaluated in terms of microstructures formed and mechanical properties. The aim of this study was to explore the composition of Ti-Fe alloys that offers improved wear resistance of titanium. X-ray diffraction and microstructural observation revealed that 5-7% Fe, 8-15% Fe, and 20-25% Fe consisted of α+ß, single ß, and ß+Ti-Fe phases, respectively. The hardness of alloys with 8-13% Fe was almost equal to that of Co-Cr alloys but lower than of the other Ti-Fe alloys. Elongation of the Ti-Fe alloys was negligible. However, dimples were observed in specimen containing 7-11% Fe. Alloys with 9% Fe demonstrated the highest strength of more than 850 MPa. We believe that Ti-Fe alloys with 8-11% Fe may be applicable in development of an alloy with good wear resistance due to the exhibited properties of high hardness and ductility albeit low.

Wear resistance of cast dental Ti-Fe alloys.

Binary Ti-Fe alloys with 5-25 mass% Fe were prepared, and subjected to reciprocating wear test. The aim of this study was to investigate the relationship between mechanical properties and the wear resistance of titanium and Ti-Fe alloys. The dimensions (length, width and depth) of wear marks on Ti-Fe alloys were less than those observed on pure Ti specimen. Wear resistance of Ti-Fe alloys was better than that of pure titanium. It was established that hardness was the main factor that influenced wear resistance of Ti-Fe alloys. Single ß Ti-Fe alloys showed better wear resistance than α+ß Ti-Fe alloys. Increase in concentration of Fe in the ß phase of Ti-Fe alloys leads to improved wear resistance of the alloy. Ti-Fe alloys with 11-15 mass% Fe form ideal candidates for fabrication of dental titanium alloys with excellent wear resistance.

In vivo behavior of untreated and compressed concentrated growth factors as biomaterials in rabbits.

To characterize concentrated growth factors (CGFs) in vivo, we examined the degradation of implanted CGF in rabbits. Untreated CGF (U-CGF) and compressed CGF (C-CGF) were subcutaneously implanted into the dorsum. Histological analyses showed that the U-CGF and C-CGF induced very few inflammatory cells and that the U-CGF and C-CGF were subsequently degraded with dendritic invasion of granulation tissue. The C-CGF histopathologically remained for longer term than the U-CGF. Aggregated CD31+ and RAM11+ cells appeared in and around the implanted CGF. The number of macrophages and blood vessels in the CGF-implanted groups was greater than that in the sham group. There were more blood vessels in the U-CGF group than that in the C-CGF and sham group. We showed that CGF was degraded by macrophages in 4 weeks and enhanced angiogenesis with dendritically branching new capillaries. Therefore, the U-CGF and C-CGF can be clinically applied as a biomaterial inducing angiogenesis.

The process of magnesium ion modification of titanium surface and the sustained-release of magnesium ions from its surface.

This study explored modification of an alkaline heat treated titanium surface, using magnesium ions, to improve bone compatibility through the sustained release of magnesium ions. Pure titanium surface was first subjected to alkaline treatment using 5 M NaOH then modified with magnesium through immersion in magnesium chloride solution before heating in a furnace at 600°C for 1 h. Use of at least 0.01 M magnesium chloride solution for at least 0.5 min, leads to introduction of 1.7 to 2.3 at% magnesium at a distribution close to saturation on the titanium surface. The modified titanium surface sustained long term release of magnesium ions in acidic solution for more than 168 h. It was further demonstrated that the process of sustained release of magnesium ions is influenced by pH and can be triggered by lowering it from neutral to 3.

Construction of Ti-Nb-Ti2Cu pseudo-ternary phase diagram.

The aim of this study was to construct a Ti-Nb-Cu ternary phase diagram that plays the role of a map for developing new titanium alloys with excellent machinability and mechanical properties. Fifteen experimental Ti-Nb-Cu ternary alloys composed of Ti-5-30%Nb-2-20%Cu were designed, and ingots made using Ar-arc melting furnace before casting to generate specimen. The alloy castings were evaluated in terms of their microstructures and alloy phases. A Ti-Nb-Ti2Cu pseudo-ternary phase diagram was constructed using X-ray diffractmetry results. Three alloy phases (α-Ti, ß-Ti and Ti2Cu) were established within the specimen. Furthermore, the prescence of two-phase coexistence regions (α+Ti2Cu, α+ß and ß+Ti2Cu), and three-phase coexistence region (α+ß+Ti2Cu) was noted. The findings obtained through microstructural observation corresponded well with the constructed phase diagram.

Mechanical properties and microstructures of dental cast Ti-6Nb-4Cu, Ti-18Nb-2Cu, and Ti-24Nb-1Cu alloys.

The mechanical properties -tensile strength, yield strength, elongation after fracture, and Vickers hardness- and alloy phases of the dental cast alloys Ti-6%Nb-4%Cu, Ti-18%Nb-2%Cu, and Ti-24%Nb-1%Cu were investigated. Ti-6%Nb-4%Cu consisted of a single α-phase, while Ti-18%Nb-2%Cu and Ti-24%Nb-1%Cu consisted of α- and ß-phases. The tensile strengths, yield strengths, and hardnesses of these alloys were higher than those of Ti-5%Cu and Ti-30%Nb; however, their breaking elongations were smaller. These differences in the mechanical properties are attributable to solid-solution strengthening or to precipitation strengthening by the dual-phase (α+ß) structure. Thus, Ti-Nb-Cu alloys are suitable for use in high-strength dental prostheses, such as implantretained superstructures and narrow-diameter implants.

Gene transfection of human mesenchymal stem cells with a nano-hydroxyapatite-collagen scaffold containing DNA-functionalized calcium phosphate nanoparticles.

This study aimed to fabricate a growth factor-releasing biodegradable scaffold for tissue regeneration. We prepared multishell calcium phosphate (CaP) nanoparticles functionalized with DNA, polyethyleneimine (PEI), protamine and octa-arginine (R8) and compared their respective transfection activity and cell viability measures using human mesenchymal stem cells. DNA-protamine complexes improved the transfection efficiency of CaP nanoparticles with the exception of those functionalized with R8. These complexes also greatly reduced the cytotoxicity of PEI. In addition, we also fabricated DNA-protamine-functionalized CaP nanoparticle-loaded nano-hydroxyapatite-collagen scaffolds and investigated their gene transfection efficiencies. These experiments showed that the scaffolds were associated with moderate hMSC cell viability and were capable of releasing the BMP-2 protein into hMSCs following gene transfection. In particular, the scaffold loaded with protamine-containing CaP nanoparticles showed the highest cell viability and transfection efficiency in hMSCs; thus, it might be suitable to serve as an efficient growth factor-releasing scaffold.

Machinability of an experimental Ti-Ag alloy in terms of tool life in a dental CAD/CAM system.

Titanium is difficult to machine because of its intrinsic properties. In a previous study, the machinability of titanium was improved by alloying with silver. This study aimed to evaluate the durability of tungsten carbide burs after the fabrication of frameworks using a Ti-20%Ag alloy and titanium with a computer-aided design and computer-aided manufacturing system. There was a significant difference in attrition area ratio between the two metals. Compared with titanium, the ratio of the area of attrition of machining burs was significantly lower for the experimental Ti-20%Ag alloy. The difference in the area of attrition for titanium and Ti-20%Ag became remarkable with increasing number of machining operations. The results show that the same burs can be used for a longer time with Ti-20%Ag than with pure titanium. Therefore, in terms of tool life, the machinability of the Ti-20%Ag alloy is superior to that of titanium.

Mechanical properties of dental Ti-Ag alloys with 22.5, 25, 27.5, and 30 mass% Ag.

The mechanical properties -tensile strength, yield strength, elongation after fracture, Vickers hardness, and Young's modulus-and the phases of Ti-Ag alloys were investigated, as prepared with 22.5, 25, 27.5, and 30 mass% Ag. The tensile strength, yield strength, hardness, and Young's modulus of the alloys increase with their Ag content up to 25 mass%, but their breaking elongation decreases. These changes in the mechanical properties are attributed to solid-solution strengthening of the α-titanium phase, to Ti2Ag precipitation, and to the formation of eutectic structures composed of α+Ti2Ag. The addition of Ag, at 25 mass% in particular, improves the mechanical properties of these alloys, making them suitable for high strength dental prostheses, such as implantretained superstructures and narrow-diameter implants.

Electrochemical evaluation of the corrosion resistance of cup-yoke-type dental magnetic attachments.

The corrosion resistance of different magnetic assemblies­Magfit DX800 (Aichi Steel), Gigauss D800 (GC), Hyper Slim 4013, and Hicorex Slim 4013 (Hitachi Metals)­were electrochemically evaluated using anodic polarization curves obtained in 0.9% NaCl solution at 37°C. Stainless steels (444, XM27, 447J1, and 316L) composing the magnetic assemblies were also examined as controls. This revealed that all of the magnetic assemblies break down at 0.6-1.1 V; however, their breakdown potentials were all still significantly higher (p<0.05) than that of 316L. The distribution of elements in the laser welding zone between the yoke and shield ring was analyzed using EPMA; except with Magfit DX800, where the Cr content of the shield ring weld was greater than that of 316L. These magnetic assemblies are expected to have good corrosion resistance in the oral cavity, as their breakdown potentials are sufficiently higher than the 316L commonly used as a surgical implant material.

A three-dimensional finite element evaluation of magnetic attachment attractive force and the influence of the magnetic circuit.

The finite element method has been considered to be excellent evaluative technique to study magnetic circuit optimization. The present study analyzed and quantitatively evaluated the different effects of magnetic circuit on attractive force and magnetic flux density using a three-dimensional finite element method for comparative evaluation. The diameter of a non-magnetic material in the shield disk of a magnetic assembly was variably increased by 0.1 mm to a maximum 2.0 mm in this study design. The analysis results demonstrate that attractive force increases until the diameter of the non-magnetic spacing material reaches a diameter of 0.5 mm where it peaks and then decreases as the overall diameter increases over 0.5 mm. The present analysis suggested that the attractive force for a magnetic attachment is optimized with an appropriate magnetic assembly shield disk diameter using a non-magnetic material to effectively change the magnetic circuit efficiency and resulting retention.

Inhibitory effect of Ti-Ag alloy on artificial biofilm formation.

Titanium-silver (Ti-Ag) alloy has been improved for machinability and mechanical properties, but its anti-biofilm properties have not been elucidated yet. Thus, this study aimed to evaluate the effects of Ti-Ag alloy on biofilm formation and bacterial viability in comparison with pure Ti, pure Ag and silver-palladium (Ag-Pd) alloy. Biofilm formation on the metal plates was evaluated by growing Streptococcus mutans and Streptococcus sobrinus in the presence of metal plates. Bactericidal activity was evaluated using a film contact method. There were no significant differences in biofilm formation between pure Ti, pure Ag and Ag-Pd alloy, while biofilm amounts on Ti-20% Ag and Ti-25% Ag alloys were significantly lower (p<0.05). In addition, Ti-Ag alloys and pure Ti were not bactericidal, although pure Ag and Ag-Pd alloy killed bacteria. These results suggest that Ti-20% Ag and Ti-25% Ag alloys are suitable for dental material that suppresses biofilm formation without disturbing healthy oral microflora.

Corrosive effect of disinfection solution containing hydroxyl radicals generated by photolysis of H(2)O(2) on dental metals.

The purpose of the present study was to evaluate the corrosive effect of disinfection solution containing hydroxyl radicals generated by photolysis of H(2)O(2)on dental metals. Static immersion test was performed on four different dental metals: Ti, Type 316L stainless steel, Ag-Pd-Cu-Au alloy, and Co-Cr alloy. Metal specimens were immersed in 1 M H(2)O(2)(=3.4%) with or without light-emitting diode (LED) light irradiation (wavelength: 400 nm) for 1 week, and then the amounts of released ions were analyzed. Corrosive effect of the disinfection solution containing hydroxyl radicals on any dental metals tested in the present study never exceeded that of H(2)O(2) alone. Therefore, disinfection systems based on the photolysis of H(2)O(2) for the cleaning of dentures and treatment of oral infectious diseases would not cause problematic metal corrosion whenever the concentration of H(2)O(2) does not exceed 3%, which is a concentration used as an oral disinfectant.

Geometric design method for occlusal outlines of complex class I and class II inlay cavities.

The purpose of this study was to establish a geometric design method for the occlusal outlines of complex inlay cavities as a continuation study of a previous design method for simple class I inlay cavity. A method for extending the occlusal outline to the buccal or lingual groove and to three preparation types of the proximal portions of class II inlay cavities -namely, straight line preparation, sweeping curve preparation, and reverse curve preparation- was investigated. To ensure the smoothness of the occlusal outline, a Bézier curve was introduced in the design. A minimal number of control points for the curve was applied to define each preparation type. The design method was experimentally applied to mandibular and maxillary first molars. Smooth outlines of the complex inlay cavities in the molars with tool accessibility throughout the cavities were achievable by using the present method.

Preparation and in vivo evaluation of apatite/collagen packed composite by alternate immersion method and Newton press.

Further development of bio-compatible, bio-absorbable, and osteo-conductive bio-materials is desired for bone grafts in dental and medical clinics. One candidate material might be a high-density apatite/collagen composite, which cures relatively large bone defects. To produce such a composite, we freeze-dried type I collagen solution, cross-linked the formed sponge by 2 wt % glutaraldehyde, immersed the insoluble sponge in CaCl(2) and Na(2)HPO(4) solutions alternately five times, and compacted the sponge by Newton press at 5000 kgf. For comparison, cross-linked collagen without alternate immersion was also pressed. SEM/EPMA, XRD, and FTIR analyses clarified that alternate immersion successfully coated the collagen sponge with hydroxyapatite. Packed apatite/collagen composite and collagen disks 6 mm in diameter and 0.5 mm in height were implanted in the subperiostea of rabbit tibiae for 2, 4, 8, and 12 weeks to assess bio-compatibility, bio-absorbability, and osteo-conductivity. Histological observations showed that the packed apatite/collagen composite was biocompatible, osteo-conductive for up to 8 weeks, and largely bio-absorbed at 12 weeks, while the packed collagen sponge caused an undesirable foreign body reaction, which worsened with the implantation period. The overall findings suggest that this packed apatite/collagen composite might be used as a new bio-absorbable bone graft material.