Hisao Fukui

Alloying titanium and tantalum by cold crucible levitation melting (CCLM) furnace

Abstract Recently, titanium alloys have been studied as implant materials for dental and orthopedic surgery. Titanium alloys have distinguished characteristics of biocompatibility, corrosion resistance and mechanical properties. Having non-poisonous character to a living body, Ta, Zr and Nb have been used for addition to titanium alloys, which are free of vanadium and aluminum. It is well-known that titanium and tantalum are difficult metals to alloy in usual furnaces as these are very reactive metals, having great differences in melting point and specific gravity. To produce an alloy of titanium and tantalum, cold crucible levitation melting (CCLM) is effective in obtaining a uniform composition. Notable features of CCLM are that it can (1) melt metals with a high melting point, (2) create an alloy of uniform composition with a strong stirring effect by an electromagnetic force and (3) allow metals to be melted without contamination. We have melted 850 g of titanium and 150 g of tantalum by a CCLM furnace and have successfully made 1.0 kg of uniform composite Ti–15wt.% Ta alloy. It is noteworthy that the alloy was produced from pure base metals which were not alloyed beforehand and was made by a single melting (no re-melting) process.

Numerical simulations of canine retraction with T-loop springs based on the updated moment-to-force ratio

The purpose of this study was to develop a new finite element method for simulating long-term tooth movements and to compare the movement process occurring in canine retraction using a T-loop spring having large bends and with that having small bends. Orthodontic tooth movement was assumed to occur in the same manner as the initial tooth movement, which was controlled by the moment-to-force (M/F) ratios acting on the tooth. The M/F ratios were calculated as the reaction forces from the spring ends. For these M/F ratios, the teeth were moved based on the initial tooth movements, which were calculated by using the bilinear elastic model of the periodontal ligament. Repeating these calculations, the teeth were moved step by step while updating the M/F ratio. In the spring with large bends, the canine at first moved bodily, followed by root distal tipping. The bodily movement was quickly achieved, but over a short distance. In the spring with small bends, the canine at first rotated and root mesial tipping occurred, subsequently the canine uprighted and the rotation decreased. After a long time elapsed, the canine moved bodily over a long distance. It was found that the long-term tooth movement produced by the T-loop springs could be simulated by the method proposed in this study. The force system acting on the teeth and the movement type remarkably changed during the long-term tooth movement. The spring with large bends could move the canine bodily faster than that with small bends.

Numeric simulations of en-masse space closure with sliding mechanics

INTRODUCTION En-masse sliding mechanics have been typically used for space closure. Because of friction created at the bracket-wire interface, the force system during tooth movement has not been clarified. METHODS Long-term tooth movements in en-masse sliding mechanics were simulated with the finite element method. RESULTS Tipping of the anterior teeth occurred immediately after application of retraction forces. The force system then changed so that the teeth moved almost bodily, and friction occurred at the bracket-wire interface. Net force transferred to the anterior teeth was approximately one fourth of the applied force. The amount of the mesial force acting on the posterior teeth was the same as that acting on the anterior teeth. Irrespective of the amount of friction, the ratio of movement distances between the posterior and anterior teeth was almost the same. By increasing the applied force or decreasing the frictional coefficient, the teeth moved rapidly, but the tipping angle of the anterior teeth increased because of the elastic deflection of the archwire. CONCLUSIONS Finite element simulation clarified the tooth movement and the force system in en-masse sliding mechanics. Long-term tooth movement could not be predicted from the initial force system. The friction was not detrimental to the anchorage. Increasing the applied force or decreasing the friction for rapid tooth movement might result in tipping of the teeth.

Effects of transpalatal arch on molar movement produced by mesial force: a finite element simulation.

INTRODUCTION The transpalatal arch (TPA), which splints together 2 maxillary molars, has been believed to preserve anchorage. The purpose of this study was to clarify this effect from a mechanical point of view. METHODS The finite element method was used to simulate the movement of anchor teeth subjected to mesial forces with and without a TPA. RESULTS In the initial movement produced by elastic deformation of the periodontal ligament, stress magnitude in the periodontal ligament was not changed by the TPA. In the orthodontic movement produced by bone remodeling, the mesial force tipped the anchor teeth irrespective of the TPA. The tipping angles of anchor teeth with and without the TPA were almost the same. The anchor teeth without the TPA were rotated in the occlusal plane and moved transversely. CONCLUSIONS The TPA had no effect on the initial movement. In the orthodontic movement, the TPA had almost no effect, preserving anchorage for mesial movement. However, the TPA prevented rotational and transverse movements of the anchor teeth. These results are valid when the assumptions used in this calculation are satisfied.

Measurement of Softening Temperatures in Dental Bake-on Porcelains

An effective porcelain softening temperature is determined from the deflection behavior of split bimaterial (metal/porcelain) rings during cooling. The effective temperature provides an upper temperature bound for thermal expansion comparison and compatibility evaluation.

Finite element analysis of the effect of force directions on tooth movement in extraction space closure with miniscrew sliding mechanics

INTRODUCTION Miniscrews placed in bone have been used as orthodontic anchorage in extraction space closure with sliding mechanics. The movement patterns of the teeth depend on the force directions. To move the teeth in a desired pattern, the appropriate direction of force must be selected. The purpose of this article is to clarify the relationship between force directions and movement patterns. METHODS By using the finite element method, orthodontic movements were simulated based on the remodeling law of the alveolar bone. The power arm length and the miniscrew position were varied to change the force directions. RESULTS When the power arm was lengthened, rotation of the entire maxillary dentition decreased. The posterior teeth were effective for preventing rotation of the anterior teeth through an archwire. In cases of a high position of a miniscrew, bodily tooth movement was almost achieved. The vertical component of the force produced intrusion or extrusion of the entire dentition. CONCLUSIONS Within the limits of the method, the mechanical simulations demonstrated the effect of force direction on movement patterns.

A finite element simulation of initial movement, orthodontic movement, and the centre of resistance of the maxillary teeth connected with an archwire

The purpose of this article is to simulate long-term movement of maxillary teeth connected with an archwire and to clarify the difference between the initial tooth movement and the long-term orthodontic movement. Initial tooth movement was calculated based on the elastic deformation of the periodontal ligament. Orthodontic tooth movement was simulated based on the bone remodeling law of the alveolar bone, while consequentially updating the force system. In the initial tooth movement, all teeth tipped individually due to an elastic deflection of the archwire. In the long-term movement, the maxillary teeth moved as one united body, as if the archwire were a rigid material. Difference of both movement patterns was due to the change in force system during tooth movement. The long-term movement could not be predicted from the initial tooth movement. Movement pattern and location of the centre of resistance in the long-term movement were almost the same as those in the initial tooth movement as calculated by assuming the archwire to be a rigid material.

Super Elastic Functional β Titanium Alloy with Low Young's Modulus for Biomedical Applications

The low modulus β type titanium alloy, Ti-29Nb-13Ta-4.6Zr, was designed, and then the practical level ingot of the alloy was successfully fabricated by Levicast method. The mechanical and biological compatibilities, and super elastic behavior of the alloys were investigated in this study. The mechanical performance of tensile properties and fatigue strength of the alloy are equal to or greater than those of conventional biomedical Ti-6Al-4V ELI. Youngs modulus of the alloy is much lower than that of Ti-6Al-4V ELI, and increases with the precipitation of α phase or ω phase in the β matrix phase. The compatibility of the alloy with bone is excellent. Low modulus of the alloy is effective to enhance the healing of bone fracture and remodeling of bone. Super elastic behavior is observed in Ti-29Nb-13Ta-4.6Zr conducted with short time solution treatment after heavy cold working. Total elastic strain in that case is around 2.8 %. The mechanism of the super elastic behavior of Ti-29Nb-13Ta-4.6Zr is still unclear.

Development of Ti-30 mass% Ta Alloy for Biomedical Applications

In the present study, the effects of Ta content on the dynamic Young’s modulus and tensile properties of Ti−Ta alloys were investigated in order to find a Ti−Ta alloy that gives low modulus and high strength for biomedical applications. For this purpose, the ingots of Ti−Ta alloys with Ta contents from 10 to 50 mass % were melted, and then rolled into the plate of 3 mm thick. All the specimens were solution treated at 1223 K in the b field for 3.6 ks and then quenched in ice water. Subsequently, some of them were aged at 773 K for 259.2 ks followed by a rapid quenching in ice water. The corrosion capacity and biocompatibility of typical Ti−Ta alloy were also evaluated. The experimental results indicate that the Ti−30% Ta alloy has better mechanical biocompatibility, corrosion capacity and cyto-toxicity than Ti−6Al−4V alloy used as a standard biomaterial, and thus it will be of considerable development for biomedical applications.

Hard-ceramic layer formed on Ti-29Nb-13Ta-4.6Zr and Ti-6Al-4V ELI during Gas Nitriding

The surface of Ti-29Nb-13Ta-4.6Zr (TNTZ) subjected to gas nitriding at 1023–1223 K was investigated in comparison with the conventional biomedical titanium alloy, Ti-6Al-4V ELI (Ti64). After gas nitriding, the microstructures near the surface of these alloys were observed by optical microscopy, X-ray diffraction, Auger electron spectroscopy, and X-ray photoelectron spectroscopy. In both alloys, two titanium nitrides (TiN and Ti2N) are formed and the α phase precipitated by gas nitriding. Furthermore, oxygen impurity in the gas nitriding atmosphere reacts with the titanium nitrides; thus, TiO2 is formed at the outermost titanium nitride layer. The surface hardening was also evaluated by Vickers hardness measurement. The Vickers hardness near the surface of TNTZ and Ti64 increases significantly by gas nitriding.