Quality Improvement of a β Type Titanium Alloy Cast for Biomedical Applications by Using a Clacia Mold

Quality Improvement of a

-Type Titanium Alloy Cast

for Biomedical Applications by Using a Clacia Mold

Harumi Tsutsumi

, Mitsuo Niinomi

, Toshikazu Akahori

,

Masaaki Nakai

, Tsutomu Takeuchi

and Shigeki Katsura

1_{Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan} 2_{Takeuchi Katan, Ltd., Toyohashi 441-8132, Japan}

3_{Yamahachi Dental Mgf., Co., Gamagori 443-0105, Japan}

The applicability of a calcia mold to casting a-type titanium alloy, Ti-29Nb-13Ta-4.6Zr (TNTZ), was evaluated with focusing on the dimensional accuracy of the casting in this study. Pure zirconium particles were added to a calcia mold to take advantage of the expansion of oxidized zirconium during the baking process in order to compensate for the solidification shrinkage of TNTZ. The morphological characteristics of the casting surface, such as the roughness and dimensional accuracy, of the cast TNTZ were investigated.

The dilation ratio of the calcia mold is found to increase with increasing the number of pure zirconium particles. The addition of 12 mass% or 14 mass% pure zirconium particles compensates for not only the solidification of TNTZ but also the occurrence of shrinkage of the calcia mold. In addition, the formation of a surface reaction layer in TNTZ is restrained to a larger extent by casting into a calcia mold than into a magnesia mold, which is the conventional investment mold for titanium casting. Furthermore, the volume fraction and number of casting defects are also restrained to a larger extent by casting into a calcia mold than into a magnesia mold. The results of this study should lead to enhancements in the creation of cast TNTZ for dental products. [doi:10.2320/matertrans.L-M2009827]

(Received June 19, 2009; Accepted September 29, 2009; Published December 25, 2009)

Keywords: -type titanium alloy, dental precision casting, calcia mold, magnesia mold, dimensional accuracy

1. Introduction

In the dental field, ion elution induced by corrosion from the surface of dental products is a suspected cause of physical allergic reactions and/or damage to dental products. At-tempts have been made to overcome these problems; there-fore, the demand for titanium (Ti) and its alloys in dental products has gradually increased due to their high corrosion resistance and other excellent properties.1–3) _Especially,

a Ti-29Nb-13Ta-4.6Zr (TNTZ) alloy composed of non-toxic and non-allergenic elements, such as Nb, Ta and Zr, has been predicted to be the next-generation biomaterial for prosthetic appliances and dental implants.4–7) _{The dental}

products are designed to fit diseased areas based on an individual patient’s condition. Therefore, dental products are usually fabricated using a dental precision casting technique. However, the melting point of TNTZ is much higher than that of a conventional Ti alloy, Ti-6Al-4V ELI, because TNTZ contains a significant amount of Ta and Nb, which have melting points of 3290 K and 5017 K, respec-tively.8) _{Molten TNTZ is very active at high temperatures,}

and TNTZ easily reacts with the mold and formed surface reaction layer. It is difficult to obtain cast TNTZ using general mold materials, such as alumina and magnesia. The development of mold materials that are stable at high temperatures for dental precision casting of the titanium alloys such as TNTZ with high melting point is, therefore, essential.

Researchers have focused on calcia particles as heat-resistant investments.9,10)Calcia particles are among the most stable oxides in terms of the free energy of formation, thus, inhibition of the interface reaction is expected.11–13) In our previous research, it was confirmed that calcia-based invest-ments inhibited the interfacial reaction and decreased the thickness of the surface reaction layer more than

conven-tional investments.14)Furthermore, the surface of cast TNTZ made using a duplex-coated wax pattern with a fine pure calcia slurry and a crushed silica fiber-reinforced fine calcia slurry was very fine. These results indicated that calcia particles were suitable for the dental precision casting of TNTZ. However, it is still difficult to obtain high-dimensional accuracy of cast TNTZ using a calcia mold. The solidification shrinkage of the cast TNTZ fabricated using a calcia mold cannot be compensated for, becuase the calcia mold shrinks 2% during the baking processes. In this study, in order to compensate for the solidification shrinkage of the cast TNTZ, cast TNTZ was fabricated using a calcia mold to which an intumescent agent had been added. In order to evaluate the applicability of the dental precision casting technique using the calcia mold for TNTZ, the surface roughness and dimensional accuracy of the cast TNTZ fabricated using a calcia mold was investigated.

2. Materials and Methods

2.1 Materials

TNTZ disks with a diameter of 30 mm or 6 mm and a thickness of 13 mm were prepared from a hot forged TNTZ bar (Nb: 29.2 mass%, Ta: 12.2 mass%, Zr: 4.3 mass%, Fe: 0.05 mass%, N: 0.04 mass%, O: 0.01 mass% and Ti: balance) with a diameter of 30 mm and a length of 1000 mm.

2.2 Wax pattern

pattern for the wettability evaluation are shown in Fig. 1. Sprue and a sprue runner were set in the square-type, dog-bone-type, and cubic-type wax patterns, as shown in Fig. 1. Several wax patterns were coated with a calcia slurry to obtain a smooth casting surface, as described in detail below.

2.3 Mold

Two different sizes of electrically fused calcia particles with diameters below 0.3 mm (C1) and 1–3 mm (C2) were

used in this study. The chemical composition of the magnesia-based investment (hereafter magnesia investment) is shown in Table 1. The bonding agent of the investment used in this study was a methanol solution with 7 mass% calcia chloride, CaCl2. C1 particles were mixed with the

bonding agent at a ratio of 4 : 1by weight, and a C1 slurry

was obtained (slurry A). Then, 0.3 mass% silica fiber meshes (55mm2_{, 2 mm in thickness) and 5–18 mass% 45-mmpure}

zirconium particles (used as expansive components) were mixed into slurry A (slurry B). Wax patterns were immersed in slurry A and subsequently in slurry B. In order to avoid mixed calcia particles, the wax patterns were coated at 1.2 ks intervals. Mixture calcia particles of 40%C1 and 60%C3 by

weight were used as the investment material. The mixed calcia particles were further mixed with the bonding agent at a ratio of 93 (calcia particles): 7 (bonding agent) by weight and then invested in a mold frame with the wax patterns

obtained with the calcia slurry coatings. A mold frame with a diameter of 70 mm and a length of 100 mm was used. The invested molds were held in a vacuum desiccator (0:06106_{Pa) for 86.4 ks at room temperature. Multiple}

baking processes were then carried out with the molds using an electrical muffle furnace. A schematic image of the multiple baking processes for the calcia mold is shown in Fig. 2(a).

A commercially available magnesia-based investment with alumina cement was also used as a control. The chemical composition of the magnesia investment is shown in Table 1. The magnesia investment was mixed with distilled water at a ratio of 100 (magnesia investment): 13 (distilled water) by weight and then invested in a mold frame with the untreated wax patterns. The invested molds were dried in air for 3.6 ks and baked at 1373 K for 3.6 ks (Fig. 2(b)).

2.4 Casting

Casting of the TNTZ was carried out using an argon pressure-type dental precision casting machine. The TNTZ disks were melted for 50 s (15 s for the plate-type wax pattern) under10:2106Pa by a 300-A mono arc and then cast under 0.7 MPa argon pressure using the calcia and the magnesia molds as described above.

2.5 Evaluation of surface roughness

The surface roughness of slurry A (first-coating layer), the magnesia mold, and the dog-bone-type cast TNTZ were evaluated using a surface roughness meter. Slurry A and the magnesia investment were placed on a slide glass and baked in the manner described above. After baking, the surface roughness of the mold contacting the slide glass was measured.

2.6 Evaluation of dimensional accuracy

The square-type cast TNTZ was used to evaluate the dimensional accuracy of the cast TNTZ. The length between

(a)

15

15 _1.5

R6

55 18 14

(b)

15

15 15

(c)

30

30

13

(d)

0.5

R = 1.7

(mm)

φ 3.0

φ 6.0

Sprue runn er

Sprue runner Sprue runner

Fig. 1 Schematic drawings of a square-type wax pattern with markers for the evaluation of the dimensional accuracy of the casting (a), dog-bone-type wax pattern for the evaluation of microstructure and hardness distribution of the casting (b), cubic-type wax pattern for the evaluation of the phase constitution of casting using an X-ray diffractometry (XRD) (c), and plate-type wax pattern for the evaluation of the wettability of the molten metal with the mold (d).

Table 1 Chemical compositions of electrically fused calcia (a) and magnesia-based investment (b).

(a) Electrically fused calsia (mass%)

MgO SiO2 Al2O3 Fe2O3 CaO

0.67 0.43 0.02 0.02 bal.

(b) Magnesia-based investment (mass%)

SiO2 Na2O Fe2O3 Al2O3 MgO

the markers on the square-type cast TNTZ was measured using digital microscopy. In addition, the dimensional accuracy of the mold was also evaluated. The mold was cut after baking, and the length between the transcribed markers in the mold was measured. The dilation ratio of the cast TNTZ and the mold, Dcast and Dmold, respectively, was

calculated by the following equations:

Dcast¼100 ðl1l0Þ=l0 ð1Þ

Dmold¼100 ðl2l0Þ=l0 ð2Þ

where l1, l2, and l0 are the length between the markers of

the cast TNTZ, the length between the markers of the mold, and the length between the markers of the wax pattern, respectively.

2.7 Evaluation of microstructure and hardness distri-bution of cast TNTZ

Cast TNTZ disks were mechanically cut from the gauge part of the dog-bone-type cast TNTZ. The cast TNTZ disks were polished with 320–1500 grid SiC paper in water followed by buffering with 0.3-mmAl2O3and SiO2. Casting

defects, mainly shrinkage (infinite form) and pore (spherical shape and below 10mm), on the cast TNTZ disks were observed using an optical microscopy (OM) and a scanning electron microscopy (SEM), and the volume fraction of the casting defects was calculated.

The cast TNTZ disks were etched in a 5%HF solution, and the microstructure of the cast TNTZ disks was observed using an OM.

The Vickers hardness (Hv) of the cast TNTZ disks was measured using a Vickers hardness tester in air at room temperature under a constant loading condition (load: 1.96 N, holding time 15 s). The Vickers hardness was measured from the surface to the inside (425mm) at intervals of 25mmin a zigzag manner.

The element profile of the cast TNTZ was measured. A cross section of the cast cubic-type TNTZ was polished with 320–1500 grid SiC paper in water followed by buffering with 0.3-mm Al2O3 and SiO2. The element profiles of the cross

section of the cubic-type cast TNTZ were measured using an energy dispersive X-ray fluorescence spectrometer (EDX). In addition, the phases of the cross section of the cubic-type

cast TNTZ were identified using an XRD. Cu-Kradiation with an accelerating voltage of 40 kV and a current of 30 mA was used.

2.8 Evaluation of wettability of mold

The wettability of the mold was evaluated using a mold fabricated with the plate-type wax pattern. After casting TNTZ into the center of the mold, the contact angle was measured.

3. Results and Discussion

3.1 Appearance of mold and cast TNTZ

The appearances and cross section of the calcia and the magnesia molds (hereafter the calcia and magnesia molds will be called moldcalcia and moldmagnesia, respectively) are

shown in Fig. 3. The surface roughness of the moldcalciaarea

where the mold contacted the molten TNTZ was 1.98mm, and a smooth surface could be obtained. The surface roughness of the moldmagnesia was 1.04mm. The surface

roughness of the mold depends on the particle size. In this case, the size of the calcia and the magnesia particles was

<300mmand<200mm, respectively. Therefore, the surface roughness of the moldcasia was higher than that of the

moldmagnesia.

The appearances of the typical dog-bone-type cast TNTZ fabricated using the moldcalciaand moldmagnesia(hereafter the

TNTZ cast using the moldcalciaand moldmagnesiawill be called

TNTZcalcia and TNTZmagnesia, respectively) is shown in

Fig. 4. The TNTZcalcia was easily separated from the

moldcalcia by hammering and had metallic luster without

penetration. Because a smooth surface of the TNTZcalcia

without a thick burned sticky layer was obtained after hammering, surface treatment by sand blasting was not required. On the other hand, a burned sticky layer was formed on the TNTZmagnesia after hammering, requiring surface

treatment of the TNTZmagnesiaby sand blasting. The surface

of the TNTZmagnesia is black and did not have any metallic

luster, in contrast to the TNTZcalcia. The surface roughness

of the TNTZcalcia and TNTZmagnesia was 127.82 nm and

692.08 nm, respectively. In general, the surface roughness of the cast TNTZ depends on the surface roughness of the mold.

Room 13.8 × 10-3 K/s

28.3 × 10-3_K/s

8.3 × 10-3_K/s

353K, 14.4ks

1373K, 3.6ks

Furnace cooling

Casting at 473K

8.3 × 10-2_K/s

1373K, 3.6ks

Furnace cooling

(a) (b)

Room temperature

323K, 14.4ks Casting at 473K

temperature

While the surface roughness of the moldcalcia was higher

than that of the moldmagnesia, the surface roughness of the

TNTZcalcia was low relative to that of the TNTZmagnesia.

Burned sticky layer was formed on the surface of the TNTZmagnesiaduring the casting and the surface roughness of

the TNTZmagnesiaincreased. On the other hand, surface of the

TNTZcalciawas smooth without a thick burned sticky layer.

Therefore, the surface roughness of TNTZcalcia was lower

than that of the TNTZmagnesia.

3.2 Dimensional accuracy of mold and cast TNTZ

Figure 5 shows the change in the dilation ratios of the moldcalcia and the TNTZcalcia as a function of number of

zirconium particles with those of moldmagnesia. The dilation

<

Mold

calcia

>

10 mm 10 mm

10 mm 10 mm

<

Mold

magnesia

>

Fig. 3 Appearances and cross sections of the moldcalciaand moldmagnesia.

10mm

10mm 10mm

As-hammered

As-hammered

<Mold

>

<Mold

>

As-blasted

Fig. 4 Appearances of the dog-bone-type TNTZcalciaand TNTZmagnesia.

TNTZ_calcia

Moldcalcia

10 15 20

4 6

Amount of zirconium powder, mass%

Dilation ratio of mold and casting (%) _-6

-4 -2 0 2

0

Dilation ratio of magnesia mold

5

Fig. 5 Changes in dilation ratios of the moldcalcia and TNTZcalcia as a

ratio of the moldcalcia and the TNTZcalcia increases with

increasing the amount of zirconium particles. The dilation ratio of the moldmagnesiais 0.2 mass%; in order to obtain the

same dilation ratio, a 5 mass% zirconium addition to the moldcalcia is required. Furthermore, in order to obtain the

same size of the TNTZcalcia and the wax pattern, 12 mass%

zirconium particles must also be added to the moldcalcia.

Therefore, the moldcalcia with 12 mass% zirconium particles

was used for TNTZ casting in the following experiment.

3.3 Microstructure of cast TNTZ

Figure 6 shows optical micrographs of the cross sections of the dog-bone-type TNTZcalciaand TNTZmagnesia. Although

a surface reaction layer is observed on the surface of both the TNTZcalcia and TNTZmagnesia, the thickness of the surface

reaction layer of the TNTZcalcia is thinner than that of the

TNTZmagnesia, as described in detail below. A dendritic

structure is observed on the surface of both the TNTZcalcia

and TNTZmagnesia.

SEM photographs of representative casting defects on cross sections of the dog-bone-type TNTZcalcia and

TNTZmagnesia are shown in Fig. 7. Casting defects mainly

include shrinkage and the occurrence of pores. Figure 8 shows the volume fraction of the casting defects on the cross sections of the dog-bone-type TNTZcalciaand TNTZmagnesia.

The volume fraction of the casting defects on the TNTZcalcia

is 3%, while the volume fraction of the casting defects on the TNTZmagnesiais 6%. Therefore, the casting defects on the

cast TNTZ could be inhibited when the moldcalcia, rather

than the moldmagnesia, was used for casting. Figure 9 shows

the distribution of casting defects on the cross sections of the dog-bone-type TNTZcalciaand TNTZmagnesia. The number of

casting defects on the TNTZcalciais smaller than that on the

TNTZmagnesia. The maximum diameter of the shrinkage on

the TNTZcalciawas 20mm, while that of the shrinkage on the

TNTZmagnesia was almost 50mm. The appearance of the

sprue of the dog-bone-type TNTZcalciaand the TNTZmagnesia

is shown in Fig. 10. The sprue of the TNTZcalcia is convex

<

TNTZ

magnesia

>

Surface

reaction layer

100 µm

50 µm

50 µm

Surface

reaction layer

<

TNTZ

calcia

>

100 µm

Fig. 6 Optical micrographs of the cross sections of the dog-bone-type TNTZcalciaand TNTZmagnesia.

10 µm

Shrinkage

(a) TNTZ

calcia

10 µm

Shrinkage

(b) TNTZ

magnesia

upward against the casting direction, while that of the TNTZmagnesia is concave downward against the casting

direction. Therefore, the wettability between the molten TNTZ and the moldcalciais considered to be lower than that

between the molten TNTZ and the moldmagnesia. Figure 11

shows the appearance of the plate-type moldcalcia and

moldmagnesia after casting in order to assess the wettability

of the moldcalcia and the moldmagnesia. The TNTZmagnesia

spreads on the moldmagnesia better than the TNTZcalcia

spreads on the moldcalcia. In addition, the contact angles

of the moldcalcia and the moldmagnesia are 170 and 120,

(b) TNTZ

0

1

2

3

4

5

6

7

Volume fraction of casting defect (%)

(a) TNTZ_{calcia magnesia}

Fig. 8 Volume fractions of the casting defects on the cross sections of the dog-bone-type TNTZcalcia(a) and TNTZmagnesia(b).

10

~₂₀ 20~₃₀ 30~₄₀ 40~₅₀ 50~₆₀ Pore

0 50 100 150 650 700 750 800 850

Shrinkage

(a) TNTZ_calcia

Number of casting def

ects

0 0 0 0

Diameter of casting defects / µm

0_~ 10

0 50 100 150 650 700 750 800 850

Shrinkage

Pore

(b) TNTZ_magnesia

Diameter of casting defects / µm

Number of casting def

ects

8

10

~₂₀ 20~₃₀ 30~₄₀ 40~₅₀ 50~₆₀ 0

0_~ 10

Fig. 9 Distributions of casting defects on the cross sections of the dog-bone-type TNTZcalcia(a) and TNTZmagnesia(b).

(a) TNTZ

10mm

(b) TNTZ

10mm

Fig. 10 Appearances of the sprues of the dog-bone-type TNTZcalcia(a) and

the TNTZmagnesia(b).

(a) Moldc

(b) Mold

Fig. 11 Appearances of the TNTZcalcia(a) and TNTZmagnesia(b) cast using

the plate-type moldcalciaand moldmagnesia, and the cross sections of their

respectively. Therefore, the wettability of the moldcalcia

against the molten TNTZ is lower than that of the moldmagnesia. As a cause of the decrease in the casting

defect of the TNTZcalcia, effect of capillarity pressure may be

considered. Capillarity pressure, which is attributed to the wettability of the interface between the molten TNTZ and the mold, is believed to generate while casting. Because of the generation of capillarity pressure, the molten TNTZ is subjected to pressure from the surface toward the inside of the cast TNTZ. In general, increasing the pressure decreases the cast defect. Because of the low wettablity of the moldcalcia, the capillarity pressure of the moldcalcia may be

greater than that of the moldmagnesia. Then, the greater

pressure generates between the moldcalcia and the molten

TNTZ, as a result, inhibit the occurrence of shrinkage more significantly than the pressure of the moldmagnesia does.

Therefore, the moldcalcia may decrease the amount and

diameter of shrinkage more than the moldmagnesia does.

However, in the case of the moldcalcia, the wettablity of the

moldcalcia is lower than that of the moldmagnesia. Therefore

thermal conductivity for moldcalciamay be lower than that of

moldmagnesia, and the cooling rate of TNTZcalcia may be low

compared with that in the case of moldmagnesia. In general,

slow cooling rate increases casting defects. Therefore, in the case of the moldcalcia, increasing of capillarity pressure may

be more effective rather than that of decreasing cooling ratio. However quantitative analyses are required to confirm above consideration.

3.4 Evaluation of surface reaction layer of cast TNTZ

Figure 12 shows the Vickers hardness distribution of the cross section of the dog-bone-type TNTZcalciaas a function of

the distance from the surface of specimens. A greater hardness is found near the specimen surface of the TNTZcalcia

and TNTZmagnesia. However, the hardness near the surface of

the TNTZcalcia (Hv300) is much lower than that of the

TNTZmagnesia(Hv600). The thickness of the hardening layer

of the TNTZ calcia was estimated at 150mm, while that of the TNTZmagnesiawas estimated at 275mm.

Figure 13 shows XRD patterns of the surface of the cubic-type TNTZcalcia and TNTZmagnesia. Only single phases are

detected from the surface of both the TNTZcalcia and

TNTZmagnesia.

SEM micrographs of the cross section of the cubic-type TNTZcalciaand the TNTZmagnesia, and Ti, Nb, Ta, Zr and O

profiles along the line detected using EDX are shown in Fig. 14. Ti, Nb, Ta and O are detected near the surfaces of both the TNTZcalcia and TNTZmagnesia. The intensity of O

is the highest at the surface and decreased to the inside until 20–50mm on the surface of both the TNTZcalcia and

TNTZmagnesia. On the other hand, the intensity of Ti, Nb, and

Ta is the lowest at the surface and increased to the inside until 20–50mm. Therefore, the O-graduated layer existed near the surface of TNTZcalcia and the TNTZmagnesia. In

addition, the O-graduated layer of the TNTZmagnesia is

thicker than that of the TNTZcalcia. It is considered that

oxide particles of the mold are reduced and generates the oxygen when oxide particles contact the molten TNTZ, and

200 300 400 500 600

0 100 200 300 400

Vickers hardness (Hv)

Distance from surface (µm)

TNTZcalcia

TNTZmagnesia

Matrix

Fig. 12 Vickers hardness distribution of the cross section of the dog-bone-type TNTZcalciaas a function of the distance from the surface of specimens

along with that of the dog-bone-type TNTZmagnesia.

2θ / θ

Intensity / cps

30 40 50 60 70 80

: β

(a) TNTZ_calcia

(b) TNTZ_magensia

(110)

(200) (211)

Fig. 13 XRD patterns of the surfaces of the cubic-type TNTZcalcia(a) and

TNTZmagnesia(b).

(b) TNTZ

100

µ

m

Detected Line

100 µm

Ti

O

Ti

O

(a) TNTZ

Nb

Ta

Zr

Nb

Ta

Zr

Detected Line

Fig. 14 SEM micrographs of the cross section of the cubic-type TNTZcalcia

(a) and TNTZmagnesia (b) and Ti, Nb, Ta, Zr, and O profiles along the

generated oxygen is soluted and diffused into the cast TNTZ. The O-graduated layer is then formed on the surface of the cast TNTZ. The free energy of the formation of calcia particles is lower than that of titanium oxide (titania) at the TNTZ melting point (around 2350 K).15) _{Therefore, calcia}

particles are stable during casting. On the other hand, the free energy of the formation of magnesia particles is higher than that of titanium oxide above 1700 K. Since magnesia particles are more unstable than titania ones, magnesia particles are reduced and generated oxygen. Because the oxygen generated from the moldmagnesia exceeds that

generated from the moldcalcia, much of the oxygen diffuses

into the TNTZmagnesia, and a thick O-graduated layer is

formed on the TNTZmagnesia. On the other hand, the

formation of the O-graduated layer is dramatically inhibited using the moldcalcia. Therefore, the hardness of the surface of

the TNTZmagnesiais greater than that of the TNTZcalcia. This

O-graduated layer having high degree of hardness is so called -case.16) _{In general, the -type Ti alloy becomes}

harder and more brittle by soluting the oxygen, and the mechanical properties, such as tensile properties and fatigue properties, of -type Ti alloy decrease. The formation of

-case has to be inhibited on the surface of cast TNTZ to improve its high degree of mechanical properties. The inhibition of -case on the surface of the cast TNTZ is achieved using the moldcalcia.

4. Conclusions

The dimensional accuracy of cast TNTZ using a calcia mold for biomedical applications was mainly evaluated in this study. It could be concluded as follows,

(1) The dilation ratio of the moldcalcia increases with an

increasing the number of pure zirconium particles. Moreover, the addition of 12 mass% or 14 mass% pure zirconium particles compensates not only for the solidification shrink-age of the TNTZcalcia but also for the shrinkage of the

moldcalcia.

(2) The formation of the-case in TNTZ is restrained to a larger extent by casting into the moldcalcia than into the

moldmagnesia.

(3) The volume fraction and number of casting defects are also restrained to a larger extent by casting into the moldcalcia

than into the moldmagnesia.

Acknowledgements

This work was supported in part by a Grant-in-Aid for Young Scientists (21760549), MEXT (Tokyo, Japan); the Global COE Materials Integration Program (International Center of Education and Research), Tohoku University; MEXT (Tokyo, Japan); R&D Institute of Metals and Composites for Future Industries (Tokyo, Japan); Inter-university Cooperative Research Program of the Advanced Research Center of Metallic Glasses, Institute for Materials Research, Tohoku University (Sendai, Japan); Interuniversity Cooperative Research Program of the Institute for Materials Research, Tohoku University (Sendai, Japan); the Light Metal Educational Foundation (Osaka, Japan); and the project between Tohoku University and Kyusyu University on ‘‘Highly-functional Interface Science: Innovation of Biomaterials with Highly functional Interface to Host and Parasite’’, MEXT (Tokyo, Japan).

REFERENCES

1) K. Ida and I. Miura:Application of Titanium for Denture Field, (1998) pp. 11–14.

2) Y. Okazaki, A. Ito, T. Tateishi and Y. Ito: J. Japan Inst. Metals57

(1993) 332–337.

3) T. Hanwa: J. Jpn. Soc. Biomat.23(2005) 83–90.

4) M. Niinomi, T. Hattori, K. Morikawa, T. Kasuga, A. Suzuki, H. Fukui and S. Niwa: Mater. Trans.43(2002) 2970–2977.

5) M. Niinomi: Biomaterials24(2003) 2673–2683.

6) Y. L. Hao, M. Niinomi, D. Kuroda, K. Fukunaga, R. Yang and A. Suzuki: Metall. Mater. Trans. A34(2003) 1007.

7) S. J. Li, M. Niinomi, T. Akahori, T. Kasuga, R. Yang and Y. L. Hao: Biomaterials25(2004) 3341–3349.

8) M. Niinomi, T. Akahori, T. Manabe, T. Takeuchi, S. Katsura, H. Fukui and A. Suzuki: Testu-to-Hagane90(2004) 154.

9) S. Motoi: Sekko to Sekkai154(1978) 123–127. 10) K. Hamano: Sekko to Sekkai157(1978) 244–253.

11) A. Sato, N. Matsumoto, Y. Yoneda, T. Takahashi and H. Iwanabe: Imono14(1990) 244–253.

12) M. G. Kim, S. K. Kim and Y. J. Kim: Mater. Trans.43(2002) 745– 750.

13) Y. Tamaoki and T. Miyazaki: Prosthodont. Res. Pract. 42 (1998) 528–534.

14) H. Tsutsumi, M. Niinomi, T. Akahori, M. Nakai, T. Takeuchi and S. Katsura: Mater. Trans.50(2009) 2057–2063.

15) F. Nishimura and N. Sunao: J. Stomatol. Soc.56(1989) 1–16. 16) O. Miyagawa and N. Siokawa: Quintessence of Dental Technology16