dental materials journal 9 (1): 91-99, 1990 91 strength

Dental Materials Journal 9 (1): 91-99, 1990 91

Oxidation Effects on Porcelain-Titanium Interface Reactions and Bond

Strength

Hiroshi KIMURA*, Chuen-Jeng HORNG**, Masayuki OKAZAKI* and Junzo TAKAHASHI**Department of Dental Technology, Osaka University, Faculty of Dentistry, 1-8 Yamadaoka, Suita, Osaka 565, Japan

**School of Dentistry, Kaohsiung Medical College, Kaohsiung, Taiwan, R.O.C.

Recived on February 1, 1990Accepted on April 13, 1990

Titanium is strong, resists corrosion and has a low density and excellent biocompatibility. Conventional

ceramic-metal restorations have been extensively used in dentistry because of their esthetic appearance and

good mechanical properties. This study investigates oxidation effects on the porcelain-titanium interface

reactions and bond strength. Pure titanium was treated in a porcelain furnace at temperatures of 600 to

1000•Ž under either vacuum or air. X-ray diffraction analysis of the surface of pure titanium revealed that

the relative peak intensity of ƒ¿-Ti decreased and that of TiO2 increased, with increasing firing temperature.

The Vickers hardness number of titanium increased with temperature especially over 900•Ž, and was harder

in air than in vacuum. The tension-shear bond strength of the porcelain-titanium system was the highest in

the green stage and lowest after 900•Ž treatment. Metallographic microscopy of the porcelain-titanium

interface revealed a thick band-like zone in the sample treated over 900•Ž. The excess thick layer of TiO2

apparently weakened the bond strength of porcelain-titanium. Unlike the conventional ceramic-gold alloy

system the recommended degassing procedure was not suitable for porcelain-pure titanium restoration.

Key words: Dental porcelain, Titanium, Titanium oxide

INTRODUCTION

Alloys currently used as substrates for fused porcelain can be classified as noble and base

metal systems. Recently, noble alloys have been gradually replaced by base metal alloys due

to the high cost and low sag-resistance of the former. Although base metal alloys have many

superior mechanical properties, most have disadvantages such as poor biocompatibility, low

tarnish and corrosion resistance, poor bond strength and discoloration of porcelain1,2). Alloys

in which the main constituent is titanium have several advantages, such as low weight,

adequate strength, good corrosion resistance, excellent biocompatibility, ease of availability

and reasonable price3). However its weak points are a high melting point and high chemical

reactivity with oxygen at high temperatures4). In the literature, elimination of impurities

from metal frameworks and bringing an oxide layer to the surface are among recognized

functions of degassing. Generally speaking, oxide layers formed during degassing act as a

bond link between the metal and porcelain. The purposes of this study were to investigate

the influence of various heat treatments on the porcelain-titanium interface reactions and

bond strength.

92 H. KIMURA, C. HORNG, M. OKAZAKI and J. TAKAHASHI

MATERIALS AND METHODS

Preparation of heat-treated specimens

The composition of the titanium* produced by processing which was used in this study

is listed in Table 1. Heat treatments were carried out in a programmable porcelain

furnace** at temperatures ranging from 600 to 1000•Ž, with either vacuum or air. The

schedules of heat treatments are listed in Fig. 1 and Table 2.

X-ray diffraction analysis

Eleven 20•~18•~1mm3 pure titanium specimens were prepared. The heat treatments

were carried out at temperatures of 600, 700, 800, 900 and 1000•Ž, under vacuum and air,

respectively. Identification of oxides formed on the metal surface was conducted with an X

-ray diffractometer# with CuK ƒ¿ radiation . Experimental conditions were 35kV, 23mA, scan

Table 1 Compositions of pure titanium (%)

Fig. 1 The running program of the furnace** .

B: stand-by temperature (•Ž)

S: closing time (sec)

Rt: raising temperature (•Ž)

Ti: initial temperature (•Ž)

Tf: final temperature (•Ž)

Vs: vacuum, 74cm/Hg, start (•Ž)

Ve: vacuum, 74cm/Hg, end (•Ž)

Ht: holding time (sec)

L: long term cooling (min)

*KS -50; Kobe Steel Co. Ltd., Tokyo, Japan**Programat P90; Ivoclar Co. Ltd., Lichtenstein#D-3F; Rigaku Denki Co. Ltd., Tokyo, Japan

OXIDE LAYER AT CERAMOTITANIUM INTERFACE 93

Table 2 Programs of heat treatment of pure titanium

unit: the same as Fig. 1.

Table 3 Firing schedule of tested porcelain

unit: the same as Fig. 1.

range of 2ƒÆ (60•‹-4•‹) and scan rate of 1/32•‹/min. Phase identification and estimation6) were

carried out by matching each characteristic peak with the JCPDS file7).

Microhardness measurement

Speciments used for microhardness analysis were the same as for X-ray diffraction

analysis. Vickers hardness numbers were determined using the microhardness test machine

at a load of 500g and a holding time of 5 seconds, five times for each set of conditions. After

surface measurement, the hardness of titanium specimens sectioned along the central axis

was determined.

Tension-shear bond strength measurement

Bond strength was measured by a tension-shear test, similar to that used by Wight, et

al8). The specimens were sized to 26•~7•~1mm3 and the porcelain bonding interface was 7•~

7mm2. Heat treatments were carried out at temperatures of 600, 700, 800 and 900•Ž under

vacuum. Five specimens were used for each condition. One type of low fusing porcelain* was

fused to the bonding interface, with a thickness of 0.5mm opaque and 1.5mm dentin-enamel,

according to a similar firing schedule to that of Tanaka9) in Table 3. The test specimens

consisted of a uniform thickness of porcelain placed between two parallel titanium plates.

The bond strength was measured in a universal testing machine** with a crosshead speed of

0.1cm/min.

Micro structure evaluation

##MVK-C; Akashi Co . Ltd., Tokyo, Japan*Titan Bond; Ohara Co . Ltd., Osaka, Japan

**Instron; Instron Co . Ltd., Mass., U.S.A.


The interface structures of these specimens were observed under a metallographic

microscope#. Further study was performed by an X-ray energy microanalyzer## at 15kV,

0.1nA and 30•‹ inclination.

(A) (B)Fig. 2 X-ray diffraction patterns of pure titanium after heat treatment in (A) vacuum

and (B) air.

#PME; Olympus Co . Ltd., Tokyo, Japan##EMAX-3700; Horiba Co . Ltd., Kyoto, Japan


RESULTS

The results from X-ray diffraction analysis of titanium treated at various temperatures

in vacuum and air are shown in Fig. 2. Both patterns showed mainly single phase ƒ¿-Ti at

the initial stage. The relative intensities of ƒ¿-Ti decreased slightly and TiO2 was gradually

identified when temperatures increased between 700 and 800•Ž. The intensities of ƒ¿-Ti were

very low while the intensities of TiO2 increased remarkably when the temperature rose over

900•Ž. No great differences were found between the relative intensities of vacuum and air

treated samples.

Results of the Vickers hardness of heat treated samples are shown in Fig. 3 . Hardness

Fig. 3 Heat treatment effects on the Vickers hardness number of pure titanium . V: under vacuum A: in air

Fig. 4 Vickers hardness number of pure titanium in various areas.


increased when the temperature increased, especially over 900•Ž. Higher values were

obtained with heat treatment under air. The peak hardness value was at the outer surface

layer, followed by the inner surface and then the middle portion. (Fig. 4)

Mean values of the tension-shear bond strength of porcelain-titanium are shown in Fig.

5. Titanium at the green stage exhibited the highest bond strength while the lowest strength

Fig. 5 Heat treatment effects on the tension-shear bond strength of the porcelain-

titanium system.

Fig. 6 Porcelain-titanium interfaces after heat treatment:

(A) green stage, (B) 700•Ž, (C) 900•Ž,

(D) 1000•Ž. T: titanium O: opaque D: dentin

g.n.: globular nodule c.z.: coalesce zone

b.s.: band-like structure s.c.: small cleft


was found in the 900•Ž treated group. Most specimens showed adhesive failure at the

metal-metal oxide interface.

Metallographic microscopic examination of the ceramotitanium interface revealed small

globular nodules beginning to form sparsely on the green stage sample after porcelain firing

(Fig. 6-A). The nodules were even larger and had begun to coalesce at 700•Ž (Fig. 6-B).

The coalescent zone, detected as TiO2 by X-ray diffraction, gradually spread out at 800•Ž,

and finally became a uniform band-like structure at 900•Ž (Fig. 6-C). This zone was

well-defined and intact at 900•Ž but exhibited small clefts at 1000•Ž (Fig. 6-D). X-ray line

analysis revealed that Ti was low at the oxidation zone of interface (Fig. 7). Elemental

analysis showed the ceramotitanium interface contained Ti, O, Al and Sn.

DISCUSSION

Pure titanium usually consists of ƒ¿-Ti at low temperatures. Over 882•Ž it undergoes a

transformation from ƒ¿-Ti to ƒÀ-Ti. X-ray diffraction analysis revealed that the relative

intensity of ƒ¿-Ti decreased while TiO2 increased when the temperature was raised. The fact

that a higher oxidation temperature gave less bond strength was because more titanium

oxide was formed. Together with the results of X-ray diffraction and microscopic observa-

tion, a small amount of TiO2 formation seems to greatly affect the interfacial bond strength

of the porcelain-titanium system. The conventional porcelain-metal bond has been consid-

Fig. 7 X-ray energy microanalysis of the porcelain-titanium interface. (A) 700•Ž, (B)

1000•Ž, •«

: ceramotitanium interface T: titanium P: porcelain


ered a direct effect of adherent oxide formation at the interface10-12) but this phenomenon

was not seen in pure titanium. It should be pointed out that the conventional degassing

procedure10) was not suitable for the ceramic-pure titanium system.

Some authors8-10) have discovered that porcelain bond strength will increase significantly

when an opaque porcelain is fired 80•‹F to 100•‹F higher than the recommended temperature.

In this study we tried decreasing the manufacturer's recommended firing temperature for

tested porcelain by about 20•Ž and thus improved the bond strength of ceramo-titanium.

This may have been due to the lower temperature causing less TiO2 formation. Adherence

bond strength reported in dental literature still has not established a universally accepted

bond test13-16). The tension-shear bond test gives good results when testing two parallel metal

plates separated by a block of porcelain8), since bending stresses are not considered. In this

study all specimens displayed adhesive failure at the metal-metal oxide interface indicating

a problem of non-adherent oxide formation. These tests suggest a need to develop an optimal

technique or a suitable porcelain system for increasing bond strength. Metal to which

porcelain is fused should be as hard as possible to prevent firing deformation. As the results

of the Vickers hardness test showed, titanium increases in hardness after suitable heat

treatment, which contributes positively to ceramo-titanium systems. However, formation of

a band-like oxidation layer upon the titanium surface was usually noted with temperatures

over 900•Ž producing extra-hardness and dramatically decreasing the ceramotitanium bond

strength. In conclusion, a decrease in the oxidation of the titanium matrix can suppress the

formation of a weak oxidation zone, thus increasing the porcelain-titanium bond strength.

CONCLUSIONS

The effects of heat treatment on the porcelain-titanium interface reactions and bond

strength were investigated. From the results of this study, the following can be stated

(1) The X-ray diffraction analysis revealed the relative intensity of the ƒ¿-Ti decreased while

that of the TiO2 increased when heat treatment temperature was raised.

(2) The tension-shear bond strength of porcelain-pure titanium system was the highest in the

green stage group.

(3) The conventional degassing procedure was not suitable for the ceramo-pure titanium

system.

(4) All specimens displayed adhesive failure at the metal-metal oxide interface indicating a

problem of non-adherent oxide formation.

(5) Vickers hardness test showed that the titanium increased hardness after suitable heat

treatment.

(6) Formation of band-like oxidation layer upon titanium surface was predominantly noted

when the temperature rose over 900•Ž at which hardness increased remarkably and

ceramo-titanium bond strength decreased drastically.

REFERENCES

1) Ida, K., Tsutsumi, S. and Togaya, T.: Titanium or titanium alloys for dental casting, J Dent Res 59

special issue B: 985, 1980.


2) Menis, D.L., Moser, J.B. and Greener, E.H.: Experimental porcelain compositions for applicaiton to cast titanium, J Dent Res 65 special issue: 343, 1986.

3) Taira, M., Moser, J.B. and Greener, E.H.: Studies of Ti alloys for dental castings, Dent Mater 5 (1): 45-50, 1989.

4) Togaya, T., Suzuki, M., Tsutsumi, S. and Ida, K.: An application of pure titanium to the metal

porcelain system, Dent Mater J 2 (2): 210-219, 1983.5) McLean, J.W. and Moffa, J.P.: Readers, round table, J Prosthet Dent 31 (6): 691-694, 1974.6) Cullity, B.D.: Elements of X-ray diffraction, 2nd ed., Addison-Wesley Publishing Co., U.S.A., 1978,

pp. 1-80.7) Smith, J.V.: Powder diffraction file, ASTM Publicaiton Co., U.S.A., 1969.8) Wight, T.A., Bauman, J.C. and Pelleu, G.B.: An evaluation of four variables affecting bond strength

of porcelain to non-precious alloy, J Prosthet Dent 37 (5): 570-577, 1977.9) Tanaka, A.: Fabrication of bonded ceramic on pure titanium, Quint Dent Tech 13 (2): 195-202, 1988.

(in Japanese)10) Daftary, F. and Donovan, T.: Effect of four pretreatment techniques on porcelain-to-metal bond

strength, J Prosthet Dent 56 (5): 535-539, 1986.11) Anusavice, K.J., Horner, J.A. and Fairhurst, C.W.: Adherence controlling elements in ceramic-metal

systems. I. Precious alloys, J Dent Res 56 (9): 1045-1052, 1977.12) Dent, R.J., Preston, J.D., Moffa, J.P. and Caputo, A.: Effect of oxidation on ceramometal bond

strength, J Prosthet Dent 47 (1): 59-62, 1982.13) Anthony, D., Burnett, A.P., Smith, D.L. and Brooks, M.S.: Shear test for measuring bonding in cast

gold alloy-porcelain composite, J Dent Res 49 (1): 27-33, 1970.14) Kelly, M., Asgar, K. and O'Brien, W.J.: Tensile strength determination of the interface between

porcelain fused to gold, J Biomed Mater Res 3 (4): 403-406, 1969.15) Moffa, J., Lugassy, A.A., Gucker, A.D. and Gettleman, L.: An evaluation of non-precious alloys for

use with porcelain veneers, Part I. Physical properties, J Prosthet Dent 30 (4): 424-431, 1973.16) Tuccillo, J.J. and Nielsen, J.P.: Shear stress measurements at a dental porcelain-gold bond interface,

J Dent Res 51 (2): 626-633, 1971.

124

ポーセレンーチタン界面への酸化の影響

木村博,洪純正,岡崎正之,高橋純造

大阪大学歯学部歯科理工学教室

チタンは耐食性が良く,軽量で,高強度,しかも生体

親和性に優れている。一方,通常の金属焼付陶材による

修復物は審美性が良く,優れた機械的性質を有するため,

歯科界では広く使用されている。本研究では,ポーセレ

ンーチタンの接着強さおよび機械的性質に対する熱処理

の影響を調べるため,真空中と大気中で,600から1000℃

までの熱処理条件を変えて実験を行った。X線回折で

は,温度の上昇とともに,純チタン表面のα-Tiの相対的

ピ-ク強度が低下したが,TiO2のピークは逆に増加し

た。チタンのビッカース硬さは温度の上昇とともに増加

し,特に900℃ 以上の場合には硬さが急増した。熱処理

しなかったポーセレンーチタン接合部の引張-せん断強

さは最も高い値を示したのに対し,1000℃ で熱処理した

場合は最も低い値を示した。金属顕微鏡で観察した結果,

1000℃ で熱処理した場合の界面に最も厚い酸化層が観

察された。以上の結果,ポーセレンーチタンの接着強さ

はチタン酸化膜の増加により低下する傾向があるため,

通常の金合金焼付陶材使用時のディギャシングはポーセ

レンー純チタンの場合には適用できないことがわかっ

た。

dental materials journal 9 (1): 91-99, 1990 91 strength

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