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Int Chin J Dent 2004; 4: 8-14.

Effect of alumina abrasion for bonding between Ti-6Al-7Nb
alloy and an indirect composite
Hidenori Sugawara, DDS,a Hiroaki Yanagida, DDS, PhD,b Naomi Tanoue, DDS,
PhD,c Yoshikazu Koishi, DDS, PhD,d Kiyoshi Nagano, DT,a Mitsuru Atsuta, DDS,
PhD,a and Hideo Matsumura, DDS, PhDeaDivision of Fixed Prosthodontics and Oral Rehabilitation, Nagasaki University Graduate School ofbcBiomedical Sciences, Department of General Dentistry, and Department of Specialized Dentistry,dNagasaki University Hospital of Medicine and Dentistry, Nagasaki, Department of DentaleMaterials Science, Nihon University School of Dentistry at Matsudo, Matsudo, and Department ofCrown and Bridge Prosthodontics, Nihon University School of Dentistry, Tokyo, Japan
Purpose: The current study aimed to examine the influence of air-pressure and alumina grain size in
air-abrasion on bonding between an indirect prosthodontic composite material and a titanium alloy.
Materials and Methods: Disk specimens were cast from a titanium-aluminum-niobium alloy (Ti-6Al-7Nb,
T-Alloy Tough) and air-abraded with eight different air-pressures (0.00-0.40 MPa) and four different sizesof alumina particles (50-250 µm). The disks were bonded with a composite material (Estenia) and 24-hour
shear bond strengths were determined.
Results: Among the eight air-pressure conditions employed for abrading 50 µm alumina, the greatest bondstrengths (33.7-38.7 MPa) were recorded with air-pressures of 0.30, 0.35, and 0.40 MPa (p<0.05). Whenthe alloy was air-abraded with 0.35 MPa pressure using four different sized alumina, the group abradedwith 50 µm alumina showed the highest bond strength (38.7 MPa, p<0.05).
Conclusion: Within the study’s limitations, the use of 50 µm particle sized alumina in combination with the
air-pressure of 0.35 MPa is recommended for bonding the Estenia composite material to Ti-6Al-7Nb alloy.
(Int Chin J Dent 2004; 4: 8-14.)
Clinical Significance: Air-pressure and alumina grain size in air-borne particle abrasion influence thebonding characteristics between an indirect composite and a titanium alloy.
Key Words: air-abrasion, alumina, bonding, niobium, Ti-6Al-7Nb alloy, titanium.

Introduction
The development of laboratory techniques, along with mould materials and casting machines, has led totitanium and titanium alloys being used for cast restorations and denture frameworks. Although the
majority of titanium castings function successfully,1-3 several problems worthy of attention have beenreported.

One of these is the insufficiency of the mechanical properties of titanium to fabricate

long-spanned fixed partial dentures and removable denture frameworks.

Titanium alloys have beendeveloped as alternatives to titanium for improved mechanical properties in an oral environment. Amongthe titanium alloys reported for medical and dental use, a titanium-aluminum-niobium (Ti-6Al-7Nb) alloy
seems to be the most suitable for dental castings because of its improved mechanical properties andcorrosion resistance. The Ti-6Al-7Nb alloy, originally developed as an orthopaedic implant material,4 has
been evaluated as a dental material. It was concluded that its mechanical properties were comparable toand corrosion resistance was superior to a titanium-aluminum-vanadium (T-6Al-4V) alloy.5,6 Additionally,
the Ti-6Al-7Nb alloy was successfully cast in a magnesia-based mould material using a centrifugal casting
apparatus.5
Bonding between polymer materials and titanium has been improved considerably by use of silane7 or

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titanate8 couplers, and carboxylic or phosphoric acid derivatives,8-14 whereas surface modification
techniques were reported to be effective for bonding titanium and the Ti-6Al-4V alloy.15-21
Ti-6Al-7Nb alloy, both a phosphate monomer

22-24

and a surface modification technique

22

For thehave improved

bonding between the alloy casting and polymeric materials.
Prior to the bonding procedure, the priming and surface modification systems require air-abrasion ofalumina to mechanically clean the surfaces and to increase the surface bonding area. Therefore, with
Ti-6Al-7Nb, it is necessary to set up an appropriate condition for alumina air-abrasion. Although theeffects of alumina abrasion on bond strength have been reported for cobalt-chromium, nickel-chromium
and gold alloys as well as titanium,25-29 no information is available about the Ti-6Al-7Nb alloy. The
purpose of the current study was to evaluate the influence of different air-pressures and alumina grain sizes
for air-borne particle abrasion on the resulting bond strength between a Ti-6Al-7Nb alloy and an indirect
prosthodontic composite.

Materials and Methods
A titanium alloy containing 7.0% niobium and 6.0% aluminum (Ti-6Al-7Nb, T-Alloy Tough, GC Corp.,
Tokyo, Japan) designed for cast restorations and partial denture frameworks was selected for the substratematerial. Four alumina materials with different particle sizes (50 µm, Hi-Aluminas, Shofu Inc., Kyoto,
Japan; 90 µm, Aluminum Oxide, Danville Engineering, San Raman, CA, USA; 125 µm, WA100, Kulzer
Inc., Irvine, CA, USA; and 250 µm, W100, Kulzer Inc.) were used for air-abrasion.

An indirect

prosthodontic composite (Estenia, Kuraray Medical Inc., Tokyo, Japan) was employed as the veneering
agent. Details of the materials are summarized in Table 1.
A total of 88 disk specimens, 10 mm in diameter and 2.5 mm thick, were prepared using amagnesia-based investment material (Selevest CB, Selec, Osaka, Japan) and a centrifugal casting apparatus(Ticast Super R, Selec). All disks were sanded with 600-grit silicon-carbide abrasive paper and divided
into two groups.
Group 1. Air-abrasion with Different Air-pressures
Sixty-four disks were divided into eight sets of eight disks. Of these, seven groups were air-abraded withthe 50-µm alumina by means of an air-borne particle abrader for 15 s (CL-FSG94, Kulzer, Inc.) withdifferent air-pressures; 1) 0.10 MPa, 2) 0.15 MPa, 3) 0.20 MPa, 4) 0.25 MPa, 5) 0.30 MPa, 6) 0.35 MPa,and 7) 0.40 MPa. The distance of the orifice from the metal surface was approximately 20 mm. The
remaining group was used as the control without air-abrasion. The Estenia Opaque Primer (Kuraray
Medical Inc.) agent was applied to the metal surface with a sponge pallet. After surface preparation, apiece of double-coated tape with a circular hole 5 mm in diameter was positioned on each disk specimen to
define the bond area. Two thin layers of an opaque resin (Estenia Opaque, OA3; Kuraray Medical Inc.)
were applied to the primed area metal surface and each layer was separately light-exposed for 30 s in alaboratory light-polymerizing unit (Alpha light II; J. Morita Corp., Osaka, Japan). A brass ring (6 mm
inside diameter, 2 mm height and 1 mm wall thickness) was placed so as to surround the opaque resin. The

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Int Chin J Dent 2004; 4: 8-14.

ring was filled with the Estenia composite material (DA3), and light-polymerized with the unit for 30 s.
The specimens were heated in an oven (KL-310, Kuraray Medical Inc.) at 100˚C for 15 minutes. Eightspecimens for each surface preparation group were prepared.

Thirty minutes after preparation, thespecimens were immersed in 37˚C water for 24 hours before testing for bond strength.
Table 1. Details of casting alloy, alumina powder and indirect composite system assessed.
Material/Trade name

Manufacturer

Component

Casting alloy
T-Alloy ToughGC Corp., Tokyo, Japan86.5 Ti, 7.0 Nb, 6.0 Al, mass%

Alumina Powder
Hi-aluminas
Aluminum Oxide
WA100
W100

Shofu, Kyoto, Japan
Danville Engineering, San Raman, CA, USA
Kulzer Inc., Irvine, CA, USA
Kulzer Inc.

50 µm
90 µm
125 µm
250 µmIndirect composite system
Estenia

Kuraray Medical Inc., Tokyo, Japan

Opaque OA3
Dentin DA3
MDP and initiator in solvent

Estenia Opaque Primer

Kuraray Medical Inc.

MDP, 10-methacryloyloxydecyl dihydrogen phosphate.

Group 2. Air-abrasion with Different Particle-sized Alumina
Twenty-four disks were divided into three sets of eight. Each set was air-abraded with one of the threesizes of alumina particles (90, 125, and 250 µm) using the CL-FSG94 abrader for 15 s at 0.35 MPa
air-pressure, and then fabricated as described for Group 1.
Each specimen was embedded in an acrylic resin mould and seated in an ISO 11405 shear-testing jig.
Shear bond strengths were then determined with a mechanical testing machine (AGS-10kNG, Shimadzu
Corp., Kyoto, Japan) at a crosshead speed of 0.5 mm/minute. The average bond strength and the standard
deviation (SD) of eight replications were calculated for each condition. The results were analyzed byanalysis of variances (ANOVAs) and the post-hoc Duncan new multiple range test. The value of statisticalsignificance was set at 0.05.
The Ti-6Al-7Nb disk surfaces air-abraded with the four different particle sized alumina were observedwith a scanning electron microscope (SEM; S-3500N, Hitachi Corp., Tokyo, Japan) operated at 20 kV.

Results
Table 2 presents the ANOVA results. One-way ANOVAs run on the shear testing results showedstatistical significance for both air-pressure (Group 1, F=9.595, p=0.0001) and difference in particle size
(Group 2, F=13.493, p=0.0001). The bond strength results were therefore analyzed using a post-hoc
Duncan new multiple range test calculated at the 0.05 significance level.
Table 3 and Figs. 1-2 indicate the results of shear testing and statistically categorized groupings. Bond10

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Int Chin J Dent 2004; 4: 8-14.

strength of Group 1 air-abraded with 50 µm alumina varied from 17.6 to 38.7 MPa according to thedifferent air-pressures.

Duncan new multiple rang test divided the results of the Group 1 into fivegroupings; (a)-(e). The 0.30 MPa (grouping d, e), 0.35 MPa (grouping e), and 0.40 MPa (grouping d, e)groups were the greatest, followed by the 0.25 MPa (grouping c, d), 0.20 MPa (grouping b, c), and 0.15
MPa (grouping b, c, d) groups. The 0.10 MPa and no-abrasion groups resulted in the lowest bond strengths(grouping a).
Table 2. Analysis of variance (ANOVA) results.
SourceDegree of freedom

Sum of squares

Mean square

F-valueP-value

One-way ANOVA for the different air-pressure group
Air pressure
72643.223
Residual
56
2203.726

377.60339.3529.595

0.0001

One-way ANOVA for the different particle size group
Particle size
3
701.681
Residual
28
485.350233.89417.33413.4930.0001

Table 3. Shear bond strength results and statistically categorized groupings.
Air-pressure variation (Alumina particle size: 50 µm)
Mean (MPa) SD
Grouping *Alumina particle size variation (Air-pressure: 0.35 MPa)
Mean (MPa) SD
Grouping*

None
0.10 MPa0.15 MPa
0.20 MPa0.25 MPa0.30 MPa0.35 MPa
0.40 MPa

50 µm
90 µm
125 µm
250 µm

17.6
22.4
28.5
26.0
30.9
33.7
38.7
34.2

3.8
5.0
6.5
4.7
5.9
8.6
6.0
8.5

a
a
b, c, d
b, c
c, d
d, e
e
d, e

38.7
30.8
27.9
26.7

6.0
2.7
4.4
2.7

B
A
A
A

SD, Standard deviation; Grouping, Identical letters indicate that the values are not statistically different (p>0.05).

Bond strength of Group 2 abraded with 0.35 MPa air-pressure varied from 26.7 to 38.7 MPa according to
the different alumina particle sizes. Shear testing results of Group 2 showed that the greatest bond strength
was achieved through the use of 50 µm grain sized alumina (grouping B). The other three groups (90, 125,and 250 µm) showed statistically lower bond strength than the 50 µm group; the differences among thesethree groups were not statistically significant (grouping A).
Fig. 3 shows Ti-6Al-7Nb alloy surfaces after air-abrasion with four different particle sized alumina; thesurfaces of the specimens were observed to become rougher in accordance with their particle size.

Discussion
The current study compared the effects of different air-pressures and alumina grain sizes for air-borne
particle abrasion on bonding between a Ti-6Al-7Nb alloy and an indirect prosthodontic composite material.
Before application of a phosphate monomer contained metal conditioning agent, the substrate alloy surfaces

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Int Chin J Dent 2004; 4: 8-14.

were air-abraded with alumina to mechanically clean the surfaces and to increase the surface bonding area.
We did not use additional mechanical retention systems to evaluate the effect of air-abrasion of the
air-pressure and particle sized of alumina.
None
0.10 MPa0.15 MPa
0.20 MPa0.25 MPa0.30 MPa0.35 MPa
0.40 MPa0510

15 20 25 30 35 40
Shear Bond Strength (MPa)4550

Fig. 1. Shear testing results for different airpressure (50 µm grain sized alumina).

Fig. 2. Shear testing results for different grain
sized alumina (0.35 MPa air-pressure).

50 µm

90 µm

125 µm
250 µmFig. 3. Scanning electron micrographs of Ti-6Al-7Nb alloy after air-abrasion with alumina.
Shear testing of Group 1 air-abraded with 50 µm alumina revealed that the 0.30, 0.35 and 0.40 MPa
exhibited considerably greater bond strengths than the other air-pressures. The results reveal the necessityof air-abrasion before bonding procedures, and that the 0.30, 0.35 and 0.40 MPa air-pressures were suitable
for the Ti-6Al-7Nb alloy. In the Group 1 study, the air-pressure of 0.35 MPa recorded the highest bondstrength, and statistical grouping divided it into the statistically highest group (group e).

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In the group 2 study results, air-abrasion with different particle sized alumina, show that the 50 µm sizedalumina recorded greater bond strength than the other three particle sized alumina. Another study hasreported that the types of alloy and the particle size used for air-abrading influenced wettability.25 The
wettability of an alloy surface is an important factor for bonding between polymeric materials and metal;
better wetting with metal surface conditioner and resin materials affects the interlocking between the resin
and the metal surface. The importance of the wettability can be seen in the reported low bond strength ofthe direct relining material with the spatulation technique; the authors speculating that this was due to thehigh viscosity of the material in the resin-metal bonding procedure, as well as to insufficient interlocking
between the resin and the roughened metal surface.23 On the particle sizes of alumina, another study forhighly pure titanium reported that air-abrading with 250 µm sized alumina was effective for bonding;28
another report described that the use of a large particle size alumina seems to be advantageous in reducing
the weight of alumina remaining on the titanium surface, while increasing surface roughness.27 According
to SEM observations in the current study, the larger particle sized alumina also caused a rougher surface,and a surface air-abraded with the 50 µm particle showed a mossy appearance (Fig. 3). Nevertheless, theresults of wear resistance of the Ti-6Al-7Nb alloy evaluated here showed it to be significantly higher thanhighly pure titanium grades 2 and 3.30 The large size alumina might not therefore affect bonding of the
Ti-6Al-7Nb alloy. It was hypothesized that surfaces roughened with the 50 µm sized alumina were insuitable condition of wettability for a phosphate conditioner and a composite opaque resin, and recorded thehighest bond strengths.
Our shear testing results clearly demonstrated the effectiveness of air-abrasion for bonding titanium alloy.
A question concerning the bonding durability remains, and needs to be evaluated. On the basis of thecurrent study, we recommend the use of the combination of 0.35 MPa air-pressure with a 50 µm particle
sized alumina for air-abrading before bonding an indirect prosthetic composite material and a Ti-6Al-7Nb
alloy framework.

Conclusion
Within the limitations of the current experimental settings, the following conclusions can be drawn:
1.

The 24-hour bond strength between a Ti-6Al-7Nb alloy (T-Alloy Tough) and an indirect composite
material (Estenia) was improved by application of 50 µm alumina air-abrasion with air-pressure
ranging from 0.15 to 0.40 MPa.

2.

Statistically, the greatest bond strength was recorded using 0.30 to 0.40 MPa air-pressure conditions
in combination with the 50 µm alumina particles.

3.

When an identical air-pressure (0.35 MPa) was employed, the use of 50 µm alumina exhibited thegreatest bond strength.

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Reprint request to:
Dr. Naomi TanoueDepartment of Specialized Dentistry, Nagasaki University Hospital of Medicine and Dentistry
1-7-1, Sakamoto, Nagasaki 852-8588, Japan
Fax: +81-95-849-7689 E-mail: t-naomi@net.nagasaki-u.ac.jp
Received December 12, 2003. Revised December 30, 2003. Accepted January 2, 2004.
Copyright ©2004 by the Editorial Council of the International Chinese Journal of Dentistry.

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