Komiyama et al.

Int Chin J Dent 2008; 8: 17-20.

Improved wear resistance of indirect composite-titanium joint on
application of a metal priming system
Karin Komiyama, DDS,a Mahoko Murakami, DDS,a Motoko Nakazawa, DDS,aTomohisa Ogino, DDS,a Momoko Shimada, DDS, PhD,b Hideo Matsumura, DDS, PhD,cHiroyasu Koizumi, DDS, PhD,c and Naomi Tanoue, DDS, PhDdabcNihon University Graduate School of Dentistry, Private Practice, Green Dental Clinic, Department ofFixed Prosthodontics, and Division of Advanced Dental Treatment, Dental Research Center, NihondUniversity School of Dentistry, Tokyo, and Nagasaki University Hospital of Medicine and Dentistry,Nagasaki, Japan
Purpose: The aim of this study was to evaluate the effect of a metal priming system on the wear resistance ofcomposite-titanium interface.
Materials and Methods: Two different types of plate specimens were prepared: composite-titanium (Estenia
C&B and T-Alloy H) joint without primer, and composite-titanium joint bonded with a priming system (AlloyPrimer and Estenia Opaque Primer). Toothbrush wear test was performed using the plate specimens,toothbrushes (Bee King), and a dentifrice (Crest).
Results: Bonded specimens with priming exhibited less wear depth (3.5 µm) than the specimens joined without
priming (8.0 µm).
Conclusion: It can be concluded that the use of a metal priming system at the composite-titanium interface
effectively enhanced the wear resistance of the joined area under repeated brushing.
(Int Chin J Dent 2008; 8: 17-20.)
Key Words: composite, primer, titanium, toothbrush, wear.

Introduction
The use of indirect composites in fabrication of restorations and partial dentures has increased substantially.
This trend could be attributed to the improvement in the properties of materials.1-9 The incisal edge or buccal
cusp of composite-veneered restoration consists of an indirect composite material and a casting alloy.10 The
composite and casting should be adequately bonded in the joints to ensure long-term survival of the restorations.
One of the problems associated with veneered restorations is unpredictable wear of the facing materials as aresult of toothbrushing. Application of non-wear resistant materials on the facial surface or buccal cusp willcause loss of anatomic form of the restoration within a short period. Although wear of composite materials has
been evaluated extensively using either simulated occlusal contact wear or toothbrush abrasion,2-9 limited
information is available about the wear characteristics of the interface between casting alloys and tooth-coloredmaterials.2,9 This study evaluated the wear resistance to toothbrush-dentifrice abrasion of a composite-titanium
joint bonded with or without a metal priming system.

Materials and Methods
A light-activated composite system designed for indirect restorations and fixed partial dentures (Estenia C&B,Kuraray Medical Inc., Tokyo, Japan) was employed. The Estenia C&B composite consisted of approximately
8% urethane tetramethacrylate (UTMA) and another methacrylate monomer, and 92% inorganic filler. The E1and OA3 shades for incisal edges and opaque materials were used for specimen preparation. A high-purity
titanium (T-Alloy H, GC Corp., Tokyo, Japan) was selected for the framework. A two-step metal primingsystem (Alloy Primer and Estenia Opaque Primer, Kuraray Medical Inc.) was used to assess the interfacialintegrity of the alloy-composite joint. Information on the materials is summarized in Table 1.

17Komiyama et al.
Table 1.

Int Chin J Dent 2008; 8: 17-20.

Materials used.

Material / Trade name

Manufacturer

Lot number

Composition (mass%)

Casting alloy
T-Alloy H

GC Corp., Tokyo, Japan

070611199.2 Ti, 0.3 Fe	 

Indirect composite
Estenia C&B E1

Kuraray Medical Inc., Tokyo, Japan

0014AA

Estenia C&B OA3Kuraray Medical Inc.

0051AA

UTMA, Methacrylate, Photo initiator,Pigment, 92 filler (Glass, Alumina)
Bis-GMA, Photo initiator, Pigment,Filler

PrimerAlloy Primer
Estenia Opaque Primer

Kuraray Medical Inc.
Kuraray Medical Inc.

0202AA
00135B

MDP, VTD, Acetone
MDP, Monomer solvent

Polymerizing unit
α-Light II
KL-310J. Morita Corp., Suita, Japan
J. Morita Corp.

0040
9108

--------------------------Halogen lamp, 360 W×1, 400-600 nm
Heat oven

Toothbrush
Bee King

Bee Brand Medico Dental Co., Ltd., Osaka, Japan

Dentifrice
Crest Tartar Protection

The Procter & Gamble Co., Cincinnati, OH, USA

Regular Paste

UTMA, Urethane tetramethacrylate; MDP, 10-methacryloyloxydecyl dihydrogen phosphate; VTD, Triazine dithione monomer.

A total of 12 rectangular specimens (18.0x12.5x2.0 mm) were cast from the titanium and polished according
to the manufacturer’s specifications. The surface to be joined (18.0x2.0 mm) was air-abraded with 50-70-µm
alumina (Hi-Aluminas, Shofu Inc., Kyoto, Japan) for 15 s (Jet-Blast II, J. Morita Corp., Suita, Japan). The airpressure was 0.5 MPa, and the distance between the orifice and the titanium surface was approximately 20 mm.
Six specimens were primed with the Alloy Primer and Estenia Opaque Primer, whereas the remaining six
specimens were left unprimed.

A thin layer of opaque material was applied to the titanium surface andlight-exposed for 90 s with a polymerizing unit (α-Light II, J. Morita Corp.). The specimens were placed in asteel mold (18.0x25.0x2.0 mm), and the vacant space in the mold was filled with Estenia C&B composite paste.
The surface of the composite-titanium specimen was covered with a piece of glass plate (0.12-0.17 mm thick,Micro Cover Glass, Matsunami Glass, Osaka, Japan), and the specimen was placed in a polymerizing unit andirradiated for 5 minutes. After light exposure, the glass plate was removed. An oxygen barrier agent (AirBarrier, Kuraray Medical Inc.) was applied to the composite surface, and the specimen was polymerized at110°C in a heated oven (KL-310, J. Morita Corp.) for 15 minutes. All of the specimens were then wet-groundwith a series of silicon carbide (SiC) paper (up to 2,000 sheets, WetorDry Tri-M-ite, 3M Corp., St. Paul, MN,USA), followed by polishing with felt and alumina (0.3 µm, Baikalox 0.3CR, Baikowski International Corp.,
Charlotte, NC, USA). After polishing, the specimens were stored in distilled water at 37˚C for 14 days.
Each specimen was fixed on a specimen holder attached to a toothbrush abrasion-testing machine (K236,Tokyo-Giken Co., Ltd., Tokyo, Japan). A dentifrice with silica abrasives (Crest Tartar Protection Regular Paste,
RDA-Value 136, The Procter & Gamble Co., Cincinnati, OH, USA) was used as a slurry with a paste-water ratioof 1:1. The vessel of the machine was filled with 150 g of slurry. A nylon toothbrush (Bee King, Bee Brand
Medico Dental Co., Ltd., Osaka, Japan) was fixed in the brush holder of the machine, and moved over thespecimen at 140 strokes per minute. A load (3.4 N) was applied vertically to the top of the toothbrush holder
with a stainless steel weight. The specimens were abraded with a total of 20,000 reciprocal strokes. The
toothbrush and slurry were replaced before each specimen testing. Six specimens were tested for each condition.

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Komiyama et al.

Int Chin J Dent 2008; 8: 17-20.

After the abrasion testing, specimens were removed from the machine, ultrasonically cleaned in distilled waterfor 10 minutes, and air-dried.
The vertical loss in µ m of each specimen was determined with a confocal scanning laser microscope(1LM21W, Lasertec Corp., Yokohama, Japan). The distance from the original specimen surface to the deepest
point was defined as wear depth. Statistical analysis was carried out using SPSS software (Version 12.0.J for
Windows, SPSS Japan Inc., Tokyo, Japan). Average values, medians, and standard deviations for wear depth
were calculated from six replications. The result was analyzed with Mann-Whitney U test with the value ofstatistical significance set at p=0.05. Selected specimens after wear testing were sputtered with osmium andobserved with a scanning electron microscope (SEM; S-4300, Hitachi High-Technologies Co. Ltd., Tokyo,Japan) operated at 15 kV.

Results
Table 2 shows the wear depths of the abraded specimens. Average wear depth at the joint between the Estenia
C&B composite and titanium was 3.5 µm for the primed group and 8.0 µm for the unprimed group. Wear depthof the primed group was significantly smaller than that of the unprimed group (p<0.01). Figures 1 and 2 show
the scanning electron micrographs of the specimens after wear testing. The composite-titanium specimens
treated with the primer (Fig. 1) show a smoother surface as compared with the composite-titanium specimens
without priming (Fig. 2). Fracture and detachment of filler particles can be observed from the worn surface of
the unprimed group (Fig. 2).
Table 2.

Wear depths of abraded specimens.

Group

Wear (µm)

MeanMedianMinimum Maximum

SD

Primed

3.5

3.6

2.5

4.1

0.5

Unprimed

8.0

7.7

5.7

10.0

1.4

Z-valueP-value

-3.36

0.001

SD, Standard deviation. Significant difference was observed between primed and unprimed specimens (Mann-Whitney U test).

Fig. 1.

Electron micrograph of the surface of aprimed specimen after wearing.

Fig. 2.

Electron micrograph of the surface of an unprimed
specimen.

Discussion
This study evaluated the wear and integrity of the composite-titanium interface with and without adhesivetreatment. Wear testing results demonstrated that the metal priming system was effective in improving the19Komiyama et al.

Int Chin J Dent 2008; 8: 17-20.

interface integrity between the composite and titanium. As shown in Table 1, the composite-to-alloy bonded
group with the Estenia priming system exhibited less wear depth as compared with the unprimed group. Inaddition, scanning electron micrographs demonstrated typical microfractures along the interface of the unprimed
group. The disparity in integrity at the interface probably arose from the difference in fracture resistance
between the two groups to cycled loading from the toothbrush and dentifrice. Both the Alloy Primer and Estenia
Opaque Primer materials contain a hydrophobic phosphate monomer MDP (Table 1). Effectiveness of the MDP
monomer in bonding titanium or titanium alloy has been evaluated through bond strength tests in metal-to-metal
bonded specimens10,11 and composite-to-metal bonded specimens.12 It was therefore reasonable to consider thatthe bonding capability of MDP monomer in the Alloy Primer and Estenia Opaque Primer materials reduced
microfracturing of the Estenia C&B composite at the composite-titanium interface during wear testing. Ishii etal. recently reported that the VTD monomer contained in Alloy Primer was effective for bonding gold alloy andineffective for bonding titanium.11 Based on this report, the Estenia C&B composite could be bonded to titanium
without application of the Alloy Primer material, because the Estenia Opaque Primer material also contains
MDP monomer in its single liquid composition.
In conclusion, dental clinicians and laboratory technicians should take extra care when designing the structureof composite-veneered restorations and super-structures of implant-supported prostheses. The use of the Estenia
C&B Priming system is indispensable for the long-term survival of composite-titanium joints.
Acknowledgments
This work was supported in part by Special Research Grant for the Development of Distinctive Education from thePromotion and Mutual Aid Corporation for Private School of Japan (2005, 2006, and 2007), a grant from Dental ResearchCenter (2006) and Sato Fund (2007), Nihon University School of Dentistry, and a Grant-in-Aid for Scientific Research B
18390525 (2006-2007) from the Japan Society for the Promotion of Science (JSPS).

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Correspondence to:Dr. Hiroyasu Koizumi
Department of Fixed Prosthodontics, Nihon University School of Dentistry
1-8-13, Kanda-Surugadai, Chiyoda-ku, Tokyo, 101-8310, Japan
Fax: +81-3-3219-8351 E-mail: Koizumi@dent.nihon-u.ac.jp
Received January 15, 2008. Accepted April 19, 2008.
Copyright ©2008 by the International Chinese Journal of Dentistry.

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