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Bond strength of prosthetic composite to primed and silicoatedcast titanium
Kenneth S. Kurtz, DDS,a Ikuya Watanabe, DDS, PhD,b Chikahiro Ohkubo, DMD, PhD,cand David Silken, DDSda

International Program in Prosthodontics, New York University College of Dentistry, New York, NY,b
USA, Department of Biomaterials Science, Baylor College of Dentistry, Texas A&M University Systemc
Health Science Center, Dallas, TX, USA, Department of Removable Prosthodontics, TsurumidUniversity School of Dental Medicine, Yokohama, Japan, and New York Hospital Queens, Fresh
Meadows, NY, USA
Purpose: The aim of this study was to examine the hypothesis that the bond strength of a polymer-glass
composite to cast commercially pure titanium (CPTi) can be improved by treating the metal surface withadhesive metal primers or with heat-processed silicoating.
Materials and Methods: Cast commercially pure titanium disks were prepared and the cast surfaces were
air-abraded with 250 µm alumina. There was one control group and four test groups having forty specimens. A
second group of forty specimens was similarly prepared, and subjected to a thermal cycling regimen. Three
metal adhesive primers (Cesead II Opaque Primer, Metal Primer II, and Solidex) or silicoating (Siloc system)
were applied to treated titanium surfaces. Two layers of polymer glass composite (Artglass) opaque and 1-mm
thick increments each of dentin and enamel composite components were applied and separately lightpolymerized following manufacturer’s directions. All specimens were stored in 37ºC water for 24 hours. Halfof the specimens were thermal cycled in water (4 and 60ºC) for 20,000 cycles. Shear bond strength for bothgroups was measured using a universal testing machine at a crosshead speed of 0.5mm/minute. Results (n=8)
were statistically analyzed using ANOVA/Duncan’s test (α=0.05).
Results: Specimens treated with the Cesead II Opaque Primer showed significantly higher (p<0.05) shear bondstrength both with and without to thermal cycling with no significant decrease in values. The other metal
primers and silicoating exhibited lower shear bond strengths with and without thermal cycling.
Conclusion: The Cesead II Opaque Primer improved the bond strength and durability of Artglass to cast puretitanium metal discs. (Int Chin J Dent 2005; 5: 12-16.)
Clinical Significance: In vitro application of the MDP phosphate primer (Cesead II Opaque) demonstrated thehighest shear bond strength of a light-polymerized laboratory composite material (Artglass) to cast CP titanium
and strength values seemed to be unaffected by thermal cycling. For cast CP titanium prostheses, this type ofmetal primer may improve the durability of the bonded composite veneer-metal interface and may enhance theesthetic longevity of the fabricated prosthesis.
Key Words: bond strength, cast titanium, metal primer, resin composite, silicoating.

Introduction
The Artglass System, a light-polymerized laboratory composite, described by the manufacturer (Heraeus
Kulzer, Wehrheim, Germany) as “polymer-glass”, was developed as an alternative veneering material for cast
fixed and removable prostheses. The Artglass system can be used for many clinical applications including
Artglass bonded to metal for tooth or implant-supported prostheses and a variety of indirect restorations, such as
laminate veneers, inlays and onlays.1,2 The manufacturer claims that this system causes less wear of opposing
dentition. With its ability to be repaired intraorally, Artglass veneering resin combined with cast titanium
prostheses may offer clinical advantages equivalent to conventional cast prostheses veneered with feldspathic
porcelain. A little information is available regarding the bond strength of Artglass veneered to cast gold alloys3,4
or titanium3,5 and its alloy,6 the latter well-established as a biocompatible material in the oral environment.
Adhesive bonding promoters for metal surfaces have been increasingly used in clinical applications in aneffort to create stronger bonding between metal and resin. Numerous studies investigated the composite strength

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to treated metal surfaces.7-13 One of these methods is the Silicoater technique (Heraeus Kulzer),10-13 in which asilica layer is pyrolytically applied to a surface, then silane coupling agents are applied, to which resins willpolymerize. The manufacturer of the Silicoater technique developed several systems, including the conventional
Silicoater, Silicoater MD, and Kevloc systems. A recent Silicoater technique, the Siloc system, incorporates
refinements and simplifications of previous methods. Principally, the heating mechanism is more controlled thanin the Kevloc system.
Adhesive metal primers that can be simply applied to metal surfaces to enhance the bond strength of resins tometal have also been studied.14-20

Cesead Opaque Primer containing MDP (10-methacryloyloxydecryl

dihydrogen phosphate) was found to provide high bond strength of resin cements or resin composite to Co-Cr
alloys and pure titanium.15-19 Metal Primer II with MEPS (thiophosphate methacryloyloxyalkyl derivatives) was
reported to yield strong bond strength of resin cements to both noble and base metal alloys.17-20 Solidex(4-acryloyloxyethyl trimellitate, 4-AET) was widely used to condition base metal alloys.19
This study examined the hypothesis that the bond strength of a polymer-glass composite to cast commerciallypure titanium can be improved by using several adhesive bonding promoters and heat-processed silicoating.

Materials and Methods
Eighty plastic disk-shaped patterns (10 mm in diameter and 2.5 mm thick) were prepared for casting
commercially pure titanium (CP Ti). The disk patterns were invested in mold rings with a magnesia-based
investment material (Selevest CB, Selec Co., Osaka, Japan).

The burn-out procedure was accomplishedaccording to the manufacturer's instructions and the patterns were then cast with CP Ti (ASTM grade 2,
Titanium Industries, Dallas, TX, USA) using a centrifugal titanium casting machine (Ticast Super R, Selec Co.).
After casting, the disc surfaces were polished with SiC abrasive paper (No. 600). They were then uniformly
air-abraded with 250 µm-sized alumina (Al2O3) perpendicular to the surface from a distance of 10 mm at 300
kPa for 10 s with a single use reservoir of alumina followed by ultrasonic cleaning with ethyl alcohol. The
surfaces were then treated with the metal primers or silicoating. Unprimed disk specimens were prepared ascontrols. The primers used in this study were: a primer containing MDP (Cesead II Opaque Primer, Kuraray Co
Ltd, Kurashiki, Japan), a metal primer (Metal Primer II, GC Co Ltd, Tokyo, Japan) with MEPS monomer and a
metal photo primer (Solidex, Shofu, Kyoto, Japan) based on 4-AET. The silicoating system (Siloc, Heraeus
Kulzer) was also applied on the cast titanium surface for comparison with the primers. The silane bonding agent
applied to the silicoated surface was Siloc Bond, a proprietary silane coupling agent (3-methacryloxypropyl
trimethoxysilane).
After application of the primers and the Siloc system on the sandblasted surfaces, a piece of sticky tape with acircular hole 4.76 mm in diameter was set on the center of the cast disc surface to define the bonding area. Twolayers of Artglass opaque resin (Heraeus Kulzer) approximately 100 µm thick each were applied within the hole,and each layer light-polymerized for 90 s with a xenon stroboscopic unit (Uni XS, Kulzer). A Teflon matrix ring
(5 mm I.D., 1 mm height) was fixed to the sticky tape around the 4.76 mm diameter area of opaque resin. The
ring was filled with Artglass dentin resin and light polymerized for 180 s. The Teflon matrix ring was replacedwith a 2 mm height ring, and the enamel resin component was applied atop the dentin layer and lightpolymerized for 180 s. All polymerization procedures were performed according to manufacturer’s instructions.
After the removal of the Teflon matrices, all specimens were immersed in 37°C water for 24 hours. This state

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was defined as 0 thermocycles (TC 0 - Baseline). Half of the specimens were then subjected to thermocycling,alternating between 4°C and 60°C water for 20,000 cycles (TC 20,000) with a dwell time of 1 minute.
Following this treatment, composite-to-metal shear bond strengths were determined for all groups using auniversal testing machine (Model 1125; Instron Corp, Canton, Mass, USA) at a crosshead speed of 0.5
mm/minute. Specimen groups were tested prior to and subsequent to thermocycling. For each experimental
condition, eight specimens were tested, and the means and standard deviations of shear bond strengths were
calculated. The results were statistically analyzed by ANOVA/Duncan’s multiple range test (α=0.05).

Results
Table 1 shows the results of shear bond strengths. Prior to thermocycling, all the surface-treated specimens
showed higher baseline shear bond strength values compared with the control specimens. There were no
statistical differences among the control, the Solidex and Siloc specimens. The Cesead II Opaque Primer and theMetal Primer II specimens showed significantly (p<0.05) higher shear bond strengths at the baseline than did theother groups. After 20,000 thermocycles, the Cesead II Opaque Primer and the Siloc specimens exhibiteddecreases in shear bond strength of 15% and 25%, respectively. There were no statistical differences in shear
bond strength between the Metal Primer II and the Siloc specimens after 20,000 thermocycles. All control
specimens delaminated during thermocycling of 20,000 cycles (100% decrease). The Cesead II Opaque Primer
specimens demonstrated the greatest shear bond strength of Artglass to the cast titanium surfaces both before andafter thermocycling.
Table 1. Shear bond strength (MPa) of resin bonded to conditioned metal surfaces.
Thermocycle

Control(No treatment)

Cesead II Opaque(MDP-based)

Metal Primer II(MEPS-based)

Solidex(4-AET-based)

Siloc(Silocoater)

0 (Baseline)

21.3 (2.4) b

36.7 (6.0) a

32.3 (4.5) a

24.2 (2.7) b

26.2 (1.3) b

20,000031.1 (3.6)

18.2 (3.6) c

8.7 (7.7)

19.7 (5.6) c

Mean (SD). Similar lower case letters indicate statistically equivalent values (Duncan’s test, p>0.05).

Discussion
The greatest shear bond strength occurred for Cesead II Opaque Primer before and after thermocycling (Table1), thus, the primers and silicoating did not exhibit equivalent bond strengths. The Cesead II Opaque Primer
contains a hydrophobic phosphate functional monomer (MDP) that strongly bonds the surface oxide layers ofbase metals such as titanium and cobalt-chromium alloy.14-18 When Metal Primer II was applied on the casttitanium surface, the bond strength value was similar to that of Cesead II Opaque Primer prior to thermocycling.
However, following thermocycling the bond strength for Metal Primer II was lower compared to that of the
Cesead II Opaque Primer. Metal Primer II contains MEPS derivatives, which were reported to produce strong
bonding of adhesive resin composite to both noble and base metal alloys.16-19 These results suggest that the
MDP-based monomer was superior to the MEPS material for bonding cast pure titanium in this study. Although
Solidex Metal Photo Primer contains 4-AET and is widely used to condition base metal alloys, specimens treatedwith this product showed the lowest bond strength pre- and post-thermocycling. This result suggested that a
carboxylic 4-AET derivative is less effective on titanium compared to the MDP and MEPS monomers.

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Specimens treated with the Siloc system had bond strengths similar to those when using the Solidex (4-AET)
system prior to thermocycling. However, after thermocycling, strength of silicoated metal was greater than thatof the Solidex specimens and closed to that of the specimens primed with Cesead II Opaque Primer. The
long-term bonding durability of various metal primers and the Siloc silicoating system has also been reported by
Yanagida et al.5,6 The results obtained in the present study were in agreement with those in their study5
conducted using cast Ti and Artglass even though they employed different particle sizes of alumina to air-abradethe metal surfaces. In one of their studies,6 the shear bond strength of Artglass to Ti-6Al-7Nb using several
types of metal primers (including the Cesead II Opaque Primer) and the Siloc system was tested. They reported
that the highest bond strength of Artglass to cast Ti-6Al-7Nb alloy was obtained for the silicoating system,
followed by the Cesead II Opaque Primer, showing lower value. In the present study, however, the silicoatedspecimens did not reach bond strength values similar to those found for the Cesead II Opaque Primer specimens.
These differences may be attributed to air abrasion conditions before priming and silicoater application. The
size of alumina particles in the present study was 250 µm, whereas they employed 50 µm particles on specimens
treated with metal primers and 125 µm particles on silicoated specimens. In the previous study,3 the effect ofalumina particle size on shear bond strength of Artglass to silicoated cast titanium and gold alloys has beenreported and it was found that using coarser alumina particles increased surface roughness, resulting in increased
shear bond strength. Thus, the present study postulates that if 125 µm alumina had been applied to all metal
primed surfaces in the study by Yanagida et al.,6 the highest shear bond strength might have been obtained for
the Cesead II Opaque Primer for Ti-6Al-7Nb.

Conclusion
Of the metal primers employed in this study, the Cesead II Opaque Primer produced the greatest bond strength
both pre-and post-thermocycling of a polymer-glass composite (Artglass) to cast pure titanium metal that had
been air-abraded with 250 µm alumina particles.
Acknowledgment
Editorial assistance by Mrs. Jeanne Santa Cruz is appreciated.

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Reprint request to:
Dr. Ikuya Watanabe
Department of Biomaterials Science, Baylor College of Dentistry
Texas A&M University System Health Science Center
3302 Gaston Ave., Dallas, TX 75246, USA
Fax: +1-214-828-8458 E-mail: iwatanabe@bcd.tamhsc.edu
Received December 6, 2004. Revised December 16, 2004. Accepted December 23, 2004.
Copyright ©2005 by the Editorial Council of the International Chinese Journal of Dentistry.

International Chinese Journal of Dentistry 2005 Outstanding Article AwardInternational Chinese Journal of Dentistry announces the fourth Outstanding Article Award.
Award:A cash prize of US$ 500 and a certificate of commendation are awarded for the most outstanding article published in theInternational Chinese Journal of Dentistry.
Criteria:
Original articles, clinical reports, and dental technology articles published in the Journal between issue 1 and issue 4 areconsidered for the award. The winning article will be selected by a committee on the basis of scientific impact on the dental
professional communities, and interest to the readers. The 2005 Award is sponsored by the International Chinese Journal of
Dentistry and the following award sponsors.
Award Sponsors:
GC Corporation, Tokyo, Japan, http://www.gcdental.co.jp
Kuraray Medical Inc., Tokyo, Japan, http://www.kuraray.co.jp/dental
Shofu Inc., Kyoto, Japan, http://www.shofu.co.jp
Sun Medical Co., Ltd., Moriyama, Japan, http://www.sunmedical.co.jp
Toho Dental Products, Saitama, Japan
Tokuyama Dental Corp., Tokyo, Japan, http://www.tokuyama-dental.co.jp
3M Health Care Limited, Sagamihara, Japan, http://www.3m.com/espe/
2004 Award winner
Hiroshi Shimizu, Kouichi Watanabe, Toru Okabe, and Yutaka Takahashi
Mold filling of titanium castings using a 45° marginal edge angle
Int Chin J Dent 2004; 4(3): 67-71.

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