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Asian Pac J Dent 2011; 11: 9-13.

Effect of two phosphate priming agents on bonding to alumina oftwo luting composites
Hiroyasu Koizumi, DDS, PhD,a,b Daisuke Nakayama, DDS,c Koji Naito, DDS,c Mamiko
Kochi, DDS,c Kazuhiro Honda, DDS,c and Hideo Matsumura, DDS, PhDa,bab

Department of Fixed Prosthodontics, and Division of Advanced Dental Treatment, Dental Research
cCenter, Nihon University School of Dentistry, and Division of Applied Oral Sciences, Nihon University
Graduate School of Dentistry, Tokyo, Japan
Purpose: The purpose of this study was to evaluate the effect of four ceramic bonding systems on adhesive
bonding to high-purity alumina.
Materials and Methods: Different sized alumina disks were bonded with one of the following bonding systems;
1) Clapearl Bonding Agent and Clapearl DC, 2) Clapearl Bonding Agent and Clearfil Esthetic Cement, 3)
Clearfil Ceramic Primer and Clapearl DC, and 4) Clearfil Ceramic Primer and Clearfil Esthetic Cement. Bondstrengths were determined both before and after application of thermocycling.
Results: Average post-thermocycling bond strengths varied from 45.4 MPa to 55.2 MPa, and were categorized
into two groups.
Two groups, primed with the Clapearl Bonding Agent, recorded the maximal
post-thermocycling bond strength. Bond strength of the two groups luted with the Clearfil Esthetic Cement
increased statistically after application of thermocycling (p≤0.01).
Conclusion: Among the four bonding systems assessed, priming with the phosphate-based Clapearl Bonding
Agent followed by luting with the Clapearl DC composite appeared to be the most consistent and durable systemfor bonding high-purity alumina. (Asian Pac J Dent 2011; 11: 9-13.)
Key Words: alumina, bonding, composite, MDP, primer

Introduction
The application of high-strength ceramic materials for anterior and posterior tooth-colored restorations has
increased substantially. This trend is probably due to improvements in the layering technique between ceramicmaterial and traditional tooth-colored porcelain. Aluminum oxide (alumina) has been used as a component ofdental porcelain as the reinforcing medium.1 High-purity alumina was introduced as a coping material in theProcera ceramic restorative system.2 It is desirable that alumina or alumina-based coping material and dentin
can be bonded durably.
A number of papers demonstrated the usefulness of adhesive systems for bonding alumina3-17 andalumina-based ceramic materials.18-20

An adhesive resin based on a carboxylic monomer enhanced bondstrength to alumina.3 Silane monomers and/or surface preparations with silicon compounds were introduced forbonding alumina ceramic restoratives.3-6,8-11,13,14 The application of acidic monomers was also effective forbonding alumina.3,6-17
Although varying acidic adhesive systems for bonding tooth structure and ceramic restorations are being
introduced, only limited information is available concerning bonding behavior of high-purity alumina, especiallyas related to chemical ingredients or functional monomers in the bonding and luting agents.3,15-17 The purpose of
the current study was to evaluate the effect of priming and luting agents on bond strength and durability of fourbonding systems joined to high-purity alumina.

Materials and Methods
High-purity alumina (99.7%) sintered at 1,600˚C for 5 days (Furuuchi Chemical Corp., Tokyo, Japan) wasused as the adherend material. Two priming agents; 1) Clapearl Bonding Agent (Kuraray Medical Inc., Tokyo,

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Asian Pac J Dent 2011; 11: 9-13.

Japan) and 2) Clearfil Ceramic Primer (Kuraray Medical Inc.), were assessed.

Both materials contained

10-methacryloyloxydecyl dihydrogen phosphate (MDP) as an adhesive functional monomer. Two dual-curable
luting composites; 1) Clapearl DC (Kuraray Medical Inc.) and 2) Clearfil Esthetic Cement (Kuraray MedicalInc.), were employed, both of which did not contain any adhesive promoting monomer. Information about thematerials is summarized in Table 1.
Table 1.

Materials assessed

Material

Composition; (Lot)

Adherend material
Sintered alumina

99.7 Al2O3, 0.08 SiO2, 0.05 MgO (%)

Priming agent
Clearfil Photo Bond

Catalyst: MDP, Bis-GMA, HEMA, dibenzoyl peroxide, CQ; (0409AA)
Universal: initiators, accelerators, ethanol; (0507BA)

Clearfil Porcelain Bond Activator

MPTS; (0214AA)

Clearfil Ceramic Primer

MDP, MPTS, ethanol; (0010AA)

Luting composite
Clapearl DC

A: Bis-GMA, TEGDMA, hydrophobic aromatic dimethacrylate, barium glass filler,colloidal silica, accelerators; (0058AB)
B: Bis-GMA, TEGDMA, hydrophobic aromatic and hydrophilic aliphatic dimethacrylates,silanated silica, barium glass, colloidal silica, CQ, initiators, accelerators, pigments; (0046AA)

Clearfil Esthetic Cement

A: Bis-GMA, TEGDMA, hydrophobic aromatic dimethacrylate, silanated barium glass,colloidal silica, accelerators; (003AAA)
B: Bis-GMA, TEGDMA, hydrophobic aromatic and aliphatic dimethacrylates, silanated silica,silanated barium glass, colloidal silica, CQ, initiators, accelerators, pigments; (003AAA)
Bis-GMA, bisphenol A diglycidyl methacrylate; TEGDMA, triethyleneglycol dimethacrylate; CQ, dl-camphorquinone; MDP,10-methacryloyloxydecyl dihydrogen phosphate; MPTS, 3-(trimethoxysilyl)propyl methacrylate; HEMA, 2-hydroxyethylmethacrylate; A, A paste; B, B paste. The Clapearl Bonding Agent consists of the following three-liquid; Clearfil Photo Bond(two-liquid) and Clearfil Porcelain Bond Activator (single-liquid)

A total of 88 pairs of disk specimens (10 and 8 mm in diameter by 3 mm thick) were wet-ground with a seriesof silicon-carbide (SiC) abrasive paper (400, 800, and 1500 grit) and ultrasonically cleaned with methanol. Aftercleaning, a piece of double-coated tape with a circular hole 5 mm in diameter and 50 µm in thickness waspositioned on the surface of the 10 mm-diameter disk to define the bond area.
The 88 specimens of alumina disk pairs were divided into four sets (four adhesive systems; Table 2) of 22
specimen pairs. Specimen disks were primed with one of the two priming agents and air-dried. The 8- and10-mm-disks were bonded with one of the two dual-polymerizing luting composites. After bonding, a 5.0 N
load was applied to the specimens. Each specimen was then light exposed for 40 s with a halogen lightpolymerization unit (Optilux 501, Kerr Corp., Orange, CA, USA) from three directions. Accumulated exposure
time period was 120 s.
After 30 minutes of bonding, the specimens were stored in 37°C water for 24 hours. This state was defined as
pre-thermocycling. One half of the specimens (four sets of 11 pairs) were tested at this stage. The remaining
one half of the specimens (four sets of 11 pairs) were subsequently thermocycled in water between 5°C and55°C for 100,000 cycles with a 60-s dwell time per bath (Thermal Shock Tester TTS-1 LM, Thomas Kagaku Co.
Ltd., Tokyo, Japan). The specimens were fixed in a steel mold and seated in an ISO TR 11405 bond test jig.
Shear bond strengths were determined with a mechanical testing device (Type 5567, Instron Corp., Canton, MA,USA) at a crosshead speed of 0.5 mm per minute. The average shear bond strength and standard deviation of 1110

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Asian Pac J Dent 2011; 11: 9-13.

replications were calculated for each group.
The results were primarily analyzed by Levene test for evaluation of homoscedasticity (SPSS 16.0, SPSS Inc.,
Chicago, IL, USA). When the results of the Levene test showed homoscedasticity for all categories, one-way
analysis of variance (ANOVA) and Tukey HSD multiple comparisons were performed with the value ofstatistical significance set at α=0.05 level. Pre- and post-thermocycling bond strength within an identicalbonding system was compared with the Mann-Whitney U-test.

Results
Levene tests run on the pre- and post-thermocycling groups showed p-values; 0.393 for pre-thermocycling and0.439 for post-thermocycling bond strengths. Results of the pre- and post-thermocycling bond strengths weretherefore analyzed by one-way ANOVA. The ANOVA results showed that p-values were less than 0.05 for bothpre- and post-thermocycling bond strengths.

The pre- and post-thermocycling results were analyzed

subsequently with the post-hoc Tukey HSD test.
Table 2.

Shear testing results (MPa)

Adhesive system
Priming agent / Luting composite

Pre-thermocycling

Post-thermocycling

Bond strength mean Category (SD)

Post-/Pre- bondstrength ratio (%)

Clearfil Ceramic Primer / Clearfil Esthetic Cement

39.7 a (2.8)

45.4 e (4.0)

114.4 p=0.01*

Clearfil Ceramic Primer / Clapearl DC

49.3 c (2.7)

48.7 e (3.3)

98.8 p=0.847*

Clapearl Bonding Agent / Clapearl DC

55.0 d (3.9)

54.5 f (4.9)

99.1 p=0.949*

Clapearl Bonding Agent / Clearfil Esthetic Cement

45.6 b (2.4)

55.2 f (3.0)

121.1 p<0.01*

Mean, n=11; SD, Standard deviation; Post-/Pre- bond strength ratio, Post-/Pre- thermocycling bond strength ratio (%); Category,Identical letters indicate that they are not statistically different at p=0.05 (Tukey HSD test). *Mann-Whitney U-test.

Results of shear bond testing are summarized in Table 2. Pre-thermocycling average bond strengths varied
from a minimum of 39.7 MPa to a maximum 55.0 MPa, and were statistically different from each other(categories a-d). Post-thermocycling average bond strengths varied from 45.4 MPa to 55.2 MPa, and werecategorized into two groups (categories e and f). Two groups, primed with the Clapearl Bonding Agent,recorded the maximal post-thermocycling bond strength (category f). Bond strength of the two groups luted
with the Clearfil Esthetic Cement increased significantly after application of thermocycling (p≤0.01), whereasthat of the two groups luted with the Clapearl DC material remain unchanged (p>0.05). In addition, the Clapearl
Bonding Agent generated greater post-thermocycling bond strength than the Clearfil Ceramic Primer regardlessof the type of luting agent.

Fig. 1. Scanning electron micrograph of ground alumina (left).
Fig. 2. Debonded surface of alumina primed with Clearfil Ceramic Primer and bonded with Clearfil Esthetic Cement (Center).
Fig. 3. Debonded surface of alumina primed with Clearfil Ceramic Primer and bonded with Clapearl DC (right).

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Asian Pac J Dent 2011; 11: 9-13.

Figure 1 shows the ground alumina surface before bonding. Ground crystalline of alumina can be seen.
Figures 2 through 5 depict debonded surface after thermocycling of alumina. Remnants of composite material
were detected for all specimens. The micrographs indicate that composite materials were cohesively fractured
substantially, and that bonding of the four bonding system is excellent even after thermocycling.

Fig. 4. Debonded surface of alumina primed with Clapearl Bonding Agent and bonded with Clapearl DC (left).
Fig. 5. Debonded surface of alumina primed with Clapearl Bonding Agent and bonded with Clearfil Esthetic Cement (right).

Discussion
This project aimed to evaluate the effect of four ceramic bonding systems on adhesive bonding to high-purity
alumina. Clearfil Ceramic Primer was selected as a representative single-liquid pre-hydrolyzed silane primer
without initiator.

Clapearl Bonding Agent was employed as a three-liquid silane bonding agent withdual-initiation system. Although previous papers revealed that a representative silane monomer, MPTS, is not a
critical compound for bonding alumina,3,15-17 the authors used the Clearfil Porcelain Bond Activator(single-liquid unhydrolyzed silane) together with the Clearfil Photo Bond (two-liquid). Application of thisthree-liquid bonding agent, identified as the Clapearl Bonding Agent, made it possible to compare difference inbonding characteristics between a pre-hydrolyzed silane agent and an in-situ hydrolyzed silane bonding agent.
Also comparison between the Clearfil Ceramic Primer and Clapearl Bonding Agent reveals difference inbonding characteristics between an MDP primer without initiator and an MDP bonding agent initiated with dual
functional initiation system.
As shown in the shear testing results, it was apparent that the Clapearl Bonding Agent was superior to theClearfil Ceramic Primer for both luting agents, and for both thermocycling conditions. The results suggest thatthe presence of an initiator is indispensable for durable bonding between MDP-based adhesives and metal oxidesubstrates. This finding is in agreement with the results of previous research concerning adhesive bonding ofsintered porcelain,21 although the bonding system employed was a little different.
Shear testing results in the current study exhibited an increase in bond strength after thermocycling of theClearfil Esthetic Cement. The result was confirmed for both of the priming agents. Considering the fact thatadherend material, priming agents, and light-exposure condition were identical, the authors speculate that theincrease in bond strength after thermocycling is derived from lower double bond conversion in the matrix of theClearfil Esthetic Cement at the pre-thermocycling stage. Although the manufacturer may have attempted torelease a luting composite with improved color stability, the Clapearl DC is not a particularly problematic
material in terms of color stability. Clinicians, therefore, should be aware that the newest version of the bonding

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Asian Pac J Dent 2011; 11: 9-13.

system is not always the best system. Within the limitation of the current experiment, it can be concluded thattraditional Clapearl Bonding Agent combined with the Clapearl DC luting composite is a suitable system forbonding high-purity alumina.
Acknowledgments
This work is supported in part by Grants-in-Aid for Scientific Research (C 20592283, C 21592474) from the Japan Society for thePromotion of Science (JSPS), Special Research Grants for the Development of Distinctive Education from the Promotion and Mutual Aid
Corporation for Private School of Japan (2009, 2010), Grant from Dental Research Center, and Sato Fund, Nihon University School ofDentistry (2009, 2010).

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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
Copyright ©2011 by the Asian Pacific Journal of Dentistry.

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Accepted December 11, 2010.
Online ISSN 2185-3487, Print ISSN 2185-3479