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Influence of dry and wet storage conditions on bond strength togold alloy of four luting agents
Mika Furuchi, DDS, PhD,a,b Akiko Oshima, DDS,a Yoshifumi Matsumoto, DDS,cMichiya Ayano, DDS,a Tsukasa Masuno, DDS,a and Hideo Matsumura, DDS, PhD,a,b
ab

Department of Fixed Prosthodontics, Nihon University School of Dentistry, Division of Advanced
Dental Treatment, Dental Research Center, Nihon University School of Dentistry, andcNihon University Graduate School of Dentistry, Tokyo, Japan
Purpose: The purpose of the current study was to evaluate the influence of water storage conditions on bondstrength of four luting agents joined to gold alloy.
Materials and Methods: Disk specimens (10 and 8 mm in diameter) were cast from a gold alloy (Degudent U),
and the surfaces were ground with abrasive paper. Two resin-modified glass ionomers (RMGIs; Fuji Lute andIonotite), a resin adhesive (Super-Bond C&B), and a conventional glass ionomer (Ketac Cem) were selected forbonding the gold alloy. A metal priming agent (Metaltite) was used together with the Fuji Lute and Super-Bond
C&B materials. The paired specimens were bonded with five systems and placed in an incubator at 37˚C under
three different conditions; 1) immersed in water for 24 h, 2) immersed in water for 24 h followed by additional
7-day-immersion in water, and 3) immersed in water for 24 h followed by dry-state storage for 7 days. Shearbond strengths were then determined and statistically analyzed. Weight change of luting agents after storage
was determined using disk-shaped specimens (10 mm in diameter by 2 mm in thickness).
Results Shear bond strength varied from a minimum of 0.1 MPa to a maximum of 40.9 MPa. Bond strength ofFuji Lute and Ketac Cem deteriorated after 7 days for both dry and wet storage conditions, whereas bondstrength of Super-Bond C&B without priming improved after dry-storage. Bond strength of Ionotite andSuper-Bond C&B with priming remain unchanged during the three storage conditions of the current experiment.
Weight change of luting agents after storage was +1.6 to +5.5% for condition #1, +2.6 to +6.0% for condition #2,and -4.5 to -0.4% for condition #3.
Conclusion: Within the limitations of this experiment, it can be concluded that the use of either Ionotite alone orSuper-Bond C&B combined with Metaltite is recommended for bonding gold alloy.
(Int Chin J Dent 2008; 8: 43-47.)
Key Words: bonding, gold alloy, primer, resin-modified glass ionomer, thione.

Introduction
The use of resin-modified glass ionomers (RMGIs) and resin-based adhesives for cementing ceramic andmetallic restorations has increased substantially. This trend is mainly derived from improvement in bonding
characteristics and the increasing application of all-ceramic and collarless metal-ceramic restorations. Seating
restorations with RMGI or resin adhesive are one of the options due to improved bond strength,1-6 adequate
sealing ability,7 and cement thickness.8
According to the literature, RMGI cements provided better bonding property than conventional glass ionomer
cements.1

Microabraded and tin-plated alloy bonded with a RMGI demonstrated strong bond strength.3

However, bond strengths of zinc-phosphate, glass ionomer, and RMGI cements were inferior to those of resin
adhesives under the specific conditions.9 In addition, the bond strength of glass ionomer joined to gold alloy wasinferior to that of composite luting agent.10
Both prepolymerized alkenoic acids soluble to water and methacrylic monomers are being incorporated into
RMGI compositions. Moreover, several RMGI luting agents do not contain water.4 This fact encourages
application of adhesive functional monomers in combination with RMGIs for bonding both ceramic and castmetal restorations. Although a number of experimental results have been reported on bonding noble metal alloys
with priming agents and adhesive resins,2,6,11,12 only limited information is available about the effect of priming
agents on bond strength of RMGIs to noble alloys,4,5 especially as related to storage conditions. This study

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evaluated the influence of dry and wet storage conditions on bond strength of four luting agents joined to goldalloy. Short-term weight change of luting agents was also determined.

Materials and Methods
Table 1 summarizes the information on the materials assessed. A gold alloy designed for porcelain-fusedto-metal technique (Degudent U, DeguDent GmbH, Hanau, Germany) was used as the substrate material. A
single-liquid metal priming agent (Metaltite, Tokuyama Dental Corp., Tokyo, Japan), with a functional monomer
6-methacryloyloxyhexyl 2-thiouracil-5-carboxylate (MTU-6), was employed. Two RMGIs (Fuji Lute,13 FL, GC
Corp., Tokyo, Japan; and Ionotite F, IT, Tokuyama Dental Corp.), a resin adhesive (Super-Bond C&B, SB, Sun
Medical Co., Ltd., Moriyama, Japan), and a conventional glass ionomer (Ketac Cem µ, KC, 3M-Espe AG,Seefeld, Germany) were selected as the luting agents.
Table 1.

Materials assessed.

MaterialAbbreviation

Component

Lot number

Composition

Gold alloy
Degudent U10011271

Au 77.3, Pt 9.8, Pd 8.9, Others 4.0 mass%

Metal priming agent
Metaltite

01403

MTU-6, Ethanol

Luting agentsResin-modified glass ionomers (RMGIs)
Fuji LuteFL
PowderLiquidIonotite FIT
PowderLiquid07110710711051005067005067

Fluoroaluminosilicate glass*
Polyalkenoic acid, HEMA, Water, UDMA
Calcium aluminosilicate glass, Silica**
HEMA, UDMA, Phosphate, MTU-6,BPO, AmineResin adhesive
Super-Bond C&B

SB

Initiator
Monomer
Powder

RL43
RK1RF1

Partially oxidized TBB
4-META, MMA
PMMA, PMMA-coated titanium oxide

Conventional glass ionomer
Ketac Cem µKC

PowderLiquid290553
290553

Glass, Polyethylene polycarboxylic acid
Water, Tartaric acid

MTU-6, 6-methacryloyloxyhexyl 2-thiouracil-5-carboxylate; HEMA, 2-hydroxyethyl methacrylate; UDMA, Dimethacryloxyethyl
2,2,4- (or 2,4,4-) trimethylhexamethylene diurethane; BPO, Benzoyl peroxide; TBB, Tri-n-butylborane; 4-META,4-methacryloyloxyethyl trimellitate anhydride; MMA: Methyl methacrylate; PMMA: Poly(methyl methacrylate.
134*Bouillaguest et al. 2003, **Amamo et al. 2004.

Bond strength test
A total of 75 pairs of disks (10 mm and 8 mm in diameter by 2.5 mm in thickness) were cast from the gold
alloy. All disks were ground flat with #1,500 silicon carbide abrasive paper and cleaned with acetone. A pieceof tape 50 µm in thickness with a circular hole 5 mm in diameter was positioned on the surface of the larger disk
to define the bond area. The 75 specimens were divided into five sets of 15 specimens. The first and second sets
were unprimed and luted either with IT or with KC, which were spatulated according to the manufacturers’instructions. The third set was primed with Metaltite, and luted with FL. The fourth set was unprimed andbonded with SB using brush-dip technique. The last set was primed with Metaltite and bonded with SB.
Immediately after bonding, a constant load of 5.0 N was applied to the bonded specimens for 30 minutes. All
specimens were immersed in 37°C distilled water for 24 hours. This state was defined as storage condition #1,and was immediately evaluated by shear bond test. Five sets of five specimens were subsequently immersed in44

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Int Chin J Dent 2008; 8: 43-47.

water for 7 days (condition #2). The remaining five sets of five specimens were subsequently stored in dry-statewith 28% humidity for 7 days (condition #3).

After storage in each condition, shear bond strength wasdetermined with a mechanical testing device (Type 5567, Instron Corp., Canton, MA, USA) at a crosshead speedof 0.5 mm/minute. Equality of variance of the bond strength results was primarily analyzed by Levene test andF test. When the Levene test and F test did not show equality of variances, Dunnett’s T3 test was performed
with the significance level set at 0.05.
Weight change
Four luting agents were spatulated and poured into plastic molds 10 mm in diameter and 2 mm in thickness.
For each luting agent, 15 specimens were prepared. Thirty minutes after preparation, the baseline weight of eachdisk specimen was determined. The 15 specimens were divided into three groups consisting of five specimens.
Specimens were stored at the different three conditions, as described in the previous section. The weight of eachspecimen was determined with an electronic balance (AL204, Mettler Toledo, Greifensee, Switzerland).
Average weight change of five specimens for each luting agent was calculated from the baseline andpost-storage weights.

Results
Levene test and F test run on the bond strength results revealed that several groups did not show equality ofvariance. Dunnett’s T3 test was applied therefore to evaluate the influence of storage conditions and luting
systems on bond strength.
Table 2.

Bond strengths (MPa) of five luting systems and statistical categories.

Storage condition
37°C water for 24 hM+FL
MedianMean
SD

31.1
31.5
1.4

37°C water for 24 h +37°C water for 7 days

Median
Mean
SD

20.9
21.3
5.9

37°C water for 24 h +37°C dry state for 7 days

Median
Mean
SD

2.8
3.4
1.9

ITbdeg

M+SB

35.8
32.8
7.0

abc

40.3
40.9
1.0

23.9
26.3
4.2

d

38.8
39.6
2.7

28.9
29.1
1.0

39.4
40.3
4.2

aSBKC

25.5
23.9
3.5

8.6
8.5
1.9

11.0
11.21.7f

35.6
35.5
1.4cef

2.0
2.5
2.4
0.1
0.1
0.2

g

Identical letters in the same horizontal lines indicate that the values are not statistically different (Dunnett's T3, p>0.05). N=5.
M+FL, Metaltite + Fuji Lute; IT, Ionotite F; M+SB, Metaltite + Super-Bond C&B; SB, Super-Bond C&B; KC, Ketac Cem.

Tables 2 and 3 show the shear bond strength results as well as statistical categories. Bond strength variedfrom 0.1 MPa to 40.9 MPa. Ketac Cem glass ionomer resulted in the lowest bond strength among the fivesystems, and reduction after 7 days was significant (category j). The specimens primed with Metaltite andbonded with Fuji Lute also showed considerable reduction in bond strength after 7 days. Deterioration of thisgroup was more remarkable for the dry-stored specimens. The 24-h bond strength of the Super-Bond C&B was23.9 MPa for the unprimed specimens. Bond strength of this system deteriorated to 11.2 MPa after storage inwater for 7 days, whereas it increased to 35.5 MPa after dry-storage for 7 days. Ionotite generated bond strengthranged from 26.3 MPa to 32.8 MPa. The average values of the luting agent, however, were not significantly
different from each other (category h). Within the system of the present experiment, Metaltite combined with45

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Super-Bond C&B exhibited the greatest bond strength (39.6 to 40.9 MPa) regardless of storage conditions. Inaddition, bond strength of Super-Bond C&B was not reduced after 7 days and was unaffected by the dry and wet
storage conditions (category i).
Table 3.

Statistical categories of the storage conditions.

Storage condition
37°C water for 24 hMedianM+FL
31.1

IT35.8hM+SB
40.3

iSB25.5

KC8.6

37°C water for 24 h + 7 days

Median

20.9

23.9

h

38.8

i

11.0

2.0

j

37°C water for 24 h +37°C dry state for 7 days

Median

2.8

28.9

h39.4

i

35.6

0.1

j

Identical letters in the same vertical columns indicate that the values are not statistically different (Dunnett's T3, p>0.05). N=5.

Table 4 summarizes the change of weight of the four luting agents as compared with the baseline set at 30minutes of specimen preparation. Weight change of luting agents after storage was +1.6 to +5.5% for condition#1 (immersion in water for 24 h), +2.6 to +6.0% for condition #2 (immersion in water for 24 h followed byadditional 7-day-immersion in water), and -4.5 to -0.4% for condition #3 (immersion in water for 24 h followedby dry-state storage for 7 days).
Table 4.

Weight change (%) of four luting agents after three storage conditions.
FLITSBKC

37°C water for 24 hMedianMeanSD

104.4
104.4
0.4

103.5
103.5
0.3

101.6101.6
0.4

105.7
105.5
0.3

37°C water for 24 h +37°C water for 7 days

MedianMeanSD

105.7
106.0
1.2

105.8
105.6
0.6

102.5
102.6
0.2

105.8
105.8
0.3

37°C water for 24 h +Dry state for 7 days

MedianMeanSD

97.4
97.4
0.4

99.9
99.6
0.7

99.6
99.5
0.3

95.4
95.5
0.8

Baseline determination, After 30 minutes of preparation.

Discussion
This study evaluated the effect of specimen storage conditions on bond strength to gold alloy of four lutingagents. The effect of MTU-6 functional monomer on bonding to gold alloy was also assessed. The 24-h bondstrength results showed that bonding to gold alloy of Super-Bond C&B without bonding agent and Ketac Cem
provided no significant advantages. The original Super-Bond C&B material contains a carboxylic monomer forbonding enamel and dentin, and does not contain any functional monomer capable of bonding noble alloys. TheKetac Cem glass ionomer does not contain any polymerizable monomer, hence its adhesive performance is notsatisfactory, except for interaction between polyalkenoic acid and tooth structure. The other three systems(Metaltite and Fuji Lute, Ionotite, and Metaltite and Super-Bond C&B) employed MTU-6 as a bonding promoter
for the gold alloy.2,12 In addition, these three systems contain a considerable amount of co-polymerizable
monomers in the liquid component. The authors speculate that the bond strength of three groups (categories aand b) in Table 2 is derived from the interaction between MTU-6 and gold alloy, and from subsequent
copolymerization between MTU-6 and monomer component of the luting agents.
The difference in bond strength between Fuji Lute and Ionotite was apparent after dry-storage of the46

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Int Chin J Dent 2008; 8: 43-47.

specimens. The former contains water in the liquid component, whereas the latter does not contain water. It isnot surprising, therefore if bond strength of the water-based material is affected negatively after dry-storage.
However, this result does not discourage the use of water-based luting agents, since luting agents are applied
generally to oral environments in the presence of saliva.
Weight change of luting agents clearly demonstrates that water-based materials are susceptible to changes in
wet and dry environments. However, this phenomenon is not particularly useful for metal priming systems.
These results may promote the combined application of hydrophilic monomer such as 2-hydroxyethyl
metahcryalte (HEMA) and adhesive functional monomer such as 4-methacryloyloxyethyl trimellitate anhydride(4-META) for bonding dentin. This is due to the fact that dentin is composed of a complex of hydrophiliccollagen fibers and inorganic hydroxyapatite.
Within the limitations of the current experiment, it can be concluded that the bond strength to gold alloy of
two water-based luting agents (Fuji Lute and Ketac Cem µ) and a resin adhesive without priming (Super-BondC&B) was negatively affected by dry or wet storage conditions.

In particular, the weight loss of two

water-based luting agents was remarkable after dry-storage. Consistent bonding to gold alloy was generated
with the combined application of MTU-6 thione monomer and two polymerizable luting agents (Ionotite andSuper-Bond C&B).
Acknowledgments
This work was supported in part by Sato Fund, Nihon University School of Dentistry (2008), Grant from Dental ResearchCenter (A), Nihon University School of Dentistry (2008), and Special Research Grant for the Development of Distinctive
Education from the Promotion and Mutual Aid Corporation for Private Schools of Japan (2008).

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Correspondence to:Dr. Mika Furuchi
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: nemoto@dent.nihon-u.ac.jp
Received July 30, 2008. Accepted September 16, 2008.
Copyright ©2008 by the International Chinese Journal of Dentistry.

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