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Int Chin J Dent 2006; 6: 82-88.

Evaluation of shear bond strength and microleakage ofdeproteinized dentin bonded with three total-etch adhesive
systemsYu Xiong, DDS, Ji-hua Chen, DDS, PhD, Hui Wang, DDS, PhD, and Ling Zhang, DDS
Department of Prosthodontics, Stomatological College, The Fourth Military Medical University, Xi’an,
P. R. China
Purpose: To evaluate the effect of NaOCl conditioning on shear bond strength and marginal sealing of resinbonded dentin with three total-etching adhesive systems.
Materials and Methods: Flat dentin surfaces were prepared and received the following treatments: Group I,
35% phosphoric acid for 15 s; Group II, 35% phosphoric acid for 15 s followed by 10% NaOCl for 60 s; GroupIII received no additional conditioning and served as control. Each group was applied with three adhesive
systems: One Step plus, Prime&Bond NT and Single Bond. Resin restorations were built up and then submitted
to bond strength test. For microleakage evaluation, 72 class V cavities were prepared and grouped as describedabove and then restored with composite resin, dye penetration along the bonding interface was assessed. Alldata were subjected to statistical analysis.
Results: All specimens conditioned with phosphoric acid showed similar shear bond strength without statisticaldifference among adhesive systems used (p>0.05). Compared with that of the acid-etched groups, One Step plus
demonstrated statistically increased bond strength following NaOCl application (p<0.05), while that ofPrime&Bond NT remains unaffected though obviously decreased values were obtained (p>0.05). Single Bondyielded significantly lower bond strength (p<0.05). No statistical difference in microleakage scores was shown
among dentin pretreatments or adhesive systems used (p>0.05). For all groups, the microleakage at the gingival
margin was much severer than that at the occlusal margin (p<0.05).
Conclusion: The efficacy of resin bonding to deproteinized dentin was systems specific, which was decided by
the composition of adhesive systems. (Int Chin J Dent 2006; 6: 82-88.)
Key Words: dentin bonding, sodium hypochlorite, microleakage, shear bond strength.

Introduction
The introduction of phosphoric acid etching technique into enamel bonding by Buonocore in 1955 resulted ina strong micromechanical bond.1 Since then, surface conditioning by different procedures has been extensively
used in adhesive dentistry, in order to modify the dental bonding substrates favorable for resin adhesion. As for
dentin bonding, acid etching was a mostly used technique, by which the dentin surface was demineralized,
exposing collagen matrix for resin infiltration to form a resin dentin interdiffusion zone. The creation of resin
dentin interdiffusion zone, also named as hybrid layer, has been considered as the essential mechanism of dentin
bonding.2
Due to the difference in the nature, bonding to dentin was not as reliable as bonding to enamel. Although thecollagen matrix exposed by acid-etching is crucial to the formation of hybrid layer, it plays a negative role indentin adhesion by presenting a delicate bonding substance susceptible to collapse.3 Without the presence ofwater, the demineralized collagen network would collapse and shrink to prevent resin monomers from
penetrating in. On the other hand, when dentin surface was too hydrated, “hybridoid layer” containing voids andporosities would be created within the bonding interface. Greatly decreased bond strength was shown both toover-dried and over-wet dentin.4 Therefore, bonding to etched dentin is technique sensitive due to the difficultyin finding the correct balance of residual moisture.

Additionally, a demineralized dentin zone termed

nanoleakage could be detected within the interface,5 which was created by the discrepancy between the depth ofdemineralization and that of resin infiltration, leaving collagen matrix at the base of hybrid layer uncoated. Even
the most current self-etching primer systems, which were known as demineralizing and priming dentin

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Int Chin J Dent 2006; 6: 82-88.

simultaneously, showed distinct nanoleakage.6

It was believed these nanoleakage channels could provide

pathway for water, enzymes, acid and bacterial products to enter into the bonded interface, resulting indegradation of uncoated collagen fibrils and elusion of incompletely polymerized resin monomers, and lead topremature failure of dentin bonding.7
Considering the negative role of collagen fibrils in dentin adhesion, removal of the exposed organic matrix
would possibly minimize these problems.

Therefore, a combined use of phosphoric acid and sodium

hypochlorite (NaOCl) was adopted to produce a porous mineralized surface similar to the etched enamel by
deproteinizing the demineralized dentin.8

Theoretically, due to the lack of uncoated collagen fibrils, thetechnical sensitivity could be eliminated. Something most important is that resin infiltrated into the mineralized
substrate could develop a more reliable resin-dentin bond without the occurrence of nanoleakage,9 thus enhanced
durability could be expected.
Although some researchers doubted the existence of potential oxide influence of residual NaOCl on resin
polymerization and reported decreased bond strength in their studies,10 most of the previous studies showed
positive results8,11,12 with the application of NaOCl on demineralized dentin. It has also been reported that thehigher the concentration of NaOCl, the greater the dentin bond strength until a plateau is reached at aconcentration of 10%, for an application time of 60 s.11
However, most of the previous studies have been focused on the concentration and application time of
NaOCl,11-13 few researches have been conducted to investigate the influence of deproteinization on dentin
bonding with different adhesive systems. Therefore, the purpose of the current study was to evaluate thebonding efficacy of three total-etching bonding systems to the dentin deproteinized with NaOCl, by shear bondstrength (SBS) test and microleakage evaluation.

Materials and Methods
Materials
Human permanent posterior teeth extracted for severe periodontitis treatment were collected. All of the teeth
were free of caries and fillings. After hand-scaled and cleaned, they were stored in distilled water at 4˚C for up
to one month following extraction. Three adhesive systems used in this study, One Step plus (OS, Bisco,
Schaumburg, IL, USA), Prime&Bond NT (PB, Densply Caulk, Milford, DE, USA), and Single Bond (SB, 3M
ESPE, St Paul, MN, USA), are detailed in Table 1.
Table 1.

Composition of the total-etch adhesive systems used in this study.

Adhesive

Lot number

Composition

One-Step plus (OS)0500002934

Bis-GMA, BPDM, HEMA, Initiator, Glass filler, Acetone

Prime&Bond NT (PB)

0011000963

PENTA, UDMA, Butylated hydroxytoluene, 4-ethyl dimethyl aminobenzoate,
Cetylamine hydrofluoride, Silica nanofiller, Acetone

Single Bond (SB)

4BK

Bis-GMA, HEMA, Dimethacrylates, Alkenoic acid co-polymer, Initiator,
Ethanol, Water

Bis-GMA, Bisphenol A diglycidyl methacrylate; BPDM, Adduct of 2-hydroxyethyl methacrylate and 3,4,4’,5’-biphenyl tetracarboxylic anhydride; HEMA, 2-hydroxylethyl methacrylate; PENTA, Dipentaerythritol pentaacrylate phosphoric acid ester;
UDMA, Urethane dimethacrylate.

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Shear bond strength (SBS) test
Thirty-six intact molars were selected for SBS test. Each molar was sectioned longitudinally into two pieces
and ground with #360 and #600 grit silicon carbide abrasive papers serially under running water to create a
uniform smear layer on the exposed dentin surface. Following this, an adhesive tape with a punched hole, whichmeasured 2 mm in diameter, was placed on the finished dentin surface to demarcate the bonding area. The
prepared specimens were then randomly assigned to three groups according to the following pretreatments.
Group I, Acid-etched group. Dentin was etched with 35% phosphoric acid for 15 s and then rinsed with tap
water for 10 s. Excess water was removed by blotting with an absorbent pellet, leaving dentin visibly moist.
Group II, Deproteinized group. Dentin was treated with 10% NaOCl for 60 s following the acid-etchingprocedures described in Group I. Rinsed with copious water for 60 s, dentin was thoroughly air-dried. Group III,
Control group. The specimens were ground and received no additional conditioning before the application ofdentin adhesive systems.
For each group, the prepared specimens were bonded with one of the three total-etch adhesives: OS, PB, and
SB. Eight specimens were used for each adhesive. Two continuous layers of dentin adhesives were applied andlight cured according to the manufacturers’ directions with a light-curing system (Spectrum 800, Densply).
Following adhesive application, a brass ring measured 3 mm in inner diameter and 2 mm in height was thenplaced on the treated surface. A composite resin (Charisma, shade A3, 067, Heraeus Kulzer, GmbH & Co.,
Hanau, Germany) was filled into it in three increments and light activated for 20 s each.
After storing in distilled water for 24 hours at room temperature, the root of dentin slabs were embedded withthe bonding interface perpendicular to the ground (Fig. 1). SBS evaluation was conducted using a universal
testing machine (Autograph AG500-A, Shimadzu, Kyoto, Japan) at a cross-head speed of 0.5 mm/minute.

Fig. 1.

Bonded specimen for shear bond strength test.

Fig. 2.

Graded criteria for microleakage scores.

Microleakge evaluation
Another 36 freshly extracted premolars and molars were used for microleakage evaluation. Box-shaped class
V cavities were prepared at the cemento-enamel junction on the buccal and lingual surfaces of each tooth. Eachcavity was measured 3 mm in mesio-distal width, 2 mm in occluso-gingival length and 2 mm in depth, with a 0.5mm and 45º enamel bevel. The occlusal margins of the preparations were in enamel and the gingival margins
were in dentin or cementum.
The prepared cavities were randomly grouped by the treatments and adhesives as described previously witheight in each. Following surface conditioning, the adhesives were applied to the cavities according to the
manufacturer’s instructions and light cured. The composite resin was then placed in two increments. Each
increment was cured for 20 s, and the final restoration was cured for another 20 s. Excessive materials were84

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removed and polished after water storage for 24 hours at room temperature. The apices of the teeth were sealedwith sticky wax, and the teeth were covered with two coats of nail vanish except at 1 mm around the margins ofrestorations. The prepared specimens were then immersed in 0.5% water solution of basic fuchsin for dye
penetration for 24 hours at room temperature.
Following this, the restorations were serially multi-sectioned longitudinally into four pieces for microleakage
evaluation. For each slab, the bonded interface was examined at the occlusal and gingival margins with astereomicroscope (SZ1145, Olympus, Tokyo, Japan) at ×20 magnification. Blind evaluations were carried out
by two independent observes, consensus were obtained between observers if there were conflicts in scores.
After the evaluation of the dye penetration in all the cut surfaces, the section with the maximum leakage value
recorded for each cavity was selected for statistical analysis. Scoring was based upon the following criteria:14 0,
no dye penetration; 1, dye penetration along the interface to 1/2 the depth of the cavity wall; 2, dye penetration to
the full depth of the cavity wall, but not including the axial wall; 3, penetration to and along the axial wall (Fig.
2).
Statistical analyses
The shear bond strength was calculated by dividing the failure load by the bonded area and expressed in MPa.
The data were analyzed using Student-Newman-Keuls (SNK) test. For microleakage evaluation, occlusal andgingival scores for each group of restorations were compared by the Kruskal-Wallis nonparametric analysis.
The Mann-Whitney U test was used to disclose a statistically significant difference between occlusal andgingival margins. Significance was considered at the 0.05 level.

Results
SBS results are summarized in Table 2. SBS was greatly enhanced following acid-etching for all the threeadhesive systems compared with the untreated control group. However, no statistical difference was shown
among the three adhesive systems when the dentin surface was treated with phosphoric acid (p>0.05), though thehighest bond strength was obtained with SB.

Compared with the acid-etched groups, OS demonstrated

statistically increased bond strength following the additional NaOCl treatment (p<0.05), while that of PB
remains unaffected though distinctly decreased values were obtained (p>0.05).

However, SB yielded asignificant lower bond strength (p<0.05), which similar to that of the untreated control group.
Table 2.

Shear bond strength (SBS), standard deviations in MPa, and statistical categories.

Group

Conditioning

One Step plus (OS)Mean SD SC

Prime&Bond (PB)
Mean SD SC

Single Bond (SB)Mean SD SC

I
II
III

Acid-etched
DeproteinizedControl

14.3 4.8
19.5 3.3
4.5 1.4

13.6 5.3
9.3 2.5
5.8 2.2

17.3 9.7
4.3 1.2
4.0 1.4

b
a
d

b, c
c, d
d

a, b
d
d

Subgroups with the same letter are not statistically significant (p>0.05). Specimen size, n=8. SD, Standard deviation.
SC, Statistical category.

Summaries of the distribution of the dye penetration scores at the occlusal and gingival margins are shown in
Table 3. None of the dentin treatments or adhesive systems tested in this study could completely eliminate
microleakage at resin-teeth interfaces. With each adhesive tested, much severer microleakage was demonstrated
at the gingival margins than at the occlusal margin (p<0.05). All of the adhesive systems tested showed similar

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marginal sealing ability at both the enamel margins and dentin margins when conventional wet-bonding
procedures were performed. As dentin treatments were concerned, no statistical differences in leakage scores
was shown between the acid-etched group and the deproteinized group for each adhesive, at both the occlusal
margins and gingival margins. However, microleakage of control groups showed significant higher scores thanthat of the treated groups (p<0.05).
Table 3.

Microleakage scores at the occlusal and gingival margins.

Group

Conditioning

MarginOne Step plus (OS)0 1 2 3 Total

Prime&Bond (PB)
0 1 2 3 Total

Single Bond (SB)
0 1 2 3 Total

I

Acid-etchedOcculusal
Gingival

5 3 0 01 1 4 2315

4 4 0 00 2 3 3417

6 1 1 01 2 3 2

3
14

II

DeproteinizedOcculusal
Gingival

6 1 1 00 1 5 2317

3 5 0 00 1 3 4519

3 4 1 00 1 4 3

6
18

III

ControlOcculusal
Gingival

3 1 4 00 0 2 6922

3 0 5 00 1 2 51020

1 3 3 10 1 3 412
19

Specimen size, n=8. No statistical difference was shown between adhesive systems used (p>0.05).

Discussion
Adhesion of dental material to enamel is a well-known reliable procedure. However, bonding to dentin withcurrent dentin adhesive systems, including both the total-etch systems and self-etching primer systems, is lessreliable than that to enamel. Due to the potential of surface modification by NaOCl treatment following acidetching, by providing an enamel-like porous mineralized bonding substrate, dentin deproteinization has beenoccasionally proposed as an alternative bonding procedure to achieve an enhanced resin-dentin bond.12
In the present study, OS resulted in increased shear bond strength when bonding to deproteinized dentin,
compared with the acid-etched group. This could be probably attribute to the increased roughness and enhanced
permeability of the deproteinized dentin. The combined steps of etching and NaOCl treatment lead to an altered“moth eaten” appearance with larger dentinal tubule openings,15 which would not shown by either treatment
alone.16 Meanwhile, a hydrophilic mineralized surface with higher energy characterized by enhanced wettability
would also be achieved due to the removal of residual collagen matrix.17 Hence, the penetration of resin into themodified dentin is improved and results in the formation of uniform resin tags with anastomoses in lateralbranches. The enhanced micromechanical interlocking between composite resin and dentin was considered tocontribute to the increased bond strength. Additionally, it was suggested that the potential chemical interaction
at the resin-dentin interface would also strengthen the bond.18
Although increased bond strength was shown with the used of OS, PB and SB demonstrated neutral or
negative results following the application of NaOCl on etched dentin. These findings indicated that the effect ofNaOCl treatment on dentin bond strength was system specific. In a previous study, Saboia et al.19 reported
increased bond strength with Prime&Bond 2.1 following NaOCl conditioning, while that obtained with Single
Bond decreased significantly. They explained it by the difference in the solvents of the adhesives, which acted
as a hydrophilic carrier to enhance the penetration of resin monomers into dentin substrate.

Being anacetone-based adhesive, Prime&Bond 2.1 showed stronger penetration of resin monomer into the deproteinizeddentin than that of the ethanol-based Single Bond. In contrast with it, the current study showed a distinct
decreasing tendency in bond strength with the use of PB, the descendant of Prime&Bond 2.1, although no86

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statistical difference was found.
As inconstant influence of NaOCl conditioning on dentin bonding was shown with different adhesives in thisstudy, it was speculated that bonding to deproteinized dentin relies on the diffusion ability of resin monomers ofadhesives. When NaOCl was applied to the etched dentin surface, it would not only remove the exposed
collagen fibrils, but also solubilize the fibrils down into the underlying mineralized matrix, leaving nano-sized
porosities within the conditioned substrate. Adhesives with litter monomers could easily penetrate into thesubmicron porosities previously occupied by collagen fibrils, to create an enhanced micromechanicalinterlocking. However, the relatively larger molecular weight of polyalkenoic acid copolymer, which was thefunctional monomer of SB, prevent it from effectively diffusing into the mineralized dentin,17 although it washigh diffusive in the collagen matrix of etched dentin. This could probably explain why SB yields decreased
bond strength to deproteinized dentin, while that of OS was increased. Additionally, it was also suggested thatsome adhesives such as OS contained acidic monomers could act as self-etchant, result in improved penetration
to the bonding substrate.8
Good marginal adaptation to the tooth structure is believed to reduce marginal discoloration, secondary caries,
postoperative sensitivity, and pulpal irritation related to microleakage. Dye penetration has been widely used totest the microleakage in vitro. Conventionally, the scoring of microleakage was simply based on the medial
section of the restorations,14 that is, the results were greatly influenced by the location and angle of the incision.
In the present study, serially multi-sectioned slabs were obtained and evaluated under stereomicroscopy, resulted
in a more sensitive and comprehensive detection throughout the interface.
Thermocycling has been commonly used in microleakage evaluation to simulate the long-term degradation ofdental bonding in vitro. However, it was doubted that if 500 cycles of thermocycling, as proposed by the ISO
standard, could effectively mimicking long-term bonding effectiveness;20 the validity and clinical significance ofit were also remains equivocal, since the temperatures and dwell time used to stress restorations may not be thereal temperatures of cold and hot food/beverage tolerated by patients.21 In order to minimize the number ofvariables that may affect microleakage, thermocycling was omitted and the immediate marginal sealability wasevaluated in this study.
The formation of marginal gaps in direct resin restorations is dependent on the polymerization shrinkage
stresses of the restorative materials, the quality and strength of the adhesive bond and the configuration of thecavity, among which the contraction forces of polymerization are considered the most important cause of bondfailure and consequently microleakage. When polymerized, the resin composite shrinks towards the stronger
bond at the occlusal margin and so pulls away from the weaker bond at the gingival margin, creating micro gapsthat allow microleakage to occur. As shown in the current study, all groups showed higher leakage scores at thegingival than at the occlusal walls. Compared with the occlusal margins, the severer microleakage shown at thegingival margins in the deproteinized groups indicated that bonding to NaOCl modified dentin surface was stillinferior to the acid-etched enamel.
As no significant difference in the leakage scores at both the enamel and gingival margins among different
pretreatments and materials were observed, bonding to deproteinized dentin was not superior to acid-etcheddentin in marginal sealing. Even without the presence of the stress produced by thermocycling, the current
adhesive systems failed to provide good sealing of resin-dentin interface. Since no materials and bonding
procedures could completely prevent microleakage at tooth-resin interface, adhesive materials incorporated with87

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Int Chin J Dent 2006; 6: 82-88.

anti-bacterial agents is advocated to minimize the occurrence of secondary caries.22
Since both bond strength and microleakage aspects are related to the quality of bonded interface, somecorrelation between data provided by these two tests would be expected. It is also suggested that high bondstrength could better compensate the polymerization shrinkage of composite resin. However, as no consistentinfluence was shown on the two aspects following NaOCl application as a surface conditioner, a lack ofrelationship between leakage and bond strength was observed. Leakage and bond strength are independent
parameters to evaluate the quality of adhesion between restorative materials and dental tissues.23

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Correspondence to:
Dr. Ji-hua Chen
Department of Prosthodontics, Stomatological College, The Fourth Military Medical University
Xi’an, 710032, P. R. China
Fax: +86-29-8253-4510 E-mail: jhchen@fmmu.edu.cn
Received April 1, 2006. Accepted May 5, 2006.
Copyright ©2006 by the International Chinese Journal of Dentistry.

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