Maruoka et al.

Int Chin J Dent 2007; 7: 1-6.

Effect of resin-coating technique on coronal leakage inhibition in
endodontically treated teeth
Rena Maruoka, DDS, PhDa Toru Nikaido, DDS, PhD,a Masaomi Ikeda, RDT, BSc,aRichard M. Foxton, BDS, PhD, MFDS, RCS(Ed),b and Junji Tagami, DDS, PhDa,caCariology and Operative Dentistry, Department of Restorative Sciences, Graduate School, Tokyo
Medical and Dental University, Tokyo, 113-8549, Japanb
Department of Conservative Dentistry, King’s College London Dental Institute at Guy’s, King’s College
and St. Thomas`s Hospitals, London, UK
cCenter of Excellence Program for Frontier Research of Molecular Destruction and Reconstruction of
Tooth and Bone, Tokyo Medical and Dental University, Tokyo, Japan
Purpose: To evaluate the effect of the resin coating technique on coronal leakage inhibition in endodonticallytreated teeth.
Materials and Methods: Thirty-six extracted human incisors were cut at the level of the cemento-enamel
junction and standard endodontic obturations were made. They were divided into two groups; resin-coatinggroup, and non-coating group. For the resin-coating group, the dentin surfaces were coated with either aone-step coating material, Hybrid Bond or a combination of Hybrid Bond and a low viscosity microfilled resin,
SB Coat. They were subjected to thermal cycling for 0 or 1,000 times. Following this, the specimens were
coated with nail varnish leaving the coronal openings exposed. The apical parts were sealed with utility wax.
They were then immersed in 1% methylene blue solution for 48 hours. After removal from the dye, the teeth
were sectioned faciolingually using a diamond saw. Linear dye penetration (in mm) from the cementoenamel
junction was measured with photomicroscope. The number of the specimens was 12 for each group. The data
were analyzed by two-way ANOVA and Dunnett’s T3 test (p=0.05).
Results: Coronal leakage was influenced by the coating material and thermal stress (p<0.05). The resin-coatinggroups of HB and HB/SB had significantly less dye penetration compared with the non-coating group (p<0.05).
The combination of Hybrid Bond and SB coat effectively inhibited coronal leakage (p<0.05).
Conclusion: The resin coating technique effectively minimized coronal leakage of endodontically treated teeth.
Thermal stress demonstrated acceleration of dye penetration into the obturated root canal space.
(Int Chin J Dent 2007; 7: 1-6.)
Key Words: coronal leakage, endodontically treated tooth, resin coating technique, thermal cycling.

Introduction
Obtaining a hermetic seal is one of the keys to achieving a successful long-term root filling. However, ahermetic seal cannot be obtained if root canal filling materials do not bond to the dentin walls.1,2 Several
methods have been reported for preventing coronal leakage through obturated root canals in the event that thecoronal restoration becomes defective or lost. These include placement of an additional material into the canalorifice after removal of part of the gutta-percha and sealer, sealing the entire chamber floor with a restorative
material, or use of a root canal filling method that provides a seal without the addition of other sealingmaterials.3 Ideally, it would be that the root canal obturation alone prevents coronal leakage, since no extra steps
would then be required.
A resin coating technique has been developed for indirect restorations, in which both a hybrid layer and a tightsealing film are produced on the dentin surface.4 In this technique, a resin coating of a dentin adhesive system
and a low-viscosity microfilled resin are recommended to be applied to the prepared cavity immediately after
tooth preparation and just before taking impression. This technique has the ability to minimize pulpal irritation
caused by mechanical and thermal stimuli and bacterial infiltration in vital teeth.4 In addition, the technique canalso be applied in the restoration of non-vital teeth. Maruoka et al. evaluated the effect of resin coating oncoronal leakage inhibition in endodontically treated teeth.5 They concluded that application of a resin coating to
the coronal openings significantly reduced coronal leakage scores. However, the sealing ability was material

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Int Chin J Dent 2007; 7: 1-6.

dependent. Perfect sealing was demonstrated by a combination of Clearfil SE Bond and Protect Liner F, while asingle coating of Hybrid Bond (reported as an experimental material, RZII), did not eliminate the coronalleakage completely. The development of the single-step resin coating material, Hybrid Bond was aimed atresin-coating crown preparations.6,7 Because of a coating created with a single application of Hybrid Bond isapproximately 5-6 µm thick,8 Hybrid Bond might have allowed dye solution to penetrate through the Hybrid
Bond adhesive, thereby resulting in an increase in the coronal leakage score.5 In the clinical situation, a greater
degree of stress may be concentrated in the root, which may adversely affect the coronal leakage scores.
Therefore, the purpose of this study was to evaluate coronal leakage inhibition using resin coating with a single
application of a single-step coating material and a combined application with a low-viscosity microfilled resin.

Materials and Methods
Materials used in this study
The materials used in this study are listed in Table 1. For the resin coating, a single coat of Hybrid Bond (HB)or a combination of Hybrid Bond and a microfilled resin, SB Coat (HB/SB, Sun Medical, Moriyama, Japan) wasapplied to dentin. Hybrid Bond is a single-step bonding material, which is appropriate for the resin coating ofcrown preparations. Hybrid Bond was applied two times to all specimens in this study. SB Coat was also
developed as a low-viscosity micro-filled resin for resin coating.
Table 1.

Materials used in this study.

Trade name / Lot

Composition

Instruction

Hybrid Bond*
Lot KL1

Liquid:Water, Acetone, 4-META, Polyfunctional acrylate,
Monomethacrylate, Photo-initiators, Stabilizers
Sponge: p-toluene sulfinate, Amine

Mix sponge and liquid, Apply 20 s,
Dry, Light exposure 10 s,
Double coat

SB Coat*
Lot GL1

Liquid:Apply, Mildly air-blow,
Light exposure 20 s

Acetone, Dimethacrylate, Aromatic amine*Sun Medical Co., Ltd., Moriyama, Japan; 4-META, 4-methacryloyloxyethyl trimellitate anhydride.

Specimen preparation
Specimen preparation is illustrated in Fig. 1. Thirty-six extracted, single-canal, human incisors stored in
distilled water within 3 months of extraction were used. All the teeth were cut at the level of the cementoenamel
junction with a diamond bur (ISO #173016, GC Corp., Tokyo, Japan) under water spray. Standard endodontic
access cavities were made and the root canal contents were removed with #15-#35 K-type files (Zipperer, VDW
GmbH, Munich, Germany). Patency of the apical foramen was determined using a #35 K-type file. The
working length was established 0.5 mm short of the length at which this file exited the foramen, ensuring that theapical preparation was complete to within 1 mm of the apical foramen. The canals were irrigated with 3%
sodium hypochlorite and chemomechanically prepared to a #35 master apical file. The canals were dried withpaper points followed by apical cleaning. Master gutta-percha cones (GC Corp.) were fitted to within 1 mm of
the working length for each root canal. The cones were coated with Sealapex (Kerr, Orange, CA, USA), placedin the canal, and condensed by cold lateral condensation. Excess gutta-percha was removed with a heated hand
instrument at the level of the cementoenamel junction. After endodontic obturation, all the specimens wereplaced in water at 37°C for 24 hours to allow the sealer to set.

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Int Chin J Dent 2007; 7: 1-6.

The specimens were randomly divided into two groups; a non-coating group and a resin-coating group. For
the resin-coating group, the dentin surface was coated with either two coats of Hybrid Bond (HB) according to
the manufacturer’s instructions or a combination of Hybrid Bond and SB coat (HB/SB). Resin coated surface
was light cured by using New Light-VL-II (GC Corp.). Half of the specimens in all the groups were thensubjected to thermal stress, which ranged from 5˚C to 55˚C for 1,000 times.

Fig. 1.

Specimen preparation.

Following this, the entire tooth surfaces were coated with nail varnish leaving only that coronal openings
exposed. The apical parts were sealed with utility wax. The teeth were then placed in 1% methylene blue
solution for 48 hours and then sectioned faciolingually using a water-cooled diamond saw (Leitz 1600, Wetzlar,
Germany).

Measurement of the dye penetration was carried out to the nearest 0.01 mm using astereomicroscope (Olympus Colposcope, Olympus Optical Japan, Tokyo, Japan) with x3 magnification. Eachside of linear dye penetration from the cementoenamel junction was measured.
Statistics
Dye penetration at a total of 12 points was scored for each group. The mean dye penetration score wascompared for each group utilizing two-way analysis of variance (ANOVA) at a 95% confidence interval. The
two factors analyzed were coating material and storage condition. Following this, Dunnett’s T3 test was
performed (p=0.05).

Results
The results of the dye penetration test are summarized in Table 2, respectively. Two-way ANOVA revealed
that coronal leakage was influenced by both coating material (F=174.71, p<0.0001) and thermal stress (F=39.21,
p<0.0001). The resin-coating groups of HB and HB/SB had significantly less dye penetration compared with the
non-coating group (p<0.05). In comparison among the resin-coating groups, resin-coating with HB/SB showedstatistically lower coronal leakage than HB (p<0.05).

All the groups that were thermal cycled exhibited

statistically increased dye penetration scores than the groups without thermal stress (p<0.05).

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Maruoka et al.
Table 2.

Int Chin J Dent 2007; 7: 1-6.

Effect of thermal stress on dye penetration score (mm).

Thermal cycling

0
1,000

No coating
Mean
SD
1.48
2.27

0.50
0.32

Categorya, da, fHybrid Bond
Mean
SD
0.41
0.87

Category

0.26
0.35

b, d, eb, fHybrid Bond / SB Coat
Mean
SD Category
0.13
0.29

0.17
0.23

c, d, ec, fSample size=12, Identical letters indicate statistically significant differences (p<0.05).

Discussion
In order to evaluate dye penetration, methylene blue solution was chosen as a tracer in this study. Previously,
several dye solutions, such as nitric acid,9 pelican ink,3,10 india ink12 and methylene blue dye solution2,5,12-14 havebeen used for the dye penetration test. Although there is no universally accepted solution, dye penetration
experiments using a 0.2-2.0 % methylene blue solution have been commonly used in leakage studies.15,16
Higher coronal leakage occurred in the non-coated groups. Temporization was not carried out in this study. It
was reported that a temporary filling material did not provide a sufficient marginal seal.5 A water-setting
temporary material, Cavit-G (3M-ESPE, Seefeld, Germany) was recommended after resin coating,17 which
reduces mixing inconsistencies commonly encountered during chairside manipulation.

However, such ahygroscopic material tends to absorb fluids, which can be demonstrated by dye penetration into the fillingmaterial.18 Therefore, temporary fillings can delay the progress of dye penetration but not inhibit coronalleakage.
A post space was not prepared at the coronal opening in this study. However, it was reported that post space
preparation increased coronal leakage in non-coated specimens.5

It is desirable that during post space

preparation, the root canal sealer/gutta-percha and root canal sealer/root dentin interfaces should be stabilized
without dislodgement or loss of seal. However, post space preparation stimulates a gap between the root androot canal filling material.19 Moreover, a post space preparation shortens the distance from the root opening to
the apex, thereby increasing the risk of coronal leakage.
Application of a resin coating to the coronal openings significantly reduced coronal leakage scores. In theprevious study, good coronal sealing was demonstrated by a combination of Clearfil SE Bond and Protect Liner
F.5 With the resin-coating technique, a suitable combination of a dentin bonding system and a low-viscosity
microfilled resin can improve adhesion to dentin.20 Furthermore, an additional application of a low-viscosity
microfilled resin can protect and promote polymerization of the underlying adhesive, resulting in increased bondstrength.21
The resin coating material, Hybrid Bond, is categorized as an all-in-one adhesive, which is composed of anadhesive and a sponge. The sponge contains co-activators of p-toluene sulfinate and an aromatic amine that
promote polymerization at the adhesive-tooth interface.22 It has been reported that a single coat of Hybrid Bond
applied to the flat dentin surface created a thin film, 5-6 µm thick, which is appropriate for resin coating a crown
preparation.7 The previous study reported that there were no significant differences in dentin bond strength
between single and double coats of Hybrid Bond.22 Therefore, a double coat of Hybrid Bond was applied in thisstudy. The present results revealed that application of Hybrid Bond reduced coronal leakage, but did not
eliminate it completely. SB Coat was developed as a low-viscosity micro-filled resin for resin coating. The
combination of Hybrid Bond and SB Coat significantly reduced coronal leakage scores, however, perfect sealing

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Int Chin J Dent 2007; 7: 1-6.

could not be achieved.
Thermal cycling allows bonded specimens to be subjected to extreme temperatures, which simulate intraoral
conditions. The ISO TR 1140523 has indicated that the thermal cycling test comprising 500 cycles in water
between 5 and 55°C is an appropriate accelerated aging test. However, the effects of thermal cycling depend on
the adhesive bonding systems used, and the number of thermal cycles.24 In the present study, the groups thatwere thermally stress demonstrated significantly higher dye penetration than the groups which were not.
Recent dentin adhesive systems can bond to root canal dentin and pulpal floor dentin as well as to coronaldentin. However, the chemical irrigants and medicaments that are used during root canal treatment are theclinical factors that influence dentin bonding.25,26 Further studies are required to evaluate the influence of suchfactors on coronal leakage inhibition. From a clinical stand-point, the resin coating technique has strong
possibilities for minimizing coronal leakage and removal of sound tooth structure, resulting in the achievementof minimally invasive restorations for non-vital teeth.
Acknowledgments
This study was supported by the grant (#15209064) from the Ministry of Education, Culture, Sports, Science andTechnology of Japan and the grant for the Center of Excellence Program for Frontier Research on Molecular Destruction andReconstruction of Tooth and Bone at Tokyo Medical and Dental University.

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Correspondence to:
Dr. Rena Maruoka
Cariology and Operative Dentistry, Department of Restorative Sciences, Graduate School,
Tokyo Medical and Dental University, 1-5-45, Yushima, Bunkyo-ku, Tokyo, 113-8549, Japan
Fax: +81-3-5803-0195 E-mail: maruoka.ope@tmd.ac.jp
Received January 6, 2007. Accepted January 30, 2007.
Copyright ©2007 by the International Chinese Journal of Dentistry.

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