Yoshikawa et al.

Asian Pac J Dent 2017; 17: 49-53

Effect of radiotherapy on resin composite bond strength andadaptation to dentin
Takako Yoshikawa, DDS, PhD (1), Alireza Sadr, DDS, PhD (1,2), and Junji Tagami,DDS, PhD (1)(1) Department of Cariology and Operative Dentistry, Division of Oral Health Sciences, Graduate
School of Medical and Dental Sciences, Tokyo Medical and Dental University (TMDU), Tokyo, Japan(2) IB3T Laboratory, Department of Restorative Dentistry, School of Dentistry, University ofWashington, Seattle, WA, USA
Purpose: To evaluate the effect of γ-ray irradiation on resin composite/dentin bond strength and the composite
adaptation to the dentin cavity wall.
Materials and Methods: Half of bovine incisors were irradiated with 60 Gy γ-rays. Flat dentin surfaces wereprepared on the labial side. Half of flat dentin surfaces were treated with Clearfil SE Bond. Clearfil AP-X
composite was built up. After light curing and 24 h storage, the teeth were sectioned and trimmed (ca. 1 mm2) atthe adhesive-dentin interface for microtensile bond strength test. The trimmed specimens were stressed to failure.
Other flat dentin surfaces were prepared cylindrical cavities. The cavities were restored with Clearfil SE Bondadhesive followed by Clearfil AP-X composite. After light curing and 24 h storage, dye penetration tests aroundthe cavities were performed. 60 Gy γ-ray irradiation significantly decreased resin composite adaptation to thecavity wall. Bond strength data were compared using the Bonferroni test. Dye penetration test scores wereanalyzed using the Kruskal-Wallis and Mann-Whitney U-tests.
Results: There was no significant difference between irradiated dentin and non-irradiated dentin of resin
composite bond strength (p > 0.05). However, 60 Gy γ-ray irradiation significantly decreased resin composite
adaptation to the cavity wall (p < 0.05).
Conclusion: Irradiation with 60 Gy γ-ray had no effect on resin-dentin bond strength. However, 60 Gy γ-rayirradiation significantly decreased resin composite adaptation to the cavity wall.
(Asian Pac J Dent 2017; 17: 49-53.)
Key Words: adaptation, bond strength, dye penetration, γ-ray irradiation, resin composite

IntroductionAdhesive dentistry is an important field of dental practice. Due to eating disorders, reflux esophagitis and theaging society, incidences of tooth wear, erosion and cancer have increased; and patients with head and neckcancer will require radiotherapy. The orofacial tissues affected by radiation include the salivary glands, mucousmembranes, taste buds, bone, and teeth [1]. Radiation caries is attributed to head or neck radiotherapy in thecervical area of the tooth [2]. Tooth wear and radiation caries cannot be treated using metal inlays placed forconventional Black’s cavities; such teeth can be restored only using resin composites with a direct bonding
technique.
Radiation induces reduction of saliva due to salivary gland lesion [3] and changes in microbial flora [4]. Most
orofacial complications are dependent on radiation dose, and severe side effects occur when doses are greaterthan 45 Gy [5]. Radiation of 60 Gy γ-ray significantly decreased the ultimate tensile strength [6] andmicrohardness of dentin [7], whereas 60 Gy γ-ray significantly increased microhardness of superficial enamel[7]. Irradiation with 70 Gy γ-ray significantly decrease shear bond strength of the bovine dentinoenamel junction
and may cause some damage to the biophysical properties [8].
Resin composite restorations with a direct bonding technique are indicated in cancer patients before or afterirradiation. However, the effect of γ-ray irradiation on dentin is still unclear. The purpose of this study was toevaluate the effect of γ-ray irradiation on resin/dentin bond strength and resin composite adaptation to the dentin
cavity wall.

49

Yoshikawa et al.

Asian Pac J Dent 2017; 17: 49-53

Materials and Methods
Specimen preparation
The materials, components, manufacturers, batch numbers, and bonding procedures used in this study are listed
in Table 1. An experimental quartz-tungsten-halogen light-curing unit (GC Corp., Tokyo, Japan), which wasconnected to a slide regulator, was used. This light-curing unit had a control system for lamp voltage andadjustable light intensity, which was measured using a curing radiometer (model 100, Demetron Research Corp.,
Danbury, CT, USA). Overall, 16 erupted intact bovine lower incisors, stored and frozen immediately after
extraction, were used in this study. Half of the incisors were irradiated with 60 Gy γ-ray using a cobalt-60
therapeutic machine (RCR-120, Toshiba Co., Tokyo, Japan); this is the total absorbed dose in one course ofradiotherapy in head or neck cancer patients. The labial enamel was ground using a model trimmer under
running water to expose a superficial flat dentin surface and then finished with a wet 600-grit SiC paper.
Table 1 Study materials
Materials and Manufacturer
Clearfil SE Bond
Kuraray Noritake Dental

Components
Batch No.
Primer: MDP, HEMA, hydrophillic aliphatic, dimethacrylates,00577A
colloidal silica, photoinitiator, accelerators, water
Bond: MDP, HEMA, Bis-GMA, hydrophobic aliphatic methacrylate,00817A
microfiller (colloidal silica), photoinitiator, initiator, accelerators
Clearfil AP-X
01118Asilanated barium glass filler, silanated silica filler, silanated colloidal silica,
Kuraray Noritake Dental
Bis-GMA, TEGDMA, photoinitiator, catalyst, accelerators, pigments, others
MDP, 10-methacryloyloxydecyl dihydrogen phosphate; HEMA, 2-hydroxyethyl methacrylate; Bis-GMA, bisphenol
A-glycidyl methacrylate; TEGDMA, triethyleneglycol dimethacrylate
Procedures: (a) apply primer for 20 s; (b) dry with gently air-blowing; (c) apply adhesive; (d) gently air-blow; (e) light-curefor 10 s

Tensile bond strength measurement
Other exposed superficial flat dentin surfaces were painted with a varnish (Protect Varnish, Kuraray Noritake
Dental Co., Tokyo, Japan), leaving a flat bonding area of length 3 mm × width 4 mm. The teeth were treatedwith a Clearfil SE Bond (Kuraray Noritake Dental Co.) adhesive. After curing of the adhesive, a resin composite(Clearfil AP-X, Kuraray Noritake Dental Co.) of length 3 mm × width 4 mm × height 2 mm was built up for themicro-tensile bond strength (µTBS) test. The composites were light cured for 40 s using a light intensity of 600
mW/cm2. After completion of light curing, the specimens were stored in water maintained at 37˚C in the dark for
24 h. After the storage, the restored non-irradiated/irradiated specimens were serially sectioned perpendicular tothe bonded surfaces creating 1-2, about 1-mm thick slabs using a diamond saw (ISOMET, Buehler, Lake Bluff,IL, USA) under copious water lubrication. The remaining dentin thickness (RDT) from the resin-dentin bond tothe nearest portion of the pulp chamber was measured in each slab, and the specimens were trimmed into anhour-glass shape with the narrowest portion (ca. 1 mm2) located at the adhesive-dentin interface using a diamondpoint (#211, Shofu Co., Kyoto, Japan) with copious air-water spray. Finishing was performed with a superfine
diamond point (#SF114S, Shofu Co.) in a high-speed handpiece.
The trimmed specimens were mounted on a µTBS jig (KDA, Tokyo, Japan) [9] with cyanoacrylate adhesive(Model repair II blue, Dentsply-Sankin, Otawara, Japan) and stressed to failure in tension at 1 mm/min in auniversal testing machine (EZ test, Shimazu, Kyoto, Japan). Each of seven tensile bond strength results wascompared and analyzed using the Bonferroni test at a significance level of 5%.
Scanning electron microscopy observation of fractured surfaces
After the tensile bond strength test, each fractured dentin specimen was fixed in 10% neutral buffered formalin

50

Yoshikawa et al.

Asian Pac J Dent 2017; 17: 49-53[9]. The dentin and composite paired specimens were then trimmed and viewed using scanning electron
microscope (SEM; JSM-5310LV; JEOL, Tokyo, Japan). The specimens were placed on SEM stubs and coatedwith gold sputter to microscopically assess the failure patterns. The fractured surfaces were classified into fourgroups: interfacial failure, mixed failure, cohesive failure within the resin (adhesive layer or composite), orcohesive failure within the dentin.
Evaluation of marginal sealing and cavity wall adaptation
Cylindrical cavities 1.5 mm in depth, 3 mm in diameter, and a C-factor of 3 were prepared on the flat dentin
surfaces of each tooth using a diamond point (#CR30, ISO No. 068 030, GC Corp.) under copious air-water
spray. Each of the seven cavities was treated with Clearfil SE Bond adhesive (Kuraray Noritake Dental Co.).
After the adhesive was cured, the cavities were bulk-filled with Clearfil AP-X resin composite (shade A3,Kuraray Noritake Dental Co.). The composites were light cured with an intensity of 600 mW/cm2 for 40 s. Aftercompletion of light curing, the specimens were stored in water maintained at 37˚C in the dark for 24 h. The dyepenetration test was used to determine the degree of adaptation to the cavity margins and walls. This test wasperformed by placing a 1.0% acid red propylene glycol solution (Caries Detector, Kuraray Noritake Dental Inc.)at the margin of the restoration for 5 s, followed by rinsing with water and gentle blow-drying. The extent of dye
penetration was observed with a stereo-microscope (20× magnification). A photographic record of eachspecimen was acquired at this stage.
The specimens were then longitudinally cut in half using a diamond saw microtome (77 model, Bronwill
Scientific Inc., NY, USA) under running water, the dye was reapplied to the sections, and images were acquired
to observe the gaps. In these images, the length of dye penetration along the cavity margins and walls wasmeasured using a digitizer (KD 4300 model, Graphtec Co., Tokyo, Japan). The degree of marginal leakage wasdetermined by the length of dye penetration, measured as a percentage of the total length of the cavity margin.
Dye penetration along the cavity walls was calculated as a percentage of the total cavity wall length. This area
was referred to as the cavity wall-resin gap. The dye penetration test scores were compared using theKruskal-Wallis and Mann-Whitney U-tests.

Results
The tensile bond strength results and RDT of the non-irradiated and irradiated groups are shown in Table 2.
There was no significantly different RDT or µTBS between the non-irradiated and irradiated groups (p > 0.05).
The results of the failure modes determined by SEM observation are shown in Table 3. Most of the fracturesurfaces of the non-irradiated group show cohesive failure within the dentin. The fractured surface of theirradiated group shows the same number of cohesive failures within the dentin as well as the mixed failure.
Figure 1 shows cohesive failure within the dentin for the non-irradiated group. Figure 2 shows cohesive failure
within the dentin for the irradiated group.
Table 2 Microtensile bond strength and RDT of γ-ray irradiatedand non-irradiated groups [mean (SD)]Non-irradiatedIrradiated

RDT (mm)
2.1 (0.1)
2.0 (0.2)µTBS (MPa)57.8 (5.9)
53.5 (6.2)

51

Yoshikawa et al.

Asian Pac J Dent 2017; 17: 49-53

Fig. 1 Fractured surface of non-irradiated dentin
side specimen. Failure mode indicated cohesive
failure within the dentin (5,000×).

Fig. 2 Fractured surface of irradiated dentin-side
specimen. Failure mode indicated cohesive
failure within the dentin (5,000×).

Table 3 Failure mode
Non-irradiatedIrradiatedInterfacial failure
01Mixed failure
33

Cohesive failure in resin
00

Cohesive failure in dentin
43

Table 4 Degree of marginal leakage and cavity-wall gap formation [%: mean (SD)]
Marginal leakage
Cavity-wall gap formation
Non-irradiatedIrradiatedNon-irradiatedIrradiated00
4.5 (9.0) a
24.4 (9.2) aSame superscript lower-case letters indicate significant differences in the strength ofbonding substrates (p < 0.05).

Degree of marginal leakage and cavity wall gap formation are shown Table 4. Both of non-irradiated andirradiated groups showed complete marginal sealing. However, 60 Gy γ-ray irradiation significantly decreased
resin composite adaptation to the cavity wall (p < 0.05).

Discussion
There was no significantly different tensile bond strength between the irradiated and non-irradiated groups.
Clearfil SE Bond adhesive showed complete marginal sealing, regardless of γ-ray irradiation. It has beenreported that 60 Gy γ-ray irradiation showed no effect on resin composite tensile bond strength of human flat
dentin with four different dentin bonding agents using divided irradiation for 6 weeks [10], supporting that 60
Gy γ-ray irradiation was ineffective on resin composite bond strength to the flat dentin surfaces. Clearfil SE
Bond showed high tensile bond strength to the superficial flat dentin surface and the flat dentin wall [11].
Therefore, Clearfil SE Bond adhesive showed excellent marginal sealing to both non-irradiated and irradiateddentin substrates.
On the other hand, 60 Gy γ-ray irradiation significantly decreased resin composite adaptation to the cavity
wall. Non-irradiated dentin surface showed well defined dentinal tubles (Fig. 1). However, irradiated dentin
surface showed dentin collagen fibers (Fig. 2). It has been reported 60 Gy γ-ray significantly decreased theultimate tensile strength [6] and microhardness of dentin [7]. Moreover, 70 Gy γ-ray irradiation significantly
decreased shear bond strength of the bovine dentinoenamel junction and may cause some damage to dentin
collagen fibers [8].
In this study, resin composite bond strength to flat dentin was not affected by γ-ray irradiation, whereas resin

52

Yoshikawa et al.

Asian Pac J Dent 2017; 17: 49-53

composite adaptation to Class V cavities was affected. γ-ray irradiation significantly decreased resin composite
adaptation to the cavity wall. We previously reported that C-factor affects resin composite bond strength [12-15]
and adaptation to the cavity wall [16-18]. C-factor of composite restoration on flat dentin is less than 1, whereasthat of composite restoration on the cylindrical cavity is 3. When C-factor is less or equal than 1, composite
restoration is likely to survive polymerization; and when it is more than 1, composite restoration shows lower
bond strength [12,13] and decreased adaptation to the cavity wall [16-18].
Therefore, dentin collagen destruction by γ-ray irradiation and C-factor seemed to decrease resin composite
adaptation to the cavity wall of irradiated dentin, suggesting that resin composite with Clearfil SE Bond adhesive
was affected by γ-ray irradiation damage of dentin on cavity restoration. Further research is required to confirm
the effect of γ-ray on resin composite bond and adaptation to the same cavity shape.
Acknowledgments
This work was supported by Grant-in-Aid for Scientific Research (B) 17390513 from the Ministry of Education, Culture,Sports, Science and Technology, Japan and Grant-in-Aid for Scientific Research (C) 16K11543 from the Japan Society for
the Promotion of Science.

References
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.

Carl W. Oral and dental care for cancer patients receiving radiation and chemotherapy. Quintessence Int Dent Dig 1981; 9:
861-9.
Pyykönen H, Malmström M, Oikarinen VJ, Salmo M, Vehkalahti N. Late effect of radiation treatment of tongue and floor-of
mouth cancer on the dentition, saliva section, mucous membranes and the lower jaw. Int J Oral Maxillofac Surg 1986; 15:401-9.
Frank RM, Herdly J, Phillipe E. Acquired dental defects and salivary gland lesions after irradiation for carcinoma. J Am Dent
Assoc 1965; 70: 868-83.
Brown LR, Dreizen S, Handler S, Johnston DA. Effect of radiation-induced xerostomia on human oral microflora. J Dent Res
1975; 54: 740-50.
Bruce R, Rothwell BR. Prevention and treatment of the orofacial complications of radiotherapy. J Am Dent Assoc 1987; 114:316-22.
Soares CJ, Castro CG, Neiva NA, Soares PV, Santos-Filho PCF, Naves LZ, et al. Effect of gamma irradiation on ultimate
tensile strength of enamel and dentin. J Dent Res 2010; 89: 159-64.
Goncalves LM, Palma-Dibb RG, Paula-Silva HF, Oliveira HF, Nelson-Filho P, Silva LA, Queiroz AM. Radiation therapy
alters microhardness and microstructure of enamel and dentin of permanent human teeth. J Dent 2014; 4: 986-92.
Pioch T, Golfels D, Staehle HJ. An experimental study of the stability of irradiated teeth in the region of the dentinoenamel
junction. Endod Dent Traumatol 1992; 8: 241-4.
Nakajima M, Sano H, Burrow MF, Tagami J, Yoshiyama M, Ebisu S, et al. Tensile bond strength and SEM evaluation ofcaries-affected dentin using dentin adhesives. J Dent Res 1995; 74: 1679-88.
Gernhardt CR, Kielbassa AM, Hahn P, Schaller HG. Tensile bond strengths of four different dentin adhesives on irradiatedand non-irradiated human dentin in vitro. J Oral Rehabil 2001; 28: 814-20.
Yoshikawa T, Wattanawongpitak N, Cho E, Tagami J. Effect of remaining dentin thickness on bond strength of various
adhesive systems to dentin. Dent Mater J 2012; 31: 1033-8.
Yoshikawa T, Sano H, Burrow MF, Tagami J, Pashley DH. Effects of dentin depth and cavity configuration on bond strength.
J Dent Res 1999, 78: 898-905.
Belli S, Dönmez N, Eskitaşcioğlu G. The effect of C-factor and flowable resin or fiber use at the interface on microtensile
bond strength to dentin. J Adhes Dent 2006; 8: 247-53.
Yoshikawa T, Sadr A, Tagami J. Effects of C-factor on bond strength to floor and wall dentin. Dent Mater J 2016; 35: 918-22.
Endo AV, Munk JD, Landuyt KV, Meerbeek BV. Effect of bulk-filling on the bonding efficacy in occlusal Class I cavities. JAdhes Dent 2016; 18: 119-24.
Yoshikawa T, Burrow MF, Tagami J. A light curing method for improving marginal sealing and cavity wall adaptation of resin
composite restorations. Dent Mater 2001; 17: 359-66.
Yoshikawa T, Burrow MF, Tagami J. The effects of bonding system and light curing method on reducing stress of different
C-factor cavities. J Adhes Dent 2001; 3: 177-83.
Wattanawongpitak N, Yoshikawa T, Burrow, MF, Tagami J. Effect of bonding system and composite type on adaptation ofdifferent C-factor restorations. Dent Mater J, 2006; 25: 45-50.

Correspondence to:Dr. Takako Yoshikawa
Department of Cariology and Operative Dentistry, Division of Oral Health Sciences,Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University (TMDU),
1-5-45, Yushima, Bunkyo-ku, Tokyo 113-8549, Japan
Fax: +81-3-5803-0195 E-mail: yoshikawa.ope@tmd.ac.jp
Accepted October 16, 2017.
Copyright ©2017 by the Asian Pacific Journal of Dentistry.
Online ISSN 2185-3487, Print ISSN 2185-3479

53