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ORIGINAL ARTICLE
Year : 2017  |  Volume : 20  |  Issue : 8  |  Page : 924-929

Effect of irradiation on the shear bond strength of self-adhesive luting cement in different preparation depths


1 Department of Prosthodontics, Faculty of Dentistry, Bülent Ecevit University, Zonguldak, Turkey
2 Department of Prosthodontics, Faculty of Dentistry, Ordu University, Ordu, Turkey
3 Department of Medical Laboratory Techniques, Health Services Vocational Collage, Trakya University, Edirne, Turkey
4 Department of Prosthodontics, Faculty of Dentistry, Cumhuriyet University, Sivas, Turkey

Date of Acceptance05-Feb-2016
Date of Web Publication11-Sep-2017

Correspondence Address:
O Sahin
Department of Prosthodontics, Faculty of Dentistry, Bulent Ecevit University, 67600 Zonguldak
Turkey
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/1119-3077.180071

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   Abstract 

Objective: The purpose of this study was to evaluate the effects of pre- and post-irradiation application on the shear bond strength of self-adhesive luting cements to dentin and enamel. Materials and Methods: Thirty-two extracted human maxillary incisor teeth were used in this study. Teeth were divided into two main groups according to preparation depth (0.5 mm and 1 mm) as Group E and Group D and were divided into four subgroups according to treatment protocol (n = 12). Teeth were irradiated and preparation was done after radiation. Adhesive luting cement was placed on the irradiated enamel and dentin surface (Groups E1, D1). Preparation was done before irradiation and resin cement was placed on the irradiated enamel and dentin surface (Groups E2, D2). The resin cement was first placed on their enamel and dentin surfaces and then the specimens were irradiated (Groups E3, D3). Irradiation was done with a total dose of 60 Gy, applied in fractions over 6 weeks for each groups (2-Gy/day fractions, 5 days per week). Nonirradiated groups were determined as controls groups (Groups C1, C2). The shear bond strengths of adhesive luting cement were examined. Results: According to the two-way ANOVA results, depth of preparation and treatment protocol and their interactions were significant on shear bond strength of resin cement (P < 0.05). Conclusions: This study detected significant differences between the irradiated and nonirradiated groups, probably due to the changes in the crystalline structure of dental hard tissues.

Keywords: Bond strength, irradiation, self-adhesive luting cement


How to cite this article:
Sahin O, Dede D &, Köroğlu A, Özgüven Y, Doğan D &. Effect of irradiation on the shear bond strength of self-adhesive luting cement in different preparation depths. Niger J Clin Pract 2017;20:924-9

How to cite this URL:
Sahin O, Dede D &, Köroğlu A, Özgüven Y, Doğan D &. Effect of irradiation on the shear bond strength of self-adhesive luting cement in different preparation depths. Niger J Clin Pract [serial online] 2017 [cited 2017 Sep 25];20:924-9. Available from: http://www.njcponline.com/text.asp?2017/20/8/924/180071


   Introduction Top


The patients undergoing radiation therapy for head and neck cancer (HNC) need multidisciplinary approach for dental management because of the side effects of this treatment.[1] Beside the temporary consequences such as loss of taste, sensitive soft tissues, and fungal infections, some side effects are more permanent such as atrophic muscles, change of bacterial microflora and proteins.[2],[3],[4] In addition, clinically, a rapid deterioration of the dental hard tissues, which consists of enamel, dentin, and dentinoenamel junction, could be observed as a side effect of radiation therapy.[2],[4],[5],[6] Some chemical changes in enamel, reduction of microhardness in dentin, and reducing stability of amelodentinal junction could be observed after radiotherapy.[7],[8],[9] Radiation caries, which is known as an indirect side effect of radiation therapy, often occur on the cervical region besides occlusal and incisal edges, and besides buccal and oral surfaces.[10],[11],[12] In the literature, adhesive restorative techniques were recommended for irradiated patients just because of the reduced life expectancy.[5],[11],[13]

Preradiotherapy dental management generally include extraction of the untreatable and having suspicious prognosis teeth, preventive dental care, use of fluoride, and education of the patient about the oral hygiene.[14] Thariat et al. reported that only 11% of the patients who have HNC did not need preradiotherapy dental care.[15] Furthermore, recently diagnosed with HNC patients have high prevalence to dental disease.[16],[17] Therefore, it is recommended that simple restorations should be done before radiotherapy.[14] The adhesive resin cements, often used for luting of ceramic restorations, are preferred for their good esthetic and mechanical characteristics such as high flexural, compressive shear, tensile bond strength, and high elastic modulus that prevent the decementation during the function.[18],[19],[20] However, resin cements require multiple sensitive clinical steps. Therefore, self-adhesive cements were recently introduced to simplify the luting procedure.[21]

In the literature, only a few studies were focused on the bond strength of adhesive restorative techniques systems that was applied to irradiated dentin,[9],[11],[22] and there is no report available about the bond strength of adhesive luting cement on irradiated enamel and dentin. Hence, the aim of this study was to evaluate the effects of pre- and post-irradiation application on the bond strength of self-adhesive luting cement onto the enamel and dentin.


   Materials and Methods Top


Thirty-two extracted human maxillary incisor teeth were used in this study. The study was approved by the Research Ethics Committee of Ordu University (2015/2). The teeth were cleaned of debris and stored in phosphate-buffered saline at room temperature for up to 3 months until the experiment. The specimens of test groups (n = 12) are given in [Table 1]. Teeth in Group E1 and D1 (nonprepared surfaces) were embedded in chemically polymerized acrylic resin (Imicryl, Konya, Turkey) blocks and were irradiated with a total dose of 60 Gy, applied in fractions over 6 weeks (2-Gy/day fractions, 5 days per week). For homogeneity of the irradiation, the teeth were stored in daily renewed saline.
Table  1: The specimens of test groups

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Teeth in Group E1 were prepared by pilot burs at 0.5 mm depth and teeth in Group D1 were prepared by pilot burs at 1 mm depth under constant water cooling. The prepared surface of each tooth was polished with 400- and 600-grit silicon carbide abrasive papers subsequently. Only enamel was etched using K-Etchant Syringe (Kuraray Noritake Dental Inc.,) and then the self-adhesive cements (Panavia SA Cement Plus Automix, Kuraray Noritake Dental Inc., Japan) were luted on the labial surface of teeth with tygon tubes (three tubes on each tooth) that have 7 mm diameter and 1 mm height and light cured for 10 s with a light-emitting diode (LED) curing light (Elipar FreeLight 2, 3M ESPE, St. Paul MN, USA) at an intensity of 750 mW/cm 2 [Figure 1].
Figure 1: Preparation process of specimens

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Teeth in Group E2 were prepared by pilot burs at 0.5 mm depth and teeth in Group D2 were prepared by pilot burs at 1 mm depth under constant water cooling. The prepared surface of each tooth was polished with 400- and 600-grit silicon carbide abrasive papers subsequently. The specimens were embedded in chemically polymerized acrylic resin blocks and prepared surfaces were irradiated by using the same protocol, afterward the resin cement was applied using the same protocol.

Teeth in Group E3 were prepared by pilot burs at 0.5 mm depth and teeth in Group D3 were prepared by pilot burs at 1 mm depth under constant water cooling. The prepared surface of each tooth was polished with 400- and 600-grit silicon carbide abrasive papers and the resin cement was applied to labial surface such as Groups E1, D1, E2, and D2. The specimens were embedded in chemically polymerized acrylic resin blocks. Prepared surfaces and bonded cement were irradiated by using the same protocol.

Teeth in Group C1 were prepared by pilot burs at 0.5 mm depth and teeth in Group C2 were prepared by pilot burs at 1 mm depth under constant water cooling. The resin cement was applied by using the same protocol and teeth were kept as nonirradiated control groups.

Specimens were placed in a universal testing machine (LF Plus, LLOYD, Instrument, Ametek Inc., England). The metal ring was connected with the cross-head and loaded (speed 1 mm/min). Loading was applied to each specimen until the bond between the exposed surface of teeth and resin cement failed. The maximum shear bond strength was recorded from a personal computer as Newton (N) and converted to MegaPascal (MPa). The shear bond strength results (MPa) were analyzed using two-way ANOVA to evaluate the effects of preparation level, treatment protocol, and their interactions. The mean shear bond strength values were then compared using the Tamhane's test. Significance was evaluated at < 0.05 for all tests. All the computational work was performed by means of SPSS 16.0 statistical software (SPSS 16.0; SPSS Inc., Chicago, USA).

To analyze the Fourier transform infrared spectroscopy (FTIR) of the specimens, the self-adhesive cements (Panavia SA Cement Plus Automix Kuraray Noritake Dental Inc., Japan) were placed in a stainless steel mold (5 mm diameter, 2 mm height) and light cured for 10 s with a LED curing light (Elipar FreeLight 2, 3M ESPE, St. Paul MN, USA) at an intensity of 750 mW/cm 2. A total of ten specimens were prepared for each group. Half of the specimens were irradiated with a total dose of 60 Gy, applied in fractions over 6 weeks (2-Gy/day fractions, 5 days per week). Specimens were stored in water until FTIR analysis. Thin transparent tablets, which were formed from the control and irradiated adhesive resin cements, were triturationed through KBr (potassium bromide) under the 200 bar. FTIR spectra of the samples were registered by using Unicam Mattson 1000 FTIR spectrometer. (Cambridge, UK).

Enamel and dentin structure was examined with a scanning electron microscope (SEM) (Nova Nano SEM 450, FEI Co., USA) for irradiated and nonirradiated teeth. The acceleration voltage of cathode was set to 14 kV. The images were obtained at ×1,000 and ×10,000 magnifications.


   Results Top


According to the two-way ANOVA results, depth of preparation and treatment protocol and their interactions were significant on shear bond strength of resin cement (P < 0.05) [Table 2].
Table  2: Two-way analysis of variance results for comparison of shear bond strength values

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The mean shear bond strength values and standard deviations for resin cement, preparation depth, and treatment protocol are shown in [Table 3]. Tamhane's post-hoc comparisons are shown as smallcaps, and values having same letters are not significantly different (P > 0.05). For the 0.5 mm depth of preparation, the mean shear bond strengths for the Groups E1, E2, and E3 were significantly lower than the control C1 group (P < 0.05). In addition, the mean shear bond strength for the Groups E2 and E3 were significantly lower than E1 group (P < 0.05). No significant differences were found between the Groups E2 and E3 (P > 0.05). For the 1 mm depth of preparation, the mean shear bond strengths for the Groups D2 and D3 were significantly lower than D1 and C2 groups (P < 0.05). No significant differences were found between the Groups D2 and D3 (P > 0.05). [Figure 2]a and [Figure 2]b shows the FTIR spectra of the nonirradiated and irradiated self-adhesive luting cement (Panavia SA Cement Plus Automix, Kuraray Noritake Dental Inc., Japan) between 550 and 4000 cm −1. According to FTIR analysis results, there were no differences between the irradiated and nonirradiated self-adhesive luting cement.
Figure 2: (a and b) Fourier transform infrared spectra of both irradiated and nonirradiated adhesive luting cement. Strong broadband at about 1020 cm-1 C—O—C diglycidylmethacrylate and triethylene glycol dimethacrylate. Absorption at about 1700 cm-1 showed the C—O stretching band of the carboxylate salts of the polyacid. 3000–3500 cm-1 band in spectra was showed to the water band, meant that O—H  (or—COOH) group probably did not react

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Table  3: Mean, standard deviation, and Tamhane's multiple comparison test results

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The SEM images show that the well-organized prisms which were observed in nonirradiated enamel changed into an amorphous structure after irradiation [Figure 3]. In addition, the well-organized collagen network and dentinal tubes which were observed in nonirradiated dentin were undergone change and degradation [Figure 4].
Figure 3: Scanning electron micrograph of the enamel. The images were obtained by scanning electron microscopy at ×1,000 (a and c) and ×10,000 (b and d). (a and b) nonirradiated enamel, (c and d) irradiated enamel

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Figure 4: Scanning electron micrograph of the dentin. The images were obtained by scanning electron microscopy at ×1,000 (a and c) and ×10,000 (b and d). (a and b) nonirradiated dentin, (c and d) irradiated dentin

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   Discussion Top


The cumulative doses of ionizing radiation to the head and neck region range from 50 to 70 Gy delivered over 5–7 weeks and causes comprehensive side effects.[23] In the present study, specimens were irradiated with 60 Gy, fractionally applied over a period of 6 weeks, which corresponded to standard clinical procedures.[7] It was reported that the storage medium of extracted teeth affects the result of the bond strength studies.[24] In the current study, buffered saline was used as storage medium.[22],[25]

It is recommended that HNC patients' restorative procedures should be kept simple to provide esthetic and function.[13] Although some authors offer adhesive restorative techniques for irradiated patients and avoid the extensive treatment,[13],[26] general objectives of dental care of the HNC patients, which include having function and esthetic dentition, have no difference from normal ones.[14] Clinically, HNC patients could already have cemented indirect restorations or restorations could be decemented during the radiotherapy or could have needed cemented indirect restorations after radiotherapy. That is the reason why we have designated four groups for each preparation depth.

Adhesive systems require technical precision during operation, such as the need for a separate set of adhesive application stage.[18] In recent years, self-adhesive resin cements have been developed to eliminate technical errors and also to decrease the chair time.[21],[22] In the present study, self-adhesive resin cement was used because of having advantages which was stated above. Self-adhesion mechanism could continue for weeks or even months.[27] As the timeframe of irradiation sequences was set as 6 weeks, all specimens were stored in water during the period of 6 weeks, until the shear bond test.

There is no study in the literature about the direct effect of irradiation on adhesive luting cement. Studies dealing with irradiation effects on dental materials focused mainly adhesive restorative techniques.[11],[22],[28] Gernhardt et al. investigated the tensile bond strength of dentin adhesives on irradiated and nonirradiated dentin and found no differences between the groups.[11] As similar, Bulucu et al. found no differences between the control and preirradiated groups.[22] In addition, it was reported that the mechanical properties of dentin seemed to be less affected by irradiation than the enamel.[29] In the present study, significant differences were observed between the Groups (preirradiated) C1 and E1 whereas no significant differences were observed between the Groups C2 and D1.

The current study was planned to find out the effect of irradiation on the restored tooth and to appraise the effects of X-ray irradiation on the interfaces between the tooth and the restoration. Therefore, their radiation also was done after restoration in test Groups E3 and D3. Yesilyurt et al.[9] investigated the effect of irradiation on glass ionomer cements and found that postirradiated group was shown lower bond strength than control groups and they claimed that irradiation might break the chemical bond between glass ionomer cements and dentin. In the present study, postirradiated Groups (E3, D3) had significant lower bond strength than control (C1, C2) and preirradiated (E1, D1) groups, but there were no significant differences found between the Groups of E2–E3 and D2–D3. Taken together, FTIR spectra of irradiated and nonirradiated luting cements were not different from each other. Moreover, no significant differences between the Groups of E2–E3 and D2–D3 were found. This could not be explained by broken chemical bonds.[30] The common feature of Groups E2, E3 and D2, D3 was surface property of teeth during the radiotherapy. Surface of the teeth in this groups was already prepared before the irradiation, had no sound enamel and dentin, and damaged surface was exposed to irradiation. The effects of irradiation on the structural changes of enamel and dentin are controversial.[7],[8],[29],[31],[32] Although enamel composition is mainly inorganic, irradiation affects the organic portion of enamel initially.[33] However, de Siqueira Mellara et al. reported that irradiation may affect both organic and inorganic compounds in the enamel.[32] Hence, the mechanical properties and integrity of the enamel could be affected.[29] In contrast to some authors,[34],[35] it was reported that irradiation could break down the dentinal collagen matrix [36] or could change crystalline structure of dentin,[37],[38] hence could affect the mechanical stiffness of dentin.[7] This study detected significant differences between the irradiated and nonirradiated groups. This situation is also supported by the SEM images. The changes in the crystalline structure of dental hard tissues after irradiation [7],[37],[38] seemed to affect the bond strength of adhesive luting cement.

The limitation of this in vitro study is that only one type of luting cement was used. Therefore, different types of adhesive resins should be evaluated under the same experimental conditions. In addition, the further investigations that assess the in vivo conditions should be made.


   Conclusions Top


Within the limitations of this study, the following conclusions can be drawn:

  • Dentin seemed to be less affected by irradiation than the enamel
  • Time of irradiation (before or after preparation) has significant effect on shear bond strength of adhesive luting cement
  • Irradiation has no effect on the chemical bonds of adhesive luting cement.


Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
   References Top

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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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