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Table of Contents   
ORIGINAL ARTICLE  
Year : 2013  |  Volume : 16  |  Issue : 2  |  Page : 148-151
Ionizing irradiation affects the microtensile resin dentin bond strength under simulated clinical conditions


1 Department of Conservative Dentistry and Endodontics, SGT Dental College, Gurgaon, Haryana, India
2 Department of Prosthodontics, SGT Dental College, Gurgaon, Haryana, India

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Date of Submission19-Oct-2012
Date of Decision04-Jan-2013
Date of Acceptance04-Jan-2013
Date of Web Publication7-Mar-2013
 

   Abstract 

Objectives: This study evaluated the effect of ionizing radiations on resin-dentin interface in terms of marginal adaptation and micro-tensile bond strength under thermocycling and mechanical loading.
Materials and Methods: Forty extracted human mandibular third molars were divided into four groups. GR I: No Irradiation and Class II MO cavities were prepared that were restored with composite restorations; GR II: Teeth were irradiated and restored; GR III: Teeth were restored and irradiated; GR IV: Teeth were restored during irradiation dosage fractions. All samples were thermal and mechanical loaded with 5000 cycles, 5 ± 2-55 ± 2°C, dwell time 30 s and 150,000 cycles at 60N. Resin-dentin slabs were trimmed into dumbbell-shaped slabs and microtensile bond strength was measured. The bond strength data was analyzed by one-way analysis of variance test.
Results and Conclusions: Irradiation before tooth preparation deteriorated the microtensile bond strength.

Keywords: Cyclic loading; composite resin; ionizing irradiation; resin dentin bond strength

How to cite this article:
Yadav S, Yadav H. Ionizing irradiation affects the microtensile resin dentin bond strength under simulated clinical conditions. J Conserv Dent 2013;16:148-51

How to cite this URL:
Yadav S, Yadav H. Ionizing irradiation affects the microtensile resin dentin bond strength under simulated clinical conditions. J Conserv Dent [serial online] 2013 [cited 2019 May 19];16:148-51. Available from: http://www.jcd.org.in/text.asp?2013/16/2/148/108198

   Introduction Top


Oral malignancies constitute a major share among the common encountered malignancies. [1] The treatment modality includes either surgical intervention, radiotherapy and chemotherapy, or a combination of these modalities. Radiotherapy includes application ionizing irradiation to cancer cells, damaging their cellular deoxyribonucleic acid and thereby preventing their replication. Unfortunately, the effects of radiotherapy are not selective and ionizing radiotherapy has serious side-effects, including the loss of salivary gland function, [2] post-irradiation gustatory dysfunction [3] and acute olfactory changes. [4] The extent of these adverse effects depends on various factors such as total irradiation dose, the area affected by irradiation, fractionation of dose and physical factors of the patient. [5],[6],[7] Majority of the patients require a total irradiation dose of 50-70 Gray (Gy), which is fractionated in a span of 5-7 weeks, with a daily dose of 2 Gy. Severe adverse effects like refractory ulcerations near the adjacent normal tissues have also been reported. There are certain clinical conditions where the adjacent teeth come in the line of irradiation and may get affected by irradiation. Several studies had evaluated the effect of radiation on bone, [5] taste bud cells, [3] osteoblasts, [5] osteoclasts, [6] salivary gland tissues [2],[7] and dentin microhardness, [8] but the effect of ionizing radiation on resin-dentin interface remains obscure.

Radiation caries is a common finding in patients undergoing radiotherapy, which may be secondary to xerostomia. [9] The treatment protocol for a patient undergoing radiotherapy includes restoration of all carious teeth before initiating radiotherapy. [10] Also, during and after radiotherapy, the caries index of the patient rises, which demands restoration of new carious lesions. It is hypothesized that existing restorations and new restorations may be affected by radiations as irradiation may affect the collagen fibril network of dentin and may affect the formation of a hybrid layer of composite restorations. The present study evaluated the effect X-ray radiotherapy on the resin-dentin interface in terms of marginal adaptation and microtensile bond strength under thermocycling and cyclic loading.


   Materials and Methods Top


Forty freshly extracted, caries-free, human permanent mandibular third molars (having approximately the same width and length) were collected. Teeth were cleaned of debris and were stored in normal saline for a maximum period of 1 month. Ten samples were kept as the control group (no irradiation). Thirty samples were divided into three groups and irradiated with low linear energy transfer (LET) X-ray radiation as follows:

Control group GR I: (no irradiation) Standard Class II MO cavities were prepared. The occlusal portion of the preparation had a facio-lingual width of. [1] 5 mm and depth of 1.8 ± 0.25 mm. The isthmus was prepared up to 1/3 rd of the facio-lingual width of the tooth. The gingival floor of the proximal box was kept the cement-enamel junction (CEJ) to keep the gingival margins in dentin. Cavities were etched with 35% phosphoric acid gel for 15 s and rinsed for 15 s, leaving a visibly moist surface. Two consecutive coats of Single Bond (3M ESPE) adhesive were applied and light-cured for 10 s. A clear plastic matrix strip was placed. A nanohybrid restorative resin (Z 350 3M ESPE) was placed in the cavity in 2 mm increments. Each increment was cured for 20 s by a quartz tungsten halogen (QTH) (Vivadent) light cure unit. Curing was done initially from the occlusal direction and then from the buccal and lingual directions. After curing, the matrix strip was removed and gingival margins contoured with a composite polishing kit (Shofu Co., Japan). Samples were subjected to thermocycling (5000 cycles, 5 ± 2-55 ± 2°C, dwell time 30 s) and cyclic loading of 150,000 cycles at 60N (simulating 6 months of oral masticatory stresses).

GR II: Ten samples were exposed to X-rays with tube voltage 120 kVp, tube current 5 mA, filtration 2.25 mm Al and 0.15 mm Cu, source to surface distance 30 cm, dose 1 Gy/min. Samples were irradiated at 2 Gy/fraction, 5 times/week, for a total dose of 60 Gy in 30 fractions during 6 weeks. Samples were stored in normal saline before and after irradiation. After radiotherapy, standard Class II MO cavities were prepared and restored and thermo-mechanical loading was applied as in the control group.

GR III: Standard Class II MO cavities were prepared in 10 samples. The cavities were restored and thermo-mechanical loading was applied as in the control group. After restoration, X-ray irradiation was done as in GR IA.

GR IV: Ten samples were exposed to X-ray irradiation. After 15 fractions/3 weeks of dosage, cavities were prepared, restored and thermo-mechanically loaded. The remaining irradiation was completed subsequently.

Each tooth was vertically sectioned into two or three 1-mm-thick serial slabs by means of an Isomet saw under water lubrication. The slabs were trimmed into dumbbell-shaped specimens according to the technique for the microtensile bond test reported by Sano et al.,[11] with the smallest dimension at the bonded interface representing the bonded tissue of interest. Trimmed specimens were mounted on a testing apparatus of Universal Instron testing machine (Zwick testing instrument [Zwick GmbH and Co., postf. 4350, D-7900u/m, Germany]) with the help of a cyanoacrylate adhesive. The samples were stressed to failure at a crosshead speed of 0.5 mm/min. The tensile bond strength was calculated as the load at failure divided by the bonded area (1 mm 2 ). The findings were recorded onto a Microsoft Excel sheet (Microsoft Office Excel 2003) for statistical evaluation using the program SPSS 11.5 for Windows (SPSS Inc., Chicago, IL, USA). One-way analysis of variance (ANOVA) was used for comparing these variables among the four groups. The significance between the individual groups was calculated using a post hoc Holm-Sidak test.


   Results Top


The control group (without irradiation) had a micro tensile bons strength (μTBS) of 22.898 ± 1.737 (MPa). The value of μTBS significantly reduced in restorations done after radiotherapy [Graph 1] [Additional file 1]. The μTBS of GR II was 17.722 ± 0.834 MPa, which was significantly lower than the control group (P < 0.05).

GR III had a bond strength of 21.662 ± 1.236 MPa. The μTBS of restorations done between radiotherapy was less than in the control group (20.448 ± 1.236 MPa), but was statistically insignificant.


   Discussion Top


Radiotherapy is an inevitable component of contemporary cancer management therapy, which includes irradiation of tumor mass with ionizing radiations. The ionizing radiation causes tissue injury by two mechanisms: Direct and indirect. [12],[13] In the direct mechanism, the ionizing radiations generate electron loss as well as electron gain centers through ejection of electrons and capture of ejected electrons, respectively. There is a direct alteration of biological molecules, and approximately one-third of the biological effects result from a direct effect. The indirect mechanism involves the reaction of target tissue with free radicals produced by the action of radiation on water. These radicals include OH radicals and hydrated electrons. Majority of the radiation-induced biological damage results from indirect effects. [14],[15],[16]

The prognosis of radiotherapy treatment depends upon various variables including radiosenstivity of the target tumor mass and radiosenstivity of the surrounding normal tissues. [16] A successful treatment requires a high ionizing radiation dosage to tumor mass and a minimal irradiation of the normal surrounding tissues. The response of cells to irradiation depends on exposure parameters like dose, dose rate, oxygen and LET. [16] A typical radiotherapy treatment of oro-pharyngeal carcinoma involves 50-60 Gy of radiation. Exposure of a given dosage at high dose rate (5 Gy/min) produces more damage to a biological system than exposure to the same dosage given at a low dose rate. When a lower dose rate is given, there is a great opportunity for repair of damage. Therefore, a dose rate of 2 Gy/min is usually chosen. Also, fractionation of total X-ray dose into multiple small doses provides greater tumor destruction and allows increased cellular repair of normal tissues. [14]

Ionizing radiations can have an array of detrimental side-effects on the oral cavity. [2],[3],[4],[5],[6],[7],[8] There is a dose-dependent relation between the radiation delivered and the damage that eventually occurs. Xerostomia is a common and serious side-effect of radiotherapy for head and neck cancer, and often enhances caries activity. [2] The treatment includes salivary substitutes and restoration of the carious lesions. [10] It has been shown that irradiation of protein leads to changes in their secondary and tertiary structures. The ionizing radiations may have a detrimental effect on the hydrated collagen fibers by the action of free OH radicals. [16] Also, it may affect the existing resin-dentin interface by affecting the hybrid layer.

The present study evaluated the effect of X-ray irradiation on the bonding of dentin with composite resins in terms of marginal adaptation and microtensile bond strength. The samples were divided on the basis of time of delivery of radiation, i.e., no radiation, radiation before restoration (affecting the collagen fibers), radiation after restoration (affecting resin dentin interface) and restoration between radiation dosage. Also, the restoration and the teeth are unavoidably subjected to thermal and mechanical stresses because of consumption of different food materials at varied temperatures and masticatory stresses. These stresses may negatively affect the resin dentin bond. Therefore, to simulate oral conditions, samples were subjected to thermocycling (5000 cycles, 5 ± 2-55 ± 2°C, dwell time 30 s) and cyclic loading of 150,000 cycles at 60N, which simulated 6 months of clinical usage.

The control group (without irradiation) had a μTBS of 22.898 ± 1.737 MPa, which was lower than the values obtained using flat dentinal surfaces. The possible explanation may be the effect of a cavity configuration factor. Bouillaguet in 2001 had reported a 20% reduction in bond strength of Class II cavity walls compared with flat dentinal surface. [15] Also, it has been reported that the tensile bond strengths were lower at the apical wall as compared with the occlusal walls because of the direction of the tubules. [16]

GR II had a μTBS value of 17.722 ± 0.834 MPa, which was significantly lower than that of the control group (P < 0.05). This signifies that ionizing radiations might have affected the collagen fibers of the dentinal tubules, which are an essential requisite in hybrid layer formation. GR III had a bond strength of 21.662 ± 1.236 MPa, suggesting that ionizing radiations had no effect on the existing hybrid layer and resin dentin bonds. The μTBS of restorations done between radiotherapy was less than the control group (20.448 ± 1.236 MPa), but was statistically insignificant, suggesting that ionizing radiations had affected the resin dentin bonds and the effect was dose dependent. As the GR IV restorations were done between the radiotherapy, there would have been a detrimental effect of collagen fibers before the cavities were restored. This effect would be less than that in GR II because of the half-dosage amount. After restoration, the exiting hybrid layer was not affected by the radiations. Thus, the values in GR IV were slightly less than in the control group. There was deterioration in marginal adaptation of samples after irradiation. But, there was no difference in marginal adaptation values in various groups of radiotherapy.


   Conclusions Top


Under the limitations of this in vitro study, it can be concluded that radiotherapy may affect the micro-tensile bond strength of composite restorations if restorations are done after radiotherapy. Therefore, it is advisable for a clinician to restore all cavities before radiotherapy and initiate caries prevention modalities in patients undergoing radiation therapy.

 
   References Top

1.Wingo PA, Tong T, Bolden S. Cancer statistics, 1995. CA Cancer J Clin 1995;45:8-30.  Back to cited text no. 1
[PUBMED]    
2.Franzén L, Funegård U, Ericson T, Henriksson R. Parotid gland function during and following radiotherapy of malignancies in the head and neck. A consecutive study of salivary flow and patient discomfort. Eur J Cancer 1992;28:457-62.  Back to cited text no. 2
    
3.Tomita Y, Osaki T. Gustatory impairment and salivary gland pathophysiology in relation to oral cancer treatment. Int J Oral Maxillofac Surg 1990;19:299-304.  Back to cited text no. 3
    
4.Ophir D, Guterman A, Gross-Isseroff R. Changes in smell acuity induced by radiation exposure of the olfactory mucosa. Arch Otolaryngol Head Neck Surg 1988;114:853-5.  Back to cited text no. 4
    
5.Arnold M, Kummermehr J, Trott KR. Radiation-induced impairment of osseous healing: Quantitative studies using a standard drilling defect in rat femur. Radiat Res 1995;143:77-84.  Back to cited text no. 5
    
6.Jacobsson M, Jönsson A, Albrektsson T, Turesson I. Alterations in bone regenerative capacity after low level gamma irradiation. A quantitative study. Scand J Plast Reconstr Surg 1985;19:231-6.  Back to cited text no. 6
    
7.Larson DL, Lindberg RD, Lane E, Goepfert H. Major complications of radiotherapy in cancer of the oral cavity and oropharynx. A 10 year retrospective study. Am J Surg 1983;146:531-6.  Back to cited text no. 7
    
8.Kielbassa AM, Beetz I, Schendera A, Hellwig E. Irradiation effects on microhardness of fluoridated and non-fluoridated bovine dentin. Eur J Oral Sci 1997;105:444-7.  Back to cited text no. 8
    
9.Jham BC, Reis PM, Miranda EL, Lopes RC, Carvalho AL, Scheper MA, et al. Oral health status of 207 head and neck cancer patients before, during and after radiotherapy. Clin Oral Investig 2008;12:19-24.  Back to cited text no. 9
    
10.Ritchie JR, Brown JR, Guerra LR, Mason G. Dental care for the irradiated cancer patient. Quintessence Int 1985;16:837-42.  Back to cited text no. 10
    
11.Sano H, Shono T, Sonoda H, Takatsu T, Ciucchi B, Carvalho R, et al. Relationship between surface area for adhesion and tensile bond strength: Evaluation of a micro-tensile bond test. Dent Mater 1994;10:236-40.  Back to cited text no. 11
    
12.Sarkaria JN, Bristow RG. Overview of cancer molecular radiobiology. Cancer Treat Res 2008;139:117-33.  Back to cited text no. 12
    
13.Chistiakov DA, Voronova NV, Chistiakov PA. Genetic variations in DNA repair genes, radiosensitivity to cancer and susceptibility to acute tissue reactions in radiotherapy-treated cancer patients. Acta Oncol 2008;47:809-24.  Back to cited text no. 13
    
14.Le QT. Nasopharyngeal and oropharyngeal carcinomas: Target delineation, therapy delivery and stereotactic boost procedures with intensity-modulated/image-guided radiation therapy. Front Radiat Ther Oncol 2007;40:208-31.  Back to cited text no. 14
    
15.Bouillaguet S, Ciucchi B, Jacoby T, Wataha JC, Pashley D. Bonding characteristics to dentin walls of class II cavities, in vitro. Dent Mater 2001;17:316-21.  Back to cited text no. 15
    
16.Ogata M, Nakajima M, Sano H, Tagami J. Effect of dentin primer application on regional bond strength to cervical wedge-shaped cavity walls. Oper Dent 1999;24:81-8.  Back to cited text no. 16
    

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Correspondence Address:
Suman Yadav
Department of Conservative Dentistry and Endodontics, SGT Dental College, Gurgaon, Haryana
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0972-0707.108198

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