|Year : 2020 | Volume
| Issue : 3 | Page : 85-89
Effect of radiotherapy on bond strength of different endodontic sealers to root dentin
Sahar A Fouda BSc 1, Ahmed H Labib2, Neveen A Shaheen2, Naser M Abd-Elbary3, Hatem A Alhadainy2
1 Department of Endodontics, Tanta University, Tanta, Egypt
2 Department of Endodontics, Faculty of Dentistry, Tanta University, Tanta, Egypt
3 Department of Oncology and Nuclear Medicine, Faculty of Medicine, Menoffia University, Menoffia, Egypt
|Date of Submission||24-Oct-2019|
|Date of Acceptance||16-Jun-2020|
|Date of Web Publication||30-Oct-2020|
Sahar A Fouda
Department of Endodontics, Faculty of Dentistry, Tanta University (BDS), Tanta, El-Garbia
Source of Support: None, Conflict of Interest: None
The aim was to evaluate the effect of radiotherapy on push-out bond strength of different sealers (Endosequence, MetaSEAL Soft, Tubliseal) to root dentin.
Materials and methods
A total of 60 extracted premolars with nearly straight single root canals were selected. All teeth were decoronated leaving root sample of nearly 15 ± 1 mm length. Root canals preparation were performed using ProTaper rotary system. Roots were randomly divided into six groups according to radiation exposure and type of sealer used. Group I: MetaSEAL Soft positive, Group II: Endosequence positive, Group III: Tubliseal positive, Group IV: MetaSEAL Soft negative, Group V: Endosequence negative and Group VI: Tubliseal negative. After obturation, positive groups were subjected to a cumulative radiation dose of 60 Gy in 30 fraction for 6 weeks. Three dentin slices were obtained from each root third and push-out test was measured using universal testing machine. The maximum failure load was recorded in Newton (N) and then converted into MegaPascal (MPa). Bond strength values were analyzed using two-way analysis of variance and multiple pairwise Tukey's test at P value less than or equal to 0.05.
Irradiated groups recorded lower bond strength values than nonirradiated groups. Groups obturated with gutta-percha/Tubliseal recorded the lowest values when comparing between sealers regardless radiation exposure and sections. Coronal sections had superior bond strength values than middle and apical sections in all groups.
Radiotherapy had a negative effect on bond strength of sealers to root dentin. Endosequence BC sealer had better bond strength to radiculer dentin than MetaSEAL Soft and Tubliseal sealers.
Keywords: Endosequence BC, MetaSEAL soft, push-out, radiotherapy, Tubliseal
|How to cite this article:|
Fouda SA, Labib AH, Shaheen NA, Abd-Elbary NM, Alhadainy HA. Effect of radiotherapy on bond strength of different endodontic sealers to root dentin. Tanta Dent J 2020;17:85-9
|How to cite this URL:|
Fouda SA, Labib AH, Shaheen NA, Abd-Elbary NM, Alhadainy HA. Effect of radiotherapy on bond strength of different endodontic sealers to root dentin. Tanta Dent J [serial online] 2020 [cited 2020 Nov 27];17:85-9. Available from: http://www.tmj.eg.net/text.asp?2020/17/3/85/299631
| Introduction|| |
Head and neck cancers are often treated with radiation therapy, a technique that utilizes ionizing radiation and exerts therapeutic effect by semiselectively damaging the genetic material of vulnerable malignant cells, either directly or through the production of free radicals resulting in cell death. Radiation has three general uses in the treatment of cancer, it may be used as a presurgical technique in an attempt to reduce the size of the lesion, eliminate its extensions and thereby minimize recurrence. In addition to, it may be used as a postsurgical procedure to control any possible residual disease and finally, it is frequently employed as the only method of therapy. Radiation induced damages include xerostomia from salivary gland damage, mucositis from epithelial damage, pathological alterations in the normal flora with resulting candidiasis and bacterial infection, radiation induced caries, reduced mouth opening due to changes in collagen structure and fibrosis, difficulty in speech and mastication, loss of taste, periodontal disease and osteoradionecrosis of the jaw from reduced bone healing capacity especially for the mandible. Therapeutic cancer radiation may result in adverse effects on root dentin. Several researchers observed a significant reduction in dentin microhardness after irradiation that is associated with physical and chemical changes in dentin structure and may be accompanied by a reduced stability of the amelodentinal junction. Resin has been introduced into endodontic sealers in an attempt to provide bonding to the tooth structure. MetaSEAL is dual cured and self-adhesive in nature therefore eliminates the use of a separate self-etching primer to create bonds to radicular dentin and gutta-percha via the formation of hybrid layer.
A new bioceramic based sealer is EndoSequence BC Sealer and also known as 'iRoot SP' has been recently introduced. This sealer is specifically designed as calcium silicate and supplied as premixed ready to use injectable paste that require water to set, Tubliseal is a catalyst/base pastes of ZOE-based sealer which has a widespread clinical use. Recently the manufacturer developed a new formulation of Tubliseal with extended working time. Push-out test has been frequently used in endodontics because it is easy to reproduce, interpret and record the bond strength to dentin.
Since limited information has been published about bond strength of endodontic sealers to radicular dentin after radiotherapy. Therefore, this study is designed to assess the influence of radiotherapy on bond strength of three different endodontic sealers to dentin using push-out test.
| Materials and Methods|| |
Sixty single rooted sound premolar teeth with fully formed apices and relatively straight single root canal were selected from the outpatient clinic of Oral Surgery Department, Faculty of Dentistry, Tanta University. All patients were informed about the research and their acceptance to use their extracted teeth in this research were taken according to the instruction of ethical committee of Faculty of Dentistry, Tanta University. Teeth with multiple canals, resorptive defects, cracks, fractures, open apices or previous root canal treatment were excluded. The selected teeth were thoroughly cleaned by removing the hard deposits using hand scaler and the soft deposits by soaking them in 5.25% sodium hypochlorite (NaOCl) for 5 min then stored in sterile normal saline solution. Each tooth was decoronated to obtain approximately 15 ± 1 mm root length. The patency of root canal was checked using hand stainless-steel K file # 10 taper 2% (Mani Inc., Tochigi, Japan). Working length (WL) was determined by inserting hand K-file (#15, 0.02) in the canal until its tip was just visible at the apical foramen, then subtract 1 mm from this length. After WL determination, a reproducible glide path was established using stainless-steel K-files until file #20 taper 2% be loose at the full WL. Root canal preparation was performed by Ni-Ti rotary ProTaper system (Dentsply Maillefer, Ballaigues, Switzerland) up to master file F3. Root canals were irrigated throughout instrumentation with freshly prepared 5 ml of 2.5% NaOCl solution using a plastic disposable syringe with 30 G side vented needle. Samples were randomly divided into six groups (n = 10) as shown in [Table 1].
|Table 1: Grouping the samples according to sealer type and exposure to therapeutic radiation|
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In all groups, ProTaper gutta-percha master cone F3 (#30/0.09) with the respective sealer according to the manufacturer instructions. All samples were kept moist in gauze saturated with sterile normal saline solution at 37°C for 1 week to insure complete setting of the sealers. Then all roots were embedded in clear acrylic resin block.
Groups (I, II, III) were fixed in plastic plate and the specimens were fully immersed in normal saline solution which were renewed daily. Radiotherapy application was conducted in the Radiation Oncology Department of Faculty of Medicine, Menoffya University. Radiotherapy was applied to the surface of saline solution, with Co—60 photons (Theratron 780C; Theratronics Int., Carrollton, Texas, USA) a single anterior field at a distance of 80 cm. Samples were irradiated at 2 Gy per fraction, five times per week for a total dose of 60 Gy in 30 fractions during 6 weeks as shown in [Figure 1].
|Figure 1: Samples of the three positive groups targeted under the radiation source at 80 cm distance.|
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Samples preparation for push-out bond strength testing
Each block was sectioned horizontally marker into three sections at 3, 8, and 12 mm from the apex representing mid-apical, mid-middle, and mid-coronal root canal levels of 2 ± 0.1 mm thickness each. Each root section was subjected to a compressive load via a universal testing machine (LIoyd Instruments Ltd, Fareham, UK) at a crosshead speed of 1 mm/min by using stainless steel plungers. The selected diameter of the plunger was positioned so that it only contacts the filling to displace it downward. The force was applied in an apicocoronal direction until bond failure occurred as manifested by extrusion of the filling material and a sudden drop in load deflection curve recorded by computer software (Instruments Ltd., Fareham, UK; Nexygen-MT; LIoyd).
The maximum failure load was recorded in Newton (N) and then converted into Mega Pascal (MPa). The bond strength was calculated from the recorded peak load divided by the surface area. Push-out strength (MPa)=maximum load (N)/adhesion area (A) (mm2) will be calculated by using the following formula:
Where π=3.14, r1 is the coronal radius, r2 is the apical radius, h is the thickness of the slice in millimeters.
Data were collected and tabulated for statistical analysis using SPSS version 20 (SPSS Inc., Chicago, Illinois, USA). Data were described as mean and SD, then testing of significancy was performed using two-way analysis of variance at P value less than or equal to 0.05 and multiple pairwise comparisons were performed using Tukeyˈs test.
| Results|| |
Comparison between the three root canal sections for each group, it was found that the coronal sections in all groups were higher in push out bond strength than apical and middle with statistical significant difference between coronal and apical sections. Moreover, comparison between different groups at each root canal section was performed, group V recorded the highest mean value of push-out bond strength while the lowest one was group III at all sections level. Also it was found that the lowest mean push-out bond strength value was recorded for group III while the highest value recorded for group V with a statistical significant difference (P ≤ 0.001). On the other hand, when comparing between root canal sections regardless the group, it revealed that coronal section recorded the highest mean push-out bond strength value while the apical section had the lowest mean value with a statistical significant difference. In addition to, groups that exposed to radiation had significantly lower mean value of push-out bond strength than not radiated groups. Moreover, comparing between groups regardless of radiation and root canal sections, Endosequence groups (I + V) recorded the highest mean push-out bond strength value while Tubliseal groups (III + VI) recorded the lowest mean value. Two-way analysis of variance revealed statistical significant difference between them (P ≤ 0.001) [Table 2].
|Table 2: Push-out bond strength (mean±SD) of all groups at the three root canal sections|
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| Discussion|| |
Gutta-percha does not bond to root dentin and should be used in conjunction with a root canal sealer. The adhesion between dental structures and resin based sealers is the result of a physicochemical interaction across the interface, allowing union between the filling material and root canal walls, this process is important in static and dynamic situations. In static circumstances, adhesion eliminates spaces that allow infiltration of fluids into sealer/dentin interface. In dynamic situations, adhesion is necessary to avoid sealer dislodgment during operative procedures. In clinical situations, radiotherapy for squamous cell carcinomas of the head and neck that is the most common cancer of oral cavity uses a dose range from 50 to 70 Gy. In this study, radiation was delivered up to a dose of 60 Gy fractionally applied over a period of 6 weeks to simulate the radiation protocol used for oncolognic patients.
According to the results of the present study, when comparing between the groups regardless the sealer used and root canal sections, the push-out bond strength of irradiated groups were significantly lower than non irradiated groups. This may be attributed to the adverse effects of radiation on dentin microstructure as changes in intertubular and peritubular dentin, also obliteration of dentinal tubules due to degeneration of odontoblastic processes. In addition to induction and activation of matrix metalloproteinase expression. Moreover, radiation can damage dentin collagen fiber network because it acts on water content of dentin (about 12% by volume) leading to increased formation of free radicals and hydrogen peroxide with harmful effects on the hydration of collagen fibers which in turn have a key role in the adhesion to dentin.
The results of this study were in agreement with Martins et al., Yamin et al., and Aggarwal.
The result of the present study revealed that samples which were obturated with gutta-percha/Endosequence BC sealer showed the highest push-out bond strength than those obturated with gutta-percha/MetaSEAL Soft and Tubliseal sealers. This may be explained by calcium-silicate composition of Endosequence BC sealer that minimizes shrinkage during the setting process. In addition to, the extremely small particles size and the level of viscosity that allow it to be adaptable to the surface of the gutta-percha and enhance its flow into dentinal tubules, lateral canals and irregularities that may further enhance its bonding effectiveness to root canal dentin which in turn resulting in increased resistance to dislocation. Moreover, the formation of intratubular tags in conjunction with an interfacial mineral interaction layer referred to as the 'mineral infiltration zone' resulted in formation of a chemical bond between the calcium-silicate based sealers and radicular dentin. While in MetaSEAL sealer, the photoactivation procedure and the highly unfavorable C-factor in the root canal maximize the polymerization stress of resin-based materials along the root canal walls which in turn resulted in inferior marginal integrity and bond strength. This was in agreement with Nagas et al. who found that iRoot SP displayed the highest bond strength to root dentin than resin based sealer (AH Plus).
Moreover MetaSEAL could form a firm bond with root dentin and the adhesion interface between them was hardly broken. Adding water to 4-META allowed hydrolysis reaction to occur, the attached carboxylic groups to the aromatic group produced acidification and demineralization of the surface and also enhanced wetting. Besides, the slow self-curing mechanism of MetaSEAL could promote stress relief via prolonged plastic flow to unbounded areas during setting allowing formation of intact interface. This explain the higher bond strength of MetaSEAL than Tubliseal sealer, This with agreement with Cecchin et al. and Skidmore et al. who confirming the bonding superiority of resin based sealers when compared with zinc oxide eugenol based one. But in disagreement with that of Fisher et al. who found that zinc oxide sealer has higher bond strength than resin based sealer. This may be attributed to testing shear bond strength using micropush-out test and using Reslion/Epiphany and EndoREZ resin based obturation systems.
Also, the significantly lowering in bond strength of Tubliseal than MetaSEAL Soft and Endosequence groups may be attributed to that Tubliseal is a zinc oxide eugenol based sealer that does not exhibit adherence to dentin wall.
The higher bond strength of the coronal sections in the MetaSEAL groups compared with those of the successive ones should be explained by the proximity of the former to the source of photoactivation, which significantly improves mechanical properties and bond strength to dentin. Consequently, the limited depth of photopolymerization in the root canal system and the low degree of monomer-polymer conversion which in turn may explain the compromised bond strengths toward the apical direction. This was in agreement with Ferrari et al., Nagas et al.. While, in contrast to Gaston et al. who evaluates tensile bond strengths of adhesive resin cements other than MetaSEAL.
For the Endosequence groups the coronal sections showed higher mean value than middle and apical sections and may be due to the fact that coronal part of the root have a wider dentinal tubules which richer in fluid than apical parts and moisture in dentinal tubules which helps BC sealer to initiate and complete its setting reaction. In the presence of tissue fluid, an interfacial layer resembling hydroxyapatite in structure and composition is formed between root canal dentin and the calcium silicate sealers. For Tubliseal sealer, this result may be attributed to the obturation technique used in this study which was single cone technique so no condensation pressure applied at the apical third of root dentin and less penetration of sealer in dentinal tubules. The coronal sections were higher in bond strength than middle and apical regardless the groups, this finding may be attributed to the marked alterations in the structure of apical root dentin which is often sclerotic and the tubules are filled with minerals that resemble those from peritubular dentin, This in agreement with Martins et al. and Neelakantan et al.. Moreover, this result was in contrary with Sagsen et al. that showed the bond strength of the apical and middle sections were higher than the coronal sections and this controversy may be due to the deeper sealer penetrations because of using higher lateral condensation forces.
| Conclusion|| |
Within the limitation of this study, it can be concluded that radiotherapy has negative effect on bond strength of both adhesive and nonadhesive sealers to radicular dentin also, bioceramic based sealers recorded higher bond strength than resin and eugenol based sealers. and the coronal sections are higher than apical ones in bond strength of all tested sealers.
Further studies are recommended to evaluate the effect of radiotherapy on push-out bond strength of the existing and new root canal filling to radicular dentin.
Financial support and sponsorship
Conflicts of interest
Sun medical company for MetaSEAL soft free samples.
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[Table 1], [Table 2]