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Table of Contents   
ORIGINAL RESEARCH  
Year : 2019  |  Volume : 30  |  Issue : 3  |  Page : 408-413
Effect of ionizing radiation on the properties of restorative materials


1 Department of Restorative Dentistry, Piracicaba Dental School, State University of Campinas, Campinas, São Paulo, Brazil
2 Department of Clinical and Preventive, Dentistry, Federal University of Pernambuco, Recife, Pernambuco, Brazil
3 Department of Dentistry Clinic, Dentistry, Federal University of Pernambuco, Recife, Pernambuco, Brazil
4 Department of Restorative Dentistry, Federal University of Paraíba, João Pessoa, Paraíba, Brazil

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Date of Web Publication9-Aug-2019
 

   Abstract 

Aim: The aim of this study is to evaluate the effect of different doses of the ionizing radiation (0 Gy, 10 Gy, 30 Gy, and 60 Gy) on the physical properties of dental materials. Methodology: Disc-shaped samples from each material (Ketac Molar Easymix, Vitro Molar, Vitremer, Vitro Fil Lc, Filtek Z 250 and Filtek Z 350) were made for water solubility, sorption analysis (n = 20), microhardness (n = 20), and surface roughness analysis (n = 24). Specimens were divided into four groups, according to radiation dose: control group (0 Gy), 10 Gy, 30 Gy, and 60 Gy. For water solubility and sorption analysis, the specimens were irradiated and were stored for 21 days to calculate the water solubility and sorption values. Microhardness analysis was carried out before and after irradiation doses. For surface roughness analysis, the specimens were submitted to brushing test, and after 24 h, initial surface roughness analysis was made in a rugosimeter. Subsequently, the samples were irradiated and final surface roughness analysis was made. The original water solubility and sorption, surface roughness, and microhardness values were subjected to ANOVA two-way statistical analysis and Paired t-test and Tukey post hoc test (α = 0.05), respectively. Results: Water solubility and sorption values, and surface roughness values presented statistical difference between groups (0, 10, 30 e 60 Gy) for all materials. Conclusions: High doses of ionizing radiation (30 Gy and 60 Gy) increased the surface roughness, sorption, and solubility for the most materials.

Keywords: Composite resins, physical properties, radiotherapy, silicate cement

How to cite this article:
E Lima RB, De Vasconcelos LC, Pontual ML, Meireles SS, Maciel Andrade AK, Duarte RM. Effect of ionizing radiation on the properties of restorative materials. Indian J Dent Res 2019;30:408-13

How to cite this URL:
E Lima RB, De Vasconcelos LC, Pontual ML, Meireles SS, Maciel Andrade AK, Duarte RM. Effect of ionizing radiation on the properties of restorative materials. Indian J Dent Res [serial online] 2019 [cited 2019 Oct 16];30:408-13. Available from: http://www.ijdr.in/text.asp?2019/30/3/408/264130

   Introduction Top


The most common malignancies encountered worldwide are oral cancers.[1] Approximately 390,000 new cases of oral cancer are diagnosed every year.[2],[3] The treatment of head-and-neck cancer may employ ionizing radiation as a therapeutic agent to destroy or impede the proliferation of cancer cells.[2],[3],[4] Radiotherapy consists of a total dose of 75 Gray (Gy) of high-energy X-ray radiation in a daily fraction of 1.8 to 2 Gy.[2],[5]

During radiation therapeutic of oral cancer, ionizing radiation may reach different healthy tissues, including dental restorations.[6] Ionizing radiation has short wavelength and high energy,[7],[8] interacting with dental materials and dental tissues through electrostatic and electromagnetic forces.[2],[3],[4],[7] The properties of dental materials may change proportionally to the increase of the radiation dose.[9] However, the effect of ionizing radiation delivered during radiotherapy treatments on dental materials is not completely known.[2],[9],[10]

Some studies have been conducted to determine the effect of irradiation on the physical properties of restorative dental materials,[9],[11],[12],[13],[14],[15] however, the results are still contradictory. There is no consensus regarding the best restorative dental materials to be used in head-and-neck cancer patients. Therefore, knowing the effect of X-ray on the mechanical properties of dental material is essential to determine the best alternative for dental treatment in oral cancer patients.

During radiation therapy, oral cancer patients are exposed to a total radiation dose up to 75 Gy.[16] Cobalt-60 or linear accelerators units can be used as a source of irradiation.[2] To simulate the clinical parameters and radiation doses used during radiotherapy, this in vitro study used a linear accelerator for application of radiation doses of 10 Gy, 30 Gy, and 60 Gy on restorative dental materials. Thus, the aim of this study was to evaluate the effect of different doses of X-rays (10 Gy, 30 Gy, and 60 Gy) on the physical properties (microhardness, surface roughness, sorption, and solubility) of dental materials (glass ionomer cements, resin-modified glass ionomer cements, and resin composites).

The null hypotheses were set in this study: (1) The microhardness, surface roughness, water sorption, and solubility of different materials are not affected by different doses of ionizing radiation (2) There is no difference in the microhardness, surface roughness, water sorption, and solubility of different material between doses of ionizing radiation (10 Gy, 30 Gy, and 60 Gy).


   Methodology Top


To evaluate the impact of radiotherapy on structure of dental materials, this study evaluated the microhardness, surface roughness, sorption, and solubility of three types of restorative material (glass ionomer cement, resin-modified glass ionomer cement, and resin composite) after application of radiation doses. For simulated radiotherapy, this in vitro study applied different radiation doses (10, 30, and 60 Gy) on restorative materials.

Two glass ionomer cements (Ketac Molar Easymix-3M ESPE Dental Products, Germany, Vitro Molar-DFL, Brazil), two resin-modified glass ionomer cements (Vitremer-3M ESPE Dental Products, Germany, Vitro Fil Lc-DFL, Brazil) and two resin composites (Filtek Z 250 XT, Filtek Z 350 XT-3M ESPE Dental Products, Germany) were used. Compositions and manufacturer of each product are shown in [Table 1].
Table 1: Composition and manufacturer of materials used

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Water sorption and solubility

The specimens of all materials were manipulated according to manufacturers' recommendations at 26°C ± 1°C and then inserted directly into Teflon molds (10 mm diameter and 2 mm thickness). These molds were previously positioned onto a polyester strip and placed on a glass slide. Immediately, the mold filled with the materials was covered with a polyester strip to achieve uniformly smooth surfaces. The molds were kept under pressure to remove excess material. The specimens that involving physical polymerization (resin-modified glass ionomer cement and resin composite) were exposed for 40 seconds to visible light with an intensity of 400 mW/cm 2 (Optilux Plus GNATUS, São Paulo, Brazil). Twenty disc-shaped samples from each material were made then were randomly distributed into four groups (n = 5): control group (without irradiation), 10 Gy, 30 Gy, and 60 Gy. To ensure that the samples would be randomly distributed among the experimental groups, one determined them by considering the random number generator from Excel. After preparation, the specimens were stored in distilled water for 4 h at 37°C. Glass ionomer cement specimens were kept in the molds for 10 min before removing and, subsequently, the specimens were kept in a humidifier for 24 h at 37°C.

The specimens were irradiated in a single session according to the dose of 10 Gy, 30 Gy, and 60 Gy, using a Primus K Linear Accelerator (Siemens-Healthineers, USA) with 6 MeV energy and source-surface-distance of 100 cm and field size (18 cm × 23 cm). The placement of the beam was based on radiotherapy routine at Napoleao Laureano Hospital, Joao Pessoa, Brazil.

The water sorption and water solubility measurements were done according to the International Standards Organization ISO 4049 (2000). After preparation of specimens and before immersion in distilled water, all specimens were weighed and kept in a humidifier until the specimens achieve constant weight (m1). Posteriorly, the specimens were immersed in distilled water until no changed was observed (m2) then the specimens were placed in a desiccator containing silica gel dried to achieve constant mass (m3).

The volume of specimens was calculated (mm 3). The values of water sorption were calculated using the following equations:

(m2 - m3/Volume).

The values of water solubility were calculated using the following equations:

(m1 – m3/Volume).

Surface roughness analysis

Teflon molds measuring 5 mm in diameter and 1.5 mm in thickness were used to made the specimens. In a controlled environment (26°C ± 1°C), materials were mixed according to manufacturers' recommendation and then inserted directly into the Teflon molds. Immediately, the mold filled with resin cement was covered with polyester strip and a glass slide. The mold was placed under a pressure of 250 g from the top to achieve uniformly smooth surfaces. Photoactivation process was performed during 40 s to visible light with an intensity of 400 mW/cm 2 (Optlux Plus GNATUS, São Paulo, Brazil).

Twenty-four disc-shaped samples from each material were made. After preparation, the specimens were stored in distillate water for 24 h at 37°C. Glass ionomer cement specimens were kept in the molds for 10 min before removing and subsequently kept in a humidifier for 24 h at 37°C. Six disc-shaped specimens from each material were randomly distributed for each experimental group: control group (without irradiation), 10 Gy, 30 Gy, and 60 Gy. To ensure that the samples would be randomly distributed among the experimental groups, one determined them by considering the random number generator from Excel.

After 24 h of preparation, the specimens were embedded in autopolymerizing acrylic resin, using a plastic matrix to adapt brushing machine. For brushing testing, the specimens were placed into a brushing machine (equilabor). Each specimen was subjected to brushing test with linear movements of the brush bristles with the speed of 250 strokes/min, totaling 10.000 cycles.

The route of brushing under the specimen was 43 mm under an axial static load of 200 g placed in the brush holder device support, to simulate the force used during the oral hygiene procedures. The specimens were brushed with diluted toothpaste (Colgate MFP-Colgate-Palmolive, Co. Osasco-SP, Brazil). The dentifrice was weighed and diluted in distilled water in a beaker at the ratio of 1:2 by weight.

The brushing machine was set to 2 ml of the solution was injected every 2 min. For this test, we used toothbrushes Kolynos Doctor (Kolynos, Brazil), soft bristles, and hexagonal.

After 24 h of brushing testing, the initial surface roughness analysis was made in a rugosimeter (Surftest SJ – 301 – Mitutoyo, Japan). For surface roughness analysis, each disc-shaped sample was adapted with wax on a glass slide under the pressure of 0.5 kgf for 3 seconds.

Three measures were made randomly at the surface of the specimens, following the test conditions: Lc – 0.25 mm and 0.5 mm/s speed. The measures were the arithmetic mean between peaks and valleys (Ra), obtained through the traveled trajectory performed by the mechanical probe of 4.0 mm. The measures were made on each specimen following which the arithmetic mean was calculated (ΔRinitial).

After initial surface roughness test, the disc shaped were irradiated in a single session with doses of 10 Gy, 30 Gy, and 60 Gy, using a Primus K Linear Accelerator (Siemens-Healthineers, USA) with 6 MeV energy and source-surface-distance of 100 cm and field size of 18 x 23 cm. The placement of the beam was based on radiotherapy routine at Napoleao Laureano Hospital, Joao Pessoa, Brazil.

After a two week storage period, the final roughness analysis was made following the same test conditions mentioned for initial surface roughness test. The measures were made on each specimen following which the arithmetic mean was calculated (ΔRfinal). The mean roughness increase (ΔR =ΔRfinal −ΔRinitial) was calculated for each group and submitted to statistical analysis.

Microhardness analysis

The specimens of all materials were manipulated according to manufacturers' recommendations at 26°C ± 1°C and then inserted directly into Teflon molds measuring 5 mm in diameter and 1.5 mm in thickness. Immediately, the mold filled with the materials was covered with a polyester strip and the mold was placed under a pressure of 250 Grams (g) from the top to achieve uniformly smooth surfaces.

The specimens that involved physical polymerization (resin-modified glass ionomer cement and resin composite) were exposed for 40 seconds to visible light with an intensity of 400 mW/cm 2 (Optlux Plus GNATUS, São Paulo, Brazil). Twenty disc-shaped samples from each material were made. After preparation, the specimens were stored in distilled water for 24 hours at 37°C. Glass ionomer cement specimens were kept in the molds for 10 min before removal and subsequently kept in a humidifier for 24 h at 37°C. Five disc-shaped specimens from each material were randomly distributed into four groups: control group (without irradiation), 10 Gy, 30 Gy, and 60 Gy. To ensure that the samples would be randomly distributed among the experimental groups, one determined them by considering the random number generator from Excel.

An initial Vickers hardness number (VHN) microhardness analysis was obtained 24 hours after specimen preparation in a Vickers (HMV)-2 (Shimadzu Corporation, Nakagyo-ku, Kyoto, Japan) microhardness tester. For each specimen, five indentations were made randomly on the top surface under a 50 g load for 15 seconds. The diagonals of Vickers indentations were measured through the eyepiece of the optical microscope of the HMV-2 microhardness tester at ×50 magnification immediately after indentation.

The means of the diagonals of each indentation were measured and the mean of five indentations for each surface was calculated. Afterwards, these means were converted in VHN using the equation (1):



where F is the force applied in km-force and d is the average length of the diagonal in mm.

The specimens were irradiated in a single session doses of 10 Gy, 30 Gy, and 60 Gy, using a Primus K Linear Accelerator (Siemens-Healthineers, USA) with 6 MeV energy and source-surface-distance of 100 cm and field size of 18 cm x 23 cm. The placement of the beam was based on radiotherapy routine at Napoleao Laureano Hospital, Josp Pessoa, Brasil.

The final mean Vickers hardness was measured in an HMV-2 microhardness tester after 24 hours irradiation.

Statistical analysis

The roughness increase (ΔR), water sorption and solubility values were subjected to ANOVA two-way statistical analysis (material and doses of ionizing radiation) and Tukey post hoc test (P = 0.05). The microhardness values were subjected to ANOVA two-way statistical analysis (material and doses of ionizing radiation) and Paired t-test (P = 0.05).


   Results Top


Water solubility values for each material are shown in [Table 2]. Conventional glass ionomer cement (Ketac Molar Easy) presented higher water solubility values for all irradiated groups compared to control (0 Gy). Water solubility values were statistically higher in the 60 Gy group than control group for Vitremer and Vitro Fill Lc. Regarding resin composites (Filtek Z 250 and Filtek Z350 XT), the group exposed to 60 Gy showed higher water solubility values compared to all groups.
Table 2: Means values of water solubility values (μg/mm3) comparing the doses of ionizing radiation for each material

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Regarding water sorption values, Vitremer presented statistically higher values for 60 Gy dose compared to control and 10Gy groups. Vitro Molar, Filtek Z 250 XT and Filtek Z 350 XT showed statistically higher values for 30 and 60 Gy groups compared to others groups (control and 10 Gy group) [Table 3].
Table 3: Means values of sorption values (μg/mm3), comparing the doses of ionizing radiation for each material

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All materials showed no statistical difference in the microhardness values between groups (0, 10, 30 Gy 60 Gy) before and after application of ionizing radiation [Table 4].
Table 4: Means values of microhardness, comparing before and after radiation for each group and the different radiation doses of radiation

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When roughness increase (ΔR) values were calculated, Ketac Molar Easimix presented statistically higher Δ R values in the 60 Gy group compared to control (0 Gy) and 10 Gy groups. The Vitremer showed statistically higher ΔR values for all irradiated group than control group (0 Gy). Regarding composite resins Filtek Z 250 XT presented statistically higher roughness increase (ΔR) values for 60 Gy group compared to others groups. The Filtek Z 350 XT showed statistically higher ΔR values for 60 Gy group compared to control group (0 Gy) [Table 5].
Table 5: Means values of roughness increase (ΔR) (μm) after brushing test, comparing the doses of ionizing radiation for each material

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   Discussion Top


To study the effect of ionizing radiation on the material properties, this in vitro study evaluated microhardness, surface roughness, and water solubility and sorption of restorative materials after application of different radiation doses (10, 30 and 60 Gy). The ionizing radiation doses influenced the properties of composite resins and glass ionomer cements, resulting in higher roughness increase values (ΔR) and water sorption and solubility when 30 Gy and 60 Gy dose were applied. Therefore, the first and second hypotheses were rejected. These findings suggest that higher ionizing doses may promote degradation phenomenon and increase of superficial roughness in dental restorations made before radiotherapy, when composite resins and glass ionomer cements are used as restorative material. Consequently, clinical survival of dental restorations in head-and-neck cancer patients may decrease over time.

In this study, alterations in water solubility and sorption after radiation were material and radiation dose dependent [Table 2] and [Table 3]. Higher radiation dose (60 Gy) promoted significant increase in water solubility and sorption for most materials in agreement with the results of others studies.[9],[14] Ionizing radiation promotes modifications in the microstructure of dental composites and glass ionomer, resulting in the linking or breaking of bond chains.[9] Based on these in vitro results, mechanical properties of these restorative materials may decrease due to the radiation effect associated with plasticization and degradation phenomenon in the oral cavity, leading to material elution and a shortened service life of dental restoration.[17],[18]

Ionizing radiation interacts with organic and/or inorganic material components. When irradiation occurred after photoactivation, the breaking of bonds has been observed due to high radiation energy and rigid structural of photopolymerized-polymeric chains.[9],[19] Based on our results, higher dose of radiation promoted degradation of restorative materials, increasing significantly the roughness values [Table 5]. One can suppose then, that when composite resins and glass ionomer cement restorations are irradiated with high doses of X-rays, an increase in the superficial roughness of these materials can contribute to the development of secondary caries and periodontal disease, negatively impacting successful restoration of radiation teeth.[20]

The differences in material composition (redox system, filler particle concentration, type, and amount of monomers) can influence some of the properties such as surface roughness and microhardness.[21] In the present study, composite resins showed higher roughness increase after application of 60 Gy dose, while glass ionomer cements presented higher roughness increase after application of all radiation doses (10, 30, and 60 Gy) [Table 5]. Thus, the composite resins may be less susceptible to effects of radiation doses. This can be explained by the way x-rays interact with the structure of water-based cements forming oxygen-reactive materials.

The microhardness values were not affected by radiation dose for all materials [Table 4], disagreeing with previous studies.[5],[22] The literature reports contradictory results regarding alterations in properties of dental materials after applications of ionizing radiation.[5],[9],[11],[12],[13],[14],[15],[19],[22] This fact may be explained by a different radiation source (60 Co source and Linear Accelerator) and dose used.[11]

In the present study, water solubility, sorption, and superficial roughness of restorative materials increased when submitted to ionizing radiation, suggesting that restorative procedures may be performed after the end of radiotherapy. However, other factors such as effect of X-rays on the human enamel and dentin should be considered while carrying out restorative procedures before or after irradiation. Furthermore, it is important to highlight that behavior of material may change when used in the oral environment. In the oral cavity, there are different agents which influence in a more complex manner than the experimental ones used in this study.[23] Thus, more in vitro and clinical studies are required to suggest the best dental protocols and restorative materials for patients subjected to radiation therapy, resulting in improved quality of life for these individuals.


   Conclusions Top


Within the limitations of the current study, it was concluded that the properties (surface roughness, sorption and solubility) of composite resin and glass ionomer cement were affected by doses of ionizing radiation. High doses of ionizing radiation (30 Gy and 60 Gy) increased the surface roughness, sorption and solubility for most materials.

Acknowledgment

The authors are grateful to the Cancer hospital of Joao Pessoa (Napoleao Laureano Hospital) for irradiation equipment support.

Financial support and sponsorship

This study was supported by CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico), process number: 476789/2008 7.

Conflicts of interest

There are no conflicts of interest.

 
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Correspondence Address:
Miss. Renally Bezerra Wanderley E Lima
Department of Restorative Dentistry, Piracicaba Dental School-Campinas State University, Av. Limeira, 901, 13414-903, Piracicaba, SP
Brazil
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijdr.IJDR_72_17

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    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]



 

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