الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Summary
The pediatric patients undergoing radiation therapy for head and neck cancer need multidisciplinary approach for dental management because of the side effects of this treatment. 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. 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.
Accordingly, this study is formulated to evaluate the effects of irradiation on four mechanical properties of a bulkfill composite resin and a high viscous glass ionomer cement (shear bond strength, flexural strength, microhardness, and surface roughness) and on microhardness and surface topography of primary teeth.
I-Effect of Ionizing Radiation on Restorative Materials
Shear bond strength:
A total of 120 specimens were divided into 12 groups (n=10 for each experimental group), according to radiation condition (Control group: restoration without irradiation, Pre-irradiation group: restoration followed irradiation, Post-irradiation group: irradiation followed by restoration); according to substrate (enamel and dentin); according to material used (resin composite or GIC). Specimens were then evaluated using a Universal Testing Machine at a crosshead speed of 0.5mm/min.
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Three–Way ANOVA revealed that the irradiation condition, the type of material used, substrate, the interaction between the irradiation condition and the material and the interaction between the material and substrate had a significant effect on shear bond strength. However, the interaction between the irradiation condition and the substrate and the interaction between the irradiation condition, material and substrate had no significant effect on the shear bond strength
Flexural strength:
Forty bar shaped mini flexural test specimens, 12mm in length, 2 mm in width and 2mm in thickness were prepared from each material, using split stainless-steel mold. Specimens were divided into four groups (n=10 for each experimental group) according to radiation condition (control and post radiation); according to the material used (Resin composite or glass ionomer cement). Specimens were stored in distilled water for 24 hours before testing. Specimens were then tested for flexural strength using the Universal Testing Machine.
Two –Way ANOVA revealed that the irradiation condition, the type of material used, and the interaction between the two independent variables had a significant effect on the flexural strength
Microhardness:
Disc-shaped specimens (a total of 40 discs) measuring (4mm in diameter x 2mm in thickness) were prepared from each material in a split stainless-steel mold. Specimens were divided into four groups (n=10 for each experimental condition) according to radiation condition (control and post radiation); and the material used (X-tra fil or Equia Fotre HT). Specimens were stored in distilled water for 24 hours before testing. Specimens were then
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evaluated for microhardness using the Nexus 4000 TM Vickers Microhardness tester.
Two –Way ANOVA revealed that the irradiation condition, the type of material used, and the interaction between the two independent variables had a significant effect on microhardness.
Surface roughness:
Disc-shaped specimens (a total of 40 discs) measuring (4mm in diameter x 2mm in thickness) were prepared from each material in a standardized mold. Specimens were divided into four groups (n=10 for each experimental condition) according to radiation condition (control and post radiation); and the material used (X-tra fil or Equia Fotre HT). Specimens were stored in distilled water for 24 hours before testing. Specimens were then evaluated for surface roughness using the stereomicroscope under 25x magnification and image J software was used for analysis.
Two -way ANOVA revealed that irradiation condition and the material had a significant effect on surface roughness. However, the interaction between them had no significant effect on flexural strength.
II- Effect of Ionizing Radiation on Primary Teeth:
Microhardness:
The buccal and lingual halves were used to measure the microhardness of enamel and dentin. Specimens were divided into four groups (n= 5 for each experimental condition) according to radiation condition (control and post ionizing radiation); according to the substrate (Enamel or dentin). Specimens
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were tested for microhardness using the Nexus 4000 TM Vicker’s Microhardness tester (INNOVATEST Europe, BV, Borgharenweg, Netherlands).
Two -way ANOVA revealed that irradiation condition, substrate, and the interaction between them had a significant effect on microhardness.
Surface topography and elemental analysis
Primary teeth were used to evaluate the surface topography and elemental analysis for sound and irradiated enamel (n=5) and dentin (n=5).
Surface was micrographed using scanning electron microscopy (SEM) (Quanta 250 FEG, FEI company, Netherlands) operated in the backscattered mode at a magnification range between 1000x-5000x to evaluate surface topography.
Elemental surface composition was analyzed for each sample using EDX (Energy Dispersive X-ray spectroscopy) analytical system attached to the SEM machine and operated by EDAX Genesis Software
SEM micrographs of non-irradiated enamel showed well organized prisms surrounded by inter prismatic substance. On the other hand, corresponding micrographs of irradiated enamel showed an amorphous appearance interfering with the visualization of prismatic structure and the identification of the inter-prismatic region, giving the enamel surface a melted appearance Surface cracks could be also visualized on the enamel surface.
SEM micrographs of non-irradiated dentin showed well-defined dentinal tubule morphology. On the other hand, corresponding micrographs of irradiated dentin showed an amorphous appearance with indistinct
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identification of the dentinal tubules and the collagen network, giving the dentin surface a melted appearance. A common finding in both irradiated enamel and dentin was the formation of cracks along the surface. EDX analysis showed that, for different substrates, irradiation had no significant effect on mineral content.
Conclusion
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Conclusions
Under the limitation of this study, several conclusions can be drawn.
1. Restorations) X-tra fil and Equia Fotre HT) placed immediately after radiotherapy have the lowest shear bond strength.
2. Irradiation with linear accelerator had a negative impact on flexural strength, microhardness and surface roughness for both materials.
3. Overall, X-tra fil presented a better performance in irradiated teeth compared to Equia Forte HT.
4. Radiotherapy affects the microhardness and surface topography of enamel and dentin in primary teeth
Recommendation
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Recommendations
1) It is recommended to restore primary teeth before radiotherapy as the restorative materials will have higher shear bond strength than restoration after radiotherapy.
2) Further investigations regarding more mechanical and physical properties of X-tra fil and Equia Fotre HT after radiotherapy are recommended.
3) Clinical trial is highly required regarding the effect of radiotherapy on restorative materials and primary teeth.