الفهرس 
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Abstract
Acrylic dentures used by patients and requiring adjustments or repair are considered a source of infection and cross contamination to the dental staff. So, simple, safe, rapid, and inexpensive methods of disinfection are needed to protect dental staff and patients from cross contamination. The aim of this study was to assess microwave disinfection versus chemical solutions disinfection of heatactivated denture base resins as regards to: 1.The antimicrobial efficacy 2.The structural changes 3.Their effects on physical and mechanical properties. The present study was carried out using two heatcured acrylic resins, one of the conventional type (Acrostone), and the other is a highimpact one (Metrocryl). The disinfection techniques used were 5 minutes microwave irradiation while samples were immersed in water, immersion in 2 % glutaraldehyde solution for 10 hours, and immersion in 0.5% sodium hypochlorite solution for 20 minutes. A total number of 333 were prepared according to the manufacturer?s instructions, and classified into three main groups: Group A: 93 samples, were constructed for testing the antimicrobial efficacy. Group B: 40 samples, were constructed for examining the internal structural changes using an xray diffractometer. Group C: 200 samples were constructed for testing the effects of various disinfection techniques on physical and mechanical properties. The following results were obtained: 1.Microwave irradiation and sodium hypochlorite were effective against Candida albicans. 2. Slight structural changes occurred at the atomic level especially for those samples disinfected using the microwave, but still the general structure is amorphous. 3. Warpage and transverse strength were found to be sensitive properties to changes in internal structure, while, surface hardness, surface roughness, and crazing were not sensitive to such changes. 4. Microwave caused dimensional changes and posterior palatal base distortion more than both sodium hypochlorite and glutaraldehyde. 5. Microwave caused the least incease in hardness values of conventional acrylic resin followed by glutaraldehyde, while the greatest changes were caused by sodium hypochlorite. Almost all changes were insignificant. Except after repeating disinfection sessions for 7 times. For the highimpact acrylic resin, the microwave showed the least decrase followed by glutaraldehyde, while the greasest changes were caused by sodium hypochlorite. 6. Microwave caused the greatest reduction in roughness values followed by sodium hypochlorite and glutaraldehyde. For highimpact acrylic resin, the the changes were statistically significant after repeating disinfection sessions for 7 times. 7. Microwave caused the greatest reduction in roughness values of conventional acrylic resin, followed by sodium hypochlorite and glutaraldehyde. For highimpact acrylic resin, the microwave showed the least increase, followed by glutaraldehyde and sodium hypochlorite. 8. For conventional acrylic resin, only sodium hypochlorite disinfectant caused cracks in the surface of the samples, while both the microwave and glutaraldehyde did not affect the surface in a harmful manner. Highimpact acrylic resin was drastically affected by chemical disinfectants, both glutaraldehyde and sodium hypochlorite. whereas, microwave disinfection resulted in mild surface effect in the form of small voids.