Effect of Microwave Disinfection on Hardness of Acrylic Base Denture Lining Material

Aims: To evaluated the effect of the repeated microwave disinfection on hardness of vertex denture lining material cured by water bath and microwave. Materials and Methods: Twenty specimens were prepared 4.5 mm thickness × 25 mm in diameter from denture lining material (Vertex , Holland) adhered to specimen 2.5 mm thickness × 50 mm in diameter form a heat-cured acrylic resin (Vertex, Holland) and divided into two main groups according to the curing method (waterbath and microwave). The specimens were divided as following, ten specimens, five for each curing method as a control group. The other ten, five specimens for each curing method for microwave disinfection, specimens immersed in 200 ml of distilled water and irradiated with 540 Watt per 3 minute, three times weekly for one month started from the first time of microwave irradiation (microwave disinfection) to twelve times, tested for hardness by using Shore –Ahardness durometer. Results: The independent t-test revealed that, significant differences between control groups (specimens cured by water bath higher than that cured by microwave method), and significant differences between first time of disinfection by domestic microwave oven cured by two methods. The analysis of variance (ANOVA) and Duncan multiple range test confirmed there is a significant difference in hardness of denture lining material in different times of disinfection by domestic microwave oven for both curing methods at significant level (P≤ 0.01). Conclusion: The repeated disinfection by microwave irradiation deteriorated the vertex denture lining material regardless to the curing methods.