The comparison of surface hardness, water sorption and staining resistance between thermoplastic nylon and heat-cured acrylic resin.

Aim: To evaluate and compare the surface hardness, water sorption and staining resistance of conventional heat cure and nylon denture base materials. Materials and Methods: A total of 120 specimens, which comprises thirty from each denture base materials (Acralyn-H, DPI, Valplast and Flexident), were fabricated by investing metal specimen analogues of dimension 65x10x2.5mm strips for hardness, 50x0.5mm discs for water sorption and 20x1mm discs for staining resistance according to ADA specification no.12. The surface hardness was evaluated using Shore D Durometer. Water sorption was tested by the differences in the weight of the specimens by desiccating in calcium chloride and immersing in water for one week. The specimens were placed in a staining solution of 3% tartrazine for 7days. Staining resistance was evaluated by the optical density of the extraction solvent (ethanol) using spectrophotometer. Results: Heat cure acrylic denture base materials demonstrated more surface hardness compared to nylon based denture materials. Tukey’s HSD showed significant differences (p<0.05) in the hardness of heat cure and nylon denture base materials. The water sorption values of Acralyn-H, DPI and Valplast were comparable and showed a statistically significant difference (p<0.05) in the water sorption with Flexident. In staining resistance test, Valplast demonstrated more optical density whereas the optical densities of the others materials were comparable. Valplast materials displayed significant differences (p<0.05) in staining resistance with heat cure denture base materials. Conclusions: Both the heat cure denture base materials exhibited greatest surface hardness compared to the flexible denture base materials. Flexident displayed the lowest water sorption and Valplast had the least staining resistance. Key words: Polymethylmethacrylate, nylon denture base materials, staining resistance., urface hardness, water sorption,