Hardness, Flexural Strength, and Flexural Modulus Comparisons of Three Differently Cured Denture Base Systems

Abstract

This study compared the surface hardness, flexural strength, and flexural modulus of a light- and heat-cured urethane dimethacrylate (UDMA) to two conventional polymethyl methacrylate (PMMA) denture base resins. The effect of less-than-optimal processing condition on the hardness of internal and external surfaces of UDMA specimens was also investigated. The materials tested were Eclipse (light- and heat-cured UDMA), Meliodent (heat-cured PMMA), and Probase Cold (auto-cured PMMA). Eclipse specimens were prepared by adapting the material onto the master cast and light curing in the processing unit for 10 minutes. Meliodent and Probase Cold specimens were prepared according to the manufacturers' instructions. Twenty rectangular specimens measuring 65 x 10 x 2.5 mm(3) were prepared for each material. They were stored in water at 37 degrees C for 30 days before testing. The surface hardness was measured using Vickers Hardness (VHN) test, and flexural strength and flexural modulus were measured using a 3-point bending test. Twenty-five additional Eclipse specimens were similarly prepared and were processed at various times of less than 20 minutes of curing. Vickers Hardness was determined on both the external and internal surfaces of specimens. Data were analyzed using a one-way ANOVA for comparisons of hardness, flexural strength, and flexural modulus between the three denture base materials and for hardness values of both the internal and external surface of Eclipse specimens with curing times. Post hoc analyses (Scheffé test) determined the difference between the groups. Student t-test was used for comparison of hardness between the external and internal surfaces of Eclipse specimens. The hardness (VHN) values were 19.4 +/- 0.7, 17.0 +/- 0.4, and 16.0 +/- 0.4; the flexural strengths (MPa) were 103 +/- 4, 78 +/- 3, and 63 +/- 4; and the flexural moduli (MPa) were 2498 +/- 143, 1969 +/- 55, and 1832 +/- 89 for Eclipse, Meliodent, and Probase Cold materials, respectively. A comparison among the three polymers showed there were significant differences in surface hardness, flexural strength, and flexural modulus (p < 0.05). No significant difference in surface hardness (VHN) between the internal (19.1 +/- 0.6 to 19.4 +/- 0.7) and external surfaces (18.9 +/- 0.4 to 19.2 +/- 0.6) of irradiated Eclipse specimens was observed at 10-, 12-, and 14-minute polymerization times. The surface hardness, flexural strength, and flexural modulus of light- and heat-cured UDMA (Eclipse) were significantly higher than the values obtained for heat-only cured (Meliodent) and auto-cured (Probase Cold) PMMA denture base systems.