الفهرس 
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Abstract
Purpose: The aim of this study was to evaluate flexural characteristics, impact strength and hardness of a Polyoxymethylene based (Bio dentaplast) and a polyamide based (Bre flex) thermoplastic denture base materials and to compare them with a conventional heat cured polymethyl methacrylate (Acrostone).
Materials and methods: 48 specimens were prepared for this study; 16 for each material. Eight specimens from each material were tested under 3-point bending test to determine the flexural strength and modulus. The other eight were tested in an Izod impact tester to assess the impact strength. The fractured specimens from the impact test were subjected to Vickers’ micro-hardness test. The obtained data were statistically analyzed using One-way ANOVA with Tukey’s post-hoc test.
Results: The conventional heat-cured acrylic resin showed the highest statistically significant mean flexural strength and modulus values (129.6 ± 9 N/mm2 and 3546 ± 45MPa respectively). While, there was no statistically significant difference between the other two thermoplastic denture base materials. On the other hand, the polyamide specimens showed the highest statistically significant mean impact strength value (26.4 ± 2.4 KJ\m2) followed by the Polyoxymethylene (9.6 ± 1.5 KJ\m2) and the conventional acrylic resin specimens (2.8 ± 0.2 KJ\m2) respectively. However, the Vickers’ micro-hardness results revealed the highest statistically significant mean value for the conventional acrylic resin specimens (17.52 ± 1.1 VHN) followed by Polyoxymethylene (14.95 ± 1.3 VHN) and polyamide (8.5 ± 1.6 VHN) respectively.
Conclusion: Polyoxymethylene and Polyamide based thermoplastic denture base resins can be used as an alternative to conventional PMMA
in cases where flexibility is required as well as in cases with repeated denture fracture.