Influence of polymerization cycle on the flexural strength of four different PMMA-based heat-polymerized denture base RESIN

Purpose: PMMA-based heat-polymerized acrylic resins used in the fabrication of denture bases may be cured in different ways. As the polymerization cycle length affects fabrication costs and time, a fast cycle is more advantageous. However, polymerization cycles may influence mechanical properties. Objective: The purpose of this study was to evaluate the influence of the polymerization cycle on the flexural strength of four types of PMMA-based heat-polymerized resins used as denture base materials. Materials and methods: The ISO Standard 1567:1999 (Dentistry - Denture base material) was followed in specimen preparation and flexural strength testing of four types of PMMA-based heat-curing resins: Characterized Lucitone (Dentsply-DeTrey); Paladon 65 (Heraeus Kulzer); ProBase Hot (Ivoclar-Vivadent); Prothyl Hot (Zhermack). Resin specimens were obtained following different curing cycles: Standard and Slow for Lucitone; Fast, Standard, and Slow for Paladon 65; the five variants defined by the manufacturer for ProBase Hot; the Standard cycle for Prothyl Hot. For each polymerization cycle six specimens (64 ± 1) mm in length, (10 ± 0,2) mm in width, and (3,3 ± 0,2) mm in height, were prepared. For flexural strength measurements each specimen was loaded until failure with a new testing device (Flexural Test Rig), developed following the indications of ISO 1567:1999. The flexural strength was calculated in MPa and the values were compared with ANOVA and Tukey’s test for post-hoc (p = 0.05). Results: The polymerization cycle has no or minimal influence on the flexural strength of the tested resins. Lucitone exhibited relatively low resistance to flexural loads as when compared with the other resins (Group 7: 78,467 ± 5,623 MPa; Group 8: 71,198 ± 3,775 MPa). Conclusion: With regard to flexural strength, a slow curing cycle does not appear to be justified for the either Lucitone or ProBase Hot, whereas slow polymerization may be advisable for Paladon 65 tested resins, whereas the fast curing cycle V3 was the most favourable to achieve the optimal flexural strength for ProBase Hot.