Characterization of polydimethacrylates and their composites by dynamic mechanical analysis

Area of Science:

• Materials Science
• Biomaterials Engineering
• Polymer Chemistry

Background:

• Dental restorations utilize polymeric materials, whose mechanical properties are temperature-dependent.
• Understanding the glass transition temperature (Tg) is crucial for evaluating material performance in the oral environment.

Purpose of the Study:

• To characterize polymeric dental restorative materials using dynamic mechanical analysis (DMA).
• To determine the glass transition temperature (Tg) of light-polymerized bis-GMA copolymer and a dental composite.
• To assess the impact of water saturation and post-polymerization treatments on Tg.

Main Methods:

• Dynamic Mechanical Analysis (DMA) was employed to measure the viscoelastic properties of dental materials.
• Glass transition temperature (Tg) was assigned based on changes in the elastic modulus, differing from the traditional tan delta maximum method.
• Materials were subjected to water saturation and post-polymerization treatments (heating, gamma-irradiation) to evaluate their effect on Tg.

Main Results:

• A bis-GMA copolymer exhibited a Tg of -25°C, while a dental composite showed a Tg of +10°C.
• Water saturation lowered the composite's Tg to -10°C.
• Post-polymerization treatments, such as heating and gamma-irradiation, significantly increased the Tg values.

Conclusions:

• Photopolymerized dental composites may experience significant changes in mechanical state (glassy, leathery, rubbery) within the oral cavity due to temperature fluctuations (0°C to 50°C).
• Variations in mechanical properties during service are likely undesirable for optimal performance, such as wear resistance.
• Further research is needed to correlate specific mechanical states with desirable service properties.