The reliability of standardized flexure strength testing procedures for a light-activated resin-based composite

Area of Science:

• Dental Materials Science
• Polymer Chemistry
• Mechanical Testing

Background:

• Dental resin-based composites (RBCs) are widely used restorative materials.
• Accurate assessment of RBC mechanical properties is crucial for clinical success.
• Light-curing units (LCUs) are essential for polymerizing dental composites.

Purpose of the Study:

• To compare the reliability of three-point flexure strength (TFS) and bi-axial flexure strength (BFS) data for dental RBCs.
• To evaluate the impact of hand-held versus oven light-curing units (LCUs) on RBC strength and reliability.
• To determine the degree of conversion (DC) differences between curing methods.

Main Methods:

• Filtek Z250 dental RBC specimens were prepared in bar (for TFS) and disc (for BFS) shapes.
• Specimens were polymerized using either a hand-held LCU or an oven-LCU.
• Flexural strength, Weibull moduli, and degree of conversion were measured after 24-hour water storage at 37°C.

Main Results:

• Both TFS and BFS were significantly lower than BFS for both LCU types.
• Weibull moduli for TFS were significantly lower with the hand-held LCU compared to the oven-LCU.
• Weibull moduli for BFS were not significantly different between the two LCU types.
• Degree of conversion was significantly lower with the hand-held LCU.

Conclusions:

• Bi-axial flexure testing is recommended as a standard for assessing light-activated dental RBCs due to improved reliability and clinical relevance of specimen geometry.
• Differences in polymerization extent suggest variations in light energy output and efficiency between hand-held and oven LCUs.
• Oven LCUs may offer superior polymerization efficiency compared to hand-held LCUs for dental composites.