Polymerization stress evolution of a bulk-fill flowable composite under different compliances

Area of Science:

• Materials Science
• Biomaterials Engineering
• Dental Materials

Background:

• Polymerization stress (PS) is a critical factor in dental composite restorations, potentially leading to marginal gaps and secondary caries.
• Bulk-fill flowable composites offer ease of placement but their polymerization stress characteristics compared to conventional packable composites require detailed investigation.

Purpose of the Study:

• To simultaneously measure and compare the polymerization stress (PS) evolution, degree of conversion (DC), and exotherm of a bulk-fill flowable composite against a packable composite.
• To evaluate the influence of varying instrumental compliances, simulating clinical cavity constraints, on these properties.

Main Methods:

• A cantilever-beam based instrument with in situ NIR spectroscopy and microprobe thermocouple was used.
• Measurements were conducted on a bulk-fill flowable composite (FBF) and a conventional packable composite (Z250) under compliances ranging from 0.3327 to 12.3215 µm/N.
• Correlations between PS, temperature change, and DC were analyzed.

Main Results:

• Maximum PS decreased with increasing cantilever beam compliance for both composites.
• FBF exhibited lower final PS than Z250 under compliances below ~4 µm/N; PS was similar at higher compliances.
• DC and exotherm were compliance-independent; FBF showed higher DC and nearly double the peak exotherm compared to Z250. A characteristic PS drop was observed in FBF during early polymerization, linked to its higher exotherm.

Conclusions:

• Contrary to the general assumption of lower PS in low-viscosity composites, FBF demonstrated lower PS under low constraint conditions.
• The findings suggest that bulk-fill flowable composites can exhibit favorable PS behavior when used as a base material in clinical scenarios with lower cavity compliance.