Objectives . Polymerization stress in dental composites remains a concern in restorative dentistry. The objective of this study was to evaluate the influence of inorganic fraction ( F i ) on polymerization stress ( σ pol ) and its determinants: volumetric shrinkage (VS), elastic modulus ( E ) and degree of conversion (DC).
Materials and methods . Eight experimental composites were produced with equal parts of BisGMA and TEGDMA (mol%) and 2 μm average size barium glass in concentrations of 25, 30, 35, 40, 45, 50, 55 and 60 vol%. σ pol was obtained in a universal testing machine by inserting the composite (1 mm thick) between acrylic rods (5 mm in diameter). VS was determined using a water pycnometer. E was determined in three-point bending. DC was measured by FT-Raman. Data were obtained 15 min into polymerization and were analyzed by one-way ANOVA and Tukey’s test ( α = 0.05). Specimens were photoactivated with quartz–tungsten–halogen light curing unit, reaching a radiant exposure of 18 J/cm 2 (570 mW/cm 2 × 32 s).
Results . The table shows the mean ± standard deviation of σ pol. VS, E and DC.
| Inorganic fraction (vol%) | Polymerization stress (MPa) | Elastic modulus (GPa) | Volumetric shrinkage (%) | Degree of conversion (%) |
|---|---|---|---|---|
| 25 | 5.8 ± 0.4 a | 1.6 ± 0.2 f | 3.3 ± 0.6 a | 53.0 ± 3.1 a |
| 30 | 5.3 ± 0.4 ab | 1.8 ± 0.2 ef | 3.2 ± 0.6 ab | 56.1 ± 1.6 a |
| 35 | 5.4 ± 0.2 ab | 2.3 ± 0.2 de | 3.1 ± 0.6 ab | 53.7 ± 2.8 a |
| 40 | 4.8 ± 0.4 bcd | 2.7 ± 0.3 cd | 2.8 ± 0.5 abc | 54.5 ± 3.1 a |
| 45 | 5.0 ± 0.1 bc | 3.1 ± 0.4 c | 2.9 ± 0.4 ab | 55.7 ± 0.8 a |
| 50 | 4.5 ± 0.3 cd | 4.3 ± 0.6 b | 2.7 ± 0.5 abc | 57.6 ± 3.6 a |
| 55 | 4.4 ± 0.3 d | 4.3 ± 0.5 b | 2.4 ± 0.3 bc | 51.1 ± 0.3 a |
| 60 | 3.9 ± 0.2 e | 5.9 ± 0.9 a | 2.1 ± 0.3 c | 51.8 ± 1.1 a |
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