Shrinkage behavior and conversion of flowable resin-composites

Objectives: To evaluate the shrinkage-strain of a range of new flowable composites in relation to the degree of conversion (DC) and filler fraction of these materials. Methods: Seven materials were studied. The bonded-disk technique was used to measure polymerization shrinkage-strain kinetics. Measurements were obtained continuously for 60 min by irradiation for 40 s at 750 mW/cm² at initial temperatures of (a) 23 °C and (b) 37 °C, (n = 3), at each temperature, per material. The DC of the flowable composites was measured by FTIR spectroscopy immediately post-cure. The percent filler was determined by combustion of the test specimens for 1 hour at 400 °C. One-Way ANOVA was used for statistical analysis. Results: The values of shrinkage strain ranged from 2.61 to 6.25% at 23 C and from 3.88 to 6.56 at 37 °C. Shrinkage-strain values increased when the temperature was raised. DC values ranged° from 60.5 % for Filtek Flow to 67.7 % for Point 4 Flowable. The percent filler ranged from 54.5 w/w for Revolution Formula 2 to 71.3 w/w for Point 4 flowable. A correlation was found between the percent filler and the polymerization shrinkage-strain for both temperatures (r²= 0.94) and (r²= 0.87) for 37 °C and 23 °C respectively Conclusion: Flowables that had the highest filler percent produced lower shrinkage-strain values. There was a wide range of shrinkage-strain values for the flowables studied.