Polymerization shrinkage stress of light curing dental composites
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OBJECTIVES: To analyze the polymerization shrinkage stresses flowable and universal dental composites at different times. MATERIALS AND METHODS: Seven flowable and four universal composites; were used in this study. Two glass cylinders were fixed in a vertical position on the INSTRON machine; leaving 1 mm gap between them. The resin was injected and light cured for 20 seconds. The load curve was recorded until 5 mins after the end of light cure. The stress values were calculated in MPa from the division of contraction forced recorded at 20 s. 60 s.180 s. and 300 s. Statistical analysis was done using ANOVA and all Pairs Tukey –Kramer (α = 0.05) RESULTS: MPa Seconds MPa Seconds Sure Fil SDR 0.18 20 0.33 300 Filtek Sup. Ultra univ. 0.21 20 0.37 300 Filtek Sup. Ultra Flow 0.39 20 0.55 300 NovaPro Ultra univ. 0.39 20 0.55 300 Beautifil II univ. 0.35 20 0.57 300 NanoPro Flow 0.40 20 0.66 300 Herculite Ultra univ. 0.43 20 0.65 300 Herculite Ultra Flow 0.42 20 0.66 300 Prime Dent 0.38 20 0.85 300 G-aenial Flo 0.64 20 0.90 300 Dentex flow 0.71 20 1.12 300 CONCLUSIONS: Within the limitation of these research we can conclude that: In general the flowable composites group presented higher polymerization shrinkage stress values at all sudied times. Our null hypothesis ”there is no shrinkage stress difference between flowable and universal composites” was partialy rejected, since the flowable composite SureFil SDR obtained the lowest shrinkage stress values in our study.