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- Emami, Nazanin, et al.
(författare)
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Effect of light intensities variations on bulk curing of dental composites
- 2002
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Ingår i: Journal of Dental Research. - 0022-0345 .- 1544-0591. ; 81:Suppl. 1
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Tidskriftsartikel (refereegranskat)abstract
- The light intensity used during curing of light curable dental composites is believed to affect the residual stress level. In this study we tested the hypothesis that low light intensity and long but clinically acceptable light curing time, can produce composites with physical/clinical properties (e.g. volumetric shrinkage, linear contraction stress, degree of conversion (DC%) and Young's modulus) comparable to those of high light intensity cured composites. Methods: Two dental composites, Z100 and Z250, were investigated. Specimens were cured with light intensities of 200, 450 and 800 mW/cm2 for 140, 60 and 35 s from a distance of 7 mm. Linear contraction strains were measured with strain-gages attached to stainless steel rings serving as molds (8 mm in diameter and 4 mm high). DC% was measured at the top and the bottom of samples as well through the bulk using FTIR. Volumetric polymerization shrinkage was determined using a water displacement method. Young's modulus was determined in tension on composite specimens with dimensions of 8 x 50 x 1 mm. Results: Polymerization stress level decreased significantly (p<0.05) when cured with 200 mW/cm2 rather than with 800 mW/cm2. Reduction in light intensity did not decrease the DC% values significantly, nevertheless the most dramatic differences existed between top and bottom surfaces (p<0.05) rather than among curing groups. Measured modulus and volumetric shrinkage values were no significantly different (p>0.05) between different light intensity groups. Conclusion: Low light intensity decreased the residual stress and DC% values (through the depth of cure) significantly (p<0.05), but did not significantly affect the Young's modulus and the volumetric shrinkage values. The lower residual stress values, reflected by lower strain levels in the metal rings used during measurement, suggest that more stress relaxation occurs in the low light intensity group during cure. Our results support the proposed hypothesis
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