engleski

Conversion Rate in Composite Samples Cured with Different LED Sources

Objectives: The trend of using high power curing lights switched to more gentle light source - LED (light emitting diode) units which enabled lesser shrinkage stress for tooth structure. At the same time polymerization process needs adequate intensity and illumination time to properly cure the composite resin layer in clinical situation. Methods: Five specimen of 10 mm diameter A3 shade composite restorative Filtek Z 250 (3M ESPE), was illuminated for 40 sec by Lux-o-Max (Akeda Dental), and 20 sec for Elipar Freelight I (3M ESPE), L.E.Demetron (Kerr) and halogen unit Elipar Trilight (3M ESPE) as a control. The degree of conversion was measured by FTIR spectroscope at the sample surface and at the 2 mm depth using previously cured underlays and overlays. The degree of conversion was calculated from the equivalent aliphatic/aromatic molar ratio between polymerized and unpolymerized samples. Results: Low intensity LED curing unit show 52.86 % (sd 1.59) conversion at the surface and 46.91% (sd 5.21) at 2 mm depth. Monomer conversion with medium intensity LED unit was 58.31% (sd 0.11) and 54.04% (sd 1.27). The results with second generation LED curing unit were 66.55% (sd 5.76) and 66.72 (sd 4.8) at 2 mm depth which is better than with control unit - 63.51% (sd 2.29) and 54.61% (sd 2.23) respectively. Conclusion: The measurements reveal that with first generation LED's curing time must be prolongued to achieve clinically acceptable composite filling even with high photosensitive resin. Medium intensity unit show better overal conversion especially at 2 mm depth. High output second generation LED unit showed no difference in conversion between layers, but the shrinkage stress may be high.

degree of conversion; LED; composite resins

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