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Quintessence Int 40 (2009), No. 3     6. Feb. 2009
Quintessence Int 40 (2009), No. 3  (06.02.2009)

Page 203-214, PubMed:19417884


Shrinkage and hardness of dental composites acquired with different curing light sources
Clifford, Stephen S. / Roman-Alicea, Karla / Tantbirojn, Daranee / Versluis, Antheunis
Objectives: Curing light sources propel the photopolymerization process. The effect of 3 curing units on polymerization shrinkage and depth of cure was investigated.
Method and Materials: The curing lights were a conventional and a soft-start quartz-tungstenhalogen (QTH) light source and a light-emitting diode (LED) source. The soft-start QTH and LED intensity outputs were 9% and 17% less than the conventional QTH source, respectively. For a 40-second light cure, the light energy was 32% and 14% lower, respectively. The light sources were applied to 4 restorative composites (microfilled, 2 hybrids, and nanofilled). For each light unit-composite combination, the development of postgel shrinkage during polymerization was measured with strain gauges (n = 15), and the Knoop hardness was tested at 0.5-mm-depth increments to assess degree of cure 15 minutes after polymerization (n = 5). The results were statistically analyzed with 2-way ANOVA at .05 significance level, followed by pairwise comparisons.
Results: Both factors, light source and composite, significantly affected postgel shrinkage and hardness (P < .05). The conventional QTH unit generally produced the highest shrinkage and hardness (at composite surface and 2-mm depth). The soft-start QTH unit generated the least shrinkage but achieved the lowest depth of cure. The resulting values for the LED unit were mostly in between the results of the other 2 units.
Conclusion: Curing lights should provide sufficient light energy to thoroughly cure composite restorations, which might be achieved without compromising shrinkage stresses if initial intensity is reduced.

Keywords: composite, cure, curing light, hardness, light energy, light intensity, shrinkage, soft start