Nadia O Alkhamis, Khamis A Hassan.
The effect of different light curing methods on surface hardness and depth of cure of various types of composite resin.
J Pak Dent Assoc Jan ;14(4):200-5.

OBJECTIVES: The effect of three different light curing methods on the hardness of three types of composite resin was investigated at three different curing depths. MATERIALS AND METHODS: A total of 90 specimens were fabricated using aluminum square split-mold in two halves each, and were divided equally into 3 groups representing the three tested composite materials; Point- 4, Z-250, and Artemis. Each group was divided again into 3 subgroups of 10 specimens each according to the type of light curing unit used. Specimens in each subgroup were cured according to specified criteria using VIP (QTH), Elipar Trilight (QTH), or Ultralume LED5 (LED) light curing units. Microhardness measurements, using Vickers hardness tester, were recorded on the top surface of each specimen`s half, and also on the split surface of each half of the specimen at 1 mm and 2mm depths from the top surface. RESULTS: The VIP (QTH) showed, in general, the highest mean hardness value for all surfaces at all depths. The Z-250 composite resin material showed the highest hardness value among other types of composite resin. The mean hardness values recorded at the surface were significantly higher for all light curing units when compared with those recorded at 1mm and 2-mm curing depths. The highest mean hardness values were recorded at the surface of Z-250 composite resin when cured with QTH LED and Soft-start light curing units had almost the same effect on Artemis composite resin where they yielded the lowest mean hardness values. The mean hardness values of the QTH groups were significantly higher when used for curing Z-250 composite resin at 1mm depth. The LED and Soft-start light curing units exhibited almost similar effects when used for curing Artemis composite resin, and yielded the least mean hardness values. A significant difference was found in mean hardness values between 1mm and 2mm curing depths for the 3 groups of tested composite resin materials. CONCLUSIONS: QTH could be considered the most effective curing source for composite resins, in spite of the presence of some drawbacks. Soft-start polymerization, though it is an effective technique used to decrease generation of polymerization contraction stresses and produce better marginal adaptation of composite resins, did not significantly improve the depth of composite cure.

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