Abstract

SHIMOKAWA, CARLOS ALBERTO KENJI; BENGSTON, CAMILLA REGINA GALVÃO; YOUSSEF, MICHEL NICOLAU  and  TURBINO, MÍRIAM LACALLE. Effect of the reduction of the initial light intensity on the polymerization of a composite resin photoactivated with halogen light and distancing of the activator point. RPG, Rev. pós-grad. [online]. 2012, vol.19, n.2, pp. 64-68. ISSN 0104-5695.

The aims of this study were to evaluate the hardness of a composite resin photoactivated by the continuous method and to compare it with methods that use lower intensity of initial light, followed by maximum intensity. There were built 60 samples divided into six groups: 1 - 1 mm thickness and conventional activation; 2 - 1 mm thickness plus soft-start activation; 3 - 1 mm thickness and distance variation; 4 - 2 mm thickness with the conventional activation; 5 - 2 mm thickness and soft-start activation; and 6 - 2 mm thickness with distance variation. All the samples were built with black polypropylene matrices, using the composite resin Z350 (3 M ESPE, Saint Paul, USA), and they were activated with the photoactivator Degulux SoftStart (DEGUSSA-HULLS, Hanau, Germany). The samples were submitted to Vickers micro-hardness test using the HMV-200 (SHIMADZU, Kyoto, Japan), on the irradiated and opposite surfaces, being the thicknesses and methods of activation used compared. After the analysis of variance e Tukey's tests, it could be noticed a statistically significant difference between the control, soft-start, and distance variation groups. The percentage of maximum hardness was considered acceptable (> 80%) in the irradiated surface and in 1 mm thickness of the opposite surface, although in the 2 mm thickness the values did not achieve the minimum of 80% of maximum hardness. In conclusion, the photoactivation progressive methods reduced the microhardness of the composite resin, when compared with the conventional one, but this was acceptable in the irradiated and opposite surfaces of this 1 mm thickness resin.

Keywords : Hardness; Dental restoration; permanent; Polymerization.