[Effect of the methods of photoactivation and insertion on the hardness of composite resins].

The purpose of this study was to assess the effect of methods of photoactivation and insertion on the Knoop hardness of the Z100 and Alert composite resins. The specimens were confected in cavities measuring 4 x 4 mm. The insertion of material was carried out by means of two methods: single-portion technique and insertion of two 2-mm-thick layers. When inserted in a single portion, the resin was compressed with a static load of 1 kgf on a glass slab recovered with a polyester strip, in order to remove the excess of material. After the removal of the glass slab and polyester strip, the materials were photoactivated by means of continuous light emitted by a XL 3000 unit with a light intensity of 520 mW/cm2 for 40 seconds; double pulse, with light emission of 150 mW/cm2 for 10 seconds, plus 30 seconds with light intensity of 520 mW/cm2 emitted by a XL 3000 unit; and pulsatile light of 520 mW/cm emitted by the Optilux 400 unit, turned on for 2 seconds and off for 2 seconds, during 60 seconds. The two layers of the material submitted to double insertion were photoactivated in the same conditions as the bulk-inserted material, and the excess of material was also removed from the second layer. After storage in a stove at 37 C and 100% relative humidity for 24 hours, the specimens were embedded in polyester resin, trimmed and polished with sandpaper and diamond slurry. Knoop hardness was assessed in 4 depths with a HMV Shimadzu penetrometer under the load of 50 g during 30 seconds. The data submitted to ANOVA and Tukey's test revealed that Z100 presented greater hardness values; double insertion was better than single insertion; the hardness at the surface was smaller than that at the bottom of the specimen, regardless of other factors. For Z100, all activation methods produced smaller hardness values when double insertion was carried out. Meanwhile, for Alert, continuous light promoted statistical similarity between the insertion techniques. For Z100, there was statistical similarity between the activation methods only when the double-insertion technique was employed. There was statistical similarity between the double-pulse and pulsatile-light techniques for Alert, when the single-portion insertion technique was carried out.