Accuracy and porosity of denture bases submitted to two polymerization cycles

In this study was verified accuracy and porosity of denture bases submitted to double cycles of polymerization. Thirty-Six master casts were made in dental stone from the impression of the metal die. They were divided in three groups. Denture bases of conventional acrylic resin were made on the casts of the groups I (GI-control) and II (GII), polymerized in water bath during 9 hours at 73 degrees C, and specific resin for microwave polymerization were made on the casts of the group III (GIII) and cured at 500 W during 3 minutes. Accuracy was verified by the weight of a impression material put between the denture base and cast die under load of 2 Kg. Afterwards, all the denture bases were relined by addition method and those of the group I and II were relined with the same material and polymerization technic. The denture bases of the group II were filled with the same resin, however cured in microwave oven with 500 W during 3 minutes. Accuracy was reevaluated. The porosity was verified by the immersion of the specimens in a solution of permanent black ink and the pores were counted through a stereo light microscope under magnification of 6.3 x. The average and standard deviation obtained for accuracy before and after the relining were respectively: GI: 0.63 +/- 0.02 - 0.66 +/- 0.03; GII: 0.63 +/- 0.03 - 0.68 +/- 0.03: GIII: 0.58 +/- 0.02 - 0.80 +/- 0.05. There was a significant difference (p < 0.05 as tested by Tukey) only for the group III. The average and standard deviation for porosity before and after the relining were respectively: GI: 8.33 +/- 0.63 - 9.25 +/- 0.85; GII: 8.17 +/- 0.98 - 10.08 +/- 1.63: GIII: 5.41 +/- 0.78 - 6.58 +/- 1.02. There was a significant difference (p < 0.05) for the group III before relining. The conclusion is that after relining, the conventional resin cured by water bath or microwaves energy showed a better adaptation, and the highest number of pores.