Influence of flask closure and flask cooling methods on tooth movement in maxillary dentures.
PURPOSE: This study investigated the tooth movement of standardized simulated dentures processed by traditional closure or the new Rafael Saide (RS) tension system when cooled in the curing water itself or in curing water followed by bench storage for 3 hours. MATERIALS AND METHODS: Forty stone casts were formed from a mold of an edentulous maxillary arch. The wax denture record bases were made on the casts; the height of the wax rim occlusion was 20 mm in the labial sulcus of the cast and 10 mm in the posterior region. The upper stone cast was mounted on a Mondial 4000 semi-adjustable articulator with wax rim interocclusal references in relation to the lower stone cast teeth. Metallic pins were placed in the incisal border of the maxillary central incisors (I), labial cusp of the first premolars (PM), and mesiolabial cusp of the second molars (M). The incisor-to-incisor (I-I), premolar-to-premolar (PM-PM), and molar-to-molar (M-M) transversal distances and left incisor-to-left molar (LI-LM), and right incisor-to-right molar (RI-RM) anteroposterior distances were measured before and after denture polymerization with an optical microscope with a tolerance of 0.0005 mm. For traditional closure, the dentures were flasked conventionally in standard metallic flasks, which were afterward placed in spring clamps. For the new RS system closure, the flasks were pressed between the metallic plates of the tension system after the final closure. The Clássico heat-polymerizing acrylic resin dough was packed in the flasks under a final packing pressure of 1.250 kg f. Twelve hours after flask closure, the dentures were polymerized in a moist heat-polymerizing cycle for 9 hours at 74 degrees C. The denture was deflasked after cooling in the water of the polymerizing cycle (groups A and C) or in the water of the polymerizing cycle and then bench-stored for 3 hours (groups B and D). Collected data were analyzed with analysis of variance and Tukey's test (p< 0.05). RESULTS: There was no statistically significant difference (p> 0.05) between the conventional and new RS system closure methods for the transversal distances after polymerization in all studied groups. The anteroposterior distances did not change with deflasking after water bath cooling. There were statistically significant differences (p< 0.05) in the anteroposterior distances with deflasking after water bath cooling and then bench storage for 3 hours. CONCLUSION: Tooth movement was similar in dentures processed by traditional closure and by the new RS tension system, with the exception of the anteroposterior distances when the flasks were cooled in their own curing water and bench-stored for 3 hours.