Two-stage technique for optimum fit and stability of light-polymerized record bases

Abstract

undergoes shrinkage during polymerization which promotes gap formation in the palatal area. Specifically, gaps form at the midpalatal region of the posterior border and compromise the posterior palatal seal. 5,7 When exposed to visible light, the composite resin material closest to the light source polymerizes first, thus causing lift-off of the material, producing a gap by drawing the material away from the cast as a result of shrinkage. Different methods have been introduced to eliminate the number of defects in an effort to obtain a more accurate fit. These methods include lining the record base with elastic impression materials or silicone resilient materials, 8 vacuum adaptation of the record base, 6 and staged polymerization by covering the palatal portion of the record base. 5 However, resilient liners tend to tear from the record base from repeated seating and removal, resulting in inaccurate seating of the bases. The use of vacuum only improves adaptation without addressing gap formation resulting from polymerization shrinkage. Multiple processing procedures in the polymerizing unit require repeated adaptation and are time consuming and impractical. The edentulous maxilla consists of a relatively flat portion in the middle of the hard palate and an inclined slope toward the residual ridge. Due to the geometric features of the palatal concavity configuration, the shrinkage occurring toward the residual ridge leads to lifting of the record base in the midpalatal region. 7 By dividing the Triad sheet into 2 pieces along the junction of the horizontal and vertical configuration of the palate, the stresses that develop during polymerization can be confined within each segment of the material, shifting the direction of shrinkage from the ridge crest area to 2 separate areas in the middle of the palate and the crest of the ridge. This article describes a simple and accurate 2-stage technique for the fabrication of a light-activated record base to maximize the fit of the record base to the cast. The procedure is versatile, allowing it to be applicable to the various palatal configurations.