Effect of finishing and polishing procedures on the gap width between a denture base resin and two long-term, resilient denture liners

Statement of problem. The junction between a long-term, resilient denture liner and the denture base is difficult to finish and polish due to differences in the hardness of the materials. Gaps tend to form during Finishing and polishing procedures. Purpose. This study measured the junctional gap between 2 long-term, resilient denture liners and a denture base material after different finishing and polishing procedures were performed. The surface smoothness of the 2 liner materials also was evaluated. Material and methods. Molloplast-B and an experimental, heat-polymerized methyl siloxane-resin-based denture liner were processed (according to the manufacturer's instructions) against Lucitone 199 acrylic resin. Control specimens (n=20) were 2 mm thick and flat. Experimental specimens (n=64) were fabricated with a raised center section: a 3- x 5- x 15-mm half-cylindrical ridge with a junction at the top of the cylinder between the liner material and acrylic resin. The specimens were finished with 1 of 6 types of burs and polished with different combinations of rubber-impregnated acrylic polishers, pumice, and tin oxide. The finished specimens were examined and photographed with a scanning electron microscope, and the largest gap along the liner/denture base junction on each specimen was measured. Three-way analysis of variance without replication (P<.05) and post-hoc t tests were used to analyze the data and compare groups. Results. Averaged across finishing and polishing techniques, a larger gap was recorded for the experimental liner material (22 μm) than for Molloplast-B (14 μm) (P<.00005). Qualitative evaluation suggested that the experimental liner material polished better than Molloplast-B. The smoothest surfaces were obtained when specimens were finished with fine-tooth cross-cut carbide burs and polished with both pumice and tin oxide. A comparison between polished and unpolished specimens, averaged over materials and Finishing techniques, revealed that polishing reduced gap size (P=.015). Conclusion. Within the limitations of this study, the 2 denture liners tested behaved similarly. The results suggest that the size of the gap at the liner/denture base junction may be affected by finishing and polishing techniques and vary among materials.