Properties of resilient denture liners in simulated mouth conditions

Abstract Tests were performed on nine resilient denture-lining materials using distilled water at 37° C. to simulate mouth conditions. The data obtained were compared to those results obtained previously at room temperature. The consistency of the self-curing resilient liners ranged from 41 to 48 mm. These values, on the average, were about 4 mm. larger than those with direct, hard, self-curing denture liners, indicating that the resilient materials flow to a greater extent during their processing. The highest temperature rise observed during the processing of these materials was 2.1° C., and the values ranged from zero to 2.1° C. This indicates that there should be no irritating effect to the oral tissues from temperature rise. The weight increases after 1 month in water at 37° C. were generally a little larger than they had been in water at 25° C. The weight increases after 6 months in water at 37° C. varied from 2 to 22.1 per cent. Of the total material leached out during 1 month in water at 37° C., the percentage of nonvolatile material varied from zero to 27 per cent, with most of the materials losing under 10 per cent nonvolatile material. Therefore, the major portion of the weight loss was due to the leaching out of volatile plasticizers and organic solvents. The Shore A hardness in water at 37° C. was much less than the hardness values in water at 25° C., except for the two silicone products. A temperature rise from 25° C. to 37° C. in air had little effect on the two silicone materials. A temperature rise alone from 25° C. to 37° C. had a greater effect on the hardness than did the effect of transferring the liners from air at 37° C. to water at 37° C. Thus, the major softening was due to an increase in temperature. The original tear resistance was slightly less at 37° C. than at 25° C. in water for all the materials except the two silicone products. After storage for 6 months in water at 37° C., the tear resistance decreased slightly for four materials, and increased extensively for one material. One liner had no harmful effect on the transverse strength of an acrylic resin base, and four materials reduced the transverse strength by about 10 per cent. The remaining four materials, which were self-curing, powder-liquid types containing monomers and organic solvents in the liquids, reduced the transverse strength of the acrylic resin base by approximately 25 per cent. A measurement of the adhesion of the resilient liners to a smooth acrylic resin base after storage for 1 month in water at 37° C. showed that six of the materials possessed enough adhesion to tear within themselves instead of stripping from the base material. One material showed a low value of 7 pounds per inch, and the two silicone products showed the poorest adhesion, 2 and zero pounds per inch. A silicone adhesive was used with the latter silicone product and improved the adhesion to 1 pound per inch. The recovery from 20 per cent compression, placed on specimens of the nine liners for 24 hours at 37° C., was measured after 1 minute and after 1 hour. On the basis of these measurements, the nine materials could be classified into four general groups. One material showed no recovery after 1 minute or 1 hour, three materials showed no recovery after 1 minute and slight recovery after 1 hour, three materials showed some recovery after 1 minute and a larger amount after 1 hour, and the two silicone products showed the greatest total recovery, which took place within the first minute.