In Vitro Evaluation of the Effect of Thermal and Mechanical Fatigues on the Bonding of an Autopolymerizing Soft Denture Liner to Denture Base Materials Using Different Primers

Abstract

This in vitro study evaluated the effect of priming procedures on bonding of an autopolymerizing silicone denture liner (Sofreliner) to a denture base material after fatigue processes using cyclic thermal stressing and repetitive mechanical stressing. Denture base specimens were fabricated by use of an autopolymerizing denture base resin and Co-Cr alloy into a cylinder shape 8-mm diameter and 4-mm high. The bonding surfaces of denture base specimens were polished with 600-grit silicon carbide paper. Resin denture base specimens were pretreated with applications of resin primer (Sofreliner Primer or Reline Primer for resin). Metal specimens were pretreated with application of metal primer (Reline Primer for metal) or coated with adhesive resin (C&B Metabond) followed by application of resin primer (Sofreliner Primer). Tensile specimens were fabricated by polymerizing a 2-mm thickness of Sofreliner between a pair of pretreated denture base cylinders. Repetitive mechanical stressing was performed by using a University of Alabama-type wear-testing apparatus as a stress generator. Vertical 75 N load with 15 degrees rotation was applied 66,700, 133,300, 266,700, and 400,000 times, then residual tensile resistance to failure was measured. Seven specimens were fabricated for 16 groups--four cyclic loading groups for four pretreatment groups. Residual tensile resistance to failure of specimens before the fatiguing process and after 5000, 10,000, 20,000, and 30,000 thermocycles were used as reference. The mean values of each group were statistically analyzed by three-way ANOVA and Bonferroni/Dunn test at a 95% confidence level. Failure modes were assessed for all specimens measured. In the denture-bonded groups, residual tensile resistance to failure of Sofreliner Primer-treated group was significantly higher than that of the Reline Primer at each thermocycling interval (p < 0.0001) and up to 133,300 times of cyclic loading (p < 0.0001). In the metal-bonded groups, residual tensile resistance to failure of the intermediate adhesive resin group was higher than the metal primer-applied group up to 5000 thermocycles (p < 0.0001); however, there was no significant difference between them after 66,667 cyclic loads (p= 0.1698). Although adhesive resin-coated specimens of metal-bonded groups showed mixed failure, metal primer-applied groups and both denture-bonded groups consistently revealed cohesive failure of the soft denture liner after cyclic loading. Application of Sofreliner Primer for a resin denture base provided better bonding after thermocycle and cyclic load testing than did Reline Primer. Using an intermediate adhesive resin layer on a Co-Cr denture base material improved the bonding for up to 5000 thermocycles; however, it did not affect cyclic loading parameters.