Fatigue limit of relined denture base resins after water storage

Objectives: The aim of this study was to evaluate the effect of water storage on the shear fatigue limit of bond interfaces between reline acrylic resins (Ufi Gel Hard-U e Tokuso Rebase-T) and denture base acrylic resins (Lucitone 550-L e Acron MC-A). Methods: Denture base resins were packed and processed in PVC cylinders (16x16 mm), following the manufacturers' instructions. After preparing with 240 grit paper, the surfaces to be bonded were brushed with detergent (20 s), washed in distilled water, and blot-dried. The bonding sites were prepared by painting the surfaces with the bonding agents of resins U or T. A label, with a center hole (3.5 mm), was set on the surface of resins. Each cylinder was placed in a stainless steel mold with a center hole (3.5x5.0 mm), where the reliners were set. For each reline acrylic resin, 30 specimens were fabricated and divided into two groups (n= 15). The fatigue limit results (MPa) were obtained using the stair-case approach (10.000 loading cycles/ 5.0 Hz) in a servo-hydraulic universal testing machine. For group 1, the tests were performed after polymerization of the reline resins and for group 2 after storage in distilled water at 37±1ºC for 30 days. Results: Results were analyzed with 2-way ANOVA and Tukey's tests (alpha= .01). After polymerization, the specimens relined with U showed higher (P<.01) fatigue limit (L/U-6.61 MPa; A/U-7.49 MPa) than T (L/T-5.30 MPa; A/T-4.80 MPa). After water storage, the specimens relined with U demonstrated an increased (P<.01) fatigue limit (L/U-7.86 MPa; A/U-8.75 MPa). The same occurred with the A/T specimens (6.40 MPa). Conclusion: The U reliner material demonstrated the highest results of shear fatigue limit. All denture base resins/reliners' interfaces demonstrated an increased fatigue limit after water storage, with the exception of L/T. Grant FAPESP 03/03278-8.