Flexural Strength of Relined Thermoplastic Denture Base Resins

Objectives: The aim of this study was to investigate the effects of relining materials for thermoplastic denture base resins on flexural strength.
Methods: For flexural strength test, 120 specimens measuring 64.00mm x 10.00mm x 3.30mm(ISO-1567:1999) were fabricated using four thermoplastic denture base resins(Polyamide: Valplast, Valplast International Corp, USA. Polyester: Estheshot-Bright, i-cast Co. Ltd, Japan. Acrylic resin: Acrytone, High dental Japan, Japan. Polypropylene: Weldenz, Weldenz , Japan) and three self-curing denture relining resins(Rapid simplified Vertex-Dental B.V.,Zeist, the Netherlands; Tokuyama Rebase II, Tokuyama Dental Corp, Tokyo, Japan; and Ufi Gel Hard, Voco, Cuxhaven, Germany) and were assigned to each group(n=10). Forty specimens using four thermoplastic denture base resins and thirty specimens using three relining materials were served as the control. For shear bond testing, 120 specimens were fabricated using the same thermoplastic resins that were bonded with relining materials with a bond area of 6.00mm diameter and were assigned to each group(n=10). All specimens were tested on the universal testing machine (AGX-KN10, Shimadzu, Kyoto, Japan). Statistical analysis was performed through analysis of variance and Tukey’s post hoc test (p=.05) using SPSS.
Results: Polyester showed the highest flexural strength, while Polypropylene showed the lowest (p<.05) flexural strength. Thermoplastic resins relined with Vertex showed higher flexural strength than with Tokuyama in all groups(p<.05). For shear bond strength, Acrylic resin groups and Polyester with Vertex group showed a higher bond strength than the other groups.
Conclusions: Flexural strength of relined thermoplastic denture base materials may be affected by properties of original materials, rather than bond strength between denture base and relining materials.