Tensile Strengths of Thermoplastic Resins for Flexible Dentures

Objectives: The use of thermoplastic resin for flexible, removable partial dentures can solve the esthetic and metal-allergy problems associated with conventional materials. To investigate the characteristics of six thermoplastic resins recently developed for flexible dentures, this study evaluated their tensile strengths.
Methods: The following six commercially available thermoplastic resins were tested in this study: two polyamide resins [Bioplast (BP) and Biotone (BT); High Dental Co., Ltd., Japan], two polycarbonate resins [ReigningN (RN); Toshinyoko, Japan, and Jet Carbo-S (JCS); High Dental Co., Ltd., Japan], a polyester resin [EstheShot Bright (ESB); i-CAST, Japan], and an acrylic resin [Acrytone (ACT); High Dental Co., Ltd., Japan]. As a control, polymethyl methacrylate [Acron (ACR); G-C Dental Corp., Japan] was used. The tensile test was conducted according to ISO 527: 1993, Plastic—Determination of tensile properties and JIS· K7113, K6920, and T6501. Flat dumbbell-shaped specimens (16±1 mm long, 3±0.2 mm wide, and 82±0.2 mm thick at the parallel segment) were prepared. Tensile strengths, elastic moduli, and proportional limits were measured using a universal testing machine (AG-20kN; Shimazu, Japan) with a 50-mm grip-to-grip distance and 5-kN load cell at 25°C. The obtained data (n=6) were analyzed using a one-way ANOVA and Tukey’s multiple comparison testing (a=0.05).
Results: BP indicated the lowest elastic moduli among all of the thermoplastic resins (p<0.05). Although the greatest tensile strengths were obtained in polycarbonate resins, ACT showed the lowest tensile strength among all of the thermoplastic resins. The six thermoplastic resins demonstrated significantly lower tensile strengths than did ACR (p<0.05).
Conclusions: Whereas the tensile strengths of all of the thermoplastic resins were lower than for conventional acrylic, they demonstrated considerable toughness. These characteristics would allow for long-term use without denture fracture.