Fracture toughness of denture resins and the plastic tooth/resin interface

Objectives: The fracture toughness of the plastic tooth/denture resin interface were evaluated and compared to that of the homogenous denture base resins in order to understand their fracture and debonding mechanics. Methods: Three denture base resins Selectaplus H (Dentsply DeTrey, GmbH, Germany), Acron MC (GC Europe, Leuven, Belgium) and Microbase MMA-free resin (Dentsply DeTrey, GmbH, Germany were tested. The fracture toughness of three denture resins was measured by using the single edge notch technique (SEN). Specimens were subjected to a three-point loading test at a crosshead speed of 1.5 mm min-1 and the results were analyzed by one-way ANOVA. Results: The fracture toughness (Klc) values of the 3 denture resins ranged from 3.4 to 4.04 MN m-3/2 and were not statistically different (p > 0.05). The (Klc) values of the tooth-resin adhesive interface of the 3 resins groups were significantly different (p < 0.05). The highest values were obtained from the plastic tooth/microwave-cured denture resin interface. Although an adhesive cement was used to bond the Microbase resin to plastic teeth, the Klc values were significantly weaker that the other groups (p < 0.5). Conclusions: The fracture toughness at the tooth/resin interface was significantly below the value for denture resin suggesting that the interface is the weak link through which the crack can propagate.