Three-Month Fracture Toughness of Resin-Modified Glass Ionomer Restorative Materials

Objectives: To compare the fracture toughness of three recently-marketed, resin-modified glass ionomer dental restorative materials (Riva II LC, Ketac Nano, Riva LC) and to investigate a change in fracture toughness over a period of 3 months. The null-hypothesis is that there will be no difference in fracture toughness between the materials and the fracture toughness will not change over time.
Methods: 144 specimens (48 per material) were fabricated using standardized, stainless-steel molds (Sabri Dental Enterprises). A mylar strip was placed above and below the mold and a microscope slide was placed with digital pressure over the top. Fabrication of the material followed manufacturers’ direction. Samples were stored in (0.2M) physiologic phosphate buffered saline solution at 37 °C until the appointed testing time. Specimens were tested to failure using a universal testing machine (Alliance RT5) on a three-point bend fixture at 0.5mm/min. Testing was accomplished at 24 hours, one week, one month, and three months. The mean results were analyzed with non-parametric Kruskal-Wallis with the Dunn's Multiple comparison post hoc test (p = 0.05).
Results: The results are listed in the table.
Conclusions: Each individual product’s fracture toughness was stable with no significant changes over a period of three months. At all evaluation times, Fuji II LC displayed a significantly greater fracture toughness than both Ketac Nano and Riva LC (p <0.001).