Long-term flexural strength of three direct aesthetic restorative materials

Objectives: This investigation evaluates the long-term flexural strength behaviour of three different glass-ionomer cement (GIC) based materials. Methods: The materials under investigation were a conventional GIC (Opusfil), a metal-reinforced GIC (Opus Silver) and a resin-modified GIC (Fuji II LC). Flexural strength specimens of the materials were prepared according to the relevant manufacturersʹ instructions for clinical use. After 10-min maturation at 37 °C, the specimens were placed in water, also at 37 °C, until required for testing. Specimens were tested under four-point bend at intervals between 7 and 130 days after manufacture. Results: Opusfil increased in strength up to day 56, but was significantly weaker after this time. Opus Silver was strongest on day 7, although there was no further decline in strength after day 14. Fuji II LC increased in strength up to day 14, but there was deterioration in strength after day 100. Opus Silver had the highest early strength of the three materials, but after day 7 there was no significant difference in strength between the three materials under test. Conclusions: The three cements tested did not exhibit the continued increase in strength with time that has been attributed to glass-ionomer cements. Each material behaved differently, but they all appeared to be adversely affected by storage in aqueous media. Materials formed by the inclusion of metal or the incorporation of resins into the glass-ionomer cement formulation should be regarded as separate sub-classes of materials in their own rights.