Comparison of the fracture toughness, flexural strength, and flexural modulus of nine restorative materials over five time intervals

The aims of this study were: 1) to determine the effect of time on the fracture toughness (K[sub iC]), flexural strength (ϭf), and flexural modulus (E[sub f]) of six groups of direct restorative materials including amalgam; and 2) to compare the selected properties of the materials at each time. The null hypotheses tested were: 1) there is no difference between the 1-hour, 1-day, 7-day, 30-day, and 90-day values of each of the K[sub iC], cjf, and E[sub f] for each of the selected materials, and 2) there is no difference between the selected materials with respect to each of their mechanical properties tested at each time. The materials selected for this study were KetacFil (KF, ESPE) - a conventional glass-inomer cement (GIC); PhotacFil (PF; ESPE) - a resin-modified glass ionomer cement (RMGIC); Dyract (Dentsply) and F2000 (3M) - polyacid-modified composite resins (PAMCR) or "compomers"; Z100 (3M) -a hybrid composite resin; Heliomolar (H; Vivadent) - a microfil composite resin; SureFil (SF; Dentsply) and Prodigy Condensable (PC; Kerr) "packable" composite resins; and Valiant PHD XT (V; Ivoclar) - a phase dispersed unicompositional amalgam. Twelve notchless triangular prisms (NTP) (6x6x6x12 mm) and twelve rectangular bars (2x2x25 mm) were made for each test at each time following manufacturers' instructions, and stored in distilled water at 37° C for the duration of the five time intervals before testing. For the K[sub iC] test, the samples were placed in a specimen holder and loaded in tension at a crosshead speed of 0.1 mm/min. The maximum load recorded before crack arrest or complete failure was used to calculate K[sub iC] in MPa*ml/2. The bars were loaded in a three point bending mode and the maximum load recorded at failure was used to calculate df. The modulus was determined from the straight portion of the stress/strain curve. The results were analyzed using a one way ANOVA followed byy Scheffe multiple means comparisons (α=0.05). Based on the limitations of this study and representative materials the results indicate that GICs are the weakest materials and are inferior to RMGIC especially in the short term. RMGICs and PAMCRs are comparable, while both are inferior to CRs and PCRs. PCRs do not show any significant improvement over conventional CRs. Amalgam has the best intrinsic properties over time. The intrinsic properties, K[sub iC] and E[sub f], appear to correlate better with the clinical success of materials than their 07 does.Dentistry, Faculty ofGraduat