Fracture Toughness of Resin-based  Cements in Different Storage Media

Objectives: to place various resin-based luting cements into neutral and acidic storage media and determine the effect of immersion time, and media on fracture toughness, and if a relationship exists between fracture toughness (KIc) and material composition. Methods: Specimens were prepared from five resin luting cements; Nexus 3 (Kerr), Panavia F (Kuraray), Calibra (Dentsply), Smart Cem2 (Dentsply), and seT (SDI). For each material a total of 36 disc-shaped specimens were prepared using a custom-made, polytetrafluorethylene split mould. Specimens were randomly divided into 6 groups of six, immersed in two solutions; distilled water, and 0.01 mol/L lactic acid at 37° C for 24 hours, 1month or 3 months. After storage, the thickness of each specimen was measured and manually wet polished to an adjusted thickness of 2 ± 0.02 mm. The specimens were loaded using a universal testing machine. The maximum load at specimen failure was recorded and the KIc (MPa. M 0.5) was calculated. Results: There was an interaction between materials, storage solution and time (P < 0.05). Nexus 3 revealed the highest KIc followed by Panavia F, Calibra, Smart Cem2 and seT. Nexus 3 showed significantly higher fracture toughness (1.3 MPa) compared with seT (0.88 MPa). Conclusions: The fracture toughness of the resin luting cements was affected by time and storage solution. Comparable fracture toughness of conventional resin cement and self-adhesive resin cements was observed. Therefore, the selection of suitable resin cement should be based not only on the adhesive behaviour but also mechanical properties such as fracture toughness.