Nanoleakage of luting agents for bonding posts after thermo-mechanical fatigue

Objectives: The aim was to investigate the depth and extension of nanoleakage of four different luting agents for bonding fiber posts after thermo-mechanical fatigue.

Methods: 24 extracted human anterior teeth were endodontically treated, sectioned at the cemento-enamel junction and restored with fiber posts using four commercially available resin cements as well as four corresponding core build-up materials (n = 6): Panavia F 2.0/Clearfil DC Core Automix (Kuraray), Variolink II/Multicore Flow (Ivoclar Vivadent), RelyX Unicem/Filtek Z250 (3M ESPE), and Multilink Sprint/Multicore Flow (Ivoclar Vivadent). The specimens received all-ceramic crowns and were subjected to thermo-mechanical fatigue (1.2 million cycles). After cutting off the crowns, the roots were isolated with nail polish except for a 1 mm-wide rim around the root canal, immersed into 50 wt% ammoniacal silver nitrate solution for 24 h and exposed to a photo-developing solution for 8 h. The specimens were sectioned perpendicular to the long axis of the tooth into four slices (thickness=0.8 mm), fixed, dehydrated and processed for FESEM. Leakage was measured using Backscattered FESEM and EDS.

Results: The depth of nanoleakage was significantly affected by the resin cement (p<0.015; Kruskall-Wallis). Multilink Sprint demonstrated significantly deeper penetration of silver particles compared to all other materials (p<0.05; Mann Whitney-U-Test). At a depth of 0.8 mm the material RelyX Unicem demonstrated only isolated silver particles whereas all other materials still showed distinctive leakage.

Conclusion: The four resin cements resulted in nanoleakage to a certain extent after thermo-mechanical fatigue and would not be able to hermetically seal the root canal if leakage occurred around the margins of the coronal restoration. Due to the different demonstrated sealing abilities of the resin cements it can be concluded that the choice of the luting agent is an important aspect regarding the long-term stability of the restoration.