Interfacial Evaluation of Dentin-Cement Interface in Fiber-Post Supported Restorations.

Purpose: The aim of this in vitro study was to evaluate the effect of curing time on the mechanical properties of fiberpost luting cement. The null hypothesis was that curing time does not affect hardness and Young's modulus. Materials and Methods: 24 premolars were endodontically treated and a class II cavity with 1.5 mm residual wall thickness and an 8-mm-deep post space was prepared. Fiber posts were luted trough a standardized procedure: etch for 20 s; rinse for 20 s; rinse with ethanol for 30 s; universal adhesive application (UBQ, Kuraray); fiber post insertion (Rabilda, Voco) after luting cement (DC Core, Kuraray) placement in the post space. Samples were divided into 3 groups according to the curing time (n = 8 each): G1, no light; G2, 20 s; G3, 120 s. Light curing was performed with an LED lamp (Celalux 2, Voco) at 1000 mW/s with the tip placed in contact with the fiber post. The occlusal cavity was restored with a nanofilled resin composite (Filtek Supreme XTE, 3M). After 7 days, half of each group's samples were submitted to cyclic fatigue testing with a chewing simulator for 500,000 cycles at 50 N load, 2 mm excursion, under water (CS 4.4, SD Mechatronik). Samples were sectioned into 1-mm-thick slices perpendicularly to the long axis of the fiber post. Samples were tested with a Nanoindenter XP, equipped with a diamond Berkovich indenter and characterized by a theoretical force resolution of 50 nN and a theoretical displacement resolution lower than 0.01 nm. The loading displacement (P-h) curves were analyzed using the Oliver-Pharr method to obtain the Young's modulus and hardness. The data were analyzed with ANOVA (α < 0.05). Results: Young's modulus and hardness were not correlated with the curing time (p = 0.0623). Cyclic fatigue significantly reduced the luting cement's mechanical properties (p = 0.0001) except when 120 s curing time was performed. Conclusion: The null hypothesis was partially rejected since curing time significantly affect the mechanical behavior of luting cement. [ABSTRACT FROM AUTHOR]