OBJECTIVE: To evaluate "in vitro" structural integrity and quantify the formation of bubbles and gaps in the cementation interface of two fiberglass post cementation techniques in large root canal. MATERIAL AND METHOD: 18 bovine incisors will be used for this study. After the selection of the teeth, the anatomical crowns will be removed 1mm above the cementoenamel junction and the standardization of the root depth of the bovine incisor in 16 mm through an Isomet 2000 precision diamond saw blade (Buheler, Lake Bluff, IL, USA) at low speed and under refrigeration. Afterwards, the biomechanical preparations of the root canals will be performed with the Step-Back Technique and the specimens will be filled with gutta-percha cones and endodontic calcium hydroxide based cement by the technique of lateral condensation. After the endodontic treatment, the specimens will be stored for 7 days in an environment with 100% humidity at 37 °C. After this period, the specimens will be randomly divided into three groups (n = 21): PCN - conventional post cemented in tooth with normal canal lumen; PCA- Conventional fiberglass post cemented in large root canal; PAA- Fiberglass post relined with composite resin and cemented in large root canal. Then, the post space preparation will be executed according to each group with pre-established drills, surface treatment of fiberglass post (WhitePost nº 3, FGM) and cemented with self-adhesive resin cement (RelyX U200, 3M ESPE). Then, the specimens will be submitted to scanning in a high-resolution micro-tomography (SkyScan 1272). From the images, three-dimensional (3D) models of the teeth will be reconstructed through specific software, such as NRecon, DataViewer, CTAnalyser and CTVOX (SkyScan, Kontich, Belgium). The analysis of the integrity, and structural defects, such as presence of bubbles or discontinuity at the cementation interface will be obtained through the 3D tooth reconstruction and analysis of structures density by specific software. The results obtained will be submitted to normality and homogeneity tests, and after that, specific statistical tests at a significance level of 0.05 will be applied to evaluate the differences between the techniques.
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