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Objectives. The aim was to investigate the fatigue survival and marginal-gap inside the rootcanal of endodontically treated (ET) premolars reinforced by various fiber-reinforced postcore composites (FRCs). Moreover, composite-curing at different depths in the canal was evaluated.Methods. 170 intact upper-premolars were collected and randomly divided into ten groups (n = 15). One group served as control (intact-teeth). After endodontic procedure standard MO cavities were prepared and restored with different post-core fiber-reinforced materials and designs. Three-group (A1-A3) were restored with either packable and flowable short fiberreinforced composite (SFRC) core or conventional composite-core. Two-group (B1-B2) were restored with SFRCs as short post (3 mm) and core. Four-group (C1-C4) were restored with SFRCs as post (6 mm) and core with or without unidirectional FRC posts (individually-made or conventional). After completing the restorations, teeth from Group C1-C4 (n = 5/group) were sectioned and stained. Specimens were viewed under a stereo-microscope and the percentage of microgaps within the root-canal was calculated. Fatigue-survival was measured using a cyclic-loading machine in the rest of the specimens.Results. Application of flowable SFRC as luting-core material with individually-made FRC post (Group C3) did not differ from intact-teeth regarding fatigue-survival (p > 0.05). The rest of the groups produced significantly lower survival (p < 0.05) compared to intact-teeth.Post/core restorations made from packable SFRC (Group C1) had a lower microgap (19.1%) at the examined interphase in the root-canal than other groups.Significance. The restoration of ET premolars with the use of individually-made FRC post and SFRC as luting-core material showed promising achievement regarding fatigue-resistance and survival.

The aim was to explore the fracture-behavior, survival and marginal-microgaps within the root-canal of immature anterior teeth restored with different fiber-reinforced post-core composites (FRCs). 180 bovine-incisors were randomly divided into 6 groups (n = 30). One group served as control (group 6). The rest of the teeth were prepared to an internal diameter of 1.6 mm and the apex was sectioned. After application of an MTA-plug, teeth were restored with FRC materials: Group 1: Bioblock technique with short fiber-reinforced composite (SFRC); Group 2: Bioblock technique with flowable SFRC; Group 3: Individually-made FRC post; Group 4: Conventional FRC post; Group 5: dual-cure core build-up composite. After restorations were completed, teeth (n = 5/group) were sectioned and then stained. Specimens were viewed under a stereo microscope and the percentage of microgaps within the root-canal was calculated. Fatigue-survival was measured using a cyclic-loading testing machine in the rest of the specimens. Flowable SFRC application in the root-canal (Group 2) did not differ from intact-teeth regarding fatigue-survival (p > 0.05). The rest of the groups produced significantly lower survival (p < 0.05) compared to intact-teeth. Post/core restorations made from conventional FRC post (Group 4) exhibited a high number of microgaps (38.3%) at the examined interphase in the root-canal. The restoration of immature incisors with the use of flowable SFRC as post-core material displayed promising performance in a matter of fatigue-resistance and survival.

Methods for restoring endodontically treated teeth fall short of restoring the physiologic mechanical properties. Fracture of endodontically treated teeth is a common type of clinical failure. New treatment modalities or perfected versions of existing treatment concepts need to be tested to find a biomimetic solution. A novel method of restoring endodontically treated teeth is presented and compared in vitro with currently accepted restorative methods. Seventy-two extracted and endodontically treated maxillary premolar teeth were divided into six groups (n = 12) depending on restorative technique (Groups 1-6). Group 1: fiber-reinforced composite post (FRC), Group 2: direct layered short FRC post and core, Group 3: short fiber-reinforced obliquely layered composite restoration, Group 4: microhybrid composite restoration, Group 5: fiber-reinforced box, Group 6: control. Specimens were submitted to static fracture resistance test. Fracture thresholds and fracture patterns were evaluated. Group 6 exhibited the highest fracture resistance. Group 2 yielded the highest fracture resistance among the restored groups. The fracture resistance of Group 2 did not differ significantly from Group 6. Groups 1, 3, 4, 5 proved to be significantly different from the control group. There was no statistically significant difference among restored groups. Fracture patterns of tested groups were dominantly non repairable opposed to control groups mostly repairable fractures. Application of direct-layered short FRC post and core in endodontically treated premolars performed statistically similarly in the studied conditions as natural teeth. Therefore, it seems a promising alternative to current endo-restorative solutions. However, further testing is required.

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