Effect of 1-Piece Post and Core Fabrication Techniques on Fracture Strength

Evaluation of Bond Strength and Fracture Load of Teeth With Flared Root Canals Restored With Prefabricated, Anatomical, and Computer-aided Design and Computer-aided Manufacturing Fiber Posts

PURPOSE

This study compared the use of anatomical glass fiber posts using bulk-fill composite resin with computer-aided design and computer-aided manufacturing (CAD/CAM) milled glass fiber post in oversized root canals, through bond strength (BS) and fracture resistance (FR) tests (fracture load).

METHODS AND MATERIALS

A total of 48 mandibular premolars were selected, half of them had their crowns removed at the cemento-enamel junction (CEJ) and the other half were sectioned 2 mm above the CEJ. Subsequently, teeth were endodontically treated. After 1 week, the standard preparation of the canals was carried out, and the roots were divided into three groups (n=16), according to the use of different restorative techniques (control: prefabricated glass fiber post [PFP], direct anatomical glass fiber post [AFP], and CAD/CAM milled glass fiber post [MFP]). After luting procedures using Single Bond Universal and RelyX Ultimate (3M ESPE), for eight teeth in each group, six specimens were obtained (two slices from each root third: cervical, middle, and apical). For the remaining eight roots of each group, standardized preparations for metal-free crowns, milling of 5 mol% yttria-stabilized tetragonal zirconia polycrystalline, cementation of the crowns, and periodontal ligament simulation were performed. Then, for each group, the BS was evaluated through the push-out test, and the FR was evaluated in compression. The data obtained from BS were submitted to two-way analysis of variance (ANOVA; group vs root region) and Tukey (α=0.05) and from FR to one-way ANOVA (group) and Tukey (α=0.05).

RESULTS

For the BS test, the MFP group was statistically superior to the PFP group in all root regions and was statistically superior to the AFP group only in the cervical region, being statistically similar in the middle and apical root regions. For the FR test, the MFP group was statistically superior to the PFP and AFP groups.

CONCLUSION

The milled fiber post technique can be a legitimate alternative in the restoration of weakened roots with flared root canals.

Compressive Strength and Porosity Evaluation of Innovative Bidirectional Spiral Winding Fiber Reinforced Composites

The aim of this in vitro study was to investigate the compressive strength and the bulk porosity of a bidirectional (bFRC) and an experimental bidirectional spiral winding reinforced fiber composite (bswFRC). Cylindrical-shape specimens were prepared for each material group and processed for the evaluation of compressive strength after different storage conditions (dry, 1 and 3 months) in distilled water at 37 °C. The specimens were also assessed for the degree of bulk porosity through X-ray tomography. A scanning electron microscope (SEM) was used to determine the fracture mode after a compressive strength test. Data were statistically analyzed using Two-Way Analysis of Variance (ANOVA). A significantly lower compressive strength was obtained in dry conditions, and after 1 month of water immersion, with the specimens created with bFRC compared to those made with bswFRC (p < 0.05). No significant difference (p > 0.05) was found between the two groups after 3 months of water immersion. However, the presence of water jeopardized significantly the compressive strength of bswFRC after water storage. The type of fracture was clearly different between the two groups; bswFRC showed a brutal fracture, whilst bFRC demonstrated a shear fracture. The bswFRC demonstrated higher pore volume density than bFRC. In conclusion, bswFRC is characterized by greater compressive strength compared to bFRC in dry conditions, but water-aging can significantly decrease the mechanical properties of such an innovative FRC. Therefore, both the novel bidirectional spiral winding reinforced fiber composites (bswFRC) and the bidirectional fiber reinforced composites (bFRC) might represent suitable materials for the production of post-and-core systems via CAD/CAM technology. These findings suggest that both FRC materials have the potential to strengthen the endodontically treated teeth.