Fracture Resistance and Initial Penetration Time of a Novel Zirconia Crown Design for Simplifying Future Endodontic...

Objectives: This study aimed to investigate the fracture strength of a novel-designed Zirconia crown before and after access opening, and to evaluate the mode of fracture and the time needed for initial penetration through the crown. Methods: This study involved the design and testing of 60 zirconia crowns, divided into three groups (20 crowns each) to compare different structural designs. Group 1 (Control) used a conventional full zirconia crown. Group 2 (Novel Design) featured a zirconia crown with an impermeable ceramic-filled opening. Group 3 (Modified Novel Design) included a zirconia crown with a permeable composite-filled opening. Each crown was designed using CAD/CAM technology with digital and cone beam CT scans to locate the pulp chamber accurately. The crowns were tested in two experiments. Experiment (A): Ten crowns from each group underwent a fracture test. Experiment (B): Ten crowns per group underwent an access cavity penetration followed by a fracture test. Key variables assessed included fracture strength, penetration time, and failure mode for each crown design, both before and after access opening. Data were analyzed using SPSS, with a significance threshold of p < 0.05. Results: The highest value of fracture strength before initial penetration was recorded for zirconia porcelain crowns (760.2 ± 25.2 MPa), while the lowest value was recorded for zirconia composite crowns (652.4 ± 25.9 MPa). The least time for initial penetration was recorded for zirconia composite crowns (2.5 ± 0.8 s). The difference in failure mode among the crowns was significant (p < 0.05) before initial penetration. All zirconia composite crowns showed crown fracture and core cracked, while all full zirconia crowns showed crown fracture only. The difference in failure mode before and after penetration was only significant for zirconia composite crowns. Conclusions: The modified novel-design crown (zirconia composite) could be an excellent choice when placing new prosthesis, since the crown provides easy access and a predictable guide to the root canal system and has good resistance to fracture before and after performing root canal therapy (RCT).