Fracture Resistance of Cad/Cam One-Piece and Two-Piece Post-Core-Crown Restorations Using Two Different Materials (In Vitro Study)

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Introduction: Restoring teeth that lost significant percentage of coronal structure necessitates using post and core before crown coverage. The most common systems are the one-piece post and core and the two-element system. Recently the one-piece restoration, the Richmond crown, could be milled using CAD/CAM to rehabilitate severely damaged teeth. A variety of aesthetic materials have become available for milling.Aim: To compare between the fracture resistance (FR) of one-piece and two-piece post-core-crown restorations using two different materials; hybrid ceramic (HC) and zirconia (ZR).Materials and methods: The study was conducted on 20 artificial maxillary canines. The teeth were prepared then randomly divided as follows: Group I, one-piece post-crown restoration (N=10) which were further subdivided into Subgroup IA: hybrid ceramic and Subgroup IB: zirconia. Group II, two-piece post-core and cemented crown (N=10) which were also subdivided into Subgroup IIA: hybrid ceramic, and Subgroup IIB: zirconia. The specimens were subjected to fracture resistance testing using universal testing machine followed by analyzing the failed specimens with the stereomicroscope. Results were statistically analyzed using F test (ANOVA) and Post-hoc test (Tukey), significance was judged at 5%.Results: The FR values (mean±SD in Newtons) were 386.6 ± 25.78N for subgroup IA, 522.2 ± 70.56N for subgroup IB, 429.6 ± 91.87N for subgroup IIA, and 648.6 ± 93.37N for subgroup IIB with no significant difference in FR between the one-piece and the two-piece restorations using either HC or Zr. Conclusion: The one-piece post-crown restorations showed good performance regarding fracture resistance.