Effect of a novel framework design in ceria-stabilized zirconia/alumina nanocomposite (Ce-TZP/A)-based all-ceramic crowns

Abstract

Purpose: Framework modification is essential to reduce chipping of the veneering porcelain in bilayered all-ceramic restorations. However, conventional modifications are insufficient, because buccal cusps did not correspond to a supporting structure. We manufactured a novel framework design, featuring an anatomical shape with additional two-sided (buccal and lingual) supporting structures, from ceria-stabilized tetragonal zirconia/alumina nanocomposite (Ce-TZP/A), and compared the fracture load and failure mode of all-ceramic crowns with Ce-TZP/A frameworks of different designs. Methods: Four different Ce-TZP/A framework designs were fabricated using CAD/CAM system. The framework designs were as follow; Group 1: anatomical shape; Group 2: with an additional lingual supporting structure; Group 3: with an additional buccal supporting structure; Group 4: with additional buccal and lingual supporting structures. Each framework was veneered with feldspathic ceramic and then cemented to resin tooth analog using self-adhesive resin cement. Fracture load of each crown either without or with mechanical preloading was measured using a universal testing machine. Scanning electron microscopy and stereomicroscopy were performed to classify failure mode as either partial fracture (cracking or chipping of porcelain veneer) or complete fracture (fracture of Ce-TZP/A framework or tooth analog). Results: Three crowns in Group 1 exhibited prefailure by mechanical preloading. Fracture load ranged from 1866–2049 N without mechanical preloading, and from 1828–2374 N with mechanical preloading; fracture load was not significant for any of the framework designs without mechanical preloading. Furthermore, fracture load did not significantly differ between framework designs except Group 1 with mechanical preloading. The most common failure mode was chipping of porcelain veneer without mechanical preloading. Although mechanical preloading promoted failure progression (from partial to complete fracture) in Groups 1–3, failure progression was inhibited in Group 4. Conclusion: This novel Ce-TZP/A framework design has the potential to reduce chipping of the veneering porcelain and improve zirconia based all-ceramic restoration reliability.