"Evaluation of Fracture Resistance of Anterior Minimally Invasive Cubic Zirconia Restorations” (In vitro Study)

Abstract

The introduction of the new generation of particle-filled and high strength ceramics as silicate glass ceramics and recent generations of zirconia has offered variety of dental materials expanding the range of their clinical indications, leading to a paradigm shift in the field of fixed prosthodontics towards minimally invasive dentistry this shift is greatly supported by advances in adhesive systems together with computer-aided design / computer-aided manufacturing (CAD\CAM) technologies. Of these materials, ultra-translucent cubic zirconia and lithium-disilicate glass-ceramics are currently considered the most popular alternatives for minimally invasive restorations. The study was performed to evaluate fracture resistance of cubic zirconium oxide ceramic (Katana UTML) in comparison lithium dislicate ceramic (GC Intial LiSi Press) in case of three minimally invasive anterior tooth preparation. Forty-two all ceramic anterior minimally invasive restorations were fabricated from Katana UTML and GC Intial LiSi Press with three different preparation design (Partial coverage restorations with opened contact, partial coverage restoration with intact contact, and full coverage restoration). The preparations were done first on typodont acrylic maxillary central incisors then the prepared teeth were duplicated using epoxy resin. The epoxy resin dies were then scanned using extra-oral scanner, the restorations were designed, then milled into Katana UTML and CAD wax. Katana UTML restorations were then sintered and glazed. While, CAD wax were invested and pressed using GC Intial LiSi Press ingots, then finished and glazed All restorations were surface treated according to manufacturer instructions then cemented to their respective epoxy resin dies using self-adhesive resin cement. The restorations cemented to epoxy resin dies were subjected to 5000 cycle of thermocycling then loaded to fracture in a universal testing machine. The fractured surfaces of the restorations were analyzed using a stereo microscope and field emission scanning electron microscope. The results showed significant difference in fracture resistance values between different preparation design regardless of the type of material with the highest was the full coverage restorations and the lowest was partial coverage restoration with intact contact. And all specimens recorded values in fracture resistance testing greater than 120- 200 N which are the normal bitting forces in the anterior region indicating that both materials can be used with this type of restorations.