Title: Fracture Load of Zirconia and Lithium Disilicate Crowns
Sung Joon Kwon (Presenter)
University of Alabama Birmingham
Nathaniel Lawson, University of Alabama Birmingham
John Burgess, University of Alabama Birmingham
Geoffrey Morris, Georgia Institute of Technology
Objectives: To measure the fracture load of traditional and translucent zirconia and lithium disilicate crowns bonded with Unicem 2 (self-adhesive resin) and Rely X Luting Plus (RMGI) cement with and without sandblasting.
Methods: Standardized crown preparations were designed with AutoCAD® software with a 0.8mm shoulder margin. Copings (n=8/group) were milled of traditional zirconia (Lava™ Plus, 3M), translucent zirconia (Lava Esthetic,3M) or lithium disilicate (e.max CAD, Ivoclar) and sintered/crystallized following manufacturers' instructions. All copings were a uniform 0.8mm thickness. Dies were milled from composite resin (Crystal Ultra). Two-thirds of the crowns were either particle-abraded with <40µm alumina at 45psi (zirconias) or etched with 5% HF for 20 seconds (lithium disilicate). Half of these crowns were cemented with Rely X Luting Plus and half were bonded with Unicem 2. One-third of the crowns received no surface treatment and were bonded with Unicem 2. All cement was self-cured for 6 minutes under 2kg of applied load. Cemented crowns were load cycled for 100,000 cycles using 100N force in a custom fatiguing device in water at 24○C with a stainless steel ball contacting all four crown cusps. After load cycling, a 1.5mm rubber sheet was placed between the indenter and the crown to simulate a food bolus and the crowns were loaded with a stainless steel indenter (7mm radius) with a crosshead speed of 1mm/min until failure in a universal testing machine. Data analyzed with ANOVA and t-Test.
Results: See table. Different letters represent statistically different groups.
Conclusions: In this limited in vitro study,<40µm alumina particle abrasion did not reduce the fracture strength (p>.05) of bonded zirconia crowns, bonded lithium disilicate and translucent zirconia produced equivalent strength, and more translucent zirconia crowns survived fatigue than lithium disilicate when cemented with RMGI cement.