Description
Presentation Blocks: 03-22-2018 - Thursday - 11:00 AM - 12:15 PM

Title: Fracture Load of Zirconia and Lithium Disilicate Crowns

Authors:

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

Abstract:

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 24C 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.

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