FRACTURE SURFACE ANALYSIS OF DENTAL CERAMICS

Ceramic systems have poor long-term fracture resistance, especially when they are used in an oral environment as fixed partial dentures. The objective of this study is to determine the site of crack initiation and the causes of fracture in clinically failed zirconia-based and lithia-disilicate-based ceramic fixed partial dentures. Five fractured three-unit lithia-disilicate-based glass-ceramic fixed partial dentures (Empress 2(R) all-ceramic system, Ivoclar Vivadent AG, Schaan, Liechtenstein) and five fractured four-unit yttria stabilized tetragonal zirconia (Y-TZP) based fixed partial dentures (Cercon(R) ceramics, DeguDent GmbH, Hanau, Germany) were retrieved and analyzed. Fractography and fracture mechanics methods were used to estimate the stresses at failure. De laminations between the glass veneer and zirconia core were observed in Y-TZP based fixed partial dentures and a secondary fracture was initiated from the zirconia core. Secondary fracture dictated the ultimate failure. Failure stresses of the fixed partial dentures that failed due to Zirconia fracture were estimated to be from 325 to 431 MPa. Fractures that had origins on the glass veneer surface had failure stresses between 31 MPa and 35 MPa. Fractures of the lithia-disilicate-based glass-ceramic fixed partial dentures were initiated within the glass veneer layer and fracture initiation sites are controlled primarily by contact damage. Failure stresses of the lithia-disilicate-based glass-ceramic fixed partial dentures were estimated to be from 19 to 68 MPa. We conclude that interfacial delamination in the glass veneer/zirconia core dental ceramic structures controlled the fracture initiation sites and failure stresses in Y-TZP based fixed partial dentures. The design and dimension of the connectors as well as span size of the fixed partial denture can be the key factors in causing fractures at relatively low occlusal loads but high fracture stresses.