d e n t a l m a t e r i a l s 2 8 ( 2 0 1 2 ) 410–415 Available online at www.sciencedirect.com jo ur n al homep age : w ww.intl.elsevierhealth.com/journals/dema The inﬂuence of pigments on the slow crack growth in dental zirconia Moustafa N. Aboushelib a , Niek de Jager b,* , Cees J. Kleverlaan b , Albert J. Feilzer b a Dental Biomaterials Department, Faculty of Dentistry, Alexandria University, Egypt b Academic Center for Dentistry Amsterdam (ACTA), University of Amsterdam and VU University Amsterdam, The Netherlands a r t i c l e i n f o Article history: Received 19 January 2011 Received in revised form 13 June 2011 Accepted 10 November 2011 Keywords: Fracture toughness Pigments R-curve behavior Slow crack growth Zirconia a b s t r a c t Objectives. Partially yttria stabilized zirconium oxide was introduced as core material for core-veneered full ceramic dental restorations, because of its biological inertness, high mechanical strength, and toughness. In order to improve the esthetical possibilities pig- ments in the core are introduced, that might inﬂuence the stabilization by yttrium. Methods. Double torsion tests were performed to study the inﬂuence of the pigments in the core ceramics on its fracture toughness. Results. A signiﬁcant difference was observed in the stress intensity factor (K 10 ) as well as in the R-curve behavior between the ceramic with and without pigment. Signiﬁcance. The lower stress intensity factor for the ceramic with pigment could affect the clinical performance of dental zirconia restorations with this material. © 2011 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. 1. Introduction The introduction of zirconia based polycrystalline framework materials to the dental ﬁeld widened up the possibilities of all-ceramic restorations [1,2] and made long span, extensive, and accurate all-ceramic restorations possible due to the high ﬂexure strength of these zirconia framework materials [3]. As pure zirconia is brittle and not strong enough, yttria is added to zirconia to stabilize the particular crystal structure of zir- conium oxide at room temperature. In this way a strong and tough stabilized ceramic is created. The ﬂexure strength of zirconia framework materials was always reported using highly polished specimens, while in reality these materials are often exposed to unavoidable differ- ent types of surface damage. The CAD/CAM milling procedure, ∗ Corresponding author at: Department of Dental Materials Science, Academic Center for Dentistry Amsterdam (ACTA), Gustav Mahlerlaan 3004, 1081 LA, Amsterdam, The Netherlands. Tel.: +31 0205980861; fax: +31 0205980726. E-mail address: n.de.jager@acta.nl (N. de Jager). airborne-particle abrasion, and milling with hard tools as dur- ing ﬁt check or dimensional corrections all together introduce surface damage and increase surface roughness leading to signiﬁcant strength reduction [4]. The produced surface dam- age could unexpected result in catastrophic failure under low loads keeping in mind that microscopic cracks could be very effective in concentrating high stresses at the crack tip region resulting in slow crack propagation [4]. This might not be applicable to direct shaping procedures like pressing without further processing. A characteristic property of partially stabilized zirconia framework materials is their unique transformation tough- ness. Under mechanical, chemical, or thermal stresses the partially stabilized tetragonal phase could transform to the relatively larger monoclinic phase (4% increase in volume) and the accompanied compressive stresses result in stopping the 0109-5641/$ – see front matter © 2011 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.dental.2011.11.011