Contents lists available at ScienceDirect Ceramics International journal homepage: www.elsevier.com/locate/ceramint Application of zirconia surface coating to improve fracture resistance and stress distribution of zirconia ceramic restorations Firas Abdulameer Farhan a,b , Eshamsul Sulaiman b , Muralithran G. Kutty b, ⁎ a Prosthodontic Department, College of Dentistry, Baghdad University, Bab Al-Muadham Campus of the University of Baghdad, 1417 Baghdad, Iraq b Restorative Department, Faculty of Dentistry, University of Malaya, 50603 Kuala Lumpur, Malaysia ARTICLE INFO Keywords: Zirconia surface coating Zirconia ceramic restoration Fracture resistance Fractographic analysis, Finite element analysis ABSTRACT Zirconia ceramic restoration (ZCR) has a higher fracture incidence rate than metal ceramic restoration. Different surface treatments were used to improve fracture performance of ZCR such as grit blasting (GB) by aluminium oxide powder. This type of surface treatment generate residual stresses on veneering ceramic causing crack initiation and ending with a fracture. In order to overcome the stress generated by GB, zirconia surface coating is used as a surface treatment to improve fracture resistance and to accommodate stresses along the ZCR layers. Fifty zirconia ceramic crowns were fabricated and divided according to the type of surface treatment into three groups; the first group is (ZG), involving 20 cores were coated with a mixture of partially-sintered zirconia powder (PZP) and glaze ceramic powder; the second group is (ZL), including of 20 cores were coated with PZP and liner ceramic paste. The third group is grit blasting (GB), preparing of 10 fully sintered cores at 1350 °C which then abraded by 50 μm aluminium oxide powder. The groups ZG and ZL were further subdivided into ZG26, ZG47, ZL26 and ZL47 based on two PZP sizes (47 and 26 μm). Each treated core was veneered with the veneering ceramic layer. Fracture resistance (FR) was measured by the universal testing machine. Finite element analysis (FEA) was used to simulate the stress distributions on the coated and non-coated zirconia crown models. The ZG47 group had higher FR (647.92 ± 97.33 N) and a significant difference (P < 0.00) compared to GB and other coated groups. The FEA exhibited lower and evenly distributed stresses of the zirconia glaze model than the zirconia liner and the non-coated models. The ZG47 coating considered as an alternative method to GB treatment which increases the FR which significantly improved the clinical performance of the ZCR. 1. Introduction Clinical follow-up studies of zirconia-ceramic restoration (ZCR) showed that it was an appropriate substitute to the metal-ceramic re- storations because of its excellent aesthetics, high strength, and su- perior biocompatibility [1,2]. Furthermore, the introduction of com- puter aided design/computer aided manufacturing (CAD/CAM) technologies in dentistry had facilitated the design and fabrication of ZCRs with minimal flaws and short time [3]. In general, the flexural strength of the zirconia core fabricated by CAD/CAM is higher than core produced by the conventional method such slip casting [4] ZCR with veneering layer considered as a favoured choice in re- storative dentistry than monolithic zirconia restoration. Because it has appearance matching the colour shade of the natural tooth while monolithic restoration lacks this property and it is too tough, which may wear the opposing tooth [5]. Unfortunately, the ZCR had met with some technical complication which was related to the weak bonding between zirconia and veneering ceramic at the interface area as a result of insufficient mechanical in- terlocking which was enhanced by providing surface roughness [6]. Furthermore, the zirconia structural matrix lacks glassy content to provide a chemical bond with the veneering ceramic material. There- fore, this will increase the fracture incidence rate of ZCRs when com- pare with metal-ceramic restorations and recognised as the main cause of clinical failure [7]. In order to improve bonding properties of zirconia substrate, surface treatment was suggested, such as grit blasting (GB) by aluminium oxide (Al 2 O 3 ) powder which is used to offer microroughness and enhancing micromechanical interlocking between zirconia and ceramic materials [8]. Nevertheless, this type of treatment may cause a phase transition of zirconia atomic matrix from tetragonal (t) to monoclinic (m). This transition accompanied with structural expansion which generates stresses at zirconia/ceramic interface causing microcracks and fracture susceptibility [9,10]. https://doi.org/10.1016/j.ceramint.2018.08.246 Received 14 August 2018; Received in revised form 20 August 2018; Accepted 21 August 2018 ⁎ Corresponding author. E-mail addresses: firas_7elfe@yahoo.com (F.A. Farhan), eshamar@um.edu.my (E. Sulaiman), muralithran@um.edu.my (M.G. Kutty). Ceramics International xxx (xxxx) xxx–xxx 0272-8842/ © 2018 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Please cite this article as: Farhan, F.A., Ceramics International (2018), https://doi.org/10.1016/j.ceramint.2018.08.246