Biomaterials 25 (2004) 2153–2160 Influence of grinding, sandblasting, polishing and heat treatment on the flexural strength of a glass-infiltrated alumina-reinforced dental ceramic Massimiliano Guazzato*, Mohammad Albakry, Linda Quach, Michael Vincent Swain Faculty of Dentistry, Biomaterials Science Research Unit, University of Sydney, 2 Chalmers Street United Dental Hospital, Surry Hills NSW 2010, Australia Received 16 June 2003; accepted 15 August 2003 Abstract The influence of processing-introduced flaws and heat treatment on the strength degradation of the dental core material has recently been observed. However, there are insufficient studies which investigate the role of grinding, grinding orientation, sandblasting, polishing and heat treatment on the strength of In-Ceram Alumina (IA), one of the most used glass-infiltrated alumina-reinforced dental core ceramics. To address these issues, the uniaxial flexural strength and reliability of eight groups of specimens (sandblasted, ground parallel to the tensile axis, ground perpendicular, and polished with and without heat treatment) were assessed. Statistical analyses indicate that heat treatment significantly improved the flexural strength of the material regardless of the surface treatment. Conversely, any surface treatment caused strength degradation, if it was not followed by heat treatment. Sandblasting caused the most marked strength degradation. Polishing alone (without heat treatment) did not strengthen the ceramic. The orientation of grinding in respect of the direction of the tensile stresses did not influence the ultimate tensile strength. The present study suggests that, in the case of IA, sandblasting, grinding and polishing should always be followed by heat treatment in order to avoid strength degradation of the material. r 2003 Elsevier Ltd. All rights reserved. Keywords: Alumina; Ceramic structure; Glass–ceramic; Mechanical properties; Surface treatment 1. Introduction In a recent review of the use of contact testing in the characterization and design of all-ceramic crown-like layer structure, Lawn et al. [1] have pointed out that the lifetime of a restoration can be improved by increasing the strength of the core material and avoiding the creation of spurious flaws on its surface. These flaws may be introduced at different stage of the fabrication of the restoration. The most common steps of the fabrication of all-ceramic restorations are grinding, sandblasting, polishing and heat treatment. Previous studies indicate that the influence of these steps on the ultimate strength of a restoration is contradictory and related to the nature of the material investigated and the operating conditions. Grinding is commonly involved during machining of an all-ceramic framework and adjustment by the technician and dentist to improve occlusion and fitting. The effect of grinding on the surface of a ceramic and its mechanical properties is contradictory. Giordano et al. [2] have shown that grinding-induced flaws of a depth of 30–40 mm in feldspathic porcelain are responsible for up to 80% strength degradation. On the other hand, grinding increases the strength of phase-transforming ceramics [3–5], such as zirconia and may increase the strength of glass–ceramics when the dimensions of the initial cracks are greater than those induced by grinding [6]. This apparent contradiction may be clarified by considering the effect of grinding on the surface of a ceramic. The effect of the diamond grains of the grinding disk has been compared to a number of closely spaced single indentations [3,7,8]. Each single indenta- tion dislocates a corresponding volume of material, creating radial compressive stresses. The overlapping of ARTICLE IN PRESS *Corresponding author. Tel./fax: +61-2-96311894. E-mail address: mgua2483@mail.usyd.edu.au (M. Guazzato). 0142-9612/$-see front matter r 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.biomaterials.2003.08.056