Genotoxicity evaluation of locally produced dental porcelain – An in vitro study using the Ames and Comet assays Mohammed Noushad, Thirumulu Ponnuraj Kannan * , Adam Husein, Haswati Abdullah, Abdul Rashid Ismail School of Dental Sciences, Universiti Sains Malaysia, 16150 Kubang Kerian, Kelantan, Malaysia article info Article history: Received 1 April 2009 Accepted 15 May 2009 Available online 6 June 2009 Keywords: Porcelain Ames assay Comet assay Mutagenicity DNA damage abstract The aim of this study was to determine the genotoxicity of a locally produced dental porcelain (Universiti Sains Malaysia, Malaysia) using the Ames and Comet assays. In the Ames assay, four genotypic variants of the Salmonella strains (TA98, TA100, TA1537 and TA1535) carrying mutations in several genes were used. The dental porcelain was incubated with these four strains in five different doses both in the presence and absence of metabolic activation (S9) and the result was assessed based on the number of revertant colonies. Concurrently, appropriate positive controls were used so as to validate the test. The average number of revertant colonies per plate treated with locally produced dental porcelain was less than dou- ble as compared to that of negative control. In the Comet assay, L929 (CCL-1 ATCC, USA) mouse fibroblast cells were treated with the dental porcelain in three different concentrations along with concurrent neg- ative and positive controls. The tail moment which was used as a measurement of DNA damage was almost equal to that of the negative control, suggesting that the locally produced dental porcelain did not induce any DNA damage. The results indicated that the locally produced dental porcelain is non- genotoxic under the present test conditions. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction The ability of a material to exist in contact with tissues of the human body without causing an unacceptable degree of harm to that body is the most important distinguishing factor of a biomate- rial, from other materials (Williams, 2008). The development of biomaterials that can be used to substitute metals in dental resto- rations represents the main challenge of future research activities, due to biocompatibility issues and environmental concerns associ- ated with metals waste and disposal and ceramics are an ideal can- didate (Jeffrey et al., 2007; Holand et al., 2008). Dental ceramics used for restoring missing tooth structure have gained consider- able attention due to their good biocompatibility and excellent physical and mechanical properties. For restoration of missing tooth structure, porcelain is the most natural-appearing synthetic replacement material (Rosenblum and Schulman, 1997), holding a special place in dentistry because of its most aesthetically pleas- ing result. Up until now, its color, translucency and vitality cannot be matched by any material, except other ceramics (Noort, 2002). Of late, the use of porcelain as a denture material has expanded due to the attainment of better properties. Even though dental ceramic materials are regarded as being more or less inert, the pos- sible effects of degradation products on human beings must not be overlooked. The composition, microstructure and physical proper- ties of newer ceramic materials are different from those of the tra- ditional ones, which may affect their inertness. Safety cannot be inferred from measurements of one ceramic formulation to other compositions or conditions (Milleding et al., 1999). The Ames assay which was specifically developed to detect chemically induced mutagenesis developed by Bruce Ames (Ames et al., 1975) is used worldwide as an initial screen to determine the mutagenic potential of new chemicals and drugs. It is perhaps the most rapid, simple, sensitive and economical screening test for mutagenicity (Mange and Mange, 1999) and has an extensive data- base and good correlation with carcinogenicity (Jukic et al., 2000). The Comet assay is a quick, simple, sensitive, reliable and fairly inexpensive genotoxicity test (Fairbairn et al., 1995; Collins et al., 1997; Ribeiro et al., 2005) which is widely used to evaluate the genotoxic potential of chemical and physical substances. Ostling and Johanson (1984), first demonstrated ‘‘comets” and described the tails in terms of DNA with relaxed supercoiling through a pro- cess of electrophoresis (pH 9.5) of cells embedded and lysed in aga- rose on a microscope slide (Collins, 2002). Later, Singh et al. (1988) used alkaline electrophoresis to analyze DNA damage from treat- ments with X-rays or H 2 O 2 . Since then, the worldwide acceptance of Comet assay makes it a good assay for detecting DNA damage. The aim of the present study was to evaluate if the locally pro- duced dental porcelain had any genotoxic effects, using the Ames and Comet assays. 0887-2333/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.tiv.2009.05.025 * Corresponding author. Tel.: +60 9 7663684; fax: +60 9 7642026. E-mail address: tpkannan@kb.usm.my (T.P. Kannan). Toxicology in Vitro 23 (2009) 1145–1150 Contents lists available at ScienceDirect Toxicology in Vitro journal homepage: www.elsevier.com/locate/toxinvit