Hindawi Publishing Corporation International Journal of Dentistry Volume 2012, Article ID 529495, 7 pages doi:10.1155/2012/529495 Research Article Antibacterial Properties of Dental Luting Agents: Potential to Hinder the Development of Secondary Caries Erik Unosson, 1 Yanling Cai, 2 Xiyuan Jiang, 1 Jesper L¨ o¨ of, 3 Ken Welch, 2 and H˚ akan Engqvist 1 1 Division of Applied Materials Science, Department of Engineering Sciences, The ˚ Angstr¨ om Laboratory, Uppsala University, Box 534, 751 21 Uppsala, Sweden 2 Division of Nanotechnology and Functional Materials, Department of Engineering Sciences, The ˚ Angstr¨ om Laboratory, Uppsala University, Box 534, 751 21 Uppsala, Sweden 3 Doxa AB, Axel Johanssons Gata 4-6, 754 51 Uppsala, Sweden Correspondence should be addressed to Erik Unosson, erik.unosson@angstrom.uu.se Received 30 November 2011; Accepted 5 January 2012 Academic Editor: Cornelis H. Pameijer Copyright © 2012 Erik Unosson et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. A modified direct contact test was used to evaluate the antibacterial properties of four commercially available dental luting agents (RelyX Unicem, Ketac Cem, Ceramir Crown & Bridge and Harvard Cement) and two reference materials (glass-ionomer cement and calcium aluminate cement) compared to a negative-control material (PMMA). Streptococcus mutans bacteria were placed in direct contact with specimens that had been aged for 10 min, 1 day, and 7 days, in order to test the antibacterial properties of the materials. A metabolic assay containing resazurin was used to quantify the amount of viable bacteria remaining after the direct contact tests. The effects of pH and fluoride on bacteria proliferation were also evaluated. Strongest antibacterial properties were found for calcium aluminate cement, followed by Ceramir Crown & Bridge and RelyX Unicem. Ketac Cem, Harvard Cement, and the reference glass-ionomer cement showed bacteria content either higher than or not significantly different from the PMMA control in all instances. pH levels below 6.3 and above 9.0 were found to have negative effects on bacterial proliferation. No correlation between either acidic materials or fluoride release and antibacterial properties could be seen; rather, basic materials showed stronger antibacterial properties. 1. Introduction Prosthetic dentistry revolves around the restoration or re- placement of lost or missing teeth using crowns, bridges, and other dentures. In fixed partial dentures (FPDs), dental luting agents serve as the link between the prepared, support- ing tooth, and the prosthetic tooth material. An ideal dental cement to be used as a luting agent should be biocompatible, inhibit caries or plaque formation, have low solubility, have correct film thickness and viscosity, have long working time and short setting time, have high strength and stiffness comparable to dentin, show no microleakage, permit easy removal of excess material, and exhibit high retention [1]. A wide range of luting agents with varying chemistries and properties are available on the market and strive to meet these high requirements. However, FPDs are prone to failure, with the number one cause of failure being secondary dental caries [2, 3]. Secondary caries is readily formed in restoration margins or gaps where plaque, a biofilm containing various bacteria, can adhere [4]. Among the bacterial species present in these biofilms, Streptococcus mutans is recognized as the one most frequently involved in caries formation [5]. These bacteria produce acids when metabolizing fermentable car- bohydrates, which can then dissolve the calcium phosphate mineral content in enamel and dentin, eventually leading to a cavity or failure of the FPD [6]. Colonization of bacteria often occurs at secluded locations in shortage of oxygen and mechanical disturbance and consequently bactericidal properties of dental cements are of particular importance since it is one of the few means by which bacteria can be inhibited in these sites. Antibacterial properties of dental cements have been evaluated in the past [7–9], and the bactericidal effects are often attributed to their low pH and/or release of fluoride