Extended Setting Shrinkage Behavior of Endodontic Sealers Mohammad Hammad, MSc, Alison Qualtrough, PhD, and Nick Silikas, PhD Abstract The aim of this study was to investigate the polymeriza- tion shrinkage behavior of newly introduced root canal sealers. Three recently developed sealers; EndoRez (dual cure resin-based), RealSeal (dual cure resin-based), and GuttaFlow (silicon-based) were tested and compared with TubliSeal (zinc oxide– eugenol– based). The bonded disk method was used. Sixty specimens were tested at body and room temperatures. Dual cure resin- based sealers were tested as chemically cured only and as dual cured. Samples were tested for 24 hours. It was found that there were statistically significant differ- ences between the tested sealers. EndoRez had the highest shrinkage-strain value, followed by RealSeal, whereas TubliSeal had the lowest. GuttaFlow exhibited expansion on polymerization. It was concluded that shrinkage associated with setting might jeopardize the seal of the root canal, leading to root canal failure. (J Endod 2008;34:90 –93) Key Words Dual-cure, resin, sealers, shrinkage O ne of the major objectives of root canal therapy is the three dimensional obturation to prevent reinfection (1, 2). It has been suggested that both apical and coronal leakage might lead to loss of more endodontically treated teeth than other failures of endodontic therapy (3). Different endodontic filling materials and technologies have been introduced to improve the seal (4). Root canal filling methods use a sealer as an integral part of the obturation technique (5). Despite apparently satisfactory performance over many decades, gutta-percha and sealer filling techniques do not represent the universal ideal. Research continues to find alternatives that might seal better and mechanically reinforce compromised roots (6). Gutta-percha does not bond to tooth structure. Resin-based cones and sealers have been introduced as a solution. In 2004, a new obturation system was introduced under the name RealSeal, containing Resilon and a resin-based sealer. Resilon (Pen- tron Clinical Technologies, Wallingford, CT) is a thermoplastic synthetic polymer-based root canal filling material. Based on polymers of polyester, Resilon contains bioactive glasses and radiopaque fillers. It performs in a similar way to gutta-percha, has the same handling properties, and for retreatment purposes might be heat-softened or dissolved with solvents such as chloroform. The RealSeal sealer (Pentron Clinical Technologies) is a dual curable dentin resin composite sealer (7) and might be used in conjunction with Resilon points. EndoRez (Ultradent, South Jordan, UT) is a new hydrophilic, urethane-dimethacrylate (UDMA)– based resin sealer that has been developed for use with a single gutta-percha cone for canal obturation (8). Its main component is a monomer commonly used as part of the organic matrix of resin composites. According to the manufacturer, EndoRez has satisfactory sealing properties and an easy delivery system (9). A new root canal filling paste GuttaFlow (Colténe/Whaledent, Altstätten, Switzerland) is a modification of RoekoSeal sealer. GuttaFlow contains gutta-percha particles as filler. The material is flowable and sets within 10 minutes. Methacrylate-based resin systems are inevitably linked with shrinkage as part of the polymerization process (10 –12). Polymerization shrinkage results from the rear- rangement of the molecules into less space than was required for the liquid phase of mobile monomer molecules (13). This arises from 2 different factors; the van der Waals distance between the monomer molecules is replaced by a covalent bond during poly- merization, and the intermolecular distance between the polymer chains becomes smaller than that between the monomers (14 –19). Polymerization shrinkage of sealers can lead to stress development on the root canal walls, resulting in marginal gaps, microleakage, and clinical failure (11). The forces of polymerization shrinkage can exceed the resin bond strength to root dentin, permitting debonding on one side of the filling to relieve stress (20). The investigation into the shrinkage kinetics could help to understand the phenomenon per se and/or give an estimation of the polymerization reaction pattern (18). Polymerization shrinkage-strain is a time-dependent phenome- non (21). The shrinkage behavior has not been thoroughly investigated. The aims of this study were to investigate the polymerization shrinkage behavior and measure the poly- merization shrinkage-strain of newly introduced root canal sealers. Materials and Methods The bonded-disk method to measure polymerization shrinkage kinetics, devel- oped by Watts and Cash (21), was used (Fig. 1). Four sealers were studied (Table 1). They were mixed following the manufacturer’s instructions. A brass ring (inner diam- eter of 16 mm and 1 mm in height) was attached to a glass slide (76  23  3 mm). A ring of soft ribbon wax (inner diameter of 8 mm and 1 mm in height) was placed From the School of Dentistry, University of Manchester, Manchester, United Kingdom. Address requests for reprints to Mohammad Hammad, School of Dentistry, The University of Manchester, Higher Cambridge St, Manchester M15 6FH, UK. E-mail address: Mohammad.Hammad@postgrad.manchester.ac.uk. 0099-2399/$0 - see front matter Copyright © 2008 by the American Association of Endodontists. doi:10.1016/j.joen.2007.10.014 Basic Research—Technology 90 Hammad et al. JOE — Volume 34, Number 1, January 2008