Bacterial penetration along different root canal filling materials in the presence or absence of smear layer I. M. Saleh 1 , I. E. Ruyter 2 , M. Haapasalo 3 & D. Ørstavik 1 1 Department of Endodontics, Faculty of Dentistry, University of Oslo, Oslo, Norway; 2 NIOM Nordic Institute of Dental Materials, Oslo, Norway; 3 Division of Endodontics, Oral Biological & Medical Sciences, Faculty of Dentistry, University of British Columbia, Vancouver, BC, Canada Abstract Saleh IM, Ruyter IE, Haapasalo M, Ørstavik D. Bacterial penetration along different root canal filling materials in the presence or absence of smear layer. International Endodontic Journal, 41, 32–40, 2008. Aim To study the effect of the smear layer on the penetration of bacteria along different root canal filling materials and to examine the dentine/sealer and sealer/ core material interfaces for the presence of bacteria. Methodology A total of 110 human root segments were instrumented to size 80 under irrigation with 1% sodium hypochlorite. Half of the roots were irrigated with a 5-mL rinse of 17% EDTA. Roots with and without smear layer were filled with gutta-percha (GP) and AH Plus sealer (AH), GP and Apexit sealer (AP), or RealSeal cones and sealer (RS). Following storage in humid conditions at 37 °C for 7 days, the specimens were mounted into a bacterial leakage test model for 135 days. Survival analyses were performed to calcu- late the median time of leakage and log-rank test was used for pairwise comparisons of groups. The level of significance was set at P ¼ 0.05. Selected specimens were longitudinally sectioned and inspected by scan- ning electron microscopy for the presence of bacteria at the interfaces. Results In the presence of the smear layer, RS and AP leaked significantly more slowly than in its absence. In the absence of the smear layer, AH leaked signifi- cantly more slowly than RS. SEM results indicated a differential pattern of bacterial penetration among the sealers. Conclusions Removal of the smear layer did not impair bacterial penetration along root canal fillings. A comparison of the sealers revealed no difference except that AH performed better than RS in the absence of the smear layer. Keywords: bacterial leakage, root canal sealers, scanning electron microscopy, smear layer. Received 19 February 2007; accepted 1 May 2007 Introduction One of the requirements for a successful root filling is the achievement and maintenance of a tight seal, chemical and/or mechanical, along the root canal system (Johnson & Gutmann 2005). A tight seal should prevent the ingress of bacteria and their by-products to the periradicular tissues or entomb the remaining microorganisms (Sundqvist & Figdor 1998) and hence prevent or heal apical periodontitis. Standard methods for filling the root canal system make use of a core material, which usually is gutta- percha (GP), in combination with a root canal sealer. Recent advances in dentine bonding have led to the development of a root filling system that consists of a thermoplastic synthetic resin core and a dual curable dental resin composite sealer (Teixeira et al. 2004). This product is used in combination with a self-etching primer, with the intention of creating a root filling that acts as a solid monoblock. A smear layer is formed on the surface of dentinal walls when the root canals are instrumented (McComb Correspondence: Iman M. Saleh, Department of Endodontics, Faculty of Dentistry, University of Oslo, P.O. Box 1109 Blindern, N-0317 Oslo, Norway (Tel.: +47 22852257; fax: +47 22852344; e-mail: imans@odont.uio.no). doi:10.1111/j.1365-2591.2007.01304.x International Endodontic Journal, 41, 32–40, 2008 ª 2007 International Endodontic Journal 32