Abstract
The aim of this study was to investigate and compare the short and long term antibacterial effects of white and gray mineral trioxide aggregate (MTA) and calcium enriched mixture (CEM) on Streptococcus Sanguinis and Enterococcus faecalis which are commonly associated with endodontic infections. The test materials, including white MTA (WMTA), gray (GMTA), and CEM were manipulated strictly in accordance with the manufacturer's instructions. A total of 72 culture plates were prepared and divided into three experimental groups (one group for each of freshly mixed and set WMTA cements; one group for each of freshly mixed and set GMTA cements; one group for each of freshly mixed and set CEM cements. Each group consisted of 24 plates in which 12 plates were cultured by S. sanguinis and the other 12 plates were cultured by E. faecalis. Antibacterial activities of the materials against the S. sanguinis and E. faecalis were evaluated using agar diffusion test (ADT). The materials were tested in form of set (24-h, 1 week and 1 month) and freshly mixed. In the E. faecalis groups, plates containing freshly mixed and set WMTA, GMTA, and CEM cements did not show any antibacterial properties. The antimicrobial activity of freshly mixed GMTA was lower than WMTA and higher that of CEM. The largest mean diameters of inhibition zone of bacterial growth were found in set WMTA cement group at any time period. In conclusion, the origin of MTA as well as the preparation techniques may affect its antimicrobial activities. Key words: White mineral trioxide aggregate (WMTA), gray mineral trioxide aggregate (GMTA), calcium enriched mixture (CEM), growth inhibition zone, S. sanguinis, antibacterial activity, agar diffusion test, E. faecalis.  
Highlights
Microorganisms and their byproducts are the main etiologic factors for the development and progression of pulpal and periapical disease as well as in endodontic treatment failures (Fouad et al, 2005)
The data obtained from the freshly mixed cements revealed that the mean growth inhibition zones of WMTA on S. sanguinis was larger in diameter than that of the calcium enriched mixture (CEM) and GMTA
Mixed GMTA group was associated with smaller growth inhibition zones compared to the WMTA group (Table 1)
Summary
Microorganisms and their byproducts are the main etiologic factors for the development and progression of pulpal and periapical disease as well as in endodontic treatment failures (Fouad et al, 2005). Most endodontic treatment failures are attributable to inadequate cleansing of the RC and egress of bacteria and other antigens into. The periradicular tissues (Hasan Zarrabi et al, 2009). Elimination of microbial flora and infected tissues during root canal (RC) treatment by instrumentation, irrigation and intracanal medication has always been an important part of successful endodontic treatments (Sundqvist, 1982). After a RC procedure, because of persistence of inflammation or infection in the bony area around the end of the tooth, it is necessary to perform an apicoectomy and a root-end filling is placed to prevent re-infection of the root (Bhavana et al, 2015)
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