Aim:
The aim of the study was to develop an in vitro method for testing the efficacy of liquid antimicrobials in artificially infected root canals and to evaluate its suitability investigating sodium hypochlorite (NaOCl) with and without stopping disinfection by sodium thiosulphate (Na2S2O3).
Materials and Methods:
Roots from bovine incisors were cut horizontally into three parts and autoclaved (121°C;25min) in Tryptic-Soy-Broth (TBS). Apical parts were fixed (RelyX Unicem;3MEspe) in extra Petri dishes, canals were filled with sterile medium. Cervical and median parts were fixed (RelyX Unicem) in a Petri dish, canals were filled with Enterococcus faecalis (ATCC29212) suspension. All three parts were covered with glass plates and incubated (7days;37°C) on a shaker. Apical parts were used as sterility controls. Median parts served as maximium bacterial-growth-controls, coronal parts were filled with test substances (NaOCl (0.5%; 1.0%; 3.0%), immersion periods 30s; 10min), half of the coronal specimen were filled with Na2S2O3 after disinfection to stop action. Specimens were cut along long axis into halves and kept in saline. Biopsies of 0.5mm,1.0mm and 1.5mm depth were taken from root canal walls perpendicular to their surfaces (sterile round bur;0.8mm). Resulting dentin chips and the bur were vortexed (2ml medium;5sec), plated on TSA, incubated (24h;37°C), and colony-forming units (CFU) were counted. Experimental groups comprised 10 samples. Disinfection was considered biologically relevant (brd), if the reduction of CFU was at least three log10-orders of magnitude.
Results:
Sterility controls showed zero CFU indicating an aseptic procedure. Growth-controls showed CFU from 8•103 to 9•104, indicating an effective artificial infection.
Immersion period | NaOCl-concentrations unstopped | NaOCl-concentrations stopped | |||||
depth | 0.5% | 1.0% | 3.0% | 0.5% | 1.0% | 3.0% | |
30sec | 0.5mm | not brd1) | brd | brd | not brd | not brd | not brd |
1.0mm | not brd | brd | brd | not brd | not brd | not brd | |
1.5mm | not brd | brd | brd | not brd | not brd | not brd | |
10min | 0.5mm | brd | brd | brd | not brd | not brd | not brd |
1.0mm | brd | brd | brd | not brd | not brd | not brd | |
1.5mm | brd | brd | brd | not brd | not brd | not brd | |
1)brd = CFU reduction >= 3 log10-orders of magnitude
Conclusions:
The in vitro test system presented revealed known clinical effects of NaOCl. Thus, it may be suitable for testing liquid antimicrobials. However, for testing time-dependent effects in vitro, it seems appropriate to stop the disinfection process.