Introduction: Recent findings indicate that dentin modifies the biological activity of dental materials and antibacterials. So far, mainly non-infected dentin has been used in such experiments. The aim of this study was to establish a new method for testing antibacterial effects using infected bovine dentin and to evaluate its suitability by examining two well known root canal disinfectants.
Materials and Methods: Dentin slices of 200µm thickness (2x8 mm surface) were cut from freshly extracted bovine incisors and etched on both sides (30s, 50% citric acid). Cultures of Enterococcus faecalis(ATTC29212) were deposited into dentinal tubules by applying subpressure (3.7m³/h; 80mbar) for 4h using a bottle top filter (150ml; Falcon35, BD, USA) and a vacuum pump (ME4, Vacuubrand, Germany). These dentin slices were incubated in Tryptic Soy Broth (TSB) (BD; 37°C, 48h), and split in halves. One half served as test specimen, the other as its control. Specimens were immersed in 5ml test/control substances for 30s and 10min, respectively. Test substances comprised NaOCl (0.5%, 1.0%, 3.0%), and CHX (0.2%); control substance was NaCl(0.9%). The specimens were rinsed in 20ml NaCl and then incubated in TSB. Bacterial growth was determined nephelometrically at 600nm wavelength during a 26h incubation period. Test parameter was the difference of the time points of maximum bacterial growth (DMG) between test and control specimens, determined from logistic-dose-response curves fitted to the experimental data. Mann-Whitney-Test and Error-Rates-Method were applied for statistical analysis of five samples per group.
Results: DMG[h], Medians(25-75% Quantiles)
|
| Immersion period | |
|
| 30s | 10min |
| NaOCl 0.5% | 4.0(2.6-4.9) | 6.4(6.1-8.7) |
| 1.0% | 5.2(3.6-7.1) | 10.8(9.0-26.0) |
| 3.0% | 13.2(9.7-15.5) | no growth |
| CHX 0.2% | 3.8(3.1-4.1) | 5.6(4.7-6.4) |
DMG values were significantly influenced by materials (for both immersion periods), and by immersion periods.
Conclusion: The results are in accordance with clinical data. Thus, the new method using artificially infected dentin can be considered suitable for in vitro testing of antibacterial agents.