Irrigation in endodontics.

Irrigation is a key part of successful root canal treatment. It has several important functions, which may vary according to the irrigant used: it reduces friction between the instrument and dentine, improves the cutting effectiveness of the files, dissolves tissue, cools the file and tooth, and furthermore, it has a washing effect and an antimicrobial/antibiofilm effect. Irrigation is also the only way to impact those areas of the root canal wall not touched by mechanical instrumentation. Sodium hypochlorite is the main irrigating solution used to dissolve organic matter and kill microbes effectively. High concentration sodium hypochlorite (NaOCl) has a better effect than 1 and 2% solutions. Ethylenediaminetetraacetic acid (EDTA) is needed as a final rinse to remove the smear layer. Sterile water or saline may be used between these two main irrigants, however, they must not be the only solutions used. The apical root canal imposes a special challenge to irrigation as the balance between safety and effectiveness is particularly important in this area. Different means of delivery are used for root canal irrigation, from traditional syringe-needle delivery to various machine-driven systems, including automatic pumps and sonic or ultrasonic energy.

Ex vivo killing of Enterococcus faecalis and mixed plaque bacteria in planktonic and biofilm culture by modified photoactivated disinfection.

AIM: To compare the efficacy of conventional and modified photoactivated disinfection (PAD) against Enterococcus faecalis and mixed plaque bacteria in suspension and biofilms. METHODOLOGY: Enterococcus faecalis (four strains) and mixed plaque bacteria from three adult volunteers were suspended in water, added to methylene blue (MB, 15 µmol L⁻¹), MB mixed with 0.5% hydrogen peroxide and 0.05% chlorhexidine (CHX), MB mixed with 0.5% hydrogen peroxide and 0.05% EDTA or MB mixed with 0.05% EDTA and 0.05% CHX and exposed to laser irradiation from 10 s to 5 min. After exposure, samples were taken, serially diluted and grown aerobically and anaerobically on Tryptic Soy Agar plates or on blood agar plates for 24 and 72 h, respectively. For biofilm experiments, E. faecalis and mixed plaque biofilms were grown on sterile hydroxyapatite (HA) discs coated overnight with bovine dermal collagen type I for 3 weeks. After exposure to MB or MB and low concentration of EDTA with either hydrogen peroxide or CHX, the percentage of killed bacteria by PAD was evaluated using viability staining and confocal laser scanning microscope. For statistical analysis, one-way analysis of variance was performed. RESULTS: Conventional PAD killed from 90.76% to 100% E. faecalis for 3 min, but failed to kill all plaque bacteria even after 5 min of laser irradiation. In modified PAD, up to 100% of suspended E. faecalis and mixed plaque bacteria were killed after 1 min and 30 s of irradiation. Up to twenty times more biofilm bacteria were killed by modified PAD than by conventional PAD with 15 µmol L⁻¹ MB (P < 0.001) and up to eight times more than 2% CHX (P < 0.001) and 1% sodium hypochlorite (P < 0.001). CONCLUSION: Modified PAD was superior to conventional PAD against planktonic and biofilm bacteria.

Bacterial penetration along different root canal filling materials in the presence or absence of smear layer.

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 degrees C for 7 days, the specimens were mounted into a bacterial leakage test model for 135 days. Survival analyses were performed to calculate the median time of leakage and log-rank test was used for pairwise comparisons of groups. The level of significance was set at P = 0.05. Selected specimens were longitudinally sectioned and inspected by scanning 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 significantly 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.

Disinfection by endodontic irrigants and dressings of experimentally infected dentinal tubules.

The effect of endodontic irrigants and dressings was tested on bacteria in bovine dentin specimens experimentally infected with Enterococcus faecalis, Streptococcus sanguis, Escherichia coli, or Pseudomonas aeruginosa. Standardized, cylindrical dentin test pieces were prepared and cleaned by ultrasonic treatment with EDTA and sodium hypochlorite. The specimens were infected with the test organism for periods up to 14 days, and the degree of infection into the tubules was monitored using Brown & Brenn stain, scanning electron microscopy, and culturing of dentin dust from sequential bur samples starting from the pulpal side. E. faecalis rapidly infected the whole length of the tubules; S. sanguis required up to 2 weeks for complete infection; E. coli only penetrated to some 600 microns, even after prolonged incubation periods. P. aeruginosa infected dentin quickly, but apparently in very low numbers. E. faecalis persisted for at least 10 d after withdrawal of nutrient support, whereas the other 3 organisms died within 4 to 48 h. Endodontic medicaments were applied to infected specimen for comparison of antibacterial potency. Camphorated p-monochlorophenol was generally more efficient than Calasept, and of the irrigants tested, iodine potassium iodide appeared more potent than sodium hypochlorite or chlorhexidine. The presence of a smear layer delayed, but did not eliminate, the effect of the medicaments.