Biofilm model systems for root canal disinfection: a literature review.

The aim of this review was to present an overview of laboratory root canal biofilm model systems described in the endodontic literature and to critically appraise the various factors that constitute these models. The electronic databases MEDLINE, Web of Science and EMBASE were searched up to and including December 2016 to identify laboratory studies using endodontic biofilm models. The following search terms were used in various combinations: biofilm, root canal, in vitro, endodontic, bacteria, root canal infection model, colony-forming unit. Only English papers from journals with an impact factor were selected. The records were screened by two reviewers, and full-text articles were assessed according to pre-defined criteria. The following data were extracted from the included studies: the microbial composition of the biofilm, the substrate, growth conditions, validation and quantification. Seventy-seven articles met the inclusion criteria. In the majority (86%) of the studies, a monospecies biofilm was cultured. In two studies, a dual-species biofilm was grown; others cultivated a multispecies biofilm, containing at least three species. Enterococcus faecalis was the most frequently used test species (in 79% of all studies, 92% of the monospecies studies). Four studies used an inoculum derived directly from the oral cavity. Human dentine was the most frequently used substratum (88% of the studies). Incubation times differed considerably, ranging from one to seventy days. The most common quantification method (in 87% of the studies) was bacterial culturing, followed by microscopy techniques. The variation in laboratory root canal biofilm model systems is notable. Because of substantial variation in experimental parameters, it is difficult to compare results between studies. This demonstrates the need for a more standardized approach and a validated endodontic biofilm model.

Effect of laser-activated irrigation on biofilms in artificial root canals.

AIM: To evaluate the antimicrobial effect of laser-activated irrigation (LAI) on biofilms formed in simulated root canals. METHODOLOGY: A dual-species biofilm of Enterococcus faecalis and Streptococcus mutans was grown in a resin root canal model. Biofilms were formed over 48 h and subsequently subjected to the following treatments, all executed for 20 s: syringe irrigation (SI) with a 27G needle, ultrasonically activated irrigation (UAI) with a size 20 Irrisafe file, and LAI with a 2940 nm Er:YAG laser (20 Hz, 50 µs, 20 or 40 mJ, conical fibre tip at two positions). Tests were performed with both sterile saline as well as NaOCl (2.5%) as the irrigant. Surviving bacteria were harvested and the number of CFU was determined by plate counting and compared across groups (anova, P ≤ 0.05). RESULTS: Using saline as the irrigant, significant reductions in viable counts compared to untreated controls were observed for ultrasonically activated irrigation (0.52 log10 reduction) and for all laser-activated irrigation groups (>1 log10 reduction), but not for syringe irrigation (<0.25 log10 reduction). The reductions in the laser-activated irrigation groups were significantly greater than those of ultrasonically activated irrigation. With NaOCl as the irrigant, significant reductions (>2.2 log10 units) in the number of attached bacteria were observed for all treatment groups with no significant differences between laser-activated and ultrasonically activated irrigation. CONCLUSIONS: Within the limitations of this in vitro set-up, laser-activated irrigation removed more biofilm than ultrasonically activated irrigation when using saline as the irrigant, indicating greater physical biofilm removal. The use of NaOCl resulted in greater biofilm reduction with no significant differences between treatment groups.

Evaluation of Nd:YAG and Er:YAG irradiation, antibacterial photodynamic therapy and sodium hypochlorite treatment on Enterococcus faecalis biofilms.

AIM: To compare the antimicrobial efficacy of two-high power lasers (Nd:YAG and Er:YAG) and two commercial antimicrobial photodynamic therapy (aPDT) systems with that of sodium hypochlorite (NaOCl) action on Enterococcus faecalis biofilms grown on dentine discs. METHODOLOGY: Enterococcus faecalis biofilms were grown on dentine discs in a microtiter plate, incubated for 24 h and subjected to the following treatments: aPDT (Denfotex and Helbo system), Er:YAG laser irradiation (2940 nm, 50 mJ or 100 mJ, 15 Hz, 40 s), Nd:YAG laser irradiation (1064 nm, 2 W, 15 Hz, 40 s) and immersion in 2.5% (w/v) NaOCl for 1, 5, 10 and 30 min. Surviving bacteria were harvested, and the number of CFU per disc was determined by plate counting. RESULTS: Significant reductions (anova, P ≤ 0.05) in viable counts were observed for aPDT (Helbo) (2 log(10) reduction), Er:YAG irradiation using 100 mJ pulses (4.3 log(10) reduction) and all NaOCl treatments (>6 log(10) reduction). NaOCl (2.5%) for 5 min effectively eliminated all bacteria. aPDT (Denfotex), Er:YAG irradiation using 50 mJ pulses and Nd:YAG treatment caused a reduction in the viable counts of <1 log(10) unit; these results were not significantly different from the untreated controls. CONCLUSION: Within the limitations of this particular laboratory set-up, NaOCl was the most effective in E. faecalis biofilm elimination, while Er:YAG laser treatment (100 mJ pulses) also resulted in high reductions in viable counts. The use of both commercial aPDT systems resulted in a weak reduction in the number of E. faecalis cells. Nd:YAG irradiation was the least effective.

Bio-inspired porous SiC ceramics loaded with vancomycin for preventing MRSA infections.

Implant-related infections are a serious complication in orthopaedic and dental surgery resulting in prolonged hospitalization, high medical costs and patient mortality. The development of porous implants loaded with antibiotics may enable a local delivery for preventing surface colonization and biofilm formation. A new generation of bio-derived porous ceramic material that mimics hierarchical structures from Nature was evaluated. Silicon carbide ceramics derived from Sapelli wood (bioSiC) were obtained by pyrolysis of Entandrophragma cylindricum wood followed by infiltration with molten silicon. This process renders disks that keep the bimodal pore size distribution (3 and 85 µm) of the original material and are highly cytocompatible (BALB/3T3 cell line). The ability of the bio-ceramic to load the antimicrobial agent vancomycin was evaluated by immersion of disks in drug solutions covering a wide range of concentrations. The disks released at pH 7.4 an important amount of drug during the first 2 h (up to 11 mg/g bioSiC) followed by a slower release, which is related to the presence of macro- and mesopores. Finally, the anti-biofilm effect against methicillin resistant Staphylococcus aureus was assessed and a considerable reduction (92%) of the bacterial film was observed. Results highlight the bioSiC potential as component of medicated medical devices.

Effectiveness of different laser systems to kill Enterococcus faecalis in aqueous suspension and in an infected tooth model.

AIM: To assess the antibacterial action of laser irradiation (Nd:YAG, KTP), photo activated disinfection (PAD) and 2.5% sodium hypochlorite (NaOCl) on Enterococcus faecalis, in an aqueous suspension and in an infected tooth model. METHODOLOGY: Root canals of 60 human teeth with single straight canals were prepared to apical size 50, autoclaved, inoculated with an E. faecalis suspension and incubated for 48 h. They were randomly allocated to four treatment and one control groups. After treatment, the root canals were sampled by flushing with physiological saline, and the number of surviving bacteria in each canal was determined by plate count and solid phase cytometry. The same experimental or control treatments were completed on aqueous suspensions of E. faecalis, and the number of surviving bacteria was determined in the same way. RESULTS: In aqueous suspension, PAD and NaOCl resulted in a significant reduction in the number of E. faecalis cells (P < 0.001), whilst Nd:YAG or KTP had no effect. In the infected tooth model, only the PAD and NaOCl treated teeth yielded significantly different results relative to the untreated controls (P < 0.001). CONCLUSIONS: The laser systems as well as PAD were less effective than NaOCl in reducing E. faecalis, both in aqueous suspension and in the infected tooth model.

Use of the modified Robbins device to study the in vitro biofilm removal efficacy of NitrAdine, a novel disinfecting formula for the maintenance of oral medical devices.

AIMS: To evaluate the use of the modified Robbins device (MRD) to test disinfection strategies against biofilms that form on oral medical devices and to test the biofilm removal efficacy of NitrAdine, a disinfectant for the maintenance of oral medical devices. METHODS AND RESULTS: Biofilms were grown on discs using the MRD and biofilms formed in this system were used to evaluate the efficacy of NitrAdine and to determine the optimal disinfection conditions. Our data indicate that the use of the MRD allows for the rapid and reproducible formation of high-density biofilms. Determination of the efficacy of NitrAdine revealed high activity against biofilms tested (e.g. >3 log reduction for Candida albicans and Staphylococcus aureus) and allowed the determination of the optimal conditions for its use. CONCLUSION: The high reproducibility and flexibility of the MRD make it an excellent candidate for standardized testing of disinfectants aimed at reducing biofilms on oral medical devices. Using this system, we were able to demonstrate that NitrAdine exhibits high activity against biofilms formed by the micro-organisms tested. SIGNIFICANCE AND IMPACT OF THE STUDY: Our data suggest that our procedure is appropriate for standardized testing of disinfectants aimed at reducing biofilms on oral medical devices.

Thermoplastic polyurethane-based intravaginal rings for prophylaxis and treatment of (recurrent) bacterial vaginosis.

The aim of the present study was to develop thermoplastic polyurethane (TPU)-based intravaginal rings (IVRs) for prophylaxis and treatment of bacterial vaginosis via hot melt extrusion/injection molding. Therefore, different TPU grades were processed in combination with lactic acid or metronidazole, targeting a sustained lactic acid release over a 28day-period and sustained metronidazole release over 4-7days. Hot melt extrusion of lactic acid/TPU combinations required a lower extrusion temperature due to the plasticizing properties of lactic acid, evidenced by the lower glass transition temperature (Tg) and cross-over point (Ttanδ=1) values. NIR-chemical imaging data showed a homogenous distribution of lactic acid in TPU matrices at drug loads up to 30% (w/w). The addition of metronidazole did not lower processing temperatures, as the active pharmaceutical ingredient remained crystalline in the TPU matrix. Hydrophobic TPUs with a low ratio between the soft and hard segments (SS/HS ratio) in the polymer structure were suitable carriers for the lactic acid-eluting device over a 28-day period, while hydrophilic TPUs were needed to achieve the required release rate of metronidazole-eluting IVRs. IVRs manufactured with a TPU grade having a higher SS/HS ratio and lactic acid/TPU ratio exhibited a more elastic behavior. The addition of 25% (w/w) metronidazole did not affect the mechanical properties of the IVRs. Hydrophilic TPUs were most prone to biofilm formation by Candida albicans and Staphylococcus aureus, but the incorporation of metronidazole in the device prevented biofilm formation. Based on the drug eluting performance and mechanical tests, a mixture of lactic acid and Tecoflex™ EG-93A (20/80, w/w) and a combination of metronidazole and Tecophilic™ SP-93A-100 (25/75, w/w) were selected to design IVRs for the prophylaxis and treatment of bacterial vaginosis, respectively. Slug mucosal irritation tests predicted low irritation potency for both devices.