Study on the disinfection effect of chlorine dioxide disinfectant (ClO2) on dental unit waterlines and its in vitro safety evaluation.

BACKGROUND: Ensuring the safety of dental unit waterlines (DUWLs) has become a pivotal issue in dental care practices, focusing on the health implications for both patients and healthcare providers. The inherent structure and usage conditions of DUWLs contribute to the risk of biofilm formation and bacterial growth, highlighting the need for effective disinfection solutions.The quest for a disinfection method that is both safe for clinical use and effective against pathogens such as Staphylococcus aureus and Escherichia coli in DUWLs underscores the urgency of this research. MATERIALS: Chlorine dioxide disinfectants at concentrations of 5, 20, and 80 mg/L were used to treat biofilms of S. aureus and E. coli cultured in DUWLs. The disinfection effectiveness was assessed through bacterial counts and culturing. Simultaneously, human skin fibroblast cells were treated with the disinfectant to observe changes in cell morphology and cytotoxicity. Additionally, the study included corrosion tests on various metals (carbon steel, brass, stainless steel, aluminum, etc.). RESULTS: Experimental results showed that chlorine dioxide disinfectants at concentrations of 20 mg/L and 80 mg/L significantly reduced the bacterial count of S. aureus and E. coli, indicating effective disinfection. In terms of cytotoxicity, higher concentrations were more harmful to cellular safety, but even at 80 mg/L, the cytotoxicity of chlorine dioxide remained within controllable limits. Corrosion tests revealed that chlorine dioxide disinfectants had a certain corrosive effect on carbon steel and brass, and the degree of corrosion increased with the concentration of the disinfectant. CONCLUSION: After thorough research, we recommend using chlorine dioxide disinfectant at a concentration of 20 mg/L for significantly reducing bacterial biofilms in dental unit waterlines (DUWLs). This concentration also ensures satisfactory cell safety and metal corrosion resistance.

Bacterial biofilm prevalence in dental unit waterlines: a systematic review and meta-analysis.

BACKGROUNDS: Numerous studies have shown that dental unit water lines (DUWLs) are often contaminated by a wide range of micro-organisms (bacteria, fungi, protozoa) and various prevalence have been reported for it in previous studies. Therefore, this review study aims to describe the prevalence of bacterial biofilm contamination of DUWLs. METHODS: This is a systematic review and meta-analysis in which the related keywords in different international databases, including Medline (via PubMed) and Scopus were searched. The retrieved studies were screened and the required data were extracted from the included studies. Three standard methods including American Dental Association (ADA), The Center for Disease Control and Prevention (CDC) and contaminated > 100 CFU/ml(C-100) standards were used to assess the bacterial biofilm contamination of DUWLs. All studies that calculated the prevalence of bacterial biofilm contamination of DUWLs, and English full-text studies were included in the meta-analysis. Studies that did not have relevant data or used unusual laboratory methods were excluded. Methodological risk of bias was assessed by a related checklist and finally, the data were pooled by fixed or random-effect models. RESULTS: Seven hundred and thirty-six studies were identified and screened and 26 related studies were included in the meta-analysis. The oldest included study was published in 1976 and the most recent study was published in 2020. According to the ADA, CDC and C-100 standards, the prevalence of bacterial contamination was estimated to be 85.0% (95% confidence interval (CI): 66.0-94.0%), 77.0% (95%CI: 66.0-85.0%) and 69.0% (95%CI: 67.0-71.0%), respectively. The prevalence of Legionella Pneumophila and Pseudomonas Aeruginosa in DUWLs was estimated to be 12.0% (95%CI: 10.0-14.0%) and 8.0% (95%CI: 2.0-24.0%), respectively. CONCLUSION: The results of this review study suggested a high prevalence of bacterial biofilm in DUWLs; therefore, the use of appropriate disinfecting protocol is recommended to reduce the prevalence of contamination and reduce the probable cross-infection.

Comparative evaluation of effect of sodium hypochlorite and chlorhexidine in dental unit waterline on aerosolized bacteria generated during dental treatment.

BACKGROUND: In dentistry, nosocomial infection poses a great challenge to clinicians. The microbial contamination of water in dental unit waterlines (DUWLs) is ubiquitous. Such infected DUWLs can transmit oral microbes in the form of aerosols. Previous studies have suggested treating DUWLs with various disinfectants to reduce cross-contamination. The literature lacks a comparative evaluation of the effect of the use of 0.2% chlorhexidine (CHX) and 0.1% sodium hypochlorite (NaOCl) in DUWLs on aerosolized bacteria generated during dental procedures. OBJECTIVE: To compare the effect of NaOCl and CHX in DUWLs on aerosolized bacteria generated during restorative and endodontic procedures. MATERIALS AND METHODS: A total of 132 patients were equally divided into three groups (n = 44 in each group) according to the content of DUWL as follows. Group I-0.1% NaOCl Group II-0.2% CHX Group III-distilled water (Positive control) One-way ANOVA was performed and the Kruskal-Wallis test was used for intergroup comparison. RESULTS: For the restorative procedure, inter-group comparison of mean colony-forming units (CFU) scores showed a statistically significant difference between the groups (p - .001) with the score of group 3 higher than group 2 followed by group 1. For the endodontics, an inter-group comparison of CFU scores showed a statistically significant difference between the groups (p - .003) with the mean score in group 1 being the lowest and group 3 being the highest. CONCLUSION: The addition of NaOCl or CHX in DUWLs shows an effective reduction in aerosolized bacteria compared to distilled water.

Efficacy of acoustic waves in preventing Streptococcus mutans adhesion on dental unit water line.

BACKGROUND: The quality and health safety of water used for refrigeration and flushing of the handpieces, water-syringes and other components of dental units is of considerable importance. Water crosses these devices by a system of intersected small plastic tubes (about 2 mm of diameter), named dental unit water lines (DUWLs). DUWLs may be heavily colonized by many bacterial species in a planktonic phase, adherent or in biofilm lifestyle, resulting in a potential risk of infection, not only for all professionals who routinely use these devices, but also for occasional-patients, especially immunocompromised patients. Contamination of DUWLs can be prevented or reduced with the use of disinfectants, but the eradication of microorganisms, especially which those are adherent or living in biofilm lifestyle on the inner surfaces of DUWLs is challenging and often, the normal methods of water disinfection are not effective. Moreover, disinfectants routinely used to disinfect DUWLs may alter the bond strength of the dentine bonding agent used for restorative practice in dentistry. STUDY DESIGN: To identify an innovative and alternative strategy, able to prevent bacterial adhesion to DUWL surfaces through a physical approach, which is more effective in overcoming the problem of DUWL contamination and the risk of infection compared to the standard methods already in use. In this pilot study we tested a member of the oral streptococci family, that is not a component of the biofilm detected on the walls of DUWL, but is frequently detected in water samples from DUWL, due to human fluid retraction during dental therapy. Namely, the pathogenic bacterial species Streptococcus mutans. METHODS: We employ elastic acoustic waves at high-energy in preventing S. mutans adhesion to the inner walls of an experimental water circuit reproducing a DUWLs. To stress the capability of acoustic waves to interfere with bacterial adhesion also in extreme conditions, a high S. mutans contamination load was adopted. RESULTS: We observe a significant decrease of adherent bacteria exposed to acoustic waves treatment respect to control. CONCLUSION: This study demonstrates the effectiveness of acoustic waves in counteracting the adhesion of S. mutans to the inner walls of an experimental water circuit reproducing a DUWL, opening up new prospects for future practical applications. The interesting results, so far obtained, require an in-depth analysis of the methods regarding both the various bacterial species involved and the infective charges to be used.

Colonization of Legionella spp. In dental unit waterlines.

Legionella spp. are ubiquitous in aquatic habitats and water distribution systems, including dental unit waterlines. Surveys have shown that the percentage of samples taken at different dental sites that were positive for Legionella spp. were highly variable and ranged from 0% to 100%. Cultivation is the principal approach to evaluating bacterial contamination employed in the past, but applying this approach to testing for Legionella spp. may result in false-negative data or underestimated bacterial counts. PCR and direct fluorescent counts can detect viable non-cultivable bacteria, which are not counted by plating procedures. Legionella spp., commonly form such viable non-culturable cells and it is likely that they contribute to the difference between plate count results and those of PCR and fluorescent-antibody detection. However, studies have shown that Legionella is present in the municipal water source in spite of the current filtration and chlorination procedures. Once Legionella reaches the building water system, it settles down into a biofilm layer of stagnant water. By means of this layer, Legionella can protect itself from antimicrobial agents and then multiply. Dental unit waterlines may be contaminated with opportunistic bacteria. The water quality in the dental units should be controlled to eliminate opportunistic pathogens and to provide water for dental treatment that meets public health standards for potable water.

The role of chemical products at low doses in preventing the proliferation of bacteria in dental unit waterlines: the ICX® experience.

In this study we evaluated (1) the efficacy of a protocol that combines hydrogen peroxide (shock treatment) and ICX® tablets (continuous treatment) for the control of microbial contamination in dental unit water lines, and (2) the in vitro antimicrobial activity of ICX® tablets on collection and wild strains isolated from dental chair output waters. To assess the treatment effectiveness, the microbial load in the output water samples of three dental chairs were investigated: one control chair received only shock treatment. In vitro bactericidal activity was tested against Staphylococcus aureus and Pseudomonas aeruginosa. Data obtained from samples collected from chairs treated with ICX® and shock treatment and data from the control chair did not differ significantly on the basis of microbial load. In the in vitro study, the product was unable to kill Gram-negative bacteria. These results show that the continuous introduction of ICX® was not effective in maintaining low counts of the heterotrophic bacteria in the output water of dental devices, and shock treatment may be needed more frequently than monthly.

Establishing a laboratory model of dental unit waterlines bacterial biofilms using a CDC biofilm reactor.

In this study, a laboratory model to reproduce dental unit waterline (DUWL) biofilms was developed using a CDC biofilm reactor (CBR). Bacteria obtained from DUWLs were filtered and cultured in Reasoner's 2A (R2A) for 10 days, and were subsequently stored at -70°C. This stock was cultivated on R2A in batch mode. After culturing for five days, the bacteria were inoculated into the CBR. Biofilms were grown on polyurethane tubing for four days. Biofilm accumulation and thickness was 1.3 × 105 CFU cm-2 and 10-14 µm respectively, after four days. Bacteria in the biofilms included cocci and rods of short and medium lengths. In addition, 38 bacterial genera were detected in biofilms. In this study, the suitability and reproducibility of the CBR model for DUWL biofilm formation were demonstrated. The model provides a foundation for the development of bacterial control methods for DUWLs.

Developing an ecologically relevant heterogeneous biofilm model for dental-unit waterlines.

This study monitored the biodiversity of microbes cultured from a heterogeneous biofilm which had formed on the lumen of a section of dental waterline tubing over a period of 910 days. By day 2 bacterial counts on the outlet-water showed that contamination of the system had occurred. After 14 days, a biofilm comparable to that of clinical waterlines, consisting of bacteria, fungi and amoebae had formed. This showed that the proprietary silver coating applied to the luminal surface of the commercial waterline tubing failed to prevent biofilm formation. Molecular barcoding of isolated culturable microorganisms showed some degree of the diversity of taxa in the biofilm, including the opportunistic pathogen Legionella pneumophila. Whilst the system used for isolation and identification of contaminating microorganisms may underestimate the diversity of organisms in the biofilm, their similarity to those found in the clinical environment makes this a promising test-bed for future biocide testing.

Risk of Fungal Infection to Dental Patients.

Fungi can cause various diseases, and some pathogenic fungi have been detected in the water of dental equipment. This environment offers suitable conditions for fungal biofilms to emerge, which can facilitate mycological contamination. This study verified whether the water employed in the dental units of two dental clinics at the University of Franca was contaminated with fungi. This study also evaluated the ability of the detected fungi to form biofilms. The high-revving engine contained the largest average amount of fungi, 14.93 ± 18.18 CFU/mL. The main fungal species verified in this equipment belonged to the genera Aspergillus spp., Fusarium spp., Candida spp., and Rhodotorula spp. Among the isolated filamentous fungi, only one fungus of the genus Fusarium spp. did not form biofilms. As for yeasts, all the Candida spp. isolates grew as biofilm, but none of the Rhodotorula spp. isolates demonstrated this ability. Given that professionals and patients are often exposed to water and aerosols generated by the dental procedure, the several fungal species detected herein represent a potential risk especially to immunocompromised patients undergoing dental treatment. Therefore, frequent microbiological monitoring of the water employed in dental equipment is crucial to reduce the presence of contaminants.

Legionella spp. in dental unit waterlines.

OBJECTIVE: To determine the current presence of Legionella spp. in the output water of dental unit waterlines (DUWLs) and examine its mitigation by disinfection at the Institute of Dentistry and Oral Sciences, Faculty of Medicine and Dentistry, Palacky University Olomouc and University Hospital Olomouc. MATERIAL AND METHODS: The first stage of our survey involved collecting samples of DUWL output water from 50 dental chair units (DCUs), and 2 samples of the incoming potable water. In October 2015, a one-time disinfection (1 % Stabimed) of DUWLs was conducted. This was followed by collecting 10 control samples (survey stage 2). RESULTS: From the total of 50 samples (survey stage 1), 18 samples (36.0 %) tested positive for Legionella spp. Following the disinfection, nine of the ten samples no longer showed any presence of Legionella. CONCLUSION: Based on culture results, the one-time disinfection (1 % Stabimed) was effective. We are unable to comment on the duration of positive effect of disinfection on the occurrence of Legionella spp. in the outlet water. It was a one-time survey (Tab. 2, Ref. 32).

Dental Unit Water Lines and their Disinfection and Management: A Review.

The perceived threat to public health from dental unit water line (DUWL) contamination comes from opportunistic and respiratory pathogens such as Legionella spp, Nontuberculous Mycobacteria (NTM) and pseudomonads. These organisms can grow and multiply in the DUWL biofilm to reach infective concentrations, with the potential for inhalation leading to respiratory infections or direct contamination of surgical wounds. In this paper we discuss current legislation and practical methods for delivering water within the DUWL that meets the standards for safety. Clinical relevance: Understanding the clinical relevance and methods for decontaminating DUWL is essential to create a safe working environment in dentistry.

Infection control in healthcare settings: perspectives for mfDNA analysis in monitoring sanitation procedures.

BACKGROUND: Appropriate sanitation procedures and monitoring of their actual efficacy represent critical points for improving hygiene and reducing the risk of healthcare-associated infections. Presently, surveillance is based on traditional protocols and classical microbiology. Innovation in monitoring is required not only to enhance safety or speed up controls but also to prevent cross infections due to novel or uncultivable pathogens. In order to improve surveillance monitoring, we propose that biological fluid microflora (mf) on reprocessed devices is a potential indicator of sanitation failure, when tested by an mfDNA-based approach. The survey focused on oral microflora traces in dental care settings. METHODS: Experimental tests (n = 48) and an "in field" trial (n = 83) were performed on dental instruments. Conventional microbiology and amplification of bacterial genes by multiple real-time PCR were applied to detect traces of salivary microflora. Six different sanitation protocols were considered. A monitoring protocol was developed and performance of the mfDNA assay was evaluated by sensitivity and specificity. RESULTS: Contaminated samples resulted positive for saliva traces by the proposed approach (CT < 35). In accordance with guidelines, only fully sanitized samples were considered negative (100 %). Culture-based tests confirmed disinfectant efficacy, but failed in detecting incomplete sanitation. The method provided sensitivity and specificity over 95 %. CONCLUSIONS: The principle of detecting biological fluids by mfDNA analysis seems promising for monitoring the effectiveness of instrument reprocessing. The molecular approach is simple, fast and can provide a valid support for surveillance in dental care or other hospital settings.

Molecular analysis for bacterial contamination in dental unit water lines.

Bacterial contamination in dental unit waterlines (DUWLs) was evaluated by molecular techniques in addition to the conventional culture method. Water samples (n=8) from DUWLs were investigated for heterotrophic bacteria by culture method using R2A agar. The selected bacterial antibiotic-resistance genes and Legionella species-specific 16SrDNA were identified by PCR. The profiles of bacterial contamination in DUWLs were further identified by PCR-DGGE. In this study, no antibiotic-resistant or Legionella genes were detected. Polycyclic aromatic hydrocarbon-degrading bacterium, Novosphingobium sp. was the most prevalent in DUWLs. Conventional PCR and PCR-DGGE were shown to be potentially useful for monitoring of bacterial contamination in DUWLs.

Health concerns of heterotrophic plate count (HPC) bacteria in dental equipment water lines.

There is an unsubstantiated concern as to the health relevance of HPC (heterotrophic plate count) bacteria in dental equipment waterlines. The American Dental Association (ADA) web site includes guidelines for controlling HPC populations and implies that HPC populations >500 CFU/mL as a "health" benchmark. The world-wide published literature including the United Nations fully examined this situation and concluded that HPC bacteria are not a health risk, but merely a general water quality parameter for all waters including dental water lines. This review provides documentation that the standard measurement of HPC bacteria in waters alone do not pose a health risk and the ADA already provides appropriate practices to minimize HPC bacteria in dental equipment water.

Potential for nosocomial transmission of Enterococcus faecalis from surfaces in dental operatories.

AIM: To assess the potential for nosocomial transmission of Enterococcus faecalis during root canal treatment by measuring its occurrence on surfaces in dental operatories in relation to the efficacy of disinfection routines. METHODOLOGY: Eight dental clinics (two endodontic specialist clinics and six general dentistry clinics) were included. Bacterial sampling was conducted in duplicate after root canal treatment and collected before and after disinfection from four surfaces expected to be frequently disinfected and six surfaces expected to be occasionally disinfected. RESULTS: A total of 320 samples were collected. Overall, 40.6% (n = 130) exhibited bacterial growth, mostly consisting of environmental bacteria (36.3%) and to a lesser extent of bacteria from salivary contamination (3.4%). Only three surfaces, all of which were probably seldomly disinfected, were positive for E. faecalis (0.9%). Disinfection routines resulted in an increased contamination in the majority of general dentistry clinics: 64% (32/50) of the surfaces were contaminated prior to and 70% (35/50) after disinfection. Conversely, disinfection of surfaces in the specialist clinics reduced contamination levels by 10%. CONCLUSIONS: The origin of E. faecalis in secondary root canal infections remains unclear, as the potential for nosocomial transmission of enterococci from environmental surfaces in dental surgeries appears to be very small. The incorrect or ineffective disinfection procedures in general dentistry clinics needs to be addressed to counteract the risk for bacterial transmission in dental operatories.

Evaluation of 3 dental unit waterline contamination testing methods.

Previous studies have found inconsistent results from testing methods used to measure heterotrophic plate count (HPC) bacteria in dental unit waterline (DUWL) samples. This study used 63 samples to compare the results obtained from an in-office chairside method and 2 currently used commercial laboratory HPC methods (Standard Methods 9215C and 9215E). The results suggest that the Standard Method 9215E is not suitable for application to DUWL quality monitoring, due to the detection of limited numbers of heterotrophic organisms at the required 35°C incubation temperature. The results also confirm that while the in-office chairside method is useful for DUWL quality monitoring, the Standard Method 9215C provided the most accurate results.

Dental unit water treatment with hydrogen peroxide and monovalent silver ions artificially contaminated with freshly isolated pathogens.

BACKGROUND: Dental unit water (DUW) could be contaminated by human pathogens coming from biological fluids penetrated during patient treatment and by opportunistic pathogens detached from aquatic biofilm. These microorganisms could be spread to following patients. We tested the disinfectant activity of hydrogen peroxide and monovalent silver ions (H(2)O(2)-Ag(+)) into DUW artificially contaminated with freshly isolated pathogens. METHODS: The tested microorganisms were Staphylococcus aureus, Enterococcus faecalis, Candida albicans, Pseudomonas aeruginosa, Legionella pneumophila, Mycobacterium chelonae, non-pathogenic Bacillus clausii spores. Bacterial suspensions were inoculated into the waterlines of pre-sterilized dental turbines. The test-turbines were connected to DUW and contaminated water was treated for 10 minutes with H(2)O(2)-Ag(+)-based disinfectant (H(2)O(2) 3% v/v, Ag(+) 0.001% w/v). The control-turbines were left untreated. Turbines were washed with sterile hard water used to assess the residual bacterial loads (expressed in colony forming units -cfu). Each strain was tested five times and the mean log loads were assessed. Following the European Standardization Committee, the disinfectant activity was evaluated as mean log load reduction, that is, the difference between the mean log load detected on the control-turbines and the mean log load detected on the test-turbines. RESULTS: Mean bacterial loads detected on the control-turbines ranged between 105-107 cfu. The mean log load reductions resulted 7.5 log cfu for S. aureus, E. faecalis, P. aeruginosa, 6.3 for C. albicans, 5.4 for L. pneumophila, 5.3 for M. chelonae, 2.9 for B. clausii spores. CONCLUSIONS: DUW disinfection with H(2)O(2)-Ag(+) could help minimize the risk that planktonic pathogens are spread to patients during dental treatment.

Is water in dental units microbiologically safe?

BACKGROUND: Water supplied to the dental units must be of sufficient quality. The article presents the results of the microbiological analysis of cold municipal water which flows into a patient's disposable mouthwash cup, and demineralized water which flows through a waterline into the tool panel of a dental unit from the tank placed in the water group. MATERIAL AND METHODS: In order to assess the degree of purity (impurities) of water used in dental units, 2 series of microbiological tests were carried out in 6 dental surgeries from April to June, 2013. The water samples for microbiological testing were collected into sterile microbiological bottles in accordance with the current methodology. The water for the tests was collected from a sterile cup-filling tap (municipal water) and from an air/water syringe (demineralized water). The bacteria were cultured according to the Polish Standards - PN-EN ISO 6222, PN-EN ISO 9308-1, and PN-EN ISO 16266. RESULTS: In the tested samples of water numerous psychrophilic bacteria (max 29 100 CFU/ml) and mesophilic bacteria (max 24 700 CFU/ml), including single coliforms, were found. CONCLUSIONS: The results show that water delivered to a dental unit should be periodically tested bacteriologically and in terms of physical and chemical properties. Water systems of dental units should also be periodically disinfected to eliminate bacteria and biofilm.

Significance of biofilms in dentistry.

In the past decades significant scientific progress has taken place in the knowledge about biofilms. They constitute multilayer conglomerates of bacteria and fungi, surrounded by carbohydrates which they produce, as well as substances derived from saliva and gingival fluid. Modern techniques showed significant diversity of the biofilm environment and a system of microbial communication (quorum sensing), enhancing their survival. At present it is believed that the majority of infections, particularly chronic with exacerbations, are a result of biofilm formation, particularly in the presence of biomaterials. It should be emphasised that penetration of antibiotics and other antimicrobial agents into deeper layers of a biofilm is poor, causing therapeutic problems and necessitating sometimes removal of the implant or prosthesis. Biofilms play an increasing role in dentistry as a result of more and more broad use in dental practice of plastic and implantable materials. Biofilms are produced on the surfaces of teeth as dental plaque, in the para-nasal sinuses, on prostheses, dental implants, as well as in waterlines of a dental unit, constituting a particular risk for severely immunocompromised patients. New methods of therapy and prevention of infections linked to biofilms are under development.

[Epidemiological investigation in five dental offices of the Clinic of Dentistry, Faculty of Medicine, Palacký University, Olomouc and of the Olomouc University Hospital]. / Epidemiologické setrení v peti ambulancích Kliniky zubního lékarství LF UP v Olomouci a FN Olomouc.

UNLABELLED: The aim of this epidemiological investigation was to determine microbial contamination of surfaces, medical devices, and equipment in five outpatient dental offices of the Clinic of Dentistry, Faculty of Medicine, Palacký University, Olomouc and of the Olomouc University Hospital. The epidemiological investigation was carried out as a one-time detection of microbial contamination from selected at risk sites on the dental unit with chair and in its immediate surroundings that had been sampled before the staff and patients arrived in the morning. The rates of culture-negative results ranged from 6.0 % in the children's dental office to 17.3 % in the dental prosthetics office. No statistically significant difference in these rates was found between different types of dental offices. The most commonly identified microorganisms were coagulase-negative staphylococci and Bacillus sp. Pseudomonas aeruginosa often reported to be the cause of hospital infection was isolated from the spit-toon drain in most of the cases. No methicillin-resistant Staphylococcus aureus was cultured from the swabs. We believe that the microorganisms isolated from the at risk sites are indoor airborne pathogens initially present in aerosols and then deposited on surfaces during the time after working hours. KEYWORDS: dental office - bioaersol - contamination of surfaces - infectious agent.