Fig 1.
Experimental setup of the dental chair unit used in this study.
Rinsing solutions in the barrel (left) were transferred into the chair unit via a pump (C). Automatic flushing of the unit was triggered by a microcontroller (right). Water samples were collected from the cup filler (A), the air/water syringe (B) and the pump (C) as indicated in each case.
Fig 2.
Timeline of flushing protocols for shock disinfection processes and continuous ClO2 applications.
The figure shows the course of the individual flushing protocols and the respective disinfection measures, whereby the individual phases including stagnation are intended to reflect a real working situation in a practice. On the days indicated (flushing day), a DCU was flushed several times at hourly intervals (hour) or in a row. Each individual rhombus in the illustration corresponds to a flushing process. The flushing processes were carried out with either tap water (dark blue rhombus) or filtrated tap water (light blue rhombus). Disinfections were performed with the low ClO2 concentrations of 1.2 mg/L (A, D) and 2.4 mg/L (D), as indicated in the individual test approaches (orange rhombus), and shock disinfections are depicted as dark orange rhombus (B, C). Days of stagnation without flushing are marked as grey rhombus.
Fig 3.
Reduction of P. aeruginosa biofilms by ClO2.
Biofilm cells of P. aeruginosa, cultured in a 96-well plate for two days, were treated twice with 15 mg/L ClO2 in PBS for 60 min. The reaction was stopped with sodium thiosulfate. Biofilms were stained with crystal violet afterwards. ClO2 treated wells (row B) showed clearly less crystal violet staining, revealing the impact of ClO2 on biofilms through visible gaps and reduced bandwidth compared to untreated wells (row A).
Table 1.
Bacterial reduction of one-day ClO2 treatment following tap water flushes.
Table 2.
Single ClO2 shock disinfection and tap water flushes.
Table 3.
ClO2 shock disinfection and flushes with filtered water.
Table 4.
Repeated rinsing protocols using different concentrations of ClO2.
Fig 4.
Plating results on R2A agar with continuous ClO2 application.
According to the flushing protocol by using 2.4 mg/L ClO2 water samples taken from the syringe were plated in 500 µl volumes on solid R2A medium followed by incubation at 36°C for 96h. Cultivatable bacteria multiplied as visible cfu. The plates represent bacterial lawn formation after stagnation (day 1, hour 1; A), reduced lawn formation on day two after six flushing hours; B), few and scattered bacteria after treatment with 2.4 mg/L ClO2 (day ten, hour six) and recovering after stagnation (day 14; hour 1 D).
Fig 5.
Correlation of the total cell counts (TCC), the intact cell counts (ICC) and the ClO2 concentration during the study period.
According to the flushing protocol (Fig 2D), the DCU was flushed at indicated days either with tap water (blue line) or with ClO2 solutions (orange line) at initial concentrations of 1.2 mg/L (A) and 2.4 mg/L (B). Total cell counts (TCC; grey columns) and intact cell counts (ICC; black columns) were calculated alongside the ClO2 concentrations (dotted line), determined using the Palintest, either from the syringe (upper diagram) and from the cup filler (lower diagram). Each column (mean value ± standard deviation) represents the flushing day and hour according to Table 4.
Fig 6.
ClO2 depletion effects in various types of water.
Fig 7.
Analyses of the ClO2 depletion effects for supply line and final use.
The DCU was flushed hourly, as indicated, and after 24 h with aqueous ClO2 solutions of initial 0.58 mg/L ClO2 (A) and 0.61 mg/L ClO2 (B). The concentrations were directly measured in mg/L with the Palintest device at the pump outflow (black line) and after passing the DCU at the final collection point (cup filler) (dashed line). A ClO2 solution prepared in a sterile glass bottle served as control (dotted line).