C. Beck, A. Filippi and F. Tilkes.
Institute of Hygiene, University of Giessen (Justus-liebig-Universltet), FR Germany
General and particular aspects of infection control are presented and discussed.
Water hygiene in the form of disinfecting drinking mater – whirlpools – and water for swimming pools and the practice of ozonization, in dental treatment units are all well-known aspects of ozonization.
In water-based systems, ozone has proved its very high level of efficacy against bacteria and in the inactivation of viruses, especially in the elimination and rapid destruction of legionella, pseudomonas, hepatitis A + Р’ viruses and HIV viruses.
In particular, our results show promising possibilities for the use of ozone in dental treatment units.
Studies on the antibacterial effect of ozone were described for the first time by OHLMUUER in 1893. In the same year, ozone was applied technically for cleansing Rhine water in the Dutch community of Oudshoon. Here, its importance is not only to be seen in disinfection, but also in its further effects such as the precipitation of iron and mangasnese, the destruction of sulfites and substances active on-the surface, the elimination of turbidity, the oxidation of aromatics, odoriferous substances and flavorings as well as other organic compounds (e.g. 3,4-benzpyrene).
Ozone, which is considered to be the strongest oxidant applicable in practice, is not only used in the disinfection of drinking and swimming pool water (hot whirlpool), but also in the pharamaceutical field for the purpose of protecting water VE preparation units, particularly their critical sections (such as ion exchangers, reversible osmosis units and sterilization filters etc.), from microorganism deposits. For example, VE*)- ozonized water can be used in autoclavlng. In an aqueous envi- *VE: aqua demineralisata ; ronment, ozone breaks down very rapidly into oxygen and water, so that no toxic decomposition products whatever are formed. When using ozone for water cleansing, care must be taken that compatible, i.e. acceptable, materials are used. Glass, ceramics, stainless/high-quality steel and Teflon are resistant to direct ozone exposure. On the other hand, rubber sealing parts and rubber tubing is extremely susceptible to corrosion from
Ozone has a wide range of action; the concentrations needed to destroy vegetative bacteria and spores are within a range of 1 – 5 mg/Liter. Approximately within the same magnitude limits, but only at a low concentration range. (0.025 mg/Liter), we find that a concentration 3 times higher is necessary to obtain a sporicidal effect. Fungi are also included in this
range, in the same way as viruses (BOTZENHART and HERBOLD, 1988).
The following factors influence the microbicide action of ozone: Concentration; The time needed for the destruction of microorganisms decreases considerably as the ozone concentration is increased. Most of the microorganisms are already killed off after less than 1 minute at a concentration of 5 ug ozone per ml. In spite of this, its concentration in water is subject to a number of different influences: – Ozone consumption: a large number of organic and inorganic
compounds react with the oxidant ozone, resulting in a decrease of the “freely available” ozone. In this aspect, ozone behaves in a way similar to chlorine or iodine.
- Light effect: ozone decomposes at a considerably more rapid rate in light than in darkness.
- Life: the life of ozone in water depends to a great extent on the composition of the water (aqueous medium) and the above factors. After a standing period of JO hours and at an -ozone concentration of 4.5 ug per ml in VE*-water, only approx. 0.3 С†g ozone/ml can still be found.
Temperature: The action and effect of ozone are better at 0 В°C (32 В°F) than at 20 0C (68 В°F) INGRAM H. and HAINES R.B. (1949). Humidity; In water, considerably lower concentrationa are necessary to destroy microorganisms than in a dry atmosphere. pH value; its antimicrobial effect is optimal in an acid pH range (pH 2) but decreases rapidly as the pH value increases, so that only 1 5 of this value is present at pH 7.8 by comparison, and its presence may be practically neglected at a pH value of 11. This drop in activity follows the pH-dependent ozone *) aqua dbermeiankedroawlni.sata
After ozone action over an extended period of time, pyrogens contained in water are inactivated, a fact which has been demonstrated by the addition of 40 ml Pyrifer strength VIII to 100 Liter bidistilled water, corresponding to 2 units/ml in the presence of 4 – 5 ppm ozone. The tests by WALLHSUSER (1988) here cited show that approx. 9 hrs are necessary for such an inactivation. The water needed for the dental treatment of a patient should have the quality of normal drinking water at. least. Nevertheless, completely germ-free water is much better, as microlesions to the mucous membrane are always possible in practically all forms of dental treatment, so that the possibility of an infection from water and air used as coolants can never be excluded. The following studies were carried out for this reason.
1. The tests were carried out in parallel on two dental units. One was opersted without water disinfection, the other with a continuous addition (by dosage) of hydrogen peroxide and silver ions (as preliminary test).
Five water samples were taken at all removal points of the unit every day, end the number of microorganisms (germ count) per ml recorded in the form of a weekly chart. Subject to circadian deviations, there was a pronounced accumulation of microorganisms at all removal points. The germ counts recorded were up to 1000 times higher than the limit of 100 cfu*) per ml laid down by the law for drinking water in the Federal Republic of Germany.Differences in reduction of (the number of) microorganisms with or without disinfection as depending on use thus became
2. Comparison of the disinfectant effect of ozonized water and hydrogen peroxide in vitro at 20 В°C (68 В°F) and 37 В°C В°F ). Microorganism tested: Pseudomonas aeruginosa Concentration: 3 x 10* colony forming units per ml Procedure: quantitative suspension test, i.e. 100 ml of the disinfectant are incubated with 1 ml suspension of the micro organism) samples are taken immediately, after 1 minute and after 5 minutes and the number of microorganisms still press
In them recorded.
Concentration of disinfectant; Ozonized water: 10 (ig ozone/ml water )
H2 O2 : SO mg H2 O2 /L water ) as in the dental unit In the case of the ozonized water, the disinfectant effect was immediate, compered with which the hydrogen peroxide and the bidistilled water selected as a reference both behaved in the tically no disinfection The hydrogen peroxide showed per definitionem, p r a c -
See Fig. 1

Ozonized water hydrogen peroxide Bidistilled Water
2*109 units/ml ) 4*107 unite/ml 2*109 units/mi
Ozonized water hydrogen peroxide Bidistilled Water
0.0 units/ml ) 2*107 units/ml 4*109 units/ml
Ozonized water hydrogen peroxide Bidistilled Water
0.0 units/ml*) 2*107 unite/ml 2*109 units/ml
Ozonized water hydrogen peroxide Bidistilled Water
0.0 units/ml ) 2*107 unite/ml 2*107 unita/ml

* ) colony forming units
3. Comparison of the disinfectant effect of ozonized water and hydrogen peroxide in the dental chair
A very high degree of microorganism contamination indeed is found on monday mornings in both disinfection systems, which drops after disinfection during the course of the day to 0 cfu } per ml, this being more rapid with ozone than with
hydrogen peroxide. The dental unit and/or the water samples taken are free of microorganisms during the remainder of week.
4. Determining the increase in the number of microorganisms over the weekend
Water samples (2 ml) were taken on Friday midday, Saturday morning, Sunday morning and Monday morning from both nozzles, of which one. had been disinfected the previous week with hydrogen peroxide, and. the other with ozonized water.
The major increase in the number of microorganisms occurred between Saturday morning and Sunday morning,- i.e. about 15 – 39 hours after termination of treatment. After this, the number of microorganisms only increased to an unimportant extent. This applied for both disinfection systems.
5. Test to reduce the number of microorganisms by simply removing a specific quantity of water on Monday prior to starting treatment *) colony forming units
Following each of the three weekends, 170 ml were removed from the nozzle on the dentist’s side in fractions of 10 ml and
examined for the number of microorganic colonies. The volume of standing water in the dental chair was 90 ml.
After each of the three weekends, disinfection was carried out by “flushing through” with another disinfectant, once with ozonized water, once with hydrogen peroxide and finally with (sterile) distilled water.
When the chair unit had been flushed clean of the remaining 90 ml and refilled with disinfected water, the number of micro- t organisms in the ozonized water immediately dropped to 0 cfu’s per ml. In the case of the hydrogen peroxide, this lasted for a further 60 ml. With distilled water, the number of microorganisms counted only dropped very slowly and this merely due to the rinsing effect. .
6. Determination of the ozone concentration at the water outlet points of a dental treatment unit as depending on external
temperature when the instant flow water heater is switched off
Titrimetric method determination according to the KJ
Water samples were tested with and without connected dental device
Ambient temperature: 15 0 C (59 В°F)
Samplinq point _without/________ with connected instrument
Cytozon (immediate) 14.16 g/ml
(Dentist’s) nozzle 6.96 g/ml 6.96 g/ml
Turbine 7.68 g/ml 0 g/ml
Micromotor 1 7.20 g/ml 0 g/ml
Micromotor 2 6.96 g/ml 0 g/ml
Ultrasonic unit 8.40 g/ml 0 g/ml
Cytozon (after 60) 14.16 g/ml
Ambient temperature: 20 В°F (68 )
Sampling point______ without/______ with connected instrument

Cytozon (immedate) 12.96 g/ml
(Dentist’s) nozzle 5.52 g/ml 5.52 g/ml
Turbine 6.72 g/ml 0 g/ml
Micromotor 1 5.52 g/ml 0 g/ml
Micromotor 2 5.28 g/ml 0 g/ml
Ultrasonic unit 6.48 g/ml 0 g/ml
Cytoron (after 60′) 12.72 g/ml
*) colony forming units

Ambient temperaturei 25 В°C (77 В«F)
Sampling point ______ without/______ with connected instrument

Cytozon ( immediate ) 11.04 g/ml
(Dentist’s) nozzle 2.88 g/ml 3.12 g/ml
Turbine 5.76 g/ml 0 g/ml
Micromotor 1 2.16 g/ml 0 g/ml
Micromotor 2 2.16 g/ml 0 g/ml
Ultrasonic unit 3.36 g/ml 0 g/ml
Cytozon (after 60′) 10.56
7. The effect of an instant flow mater heater on the invitro ozone concentration Simulation of a heater by using a Siemens cooler and HOG ) determination of the ozone concentration using the KJ method.
In this case, the moat important result obtained was that approx. 40 % of the initial ozone concentration was lost through heating of the water by theinstant flow heater to 37 В°C (98.6 В°F). In total, the concentration dropped in a linear slope. *) special cylindrical ozonization container
8. The effect of the heater on the ozone concentration in the dental chair unit The in vitro results mere confirmed.
9. The influence of the heater on the degree of contamination of the water through microorganisms
In spite of the ozone concentrations reduced by the heating effect, no significant differences could be established upon comparison with the weekly charts recorded without the instant flow heater.
10. Determination of the ozone concentration at work site when operating an ozone water disinfection system
DrSger tubes were used for ozone detection and recording. No atmospheric ozone at all could be detected at any of the water outlets and in the vicinity of the Cytozon unit, either during operation or during ozonizing.
As an infection-controlling agent, ozone has proved itself to be invaluable in preventive medicine and, particularly here,
in the case of water hygiene.
Both our own tests as well the studies on the microbiological water quality in dental treatment units described in literature show that, particularly on Monday mornings before starting work, the turbine spray and the water of the mouth rinsing device are contaminated to a very high degree by potentially pathogenic microorganisms.
The reproduction of bacteria in dental treatment units is encouraged by the following criteria:
- The water ia kept in the unit for a long time,
- The water is heated,
- Tubes and other water-conducting unit elements are made of plastic,
- Different passage widths for the water in the units, on account of which water exchange can only take place slowly,
- The presence of hollow spaces in which microorganisms are able to multiply unhindered.
When non-disinfected water is used, the number of colonies counted can rise to 10,000 per ml. This number decreases once more after a treatment period of 1 – 2 hours. Another increase of microorganism contamination takes place during the lunch break. In the.- first place, the source of such a contamination is to be looked for in the water supply of the dental treatment- unit in question. The not infrequently contaminated water tubes, with which the turbines, angular handpieces, angular motor units and mouth rinsing devices are connected, present a hygiene problem. Microorganisms introduced into the unit via unaterilized water or insterile containers are able to multiply in the water which is kept still for- long periods of time.
They are then also able to form colonies in the turbine. However, microorganisms are also capable of entering the treatment unit due to the properties of back-pressure suction valves, this also being possible from the patients’ “end. In the microbial contamination of water paasages in dental treatment units, we are dealing for the most part with pseudomonaa aeruginosa and pseudomonads of the fluorescent group and legibnella; furthermore, the-presence of alcaligenes faecalis, flavobacteria and escherichia coll has also been demonstrated (BECK and SCHMIDT 1986, J. BORNEFF 1982, M. BORNEFF 1986, PRUCHA and TILKES 1986), The various plastic tubes and connections inside a dental unit are known to favor the growth of paeudomonas aeruginosa, whose pathological effects need not be described here. A reduction in the number of microorganisms colonizing such a system to values lying within the legally allowed contamination of drinking water (less than 100 colonies per ml) is not only possible through disinfection of the water used in it. Although simply allowing the residual water to flow off prior to dental treatment produces a reduction in microorganisms, the values of the main water supply to the unit are still never reached. A one-time cleansing of the unit by chemical disinfectants or steam can have no permanent effect, as a continuous supply of new microorganisms comes from the water itself or from the patients. Therefore-, success can only be expected when the water throughout the entire unit is subjected to a continuous disinfection process. As our tests have shown, a noticable hygienic improvement is, fundamentally, only possible where an ozone-dosing disinfection unit is put into use.

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