Background of the Invention The microbial contamination of dental unit waterlines (DUWS) is being increasingly recognized as a potential health concern. Dental unit waterlines, which comprise the tubes that connect a water supply to the various dental handpieces which use water to operate, e. g. the high-speed handpiece, air/water syringe and ultrasonic scaler, have been shown to harbor a wide variety of microorganisms, including various bacteria, fungi and protozoa. These microorganisms can colonize and replicate on the interior surfaces of the waterline tubing, resulting in microbial accumulations, referred to as biofilms. These biofilms, once formed on the interior surfaces of the tubing, in effect serve as a reservoir of microorganisms, significantly increasing the number of microorganisms in the water which moves through the waterlines.

Health concerns of contaminated waterlines include the water supplied to the mouth of a patient via an air/water syringe. Infection of the patient can occur directly from the water which is contaminated by the biofilm microorganisms as it moves through the dental unit waterlines to the syringe. Dental air turbines present a different possibility of infection for a patient, by infected body fluids and/or blood from another patient which may be introduced into the tubing due to a"suck-

back"malfunction of the equipment, due to faulty check valves, etc. In addition, the water supplied to the dental turbine, including the inner surfaces of the turbine, may become exposed to the infected patient's blood and/or saliva during normal operation, such as by the spray created by the turbine handpiece when it is in operation. The now-contaminated dental turbine, with its soiled inner surfaces, will then be idle until the next patient is available. Subsequent patients can thus be infected by further use of the contaminated appliance.

As indicated above, all dental waterlines will have biofilm accumulation to some degree, whether they are routinely used or not. These lines are thus a source of bacterial and other microorganisms which will readily contaminate the entire dental waterline and appliance system.

It is well known that various kinds of infections, including both bacterial and viral, can reach patients through existing waterline systems, including the hepatitis-B and hepatitis-C viruses and T-cell leukemia. While the actual risk of serious microbial infection in healthy individuals may be relatively small, the potential health risk to immuno- compromised or surgical patients is possibly quite high. The risk to normal patients will also likely increase if the matter of dental unit waterline contamination is not addressed in the near future.

For such reasons, the American Dental Association (ADA) and the Center for Disease Control (CDC) have recognized and begun to study the problem of microbial infection from dental waterlines. The ADA Council has recommended an aggressive course to encourage the industry and the research community to improve the design of dental equipment, so that by the year 2000, water delivered to the patient through the dental unit waterlines during non-surgical dental procedures will consistently contain no more than 200 colony-forming units of bacteria per milliliter of fluid at any output point in the dental water system.

In order to combat the presence of microorganisms in dental waterlines, various methods of disinfecting the lines have been used, and the number of current commercial devices which claim some efficacy in reducing microbial content in waterlines is increasing. One method, recommended by the ADA, involves the flushing of the various dental appliances and the waterlines for several minutes at the start of each workday.

However, flushing typically takes at least 30 minutes to be significantly effective, and further, microbial contaminations have been found to be restored to their original levels within 30 minutes of initial use of the waterlines after flushing.

Another method involves weekly bleach disinfecting of the waterlines. While this method has also been found to have some effect, the biofilm layer has typically been found to be relatively intact after the use of disinfectant, with early complete recolonization of the biofilm on the luminal walls, such that the waterline fluid quickly reaches initial levels of contamination.

Other attempts to control microbial contamination of waterlines include the use of an independent water supply unit, where the dental system is disconnected from the municipal water supply (tap water) and connected to a source of sterile water maintained within the dental office. Such a system, however, still must be used with a bleaching regimen to reduce bacterial growth in the stagnant water in the system, as well as presenting issues of cost and storage. Filters of various kinds have been also used, but have been shown to be relatively ineffective against the bacterial and viral microorganisms present in the ordinary dental waterline.

More sophisticated methods include the use of sterilization, radiation and ultraviolet exposure procedures.

Heat and high pressure steam (autoclave) sterilization as well as gas sterilization have been used. However, these methods result in early deterioration of the dental elements subjected to those processes, and radioactive sterilization in particular is questionable relative to any proximity to human beings.

These more sophisticated systems, while in some cases effective against particular (but not all) microorganisms, are typically quite expensive, often beyond the means of the typical dentist.

Hence, a system for decontamination of dental unit waterlines which is reliable, effective and inexpensive is quite desirable, particularly relative to meeting the stated goal of significant reduction in microbial decontamination of DUWS by the year 2000.

Disclosure of the Invention Accordingly, the present invention is a system for decontaminating dental unit waterlines, comprising: means for producing acidic electrolyzed water having a pH in the range of 2.5-3.5 and an ORP of 400-1400 millivolts in one embodiment and a pH in the range of 3.5-6.5 and an ORP of 400-1400 millivolts in another embodiment, wherein the electrolyzed water is otherwise characterized as having a significant anti-microbial effect; and means directing the electrolyzed water to dental appliances through dental unit waterlines, wherein the electrolyzed water comes into continuous contact with the interior surfaces of the dental unit waterlines during operation of the dental appliances, substantially reducing biofilm concentrations therein and itself remaining substantially contamination-free of microorganisms while also serving as operating fluid for the dental appliances.

Brief Description of the Drawings Figure 1 is a block diagram showing one embodiment of the system of the present invention.

Figure 2 is a simple schematic drawing showing operation of the electrolyzer.

Figure 3 is a table showing relative effectiveness of the system of the present invention for several different microorganisms.

Figure 4 is a block diagram showing an alternative embodiment of the system of the present invention.

Figures 5 and 6 are tables showing additional information on the effectiveness of the system of the present invention.

Best Mode for Carrying Out the Invention Dental unit waterlines (DUWS) are defined as those water-carrying lines, which are typically plastic tubing, which connect a source of water to one or more dental appliances, typically a high-speed turbine dental drill, an ultrasonic scaler and/or an air/water syringe. Other appliances in the dental office may also be connected to a water supply.

Virtually all dental offices will include at least one if not more of the above appliances.

The source of the water for the appliances may be from a municipal water tap available in the dental office, or from a source of sterilized water within the office. Some of the water systems in dental offices include filters, while still others include some sort of water treatment device.

Figure 1 shows one embodiment of the dental water system of the present invention, which is capable of decontaminating dental waterlines and maintaining them in a decontaminated condition, while at the same time being completely safe, without any adverse side effects or safety concerns. Safety concerns are often present with existing decontamination systems.

In the embodiment of Figure 1, an electrolyzer 10 in operation produces acidic water, having a pH in the range of 2.5-3.5. Electrolyzer 10 and its associated control unit 12 are both well known and commercially available. The electrolyzer 10 uses an electrolysis process, which is well known, in which tap water is ionized to produce hydrogen gas, while the hydroxide ions are oxidized to give oxygen gas, by the action of an electric current which is passed between positive and negative electrodes positioned in the water present in the electrolyzer.

Typically, a mineral is added to the water in order to

facilitate creation and passage of the electric current between the electrodes.

Electrolyzer 10 uses a source of tap water 14 which is directed through a two-port valve 16 which has a control sensor 17 connected thereto which senses the level of water in the electrolyzer. Information from sensor 17 is applied to control unit 12, and control unit 12 controls the operation of valve 16. The water from valve 16 is directed through a three- port valve 18 and then to electrolyzer 10 through line 22.

Sodium chloride, NaCl, (salt) is added to the tap water in the electrolyzer from a storage tank 20. Only a relatively small amount of NaCl is added to the electrolyzer. For approximately one liter of tap water, the amount of NaCl will be approximately 0.1-0.5 grams.

As indicated above, the basic electrolysis process which occurs in electrolyzer 10 is well known. Briefly, negative ions (labeled X in Figure 2) present in the water are attracted to the positive electrodes 21, while positive ions (labeled M in Figure 2) are attracted to the negative electrodes 19. Positive ions include sodium, calcium and magnesium ions, while negative ions include chloride and sulfate ions. One textbook which explains the electrolysis process is SCHOAC Electrochemistry: Introduction, by Tom Stretton, 1997. Such electrolyzers are also available commercially. One example is the Aqua Refine, by A. R. V. Co. Ltd., a Japanese company.

In the embodiment of Figure 1, both acidic and alkaline water are produced, which requires an internal membrane which maintain the two different water types separate within the electrolyzer. A simplified cross-section of such an electrolyzer is shown in Figure 2. The cathodic electrodes (poles) 19 and the anodic electrodes (poles) 21 are separated by membrane portions 23-23. The electrodes could be made from a variety of elements, such as platinum or palladium. Connecting the top edges of membrane portions 23-23 are plastic cap portions 27 and 27a, which form a channel or path to exit port 29. Tap water enters the electrolyzer chamber at inlet port 25,

while acidic and alkaline water exit through ports 29 and 31, respectively.

In the electrolysis process of Figure 1, acidic electrolyzed water and alkaline water are produced in accordance with the following formulas: H20----+ H'+ OH- 40H- (at anode)---- 4e-+ , +2H, 0 2e-(atcathode)#H22H++ The overall reaction is thus tLO---L+02. In this electrolysis process, the sodium chloride salt facilitates current passing between the two electrodes (poles) and ionizes as follows: Cl-NaCl#Na++ During the electrolysis of water in the presence of sodium chloride, sodium ions Na+ are attracted to the negatively charged electrodes and will counterbalance the hydroxide ions on the alkaline side, while the chloride ions C1-are attracted to the positive electrodes. The chloride ions then undergo an oxidation process that results in the production of very small quantities of chlorine gas, which immediately is used to form hypochlorus acid, as follows: <BR> <BR> <BR> <BR> <BR> 2e-#Cl22Cl-- <BR> <BR> <BR> <BR> <BR> <BR> H2O#HClO+Cl-+H+Cl2+ HCIO---* C10-+ H+ The amount of Cl-ions in the water in the form of HC10, C10- and Cl'and the balance among those ions is greatly affected by the pH of the resulting water. HC10 and Crions are effective sanitizers against microbes, although HClO is many times more effective than C10'. In the acid water produced by the electrolyzer 10, most of the C10-ions are in the form of HC10.

Low levels of ozone are also formed during the electrolysis process according to the following reactions:

H20oH+ +OH- 40H--4e----- 2H, + °2 H20+02-2e---<03 +2H+ The acidic electrolyzed water produced by electrolyzer 10 has a pH in the range of 2.5-3.5, with a preferred value of 2.6. The acidic water is directed through line 26 to a holding tank 30 which in the embodiment shown is the source of water for the dental appliances. Tap water may be provided to tank 30 in line 39 through valve 18 if it is desirable to dilute the acidic water. The operation of valve 18 is controlled by control unit 12, while information obtained by associated sensor 24 is directed to control unit 12. The acidic water from tank 30 is directed by a pump 32 through the office dental lines to the syringes, scalers and high-speed appliances, shown generally at 34.

In the line between pump 32 and the appliance is an optional microfilter 36 which provides some filtering effect.

Tank 30 can be drained by valve 38, controlled by control unit 12, with the aid of sensor 40, if it is necessary to clean the system, including tank 30, for instance. Positioned within tank 30 is a five float (level) sensor 41. Information from sensor 41 is used to control the filling of the tank 30 and the operation of the electrolyzer. The alkaline water produced by electrolyzer 10 is directed through line 28 to a drain or storage containers, as desired.

The acidic electrolyzed water has a preferred range of ORP (oxidation reduction potential) of 900-1200 millivolts, with a preferred value of 1100 millivolts, although the range could be 400-1400 millivolts. The free chlorine in the water is 1 ppm to 100 ppm, with a preferred value of approximately 30 ppm. The free chlorine values should be relatively low for safety reasons. The C12 and HC10 will be in equilibrium. HC10 is 10-100 ppm, while 03 is 0. 1-1 ppm.

The acidic electrolyzed water can easily destroy 108 microorganisms/ml (8 logs cells/milliliter of vegetative cells) in an exposure time of less than 5 seconds, and spores at 106 (6

logs/milliliter) for 8 minutes of exposure, at 30 ppm free chlorine concentration.

In the present system, tap water never reaches the dental waterlines, the dental waterlines are continuously decontaminated by the acidic electrolyzed water which flows through them from holding tank 30 to the dental appliances. One key advantage to the present invention is that separate, independent decontamination steps or events apart from the operation of the appliances are not necessary; rather, the dental waterlines are continuously and automatically decontaminated when the dental appliances are in use by the fluid used in their normal operation. The sanitizing, decontaminating fluid is the same fluid used in the operation of the dental appliances, including the air/water syringe. The entire dental system is thus being continuously sanitized by the very fluid which is used in the dental appliances, and in the case of the air/water syringe, used directly on the patient, with the fluid being completely safe for humans.

Figure 3 is a table which shows the bactericidal effect of acidic electrolyzed water. Three separate microorganism agents are shown, relative to various sanitizing solutions, including straight chlorine solution in water at 50 ppm concentration in a commercial sanitizing system, acidic electrolyzed water with a pH of 2.87 and distilled water with a pH of 7.6. It can be seen from the table of Figure 3 that while the chlorine and the sanitizer are effective only on particular microbial agents after a selected amount of exposure time, the acidic electrolyzed water is effective on all of the microorganisms tested, with less than 10 seconds of exposure time necessary to produce the desired effect. The acidic electrolyzed water is also effective in destroying yeast.

Figures 5 and 6 are additional tables showing the antimicrobial effect of acidic electrolyzed water. For Figure 5, the electrolyzed water had a pH of 3.2, an ORP >700 and a free chlorine concentration of 8 ppm. A six log of destruction (destruct indicated by"minus"symbols) was achieved for E. coli

and P. aeriuginosa. In Figure 6, the acidic electrolyzed water had a pH of 2.5, an ORP >700 and a free chlorine concentration of 30 ppm. The spore tested was Bacillus subtilis. Significant effects were observed quickly with the acidic water system of the present invention. The results of Figure 6 show better than a 6 log reduction of spores after five minutes of exposure and better than a 7 log reduction after 10 minutes of exposure to acidic electrolyzed water.

The antibactericidal action of the acidic water is thus quite good, and does not have any deleterious effects. The acidic water is equally effective against viral agents. As indicated above, one important advantage of applicant's system is that dental waterlines can be sanitized continuously, with the sanitizing fluid which kills the bacteria and viral agents being used as the actual dental appliance water, including the water used in the air/water syringe directly on the patient.

Figure 4 shows another embodiment of the system of the present invention, in which an electrolyzer 50 produces what is referred to herein as acidulous water, meaning acidic water with a pH in the range of 3.5-6.5, although a pH of 5-6 is typical. In this system, there is no membrane to separate the electrodes and the acidic and alkaline electrolyzed waters. As a result, only one effluent is produced, referred to as acidulous water.

The electrolyzer 50 is filled from a source of tap water 55 through inlet valve 52 which is controlled by control unit 51 with information from sensor 54 which senses the level of water in the electrolyzer 50. From there, the water proceeds through three port valve 56 into electrolyzer 50, through line 57. Small quantities of sodium chloride (NaCl) and dilute hydrochloric acid (HC1) are added to the electrolyzer 50 from tanks 53 and 60, respectively. The HC1 is added to increase the chlorine concentration, resulting in additional chlorine ions, which increases the cleansing effect. Electrolyzer 50 operates similarly to electrolyzer 10, producing acidulous water which is directed to a holding tank 64, through line 65. Tap water can

be added to tank 64, if desired, through valve 56 and line 67.

Holding tank 64 also includes a five float sensor 66, like the embodiment of Figure 1 and can be drained through valve 69, under the control of control unit 51.

The acidulous water is pumped from tank 64 to the dental appliances, shown collectively at 68, through dental lines which could include an optional microfilter 70. The acidulous water has a pH of 3.5-6.5, with a preferred value of 5.6, and an ORP of 800-1300 millivolts, with a preferred value of 900 millivolts, although the range could be as great as 400- 1400 millivolts. The range of free chlorine concentration is 1 ppm to 200 ppm, with a preferred value of 30-50 ppm.

The efficacy of the system of Figurer 4 is also 108 cells/milliliter reduction of vegetative cells, with an exposure time of less than 5 seconds, while spores is 106/milliliter reduction after 2 minutes of exposure, with 10 ppm free chlorine concentration.

Although a preferred embodiment of the invention has been disclosed herein for illustration, it should be understood that various changes, modifications and substitutions may be incorporated in such embodiment without departing from the spirit of the invention, which is defined by the claims which follow.

What is claimed is: