Liquid purification or separation – Processes – Chemical treatment
Reexamination Certificate
2001-05-02
2003-07-29
Hruskoci, Peter A. (Department: 1724)
Liquid purification or separation
Processes
Chemical treatment
C210S764000, C422S037000, C424S661000, C433S080000
Reexamination Certificate
active
06599432
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the disinfection of dental water unit lines, using aqueous chlorine dioxide solutions, and more particularly to the reduction and destruction of bacteria in biofilms which form on the inner walls of such water lines.
BACKGROUND OF THE INVENTION
The dental profession is becoming increasingly aware, and concerned, that small diameter pipes carrying fresh water from operatory equipment to their patients are contaminated by bacteria and other microorganisms contained in the water flowing through them. Some of the microorganisms inevitably adhere to the inner walls of the pipes and accumulate together with microscopic sediments or other substances into what is commonly known as a biofilm. The biofilm quickly and tenaciously coats the inner walls of the pipes. As it grows, it absorbs nutrients from the water, becoming a culture medium for more microorganisms. These films are typically 30-50 microns thick, and the microbes are distributed throughout the biofilm matrix. Many different types of micro-organism are found in these films including bacteria, fungi, algae and amoebae.
The bacteria found in biofilm are primarily of environmental origin such as Bacillus, Pseudomonas and related genera, and Corynebacterium, but can include organisms from dental patients which are capable of causing serious human infections such as Legionella. There have also been reports of the isolation of human oral bacteria, presumably from back-flow through dental instruments attached to the water line. Sloughing off of microbial aggregates from these biofilms into the lumen will result in bacterial populations reaching alarming levels in the water discharge from the dental instruments connected to the fresh water line. The average bacteria count in the water discharge of dental instruments is approximately 200,000 [2×10
5
] colony forming units per milliliter (cfu/ml) and in some extreme cases can reach 10,000,000 [10
7
] cfu/ml. This is of particular concern since dentists, dental surgeons and dental hygienists, as well as many of their patients, are well aware of the importance of meticulously sterilizing dental instruments to minimize bacterial contamination of these patients. In particular, since dental instruments are used directly in a patient's mouth, when bleeding may sometimes occur as a result of a dental procedure, it is of paramount importance to minimize the presence of microorganisms carried by dental instruments. The microorganisms can of course range from relatively harmless bacteria to dangerous pathogens. Thus, efforts are continuously made to remove microorganisms from dental instruments and from the fresh water lines feeding dental instruments. These include such equipment as air/water guns, high speed water turbines and ultrasonic tartar removers. Where applicable, thermal sterilization remains one of the best methods for eradicating the presence of microorganisms, such as for most hand held dental instruments. However, thermal sterilization is obviously not practical for the decontamination of fresh water lines, which continue to be inordinately difficult to clean, and maintain free from microorganisms.
Many efforts have been expended to accomplish this reduction/destruction, although none has proved completely satisfactory. For example, in the most obvious approach, it has been suggested to use sterile water, particularly to drain the fresh water lines during periods of non-use. Or, as taught in U.S. Pat. Nos. 5,360,338, 5,824,323, and 5,942,125 to create sterile water in the equipment itself, such as by ozonization. Besides the expense, the considerable effort to accomplish these complex operations makes such procedures realistically unacceptable. It is also known that a detergent such as polyoxyethylene sorbitan monooleate (Tween 80™) at approximately 4% dislodges biofilm from small diameter water lines used in dental equipment. However, the use of detergent alone does not effectively destroy the microorganism population. Even the teachings of U.S. Pat. No. 5,942,480, combining detergent, denaturing agent and antimicrobials have not been adopted by dental practitioners as being an effective solution to the elimination of bacterial biofilm.
A number of patents, such as U.S. Pat. Nos. 5,971,757, 5,961,326, 5,749,726, and 5,204,004 teach the use of a variety of replaceable in-line water filters to trap bacteria, such as from biofilm sloughing. These approaches have been found to be impractical, generally because of rapid clogging of the filters whose pore-sizes are sufficiently small to trap bacteria, and which also trap shed biofilm fragments and scale. Since the biofilms in the water lines continue to build up, even in the presence of disinfecting agents, none of those methods has been shown to effectively remedy the microorganism proliferation for any length of time.
It is also known in the art that disinfectants, such as povidone-iodine at a concentration of approximately 10%, reduce the number of microorganisms in small diameter water lines. It is further known from U.S. Pat. No. 5,942,480 that a mixture of mandelic and lactic acids reduces the number of susceptible microorganisms in contaminated tubing. However, such disinfection is somewhat superficial since it fails to effectively attack and destroy the microorganisms found in the biofilm. Consequently, the disinfection effect is short-lived. After 24 hours of treatment with povidone-iodine, the numbers of bacteria are greatly reduced but quickly begin to rise after eight days. Related systems, such as those using iodinated ion-exchange resins, as in U.S. Pat. Nos. 5,556,279 and 5,320,624, also suffer from the same problem, i.e. the inability to penetrate the biofilm and destroy the resident organisms.
In an effort to penetrate and remove biofilms and related deposits, the Ultra-Kleen™ company markets a product based on an alkaline peroxide and a phase transfer catalyst, as taught in U.S. Pat. Nos. 4,847,089 4,941,989, 5,320,805 and 5,620,527. The product makes a claim as a specialty cleaner for dental unit water lines, rather than a more stringent disinfectant or sterilant. Several more potent germicides have been evaluated, including bleach and acidified bleach (U.S. Pat. No. 6,019,905), glutaraldehyde and an alkaline glutaraldehyde-phenolic disinfectant (U.S. Pat. No. 6,040,283), cetyl pyridinium chloride, peracetic acid, chlorhexidine and isopropanol. A recent report in the Journal of the American Dental Association (January, 1999) showed that 15-hours contact with household bleach (5.25%), glutaraldehyde (3%), or isopropanol (15.3%) resulted in effluents from biofilms that were free of recoverable bacteria, but that recolonization returned to pretreatment levels by day 3 for glutaraldehyde, day 6 for bleach, and day 15 for isopropanol. The report stated that the residual effect of these agents raises concerns about the slow release of potentially toxic substances from the residual biofilm matrix into water reaching the dental patient. Furthermore, while the agents temporarily reduce microorganisms in effluent water, they do little to destroy the biofilm matrix in the water lines, even with periodic treatments. A subsequent article suggested that weekly treatment with 5000 ppm chlorine (diluted bleach) coupled with the use of 3 ppm chlorinated water in the dental unit consistently attained the desired bacterial level of <200 cfu/ml. Two concerns arise however with this approach. One is that chlorine has been shown to elevate levels of trihalomethanes (THMs) and other chlorinated byproducts in water, where the EPA has placed limits on THMs in water. Additionally chlorine is a strong oxidant, and causes corrosion of most metals used in operatory equipment. While a 3 ppm level is of little concern, chlorine at the 5000 ppm level has significant corrosion potential for components of expensive dental equipment.
A so-called Stabilized Chlorine Dioxide (SCD) mouthrinse has recently been evaluated for the decontamination of the water line
Kross Robert D.
Wade William
Coleman Henry D.
Coleman Sudor Sapone, P.C.
Hruskoci Peter A.
LandOfFree
Methods for disinfecting small diameter water lines does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Methods for disinfecting small diameter water lines, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Methods for disinfecting small diameter water lines will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3083498