Chemical apparatus and process disinfecting – deodorizing – preser – Process disinfecting – preserving – deodorizing – or sterilizing – Using disinfecting or sterilizing substance
Reexamination Certificate
1999-07-30
2003-04-29
Warden, Sr., Robert J. (Department: 1744)
Chemical apparatus and process disinfecting, deodorizing, preser
Process disinfecting, preserving, deodorizing, or sterilizing
Using disinfecting or sterilizing substance
C422S022000, C422S029000, C422S062000, C422S198000, C422S292000, C422S305000, C134S002000, C134S102100, C134S022100, C134S107000, C134S036000, C134S042000, C210S136000, C210S177000, C210S205000, C210S759000, C210S764000, C210S766000, C205S343000, C205S464000, C205S628000, C205S687000, C205S701000, C205S742000, C204S266000, C204S269000, C204S270000, C204S271000, C204S274000, C204S278000
Reexamination Certificate
active
06555055
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the prevention and remediation of biofilms in dental equipment.
BACKGROUND OF THE INVENTION
Over the years the dental services community has become aware that the water systems currently designed for general dental practice do not deliver water of an optimal microbiological quality. It has been documented that dental unit waterlines harbor a wide variety of microorganisms including bacteria, fungi, and protozoans, which adhere to the interior surfaces of the waterline tubing to form colonies.
The American Dental Association (ADA) has recommended an ambitious and aggressive effort to encourage industry and independent researchers to improve the design of dental equipment by the year 2000 so that water delivered to patients during nonsurgical dental procedures contains no more than 200 colony forming units (cfu) of aerobic mesophilic heteretrophic bacteria per milliliter at any time in the unfiltered output of the dental unit (equivalent to an existing quality assurance standard for dialysate fluid in hemodyalisis units). This represents a massive decrease in microbial contamination of dental unit water from values that frequently run over 10,000 cfu/mL under current practice.
The organisms that currently contaminate dental units originate from a variety of sources, but the water lines of dental units represent the largest single source of biofilms. These biofilms live on the luminal walls of the water lines within the dental unit itself. The presence of adherent microbial biofilms in dental unit water lines was first reported more than 30 years ago. Interest in this issue has recently escalated throughout the world because many studies have confirmed the magnitude and widespread occurrence of contamination. In fact, one study found that the water coming out of dental unit water lines was of uniformly poorer quality than water coming out of taps in the same rooms.
The predominant organisms in dental water lines are Pseudomonas and Legionella species. Pseudomnonas are the most common organisms, but Legionella represent perhaps the most dangerous of the organisms routinely found in dental unit water lines (DUWLs). In one recent study, Legionella organisms were found in 29 out of 47 dental units tested. In many cases the organisms were present at a concentration of >10
3
per 10 mL sample.
The fact that aerosols generated from water within dental operatories are the source responsible for the elevated seropositivity to Legionella antibodies for dental personnel has been confirmed by several research studies. An Austrian serological study analyzing samples from 107 dentists, dental assistants and technicians found that thirty four percent (34%) tested positive to the polyvalent
L. pneumophila
antigen (the species considered most pathogenic to humans) comparing to only five percent (5%) from a non-medical workers control group. The highest prevalence (50%) was demonstrated among dentists, followed by assistants (38%) and technicians (20%). In an analogous study in the United States, 20% of the students and employees at a dental clinic in Virginia were seropositive for Legionella antibodies. Even though the higher seroprevalence rates have not been directly correlated with higher rates of disease among dental personnel, investigators speculate that it may reflect continuous exposure to small numbers of organisms resulting in mild (Pontiac fever) or inapparent infections.
Microbiologists have traditionally focused on free-floating bacteria growing in laboratory cultures. Recently they have realized that 99% of bacterial activity in open ecosystems occurs in biofilms adhered to surfaces. By 1990, researchers confirmed that biofilm bacteria are morphologically and metabolically distinct from free-floating ones, and that any bacterium can form a biofilm, once it finds a place to stick. As a result, biofilms, which were once considered odd curiosities, today are one of the hottest topics in microbiology since their occurrence has consequences for everything from medical technology to oil recovery.
Any solid surface immersed in an aquatic environment immediately serves as an adhesion site for macromolecules and other, low-molecular-weight hydrophobic molecules present in the water. This forms a so-called conditioning film which alters surface characteristics (such as hydrophobicity) and enhances the efficiency of subsequent bacterial adhesion.
The fundamental process of biofilm formation may be either passive or active. Some microorganisms already possess the necessary tools, such as extracellular polymeric substances or fimbriae and can immediately passively attach to a surface. Other bacteria require prolonged exposure to the surface to attach firmly. The active biofilm formation is a time-dependent process that begins with an initial reversible association between the microbe and the surface. During this period a genetic cascade is set off that turns on specific genes to make polysaccharides.
Due to the secretion of these substances and subsequent microbial multiplication, an irreversible adhesion and colonization of the surface is achieved. The production of a continuous fixed biofilm on the surface is then a function of cell division within the described polymeric matrix and can include the physical inclusion of other bacteria, fungi and protozoa from the free-floating microbial community of the surrounding water. All this eventually creates a slime layer composed of columns permeated by water-filled spaces through which materials and microbial by-products flow. The attached microbes have several survival advantages, in comparison to free-floating microorganisms.
Dental water lines, with their high surface-to-volume ratio, intermittent pattern of operation (with short periods of flow alternating with long, stagnant periods), and the characteristic of fluid dynamics in narrow, smooth-walled channels with only laminar flow, provide an ideal environment for microbial colonization.
The recognition of this health threat comes at the same time as an increasing awareness of potential occupational hazards in the dental office and concerns about increasing numbers of immunocompromised patients, such as elderly people, people with AIDS, cancer patients, diabetics, persons with chronic organic disorders or autoimmune diseases, and people who have received organ transplants or have recently received blood transfusions, all of whom have diminished resistance to opportunistic pathogens. All of these factors provide motivation for improving the quality of water for dental procedures.
Current methods for reducing water contamination are based on purging water lines for an extended period daily and a short period between patients or using independent water systems. The former method requires diligently following the procedure, and only reduces the bacterial count temporarily, and even then the reduction is not enough to meet the new standards. The latter method is only effective until the water system is contaminated once, and is then no better than using tap water.
Semiautomatic chemical treatments have been introduced that can be effective, but they require regular attention to keep the system filled with the disinfecting agent, and require an inventory of the agent be kept on hand at all times.
The current recommendations from the CDC for reducing the risk of contamination from dental unit water lines (DUWLs) involve a series of steps that must be followed conscientiously if they are to succeed. The first of these is the installation and use of anti-retraction valves (check valves to limit flow in a line to one direction) on all water and air lines. These devices prevent saliva and other fluids from the patient from being sucked back into water lines and colonizing the biofilm present in the water line. This is a concern because saliva from a patient's mouth is more likely to contain pathogenic organisms than the incoming water from a municipal water system. Accordingly, these valves must be regularly maintained to remain effective.
Cisar Alan J.
Denvir Adrain
Hitchens G. Duncan
Rogers Thomas D.
Chorbaji Monzer R.
Lynntech Inc.
Streets Jeffrey L.
Streets & Steele
Warden, Sr. Robert J.
LandOfFree
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