Abstract:
A dental handpiece having a filter unit containing a filter that minimizes the exposure of patients to pathogens found in the dental unit water lines (DUWL) while promoting frequent replacement of DUWL filters, by providing a disposable microfiltration filter that is easily replaced at low cost. A disk or membrane type filter is placed in a disconnectable autoclavable filter unit in the handle of an existing design dental instrument such that the form and function of the dental instrument are not adversely affected. The components of the handpiece, including the filter unit, are autoclavable, making the handpiece with its filter unit both economical to produce and ideal for its intended use.

Description:
REFERENCE TO RELATED APPLICATIONS 
     This is a continuation-in-part of parent patent application Ser. No. 09/670,252, entitled “Improved Dental Handpiece Filter Unit”, filed Sep. 26, 2000, now U.S. Pat. No. 6,379,150. The aforementioned application is hereby incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a handpiece filter unit for a dental instrument designed for use inside a patient&#39;s mouth, and in particular, to an in-line disk filter and filter handpiece for the type of a dental instrument that delivers water within a patient&#39;s mouth. 
     2. Description of Related Art 
     Dentists often use instruments, such as handpieces, ultrasonic scalers, or syringes, that deliver water and air into a patient&#39;s mouth during the course of a dental procedure. A pressing concern in the use of such instruments is the risk of infection created by disease-causing microorganisms (pathogens) which build up over the course of time in both the dental unit water line (DUWL) that supplies the instrument and in the tips of the instruments themselves. The DUWL typically extends from the dental instrument to a water source originating either from the municipal water supply or from bottled supplies within the dentist&#39;s office. Contamination is particularly promoted within DUWL&#39;s because the water in these lines is frequently stagnant since the water flows only when the instrument is in use. There are two principal sources of instrument contamination. The first source of contamination is the pathogens found in the water supply that attach themselves to the walls of the DUWL&#39;s. The second source of contamination is the pathogens that are sucked into the instrument and DUWL due to backflow from the patient&#39;s mouth (the point of use). 
     The way in which DUWL&#39;s become contaminated is well known. Basic principles of fluid mechanics dictate that zones of stagnation form around the perimeter of a DUWL. These zones exist because the velocity of flowing water is zero at the walls of the tube. In the absence of agitation, microorganisms breed and flourish in the form of thin biofilms. Found among these organisms are pathogens such as legionella, pseudomonas, and mycobacteria. Biofilms occasionally break off from the walls of the DUWL and float downstream into a patient&#39;s mouth, greatly increasing the risk of infection. Backflow is another significant source of pathogens. Backflow occurs when some of an infected patient&#39;s fluids are sucked into the tip of the instrument, eventually contaminating the entire instrument. The risk of pathogen transmission and infection becomes especially significant when immuno-compromised patients, such as HIV-positive victims and cancer victims, are exposed to water from the DUWL. 
     Conventional methods of sterilization fail to prevent the breeding and growth of pathogens in DUWL&#39;s. Simple liquid flushing does not solve the problem, as the biofilms are generally unaffected by flowing liquid. Likewise, flushing with biocide or other decontaminants is ineffective as many organisms are resistant to these chemical treatments. Finally, use of purified water sources to minimize the contaminants in the entering water flow is not a viable solution because pathogens multiply rapidly once the seal on the water supply is opened. 
     Autoclaving is the most effective method of contaminant control. Although the instrument or instrument head usually is detachable and therefore suitable for autoclaving, the DUWL&#39;s generally are not detachable and are too long and unwieldy to be autoclaved. In addition, DUWL&#39;s usually are not designed to withstand this sort of treatment. 
     Several attempts at filtering water flowing via the DUWL through the instrument have proven cumbersome and economically inefficient. 
     In Hansen, U.S. Pat. No. 4,950,159, a disposable cartridge filter is disclosed which uses activated charcoal in the filter. This material is ill suited for filtering the water in the DUWL because the pore size of activated charcoal is too large to effectively filter out pathogens. 
     In Johnston, et. al, U.S. Pat. No. 5,204,004, the filter is not placed in the handle and the DUWL must be cut in order to install a new filter. These limitations are likely to make the instrument cumbersome for a dentist to use and time-consuming to replace. Due to the position of the filter, it does not solve the backflow problem without the use of a separate check-valve or the chemical disinfection of the DUWL between patients, thus adding cost and complexity to its use. 
     In Dalrymple, et. al, U.S. Pat. No. 5,474,451, a series of air/water filter housings are disclosed. However, the filtering mechanisms entail a multivalent iodine resin/halogen scavenging system. The cost of this scheme precludes frequent replacement and disposal of the filter cartridges. In addition, several of the preferred water treatment embodiments require a filter manifold approximately two inches in length which makes the dental instrument unwieldy. This unwieldiness undercuts the purpose of dental instruments designed for easy manipulation within a patient&#39;s mouth. This approach also introduces chemicals into the water which is delivered to the patient&#39;s mouth. 
     In Wolf, et. al, U.S. Pat. No. 5,556,279, the filter is based on a chemical method of decontamination, thus making the filters more expensive and not amenable to frequent disposal. As in Dalrymple, this approach also introduces chemicals into the water which is delivered to the patient&#39;s mouth. 
     In Kinsel, U.S. Pat. No. 5,554,025, the filter is placed very close to the tip of the instrument, in close proximity to the point of use. While this is beneficial for decontamination purposes, it can make the instrument unwieldy due to the location of the filter housing. In addition, the proposed filter design is not suitable for the actual physical orientation of liquid and air tubes in a DUWL. This approach requires the entire filter and housing to be disposed of when changing filters, thus adding to cost. Also, while Kinsel&#39;s filter arrangement might be suitable for a dental syringe, it might not be suitable for a handpiece due to the greater volume of water required to cool a handpiece. 
     Novak, U.S. Pat. No. 5,716,210, is similar to the present invention in that there is a section inserted between the DUWL and the dental unit, which contains a filter. In Novak, each of the conduits pass through the filter cartridge, which makes the cartridge more complicated to machine and produce. The filter cartridge is disposable, not autoclavable. 
     In Hansen, U.S. Pat. No. 5,897,317, the filter cartridge is disposable. The filter cartridge filters, water, air, and the exhaust through a combination of filters. There are three cavities in the filter cartridge. The first cavity holds a filter for filtering air, the second cavity holds a filter for filtering water, and the third cavity holds a filter for filtering the exhaust. This configuration of the filter cartridge is potentially complicated and expensive to manufacture. 
     In Kipke et al., U.S. Pat. No. 5,908,296, a syringe includes a replaceable device for purifying water. The water-purifying device consists of disinfecting iodide beads in the tip of the syringe. 
     In Johnston et al., U.S. Pat. No. 5,961,326, a one-way valve protects a dental patient from bacteria. The valve is preferably combined with a filter. The valve is installed in the water line itself, and the waterline must be cut each time a new valve is installed. This limitation is likely to make the instrument cumbersome for a dentist to use and time-consuming to replace. 
     The presence and potential harm of pathogens in DUWL&#39;s and dental instruments are well documented and the American Dental Association has called for a solution. 
     U.S. Pat. No. 5,971,757, by the present inventors, discloses a disk or membrane type filter placed in an autoclavable filter unit in the handle of an existing design dental instrument such that the form and function of the dental instrument are not adversely affected. The filter unit, which fits in-line between the dental unit and the water line fitting, includes two portions that are detachably connected by an annular sleeve. When connected, a recess between the portions forms a recess that holds a microfiltration disk filter for filtering water that flows through the dental instrument before it reaches a patient&#39;s mouth. This design, while entirely functional, can be difficult and expensive to manufacture, because of the need to machine passages through a solid body for each fluid. 
     The parent application of which this application is a continuation-in-part, Ser. No. 09/670,252, entitled “Improved Dental Handpiece Filter Unit”, filed Sep. 26, 2000, which is incorporated herein by reference, addressed these problems through the use of a disk or membrane type filter, placed in a disconnectable autoclavable filter unit in a handpiece filter unit, which fits in-line between the dental unit and the water line fitting. While this approach is entirely functional, there is a need for a similar arrangement built in to the handpiece of the dental unit itself. 
     SUMMARY OF THE INVENTION 
     The present invention provides a dental handpiece having a filter unit containing a filter that minimizes the exposure of patients to pathogens found in the dental unit water lines (DUWL) while promoting frequent replacement of DUWL filters, by providing a disposable microfiltration filter that is easily replaced at low cost. A disk or membrane type filter is placed in a disconnectable autoclavable filter unit in the handle of an existing design dental instrument such that the form and function of the dental instrument are not adversely affected. The components of the handpiece, including the filter unit, are autoclavable, making the handpiece with its filter unit both economical to produce and ideal for its intended use. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a side view of the dental handpiece of the invention, with the cover on. 
     FIG. 2 shows a side view of the dental handpiece, with the cover removed, showing the filter housing and the tubing of the present invention. 
     FIG. 3 shows a view of one type of waterline connector for the present invention. 
     FIG. 4 shows an open view of the filter-housing unit of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention minimizes pathogen exposure by preventing pathogens within the dental unit water line (DUWL) from migrating to the patient&#39;s mouth and by permitting sterilization of filter-housing unit. Those pathogens in locations not subject to sterilization are filtered before reaching the patient&#39;s mouth. The water flowing in from the DUWL is filtered and both parts of the filter housing are readily autoclavable. In addition, the invention prevents pathogens from a patient&#39;s mouth from migrating into the DUWL. 
     FIG. 1 shows a dental handpiece ( 1 ) having a built-in handpiece filter unit of the invention. The operating part of the dental handpiece or drill ( 5 ) has a removable cover or housing ( 2 ), affixed to the drill portion ( 5 ) and the waterline connector ( 4 ) with set-screws ( 3 ), which forms a grip for comfortably holding the handpiece ( 1 ). It will be understood that the cover ( 2 ) could be threaded to the drill ( 5 ) or affixed with a bayonet fitting, tightly press-fit, or any other convenient method of attachment. It will also be understood that although the handpiece is here shown as a drill, the invention is equally applicable to syringes or ultrasonic scalers, or any other dental instrument having a water supply. 
     FIG. 2 shows the components which are located beneath the cover, which is removed for the figure. The handpiece filter unit ( 6 ), which is separable into two portions ( 7 ) and ( 8 ), which together form a filter chamber for housing a filter, connects to a water line connector ( 4 ), which is standardized to allow interconnection of the instrument to the dental unit waterline (DUWL). 
     In the embodiment shown in the drawing, two pieces of tubing ( 10 ) and ( 11 ) are attached to the waterline connector ( 4 ). A plastic tube ( 9 ) carries air to power the drill ( 5 ) from the connector tubing ( 11 ) into the drill portion ( 5 ). All of the tubing described herein is preferably either metal or plastic, reusable and autoclavable. Although two pieces of tubing are described in this example, any number of pieces of tubing necessary for transfer of air, and/or exhaust to and from the dental instrument would not deviate from the spirit of the invention as long as one of the pieces of tubing ( 10 ) was available to deliver fluid to the filter-housing unit ( 6 ). Tubing ( 10 ), which is the first half of the tubing through which water flows, transmits water from the waterline connector ( 4 ) into a filter-housing unit ( 6 ). The filter-housing unit ( 6 ) is divided into a first section ( 7 ) and a second section ( 8 ), which are separable, as will be seen in the discussion of FIG. 4, below. 
     Referring to FIG. 3, the waterline connector ( 4 ) of the handpiece typically includes a connector insert ( 35 ) which connects to the various fluid conduits discussed below, and a threaded or bayonet-equipped sleeve ( 36 ), which surrounds the insert ( 35 ) and connects it firmly to the mating threads on the waterline connector of the DUWL (not shown). 
     Water flows into the instrument through a dental unit water line (DUWL), flowing left to right in FIG.  1 . Water is typically used both to cool the tip of the dental instrument and to clear debris formed at a point of use (not shown) within a patient&#39;s mouth. The waterline conduit connects to a fitting ( 34 ) to allow water transfer into tube ( 10 ) and on through the dental instrument. Other conduits might include a line connecting to fitting ( 33 ) to supply pressurized air to power the instrument ( 5 ) through tubes ( 11 ) and ( 9 ), and possibly a fitting ( 32 ) to connect to a conduit to carry air exhaust away, and a fitting ( 31 ) to provide air for the aeration of water used within the patient&#39;s mouth (although in the embodiment shown, with only two tubes ( 10 ) and ( 11 ) entering the handpiece, fittings ( 31 ) and ( 32 ) are not used). This four-conduit arrangement is currently the most widely used in dentistry, and thus the four fitting plug is used, even if not all are connected. An optical fiber line (not shown) is sometimes provided as well, to supply illumination at the tip of the instrument. 
     It will be understood that the number and function of these conduits, the number of fittings on the waterline connector ( 2 ), the matching sockets on the second section of the waterline connector ( 2 ), and the number of pieces of tubing will vary according to the individual dentist&#39;s equipment. So long as there is a water line which requires filtering, adapting the invention to the arrangement of conduits is within the ability of one skilled in the art. 
     Referring to FIG. 4, the first section ( 7 ) of the filter-housing unit ( 6 ) has a conduit for receiving the waterline tubing ( 10 ). The first section ( 7 ) is adapted to hold an o-ring or ring washer ( 43 ) snugly within it, along with a microfiltration disk ( 41 ), and a screen ( 42 ) to hold the disk ( 41 ) rigid and in place during use. The microfiltration disk ( 41 ) is made of autoclavable filter material such as polyethersulfone, and preferably has a pore size of at most 0.22 μm. Water preferably leaves the microfiltration disk with less than 200 colony forming units per milliliter (cfu/mL) at a minimum flow rate of 50 milliliters per minute (mL/min). The filter is preferably disposable and inexpensive, although it could be made of a material which can be sterilized and replaced if desired. 
     The first section ( 7 ) also preferably has internal threading ( 45 ). This internal threading ( 45 ) interfits with threading ( 44 ) on the second section ( 8 ) of the filter-housing unit ( 6 ), allowing the filter-housing unit ( 6 ) to be tightly sealed. Alternatively, the coupling between the first section ( 7 ) and the second section ( 8 ) of the filter-housing unit ( 6 ) is achieved using protruding tubular portions that fit snugly into corresponding recesses in a male-female connection. The water leaves the second section ( 8 ) and is carried on into the handpiece ( 5 ) through tubing ( 12 ). 
     Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.