Patent Publication Number: US-2006003288-A1

Title: Impactor and paste feeder

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This application is a continuation of U.S. patent application Ser. No. 10/625,476 that was filed on Jul. 22, 2003 which claims priority of pending U.S. patent application Ser. No. 60/397,704 filed on Jul. 22, 2002 and entitled Impact Condenser Slurry Feeder. 
    
    
     TECHNICAL FIELD OF THE INVENTION  
      The present invention relates to paste feeders in general. The present invention is described in the context of medical devices, particularly dental devices and practices.  
     DESCRIPTION OF THE RELATED ART  
      Several different types of dental restorative materials, primarily mercury-containing silver alloys (also known as silver amalgams), gold foils, and polymeric fillings, are currently placed in situ in the dental office. In contrast, ceramic and solid gold restorations require laboratory preparation.  
      Currently, the predominant dental restorative or filling material is mercury-containing silver alloy because of its relative convenience and longevity. Unfortunately, mercury-containing silver alloy contains approximately 50 percent weight mercury, which has serious negative health consequences for patients, dental practitioners and the environment.  
      When silver amalgams are administered, patients and dental practitioners are exposed to mercury. When mercury-containing alloy fillings are removed, the patients can once again be exposed to mercury vapor. Further, these mercury-containing alloy fillings are discarded as waste, which causes serious environmental concerns as mercury waste can enter public water treatment plants.  
      The advantages of mercury-containing silver amalgam are its high strength, the bactericidal properties of its silver oxide, its low cost, and its suitability for an efficient in-office restoration. While a pure silver restoration exists (U.S. Pat. No. 5,711,866 to Lashmore) which meets the present need for a mercury-free alternative to mercury-containing amalgam, the drawbacks of the prior art precluded its commercialization. The present invention addresses and resolves these drawbacks and thus meets the existing need for a mercury-free restoration that can be successfully commercialized and that provides in one system a combination of advantages (superior safety, efficiency, effectiveness, convenience, ease of proper installation, and lower cost) that is not provided by any one commercially available alternative.  
     SUMMARY OF THE INVENTION  
      The present invention consists of an impactor, a paste feeder, thermally sealed disposable cartridges containing restorative paste, and a power supply. The impactor uses a solenoid-driven hammer to strike an anvil tip which contacts the restoration paste. The anvil tip welds the paste into a solid metal restoration in the cavity of a patient&#39;s tooth. The paste feeder can either be incorporated into the handle of the impactor or it can be part of a separate instrument. The cartridges contain a restoration paste of pure silver and dilute 2% tetrafluoroboric acid (HBF 4 ).  
      The purpose of this invention is to provide a safer, more precise, more effective, more efficient system for the placement of an in situ dental restoration that is free of mercury, gallium, and indium and that is inherently safer, better performing, longer lasting, easier to install properly, and more convenient than a silver-mercury restoration.  
      The present invention also provides a means of reducing the amount of mercury waste entering wastewater treatment systems, reducing waste water treatment requirements for dental practitioners, and reducing the amount of mercury waste released into the environment.  
      The present invention solves at least three problems in the prior art: (1) the time required to install the restoration, (2) the low density of the restoration when installed by hand instruments, and (3) the need to remove the activating solution during the condensation. The present invention solves these three problems by offering a means for automatically and rapidly injecting a paste of silver and dilute 2% tetrafluoroboric acid into the cavity of a patient&#39;s tooth and rapidly impact condensing the silver paste into a highly dense in situ restoration. With alternative embodiments of the subject impactor, gold foil or gold alloy powder is impact condensed into a gold restoration. The high density of the materials and short time to impact condense them solves the major problems in the prior art.  
      The present invention also has applications beyond that of dental restoration. For example, the impactor has a solenoid that can be scaled up and applied to the pressing of powders in larger powder metallurgy dies to mass-produce parts. The advantage of compacting powders with a repetitive impacting solenoid system is that very high impulse loading is obtained with relatively low static loads, resulting in parts of much higher density and lower part expansion in the die.  
      In an alternative embodiment of the present invention, the impactor is battery-powered making it ideal for veterinary and military applications and for general field use.  
      In another alternative embodiment, a paste feeder moves paste from a paste cartridge to a cavity in a patient&#39;s mouth. The paste feeder has a paste cartridge for holding a paste and a paste channel defining a cavity for holding the paste cartridge. The paste feeder also has a paste feeder tube, operatively connected between the paste channel and a dispensing tip. A ratcheting device of the paste feeder operatively connects to a plunger. The plunger moves the paste from the paste cartridge through the paste feeder tube to the dispensing tip in controlled incremental amounts. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      These and other features and advantages of the present invention will be better understood by reading the following detailed description, drawings, and claims, wherein:  
       FIG. 1  is a side view of an impactor having a head and a handle with a cross-sectional view through the head according to the present invention;  
       FIG. 2 , an enlarged, exploded view of the head of the impactor shown in  FIG. 1 , shows a solenoid, hammer, anvil, and end cap;  
       FIG. 3  is a side view of the hammer of the impactor;  
       FIG. 4  is a side view of a second alternative embodiment of a paste feeder; and  
       FIG. 5  is a side view of a third alternative embodiment of a paste feeder. 
    
    
     DETAILED DESCRIPTION  
      U.S. Pat. No. 5,711,866 to Lashmore, which is hereby incorporated by reference, is a process for providing a mercury-free in situ dental restoration. The process uses hand pressure to condense paste of gold, silver or silver alloys and an activation solution of dilute 2% tetrafluoroboric acid. The tetrafluoroboric acid is a flux to remove the oxide during condensation, enabling the silver particles to cold weld to each other. Concentrations of the activation solution range from 0.5% to about 10%; an optimal concentration is about 2%. Particle sizes range from about 5 microns to about 50 microns. Both the silver and gold powders or foils are well annealed. The process offers a low cost, superior alternative to mercury-containing restorations. The principal drawbacks are the time required to install the restoration, the low density of the restoration when installed by hand instruments, and the need to remove the activation solution during the condensation.  
      The present invention addresses and resolves these drawbacks. An impactor  10  according to the present invention is shown in  FIG. 1 . The impactor  10  has a handle  20  and a head  30 . The handle  20  has a cavity  40  for receiving a removable paste cartridge  22 . The paste cartridge  22  holds paste and is either disposable or reusable. The paste cartridge  22  is pressurized as described below. In the disposable embodiment, the paste cartridge  22  is preferably heat sealed for long-term storage, and both ends of the paste cartridge  22  are cut open prior to insertion into the cavity  40  of the handle  20  or other paste feeding system.  
      The paste preferably has a combination of silver and activation solution. In the preferred embodiment, the activation solution is dilute 2% tetrafluoroboric (HBF 4 ) acid. Alternatively, the paste has a silver alloy or gold alloy. Gold foil combined with the activation solution may be used in lieu of the paste but would require hand placement. The resultant silver, gold-alloy powder, or gold foil is condensed in the cavity of a patient&#39;s tooth. This technology is designed to repair the damage caused by decay or corrosion of existing fillings.  
      The paste is fed into the cavity of the patient&#39;s tooth with either a pneumatic or a mechanical feeder. In an exemplary embodiment, a paste feeder tube  24  is used to transport the paste from the paste cartridge  22  to a paste dispensing tip  15  which is located adjacent to an anvil  32  which extends from the head  30 . The paste feeder tube  24  may extend along, in, or be integral to, the handle  20 . When the paste feeder tube  24  extends along the handle  20  and the head  30 , grooves (not shown) on the exterior of the handle are used to receive and secure the paste feeder tube  24  thereto. Clips (not shown) could be used in lieu of the grooves. When assembled, the paste cartridge  22  and paste feeder tube  24  are sealed, creating a pressurized capsule. The paste is forced from the paste cartridge  22  through the paste feeder tube  24  to the paste dispensing tip  15  via a pneumatic supply source (not shown). The supply source, known to those having ordinary skill in the art, is operatively attached to the paste cartridge  22  and/or paste feeder tube  24  via a pneumatic control valve  53  or other similar means. The pneumatic control valve  53  controls the flow of air in the paste feeder tube  24 . The dental practitioner uses the pneumatic control valve  53  to control the air pressure from the supply source to urge or force the paste from the paste cartridge  22  to the anvil tip  32   a  and ultimately into the cavity of the patient&#39;s tooth. This valve  53  is preferably located on the handle  20  of the device. The valve  53  could also be a foot activated valve.  
      In a first alternative embodiment, the paste feeder tube  24  is operatively connected to an external source of paste material instead of the paste cartridge  22 . In a second alternative embodiment, a mechanical paste feeder  50 ,  FIG. 4 , is used to allow preliminary condensation of the paste prior to contact by the anvil  32 . A spring  51  pushes a plunger  54 , which forces a certain amount of the paste, as determined by the operator, into the paste feeder tube  24 . An ejector pin  52  forces the paste in the feeder  50  into the cavity of the patient&#39;s tooth and applies pressure onto the dispensed paste until the operator starts the condensation process. The mechanical paste feeder  50  delivers the same amount of material each time it is activated, pre-compacts the paste, and eliminates the need for a pneumatic supply source.  
      The head  30  has a housing  35  made of a corrosion-resistant material, such as nonmagnetic stainless steel, preferably  316  stainless steel, or a polymer such as Teflon®, nylon, or Vespel®. The housing  35 ,  FIG. 2 , has a diameter of approximately 0.5 of an inch, and a height of approximately 0.75 of an inch although such dimensions are not a limitation to the present invention. The housing  35  has an opening  42  for receiving the anvil  32  and a threaded hole  59  for receiving a set screw  41 . The set screw  41  is used to hold the anvil  32  in place during use and to release the anvil  32  during non-use. One of the ends of the set screw  41  almost contacts the anvil  32  between stops  58 . The anvil  32  is allowed to move vertically while the set screw  41  and the stops  58  limit the vertical movement. There are other devices for holding and releasing the anvil  32 , such as a spring clip (not shown), which can be substituted for the set screw  41 . The set screw  41  or spring clip allows efficient removal of the anvil  32  and other parts of the impactor  10  for cleaning and sterilization.  
      The anvil tip  32   a  may be flat, serrated, rounded, concave, or shaped in any other configuration desired by the dental practitioner to access portions of the cavity that are difficult to reach. The anvil tip  32   a  directly contacts the paste or filling material during impaction. The anvil tip  32   a  may have a smaller diameter than a remaining portion of the anvil  32  and thus may form a small ledge near a bottom of the anvil  32 , which acts as a pump to help move the paste to the anvil tip  32   a.    
      The solenoid  31  is operatively mounted between an end cap  49  and the housing  35 . In one embodiment, the solenoid  31  is bonded into the housing  35 . The solenoid  31  generates impact energy which is small but powerful. Alternatively, the impact energy is generated by a piezoelectric transducer, a magnetostrictive transducer, an electrostatic transducer, a small electric motor driving a cam, or a pneumatic transducer. Other solenoids that are known by those having ordinary skill in the art include full conical, tapered plunger, and cylindrical magnet types. Herbert C. Roters, Electromagnetic Devices, 1 st  ed., John Wiley and Sons Inc., New York, 1941, p. 228, which is hereby incorporated by reference, describes some of these devices. The static force is about 8 pounds and the impact force is about 16 pounds. The frequency varies from 5 hertz (Hz) to 20 Hz, preferably around 8 Hz to 10 Hz.  
      In the preferred embodiment, a solenoid control unit (not shown) is operatively connected to the solenoid  31 . The solenoid control unit provides current pulses for controlling the solenoid  31 .  
      A constant current waveform is used to drive the solenoid  31 . The waveform frequency varies from approximately 5 Hz to approximately 20 Hz. In the preferred embodiment, the waveform frequency is approximately 10 Hz. A pulsed current is ideally timed to turn on when a hammer  33  is furthest from the top surface  44  of the solenoid  31 ; however, a free running waveform is also possible. This waveform is preferably a square wave; however, the waveform can be sinusoid. A 110V ac driven system and battery driven system can be substituted for the constant current waveform.  
      The solenoid  31  includes a stator  31   a.  The stator  31   a  is made from a soft magnetic material such as a silicon iron alloy. The stator  31   a  has a coil pocket with a preformed copper coil capable of supporting approximately 200 amp turns. Alternately, the stator  31   a  may be made of an encapsulated soft magnetic material such as Somalloy 500 (from Haganous in Sweden). The preformed copper coil is injection molded and sealed so that the entire unit can be taken apart and sterilized.  
      The hammer  33  includes portions  45  and  46  made from a hardened steel, steel, or preferably Inconel®. Bonded to the horizontal portion  45  of the hammer  33  is a top surface  44 . The top surface  44  is made of a soft magnetic material such as 2.5% SiFe, silicon iron alloys, phosphorus-containing iron alloy, nickel, chromium, iron alloy, iron polymer composite, iron-inorganic coated composites, iron phosphorus, or iron aluminum alloy. The hammer  33  is “T” shaped in the preferred embodiment as shown in  FIG. 3 . The hammer  33  has a horizontal portion  45  and a vertical portion  46 . In the preferred embodiment, the horizontal portion  45  is an Inconel® disk integrated with the vertical portion  46  and machined out of a single piece of Inconel® to which the soft magnetic disk is bonded.  
      A bottom surface of the horizontal portion  45  is above the top surface  44  of the solenoid  31 , shown in  FIG. 2 . The solenoid  31  has a slot  47  and an inner surface of the slot  47  has a sleeve bearing  34  thereon. The sleeve bearing  34  of the slot  47  receives the vertical portion  46  of the hammer  33 . The vertical portion  46  extends beyond the bottom surface  43  of the solenoid  31  and is used to strike or contact the anvil  32 . The vertical portion  46  of the hammer  33  slides up and down in the sleeve bearing  34  of the slot  47 . The sleeve bearing  34  can be made of any suitable material, such as a phosphorous bronze or polytetraflouethylene (PTFE or Teflon®). The vertical portion  46  of the hammer  33  is in contact with a top surface  48  of the anvil  32 .  
      The hammer  33  is forced downward by a magnetic attraction created by the solenoid  31 . When the hammer  33  is forced downward by the solenoid  31 , the vertical portion  46  of the hammer  33  strikes the anvil  32 , thereby driving the anvil  32  into the paste. The solenoid  31  has a static force of about 8 pounds at contact. The hammer  33  moves upward because of the elastic rebound following the collision with the anvil  32 . The rebound from this impact serves as a return spring.  
      When the hammer  33  moves up and down in the sleeve bearing  34  of the slot  47 , the hammer  33  moves a vertical distance between approximately 0.010 to 0.040 of an inch. In the preferred embodiment, the hammer  33  moves a vertical distance of approximately 0.020 of an inch. The hammer  33  is restricted in its downward movement by the top surface  48  of the anvil  32  and in its upward movement by the end cap  49 . The hammer  33  drives the anvil  32 , thereby providing impulse loading to a silver powder in the paste, which was previously fed through the paste feeder tube  24  to the cavity in the patient&#39;s tooth, causing it to cold weld together into a dense filling.  
      The end cap  49  is removably mounted to the housing  35 . In the preferred embodiment, the end cap  49  is screwed onto the housing  35 . The end cap  49  and the housing  35  have mating threads. In an alternative embodiment, the end cap  49  is fastened to the housing  35  with spring clips (not shown).  
      A power supply (not shown) is used to give the dental practitioner the ability to independently control the force and the frequency of the impact of the anvil  32  by providing a series of current (voltage) pulses that periodically turn the electromagnet of the solenoid  31  on and off.  
      The power supply is a free running square wave current source or waveform synchronized with the position of the hammer  31 , thereby turning on the current when the hammer  31  is furthest from the top surface  44  of the solenoid  31 . The frequency ranges from 5 Hz to 20 Hz, preferably around 10 Hz. The current waveform is approximately a square-wave and is achieved by rapidly switching a constant current power supply at the desired frequency. Both the magnitude of the current and the frequency can be varied. It is possible to drive the solenoid  31  with a constant voltage waveform.  
      The frequency of this current waveform varies from approximately 5 Hz to approximately 20 Hz. The most desirable frequency is approximately 10 Hz, although this device can operate at frequencies up to 1000 Hz. A 110V ac driven system or a battery driven system can be used to drive the solenoid  31 .  
      A suction tube  37  has a first end  37   a  operatively attached to the housing  35  and a second end operatively attached to a vacuum system  36 . The vacuum system  36  is preferably a continuously operating system. The suction tube  37  has a hollow core for removing liquids, semi-liquids, solids, and foreign matter from the patient&#39;s mouth. The first end  37   a  of the suction tube  37  is proximate to the anvil tip  32   a  of the anvil  32 . The vacuum system  36  creates suction or a vacuum for removing the activation solution of the paste once the silver is condensed.  
      A separate vacuum system (not shown) known to those having ordinary skill in the art can be used for removing the patient&#39;s saliva, paste, particles from the removed filling, and other matter from the patient&#39;s mouth.  
      The external parts of the impactor  10  are stainless steel or as otherwise indicated herein, and the internal parts are removable for sterilization.  
      In an alternative embodiment, the impactor  10  is also used for cold welding, including solder bonding with pure silver or pure gold, thereby eliminating lead from the workplace and the undesirable side effects of tin, such as whisker formation and inter-metallic development.  
      In another alternative embodiment, the impactor  10  is scaled up to approximately 15 inches or greater in diameter and used to compact metal powders in a powder metallurgy die. The effective stress under the anvil  32  is greater than a factor of two and greater than the static stress under the solenoid  31 , thereby magnifying the compaction and increasing density. For example, if the solenoid  31  is increased to 20 inches in diameter, the solenoid  31  will produce a compaction stress of over 14 tons. This compaction could then be repeated as often as required to obtain the required density.  
      The impactor  10  is assembled by placing the anvil  32  in the opening  42  of the housing  35 . The anvil  32  is secured to the housing  35  via the set screw  41 . One of the ends of the set screw  41  contacts the anvil  32  between the stops  58 . The anvil  32  is allowed to move vertically but the set screw  41  and the stops  58  limit the vertical movement. The solenoid  31  is placed on the anvil  32  so that the slot  47  receives the top portion  48  of the anvil  32 . The vertical portion  46  of the hammer  33  is placed through the slot  47  having the sleeve bearing  34  and rests on the top portion  48  of the anvil  32 . The end cap  49  is secured to the housing  35 .  
      To operate the impactor  10 , one or more of the ends of the paste cartridge  22  are cut, and the paste cartridge  22  is placed into the cavity  40  of the handle  20 . The solenoid  31  is periodically activated via the power unit or pneumatic control unit. When the solenoid  31  is activated, the hammer  33  is forced downward by a magnetic attraction created by the solenoid  31 . When the hammer  33  is forced downward by the solenoid  31 , the vertical portion  46  of the hammer  33  strikes the anvil  32 , thereby driving the anvil  32  into the paste. The periodic impulse causes a high contact stress sufficient to condense the layer of metal paste to a high-density metal suitable for dental restorations. After the collision between the hammer  33  and the anvil  32 , the hammer  33  moves upward because of the elastic rebound. The rebound from this impact serves as a return spring. Layers of paste are impacted until the cavity in the patient&#39;s tooth is filled.  
      In a third alternative embodiment, a mechanical paste feeder  60 ,  FIG. 5 , is used to feed paste into the cavity of the patient. The mechanical paste feeder  60  provides an accurate application of the paste into the cavity of the patient&#39;s tooth. The operator squeezes the handle  62  in the direction of the arrow shown in  FIG. 5 . The handle  62  drives a plunger  64  forward, compressing the paste with the paste feeder tube  66 . The compacted paste is forced out of an aperture at the tip  68  of the paste feeder tube  66 . The plunger  64  has a saw tooth profile  69  that allows a racket  70  driven by the handle  62  to drive the plunger  64 . The saw tooth profile  69  allows a predetermined amount of paste to be ejected from the paste feeder tube  66 . The distance the plunger  64  is driven forward is controlled by the period of the saw tooth profile  69 . For example, increasing the period of the saw tooth would increase the distance the plunger  64  is driven forward and hence eject a greater amount of paste from the paste feeder tube  66 . The saw tooth profile  69  is not limited to having a constant period. The period of the saw tooth profile  69  may gradually decrease, providing the operator with decreasing amounts of paste for each squeeze of the handle as the cavity fills with paste.  
      Once the paste feeder tube  66  is empty, the mechanical paste feeder  60  may be reloaded with paste by the operator. The operator removes the tip  68  of the mechanical paste feeder  60 . The tip  68  may be removable and coupled to the mechanical paste feeder by screwing off the tip  68  from threads on the paste feeder tube  66 . The tip  68  may also be coupled to the paste feeder tube  66  using a variety of other coupling devices, for example, but not limited to a snap fitting or frictional fitting. Prior to adding paste to the paste feeder tube  66 , the operator may press a release switch  72  and pull backwards on the rear end of the plunger  64 , thus pulling the plunger to the rear and allowing room within the paste feeder tube  66  to add additional paste. The paste may be added to the paste feeder tube  66  via a cartridge or other device designed for handling the paste.  
      Once paste is added to the paste feeder tube  66 , the tip  68  is coupled back onto the mechanical paste feeder  60 . The operator may squeeze the handle  62  initially to advance the plunger  64  forward and compact the paste within the paste feeder tube  66 . A pistol grip may be used to allow the operator to ergonomically hold the mechanical paste feeder  60  and position the tip  68  into the cavity of the patient&#39;s tooth. The operator squeezes the handle  62  allowing the plunger to ratchet forward and drive the paste within the paste feeder tube  66  out of the aperture. As previously discussed, the saw tooth profile  69  provides a precise amount of ejected paste. A spring  74  may be used to drive the ratchet  70  and handle back into position, thereby allowing the operator to repeatedly squeeze the handle and provide additional precise amounts of ejected paste into the cavity.  
      Modifications and substitutions by one of ordinary skill in the art are considered to be within the scope of the present invention.