Abstract:
A dispenser for dispensing extrudable material from a cartridge. The dispenser includes a housing having a first recess for holding the cartridge, a plunger movable along the longitudinal axis of the first recess, a driver element for selectively engaging and moving the plunger in a forward direction along the longitudinal axis, and a clutch element for and selectively engaging the plunger to restrain movement of the plunger in a rearward direction. When the clutch element restrains the plunger, movement of the plunger in the rearward direction is limited to a predetermined distance.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    The present application claims priority under 35 U.S.C. § 119(e) from U.S. Serial No. 60/415,020, filed on Oct. 1, 2002. U.S. Serial No. 60/415,020 was filed by inventors common to the present application, and is hereby incorporated by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to a hand-held dispenser for extruding composite dental materials, and in a particular to a hand held dispenser for avoiding continued extrusion of material following actuation of the dispenser.  
         BACKGROUND OF THE INVENTION  
         [0003]    A variety of materials are commonly used in the field of dental treatment, including impression materials, filling materials, and adhering materials. Often, these materials are formed at or near the time of use from a combination of two or more kinds of component materials. For example, dentists or dental technicians may remove required amounts of the component materials from their respective containers (for example, by weight, volume or length) and place these on a mixing pad to be mixed with each other and put into use. These mixed materials may then be placed in a cartridge suitable for application using a dispenser. In other cases, non-composite and pre-mixed dental materials may be directly provided by manufacturers in dispenser cartridges.  
           [0004]    Conventional dispensers may use a variety of means for extruding these mixed materials from a cartridge. For example, a pistol-shaped cartridge dispenser maybe used that positions the cartridge in a predetermined position at the front of the device, and employs a piston coupled to a push rod for pressing against the mixed material from an opening in the rear of the tube in order to extrude the mixed material from a nozzle positioned at the front of the tube. The piston and push rod typically move in response to a mechanical force directly applied to the dispenser by a human operator, and may alternatively move in response to a force applied by other means (for example, supplied by a pressurized fluid or electric motor).  
           [0005]    When operating such dispensers, it is desirable to precisely control the amount of material that is extruded. If an excess of material is supplied (over-extruded), for example, the dentist or dental technician will be required to remove the over-extruded material. This creates additional work for the dentist or dental technician, and may be difficult, for example, if the extruded material is a composition that hardens quickly once extruded. Removing over-extruded material may also create discomfort and or unwanted delay for the dental patient. In particular, it is desirable to avoid continued extrusion of material from the dispenser after actuation ceases (“drooling”).  
         SUMMARY OF THE INVENTION  
         [0006]    The deficiencies of the prior art may be largely overcome by a novel dental composite dispenser having a mechanism for reducing drooling. In a preferred embodiment, the dispenser comprises a handle having a frontward cavity for positioning a cartridge, a piston for extruding material from the tube and a push rod for driving the piston. A driver element positioned in the housing comprises a block bored with a hole through which the push rod is inserted, the hole having a size slightly larger than that of an outer diameter of the push rod. The block, for example, may comprise a stamped metal leaf, or a stack of such leaves.  
           [0007]    An actuator in the handle is brought into contact with a lower portion of the driver element, causing the driver element to incline and the push rod to come into contact with an edge of the hole. The actuator then causes the driver element to advance, such that a contact resistance (friction) resulting from an edge of the hole contacting the push rod advances the push rod with the driver element. Once the trigger is released, a driver spring returns the driver element to a non-inclined position so that the push rod is able to move freely through the hole in the driver element.  
           [0008]    A clutch element positioned in the housing comprises a plate bored with a hole through which the push rod is inserted, the hole having a size slightly larger than that of the outer diameter of the push rod. The clutch element is pivotally fixed in a recess in the housing above the push rod, and remains in a non-inclined position as the push rod is advanced. Once the actuator is released, compressive energy retained in the cartridge causes push rod and the driver element to move rearward. The clutch element, urged by a clutch spring, inclines to cause the push rod to engage an edge of the hole in the clutch element. Contact resistance between the clutch element and the push rod limits rearward travel of the push rod to a distance controlled by the geometry of a cavity in the housing for confining movement of the clutch element.  
           [0009]    The clutch element is located forward of the actuator and driving mechanism to facilitate compactness of the dispenser, and has a portion extending through a hood of the dispenser which can be pushed by finger pressure in order to return the clutch element to its non-inclined position, and thereby remove contact resistance between the clutch element and push rod so that the push rod may be retracted to its most rearward position in order, for example, to remove a spent cartridge from the dispenser and install a new cartridge. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0010]    A more complete understanding of the invention may be obtained by reading the following description of specific illustrative embodiments of the invention in conjunction with the appended drawing in which:  
         [0011]    FIGS.  1 A- 1 D respectively show front, side sectional, rear and top isometric views of a first embodiment of the present invention; and  
         [0012]    [0012]FIG. 2 shows an exploded perspective view of the embodiment of FIGS.  1 A- 1 D. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]    The following detailed description includes a description of the best mode or modes of the invention presently contemplated. Such description is not intended to be understood in a limiting sense, but to be an example of the invention presented solely for illustration thereof, and by reference to which in connection with the following description and the accompanying drawings one skilled in the art may be advised of the advantages and construction of the invention.  
         [0014]    With reference to FIGS.  1 A- 1 D and  2 , a dispenser  100  is disclosed comprising a handle  7  having a forward recess  20  for holding a dental material cartridge  4 , and a bottom recess  21  for mounting an actuator  18 , rotatable around fulcrum  19  such that an operator is able to squeeze actuator  18  and rear portion  22  of handle  7  in order to rotate actuator  18 . Tensile spring  15  is fastened at one end to actuator  18  and at another end to spring holder  16 , fixed near a bottom area of rear portion  22 , in order for tensile spring  15  to generate a tensile force for returning actuator  18  to a rest position as actuator  18  is released by the operator.  
         [0015]    Dispenser  100  further comprises a plunger stop  17  fastened to a forward end of a push rod  12 , for example, by screw  13 . Push rod  12  and plunger stop  17  extend from a rearward recess  23  of the handle  7 , and cart ridge  4  is positioned in forward recess  20  such that longitudinal axes of push rod  12 , plunger stop  17  and cartridge  4  are coincident. Piston  10  may be, for example, inserted into an open, rearward end of cartridge  4  so that plunger stop  17  may be driven against piston  10  in order to extrude material through a front nozzle  24  of cartridge  4 . Piston  10  provides a seal against an inner circumference of cartridge  4  so that substantially no material is extended at the rearward end of cartridge  4  when piston  10  is driven by plunger stop  17 .  
         [0016]    Bearing  1  is retained in a rearward cavity  23   a  of rearward recess  23  and incorporates a bore  1   a  for receiving push rod  12  with a slip fit. Bearing  1  operates in conjunction with plunger stop  17  to laterally contain push rod  12  so that push rod  12  may be moved along its longitudinal axis. Portions of rear recess  23  may also restrain push rod  12  to travel along its longitudinal axis.  
         [0017]    Push rod handle  8  is fastened, for example by means of screw  14 , to a rearmost end of push rod  12  extending through rear portion  22  in order to provide a means for the operator to manually adjust the position  10  pushrod  12  (for example, to withdraw push rod  12  to a rearmost position in order to remove and replace cartridge  4 ).  
         [0018]    A driver element  6  is positioned in a second cavity  23   b  of rear recess  23 , adjacent to bearing  1 . Driver element  6  comprises a block having a bore  6   a  with a hole through which the push rod is inserted, the bore  6   a  having a size slightly larger than that of an outer diameter of the push rod. An upper cam portion  25  of actuator  18  is positioned to come into contact with a lower portion of a rearward surface of driver element  6 , such that, when actuator  18  is squeezed by the operator, upper cam portion  25  rotates, engages the rearward surface of driver element  6 , and causes driver element  6  to incline so that push rod  12  comes into contact with an edge of the hole in driver element  6 . Further rotation of upper cam portion  25  causes driver element  6  to advance, such that a contact resistance (friction) produced at the edge of bore  6   a  contacting push rod  12  causes push rod  12  to advance together with driver element  6 . As push rod  12  advances, plunger stop  17  urges piston  10  forward in cartridge  4  so that composite material is extruded at nozzle  24 .  
         [0019]    Divider  5  is fixedly mounted in a third cavity  23   c  in rearward recess  23  adjacent to the second cavity  23   b . Divider  5  provides a rear-facing stop surface for receiving driver spring  11 . Driver spring  11  contacts a frontward surface of driver element  6  and compresses as driver element  6  advances, thereby generating a force to return driver element  6  to a non-inclined state upon release of actuator  18  by the operator and to return driver element  6  to a position in rearward recess  23  wherein the rearward surface of driver element  6  remains in contact with bearing  1  in its rest position. Bearing  1  includes a slot  1   b  through which upper cam portion  25  is moved to engage the lower portion of the rearward surface of driver element  6 .  
         [0020]    A clutch element  3  is located in a fourth cavity  23   d  in rearward recess  23  adjacent to divider  5 . Clutch element  3  comprises a plate having a bore  3   a  through which push rod  12  is inserted, bore  3   a  having a size slightly larger than that of the outer diameter of push rod  12 . Clutch element  3  is pivotally confined within the fourth cavity  23   d  by tabs  3   d . Lever  3   b  of clutch element  3  is inserted through a recess  9   a  of hood  9 , which is fixedly snapped into position over rearward recess  23 . A lower frontward surface  3   c  of clutch element  3  is biased by clutch spring  2  so that clutch element  3  remains in a non-inclined position as push rod  12  is advanced by an operator squeezing actuator  18 . Once actuator  18  is released, driver spring  11  causes driver element  6  and push rod  12  to move rearward so that driver element  6  and push rod  12  disengage, and with the assistance of clutch spring  2 , clutch element  3  inclines, causing push rod  12  to come into contact with an edge of bore  3   a . Contact resistance between bore  3   a  and push rod  12  limits rearward travel of push rod  12  to a distance Y controlled by the geometry of the fourth cavity relative to a compressed length of clutch spring  2  and the position of divider  5 .  
         [0021]    As push rod  12  moves rearward, clutch element  3  also moves rearward a distance Y defined by the difference between a thickness of slot  23   d  and a thickness of the portion of clutch element  3  positioned in slot  23   d . Biased by clutch spring  2 , clutch element  3  also inclines. As a result, a contact resistance between bore  3   a  and push rod  12  develops from an interference of bore  3   a  and push rod  12 , preventing push rod  12  from retracting further. Piston  10  is able to rearwardly retreat approximately a distance Y in cartridge  4 , thereby diminishing the compressive energy in cartridge  4  so that drooling is reduced. It should be noted that clutch spring  2  and drier spring  11  are preferably conventional coil springs selected to provide suitable compressive forces.  
         [0022]    Clutch element  3  is located forward of trigger  18  and divider  5  in order to facilitate a compact profile for dispenser  100 . Lever  3   b  can be conveniently pushed by finger pressure to move clutch element  3  to a non-inclined position, and thereby remove contact resistance between clutch element  3  and push rod  12 . Push rod  12  may then be retracted, for example, to its most rearward position in order for a spent cartridge  4  to be removed from the dispenser and a new cartridge  4  installed.  
         [0023]    The foregoing describes the invention in terms of embodiments foreseen by the inventor for which an enabling description was available, notwithstanding that insubstantial modifications of the invention, not presently foreseen, may nonetheless represent equivalents thereto.