Abstract:
A self-contained root canal dental instrument that combines the operations of a root canal spreader, a root canal condenser, and a root canal filling material heater in a less expensive and easier to replace plugger unit. A different heating circuit using balanced resistor elements in both the hand piece and the tip makes use of the instrument more cost effective for the dentist. The instrument combines a sterilizable condenser tip with the capability of achieving the correct heating temperature via standard AA alkaline batteries.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to dental treatment equipment and root canal dental instruments. Specifically, it relates to a self-contained root canal dental instrument that combines the operations of a root canal spreader, a root canal condenser, and a root canal filling material heater. 
     2. Description of the Background 
     A need has existed for a long time for a way to reduce the time involved in filling a prepared root canal of a human tooth with the filling material. The time involved being used in the continual pick up of separate dental tools for spreading filling material, condensing the filling material, and the alternate heating and reheating of the filling material, during the spreading and condensing operations. Equally important is the complete adaptation of the filling material to secure a hermetic seal against leakage. 
     Gutta percha is the usual material that is used for filling root canals. Gutta percha, as with other root canal filling materials, must be spread and condensed in the root canal and heated to improve its flow and adaptation qualities. Gutta percha material deforms when warmed and compressed. It becomes pliable at 25 to 30 degrees Celsius, it becomes soft at 60 degrees Celsius, and it decomposes at 100 degrees Celsius. At such temperatures a phase transition occurs allowing the gutta percha to flow into the many irregularities of the prepared root canal, thus allowing for a three-dimensional obturation and sealing to occur. Such a three-dimensional obturation and sealing is necessary for success in root canal therapy. 
     When the filling material is softened, it is then compressed into the numerous aberrations of the root canal in order to effectively seal the root canal cavity. The compressing of the filling material in the prior art is performed by using root canal filling spreaders and filling condensers of a variety of sizes and with several handle designs (both long and short). The root canal filling spreaders and filling condensers deform the filling material under heat and stress and allow compaction and condensation that leads to the lateral spreading to fill the voids in the root canal. As bits or points of filling material are placed into the root canal, as hereinbefore described, the heated, spreader tool is forced between the bits or points of material after each such insertion which pushes and compacts the filling material vertically to the apex of the root canal and, concurrently, laterally. The tool is pressed manually and also rotated side to side to achieve the spreading of the material. It also acts as a heat sink cooling down quickly for controlled concentration. 
     The filling spreaders and condensers of the prior art for root canal work are generally of stainless steel or chromium plated brass. The filling spreaders are smooth, flat ended and slightly tapered. For the most part, the prior root canal filling spreaders and condensers had to be heated over a flame, such as over the flame of a Bunsen burner, and then passed into the mouth of a dental patient and then into the prepared root canal where the filling material has been placed. Such tools had to be transported quickly from the Bunsen burner into the mouth of the patient and into the tooth and the root canal and against the cold mass of filling material. There is the constant danger of burning the patient about the mouth each time a heated dental tool is moved from the flame to inside the mouth. Moreover, if it becomes too hot the filling material will stick to the dental tools of the prior art. 
     A few prior art attempts have been made to provide for heating the tools while in the mouth. However, problems have been encountered. For example, the tips have been bulky and too wide. Also, the tips do not wedge lock into place and 360 degree rotation has been encountered which reduces the effectiveness of the condensing operation. Further, the heat control has been unreliable, the system having as many as ten dial settings which required an assistant or required the dentist to stop the condensing operations to attempt to make a better heat selection or to interrupt the heat process. In addition to the above problems, the filling material sticks to the surface of the so called heat control tools, and the system has a cumbersome power box and control means. 
     U.S. Pat. No. 4,392,827 issued Jul. 12, 1983 to the inventor herein proposes a solution in the form of a self-contained dental instrument inclusive of a combination spreader, condenser, and a filling material heating unit, each of which is alternately and/or concurrently useable while inserted within the root canal structure of a patient. The &#39;827 invention generally includes a plugger component or “tip” which combines the functions of a spreader, a condenser, and a material heating unit; a handle component affixed to the plugger component; a power supply component for producing heat; and a transmission component for transmitting heat produced by the power supply component to the material heating unit of the plugger component. The transmission component has a conveniently located finger operation switch to interrupt the power supply and cut off the flow of heat. A variety of plugger components are provided in a range of sizes to fit the range of internal sizes in different parts of the root canal. The &#39;827 invention reduces the number of entries into the mouth that are necessary during a root canal filling, and also provides for inducing the heat for the tool after the tool is in the tooth at the root canal cavity. The plugger unit or tip is used to heat the filling material and then laterally condense or press the filling material into the root canal areas. Thereafter, the tip may also be used to maintain the heat or reheat the filling material and to vertically condense the filling material into the root canal in a compacting type of operation. While the use of the filling condenser to vertically condense the filling material is often referred to as a plugging operation, the use of the filling spreader to laterally condense the material before the vertical condensing is is also a part of the total plugging operation. Additional bits or points of filling material are placed into the root canal cavity and then followed by the spreading and condensing operations described hereinbefore for the filling spreader and condenser root canal tools. These operations are continued until the required amount of filling material plugs and seals the root canal in accordance with dental art. 
     The above-described invention eliminates the risk and expense of the many repeated tool exchanges and reheating operations. However, the device itself has proven expensive. The &#39;827 device made use of a tip which housed both heating element and resistor. The presence of the resistor within the tip increased the cost. More significantly, the tip could not be sterilized due to the resistor. 
     It would be greatly advantageous to provide a modified design in which the resistor is moved out of the tip and into the hand piece, along with other design modifications, to thereby make the instrument more cost effective for the dentist and sterilizable for infection control requirements. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide A self-contained root canal dental instrument that combines the operations of a root canal spreader, a root canal condenser, and a root canal filling material heater in a less expensive and easier to replace plugger unit. 
     It is another object to accomplish the foregoing by incorporating a heating resistor element in the hand piece rather than the condenser tip, thereby making the tip removable and sterilizable. This in turn satisfies the infection control requirements of the Food and Drug administration, and makes the use of the instrument much more convenient and cost effective for the dentist. 
     It is a necessary object to accomplish the foregoing by employing a different heating circuit within the hand piece, the heating circuit being adapted to provide a proper impedance (inclusive of parallel resistances, proper length and proper amounts of copper flashing) to allow correct heating within the tip. 
     It is a further object to provide an improved insulation system for the tip described above. 
     It is still another object to replace the NiCad batteries and recharger as suggested in U.S. Pat. No. 4,392,827 issued Jul. 12, 1983 to the inventor herein with conventional alkaline batteries, and to adapt the electronics and housing accordingly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, features, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiment and certain modifications thereof when taken together with the accompanying drawings in which: 
     FIG. 1 is a pictorial view of a self-contained root canal heated condenser dental instrument according to the present invention; 
     FIG. 2 is a side view of the instrument of FIG. 1; 
     FIG. 3 is an enlarged cross sectional view on line  6 — 6  of FIG. 2; 
     FIG. 4 is an enlarged cross sectional view on line  7 — 7  of FIG. 2; 
     FIG. 5 is an enlarged side perspective view of the tapered tip  26  of plugger component  16 . 
     FIG. 6 is a side partial cut away view of the handle component  17  of dental instrument  15 . 
     FIG. 7 is a side cross-section of the handle component  17  of dental instrument  15 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Gutta percha is a high molecular weight polymer trans polyiosprene. If it is heated above 65° C. it becomes amorphous. It is cooled at 0.5° C. per hour and will slowly recrystallize in the beta form which is the form of dental gutta percha usage. Gutta percha may be applied by the lateral condensation technique. This is a compression of solid gutta percha cones together and adaptation to the root canal walls. 
     Referring now to the drawings and particularly to FIG. 1, an improved self-contained root canal heated condenser dental instrument  15  is shown for practicing the lateral condensation technique. The instrument  15  of FIG. 1 includes a plugger component  16  and a handle component  17 . 
     FIG. 2 is a side view of the instrument  15  of FIG. 1 with internal components indicated by dotted lines. Inside the handle component  17  is a power source  18  and a heat transmission coupling  19 . The structure of each of the plugger component  16 , handle component  17 , power source  18 , and a coupling  19  for plugger component  16  as described hereinafter. 
     The power source  18  must be sufficient to provide the control heat as hereinafter described. Preferably, the power source  18  comprises a pair of standard alkaline AA batteries that fit inside the end of the handle component  17  at the distal end from the plugger component  16 . A screw-on end closure  44  with terminal spring  5 A provides an easy access means for inserting the power source  18 . When screw-on end closure  44  is installed, a conductive path exists from one output terminal of the power source  18  through terminal spring  5 A and handle component  17  (via a conductive metal trace or a conductor wire housed therein). The instant use of ordinary alkaline batteries rather than NiCad batteries and recharger helps to keep the unit cost low. 
     The plugger component  16  is preferably formed as two pieces including a tapered tip  26  joined to an extended portion  30 . The tapered tip  26  consists of a main resistive core  20  with a Teflon coating  22 , both as shown in FIG. 3, which is an enlarged cross sectional view on line  6 — 6  of FIG.  2 . Resistive core  20  may be formed of conventional ceramic resistor material. 
     Referring to FIG. 2, the Teflon coating  22  extends from the pointed end of tapered tip  26  to the top  28  of the tapered portion  26 . The Teflon coating  22  covers both the end  24  of the core  20  as well as the tapered portion  26 . The extended portion  30  is a more or less uniform diameter for the balance of the extension, as hereinafter described, to the an end that inserts into the heat transmission coupling  19 . The extended portion  30  is bent in a convenient goose neck like configuration to a straight portion  32  that inserts into the aforementioned coupling  19 . It is to be understood that the extended portion  30  may be maintained straight, bent at a right angle, or formed into any other configuration, and all such variations are within the scope and intent of the invention. The plugger component  16  includes tapered portion  26  (core  20  and the Teflon coating  22 ), as well as the extended portion  30  and straight portion  32 . 
     FIG. 4 is an enlarged cross sectional view of the extended portion  30  of plugger component  16  along line  7 — 7  of FIG.  2 . The extended portion  30  is insulated  74  about the periphery, as shown in FIG.  4 . In addition, a central layer of insulation  76  separates two conductive leads  78   a  and  78   b . The outer insulation  74 , central layer of insulation  76 , and conductive leads  78   a  and  78   b  run the entire extent of the extended portion  30  from the interface with the tapered portion  26  to a point  36  just clear of chuck  38 . The outer insulation  74  is preferably a layer of Pyre-ML, which is an enamel used in the motor industry for coating electrical windings. The insulation  74  also provides protection against burning of parts of the mouth of a dental patient while root canal work is being done. 
     In accordance with the present invention, the tapered tip  26  is bonded to extended portion  30  at a junction  28  using Master Bond® Epoxy No. EP42Ht. This particular epoxy has been tested under a force gage at 50 lbs. until shearing took place. Thus, using the International standard for hypodermic needles ISO 7864, it has been determined that the tapered tip  26  can withstand an acceptable push-out force of at least 9.25 lbs. This bonding material also acts as a heat shield to confine the heat to the tapered portion  26  and to keep the extended portion cool. This is an important safety feature and it allows almost immediate cold compaction of the root canal filling material. 
     FIG. 4 is a cross-section of the extended portion  30 , and FIG. 5 is an enlarged side perspective view of the tapered tip  26  of plugger component  16 , both showing the internal conductive leads  78   a . Tapered tip  26  is bonded such that both conductive leads  78   a  and  78   b  make electrical contact with the resistive core  20  of the tapered portion  26 . Heating at the tapered portion  26  is accomplished with the insulated lead  78   a  extending downward through the extended portion  30  to the tapered portion  26 , and with identical return  78   b . Both conductive leads  78   a  and  78   b  are insulated. This way, application of power from power source  18  through the conductive leads  78   a  and  78   b  and into the resistive core  20  generates heat therein which is quickly transmitted outward through the Teflon coating  22 . The Teflon coating  22  prevents the root canal filling material from sticking or adhering to the plugger component  16  at the area of contact during a root canal treatment. The heat in the core  20  will readily pass through the Teflon coating  22  to heat the root canal filling material during treatment. 
     The extended portion  30  of plugger component  16  may be provided in a variety of sizes and shapes for use in root canal work that may vary from near the front of the mouth to the very back of the mouth. For example, a long neck exterior portion  40  facilitates reaching the back teeth. 
     FIG. 6 is a partial cross-section showing the plugger component  16  coupled into the end of the handle component  17  with the conductive leads  78   a  and  78   b  extending into coupling  19 . This is accomplished by inserting the plugger component  16  into the end of the handle with leads  78   a  and  78   b  inserted into mating receptacles in coupling  19 , and then anchoring the plugger component  16  therein by screw-tightening a chuck  38 . Once connected, one of the leads  78   b  completes an electrical circuit with power source  18  through a balance resistor  21  which allows control over the amount of heat dissipated by the plugger component  16 . The other conductive lead  78   a  is connected to one terminal of switch  50 . The combined conductive leads  78   a  and  78   b  essentially make a loop down to the end of the plugger component  16 , starting as aforementioned at switch  50 , running out through the extended portion of plugger component  16 , around the gooseneck bend of the extended section  30 , then down the tapered section  20 , then back through the gooseneck bend of the extended section  30 , through the straight section  66  and making the aforementioned contact with the opposite terminal of power source  18 . 
     FIG. 7 is a cross-section of the handle component showing the chuck  38  for connecting and holding the plugger component  16  in place. The chuck  38  is affixed to the handle component  17  at an aperture in the handle component  17  through which the end of the plugger component  16  passes to insert into the heat transmission coupling  19 . The handle component  17 , in addition to serving as the means for a dentist to hold and use the root canal dental instrument  15  manually, also serves as a case or housing for the power source  18  and the heat transmission coupling  19 . The chuck  38  is threaded onto the distal end of handle component  17 , the tightening or which secures the plugger component  16  (not shown) in place. 
     The power source  18  aforementioned is biased at the leading end by another terminal spring  5 B, terminal spring  5 B also serving as a conductive path to a spacer switch  50 . Depression of the spacer switch  50  further completes the conductive path to the heat transmission coupling  19  as hereinafter described. The switch  50  is preferably a push-button activator pad positioned for thumb operation at the neck of the instrument  15  and easily depressed while holding the root canal dental instrument  15  by the handle component  17 . A variety of suitable switches are readily available for use as spacer switch  50 . The spacer switch  50  is set in a normally “off” position and depressing it with the finger, as hereinbefore described, turns the switch “on” to provide power to the heat transmission coupling  19 . The switch  50  is spring-loaded and it automatically returns to the “off” position when the finger is removed or lifted. The switch  50  is connected in series between the power source  18  via terminal spring  5 B and through a conventional resistor  21 , resistor  21  in turn being connected through the handle component  17  (either directly or by an internal conductor) to the opposite polarity terminal spring  5 A. The resistor  21  is an integral part of the heat transmission coupling  19 , such that when the end of the plugger component  16  is inserted into the heat transmission coupling  19 , the resistance of resistor  21  is in series with that of tapered portion  16 , and the two resistances are balanced to provide appropriate heating of the tip as desired. Thus, upon depression of spacer switch  50  approximately 3 volts of power is applied across the series-coupled heat-dissipating core  20  of tapered portion  16  and the resistor  21 , and heat is generated thereby at the tip. The leads of resistor  21  and all other series conductors as necessary are preferably formed from nickel-chrome wire. A conventional 1.4 ohm resistor makes a suitable resistor  21 . A layer of insulation encircles the immediate area around the resistor  21 . The insulation is preferably a section of polyester shrink tubing with an average wall thickness of 0.00025 inches. Heat transmission coupling  19  is open at the other end to surround the straight portion  32  of the plugger component  16 . The heat in the heated tapered portion  26  passes through the Teflon coating  22  for use in heating the root canal filling material, as hereinbefore described, so that the root canal dental work can be performed. 
     Given the above-described configuration, the heat in the heated tapered portion  26  has been found to vary between 150 to 250 degrees Fahrenheit. This is a higher heating capacity when compared to the device of the &#39;827 patent. During clinical testing the heat resulted in thermo-softening of the gutta percha in approximately three seconds. Compacting was then easily accomplished to provide excellent results. Moreover, the utilization of standard AA batteries, and the placement of the resistor  21  inside the handle unit have greatly reduced the cost of the device. Further, inasmuch as the resistor  21  resides within the handle rather than the plugger component  16 , the entire plugger component  16  can now be removed and sterilized. This is extremely important inasmuch as the Food and Drug administration and Occupational Safety and Health administration require adequate sterilization to control infection. In clinical testing the instrument  15  has been found to be easy to use, consistent in both heating and compaction, and generally improving of the quality of root canal fills. 
     Having now fully set forth the preferred embodiments and certain modifications of the concept underlying the present invention, various other embodiments as well as certain variations and modifications of the embodiments herein shown and described will obviously occur to those skilled in the art upon becoming familiar with said underlying concept. For example, the range of sizes of the plugger component  16  may provide the range of lengths of the exterior neck  40 , as mentioned hereinbefore, and may also provide a range of diameters at the small end of the tapered portion  26 . The range of these small end diameters may begin with a very small diameter of less than one-half millimeter that is measured over the end of the core  20  and its Teflon coating  22 . It is to be understood, therefore, that the invention may be practiced otherwise than as specifically set forth in the appended claims.