Abstract:
A dental training aid and method which assists a student in learning how to determine the position of a root canal apex, repair of dental decay, and how to perform crown and bridge procedures. In certain embodiments, modular inserts are utilized that include structure thereon for performing root canal procedures, repair of dental decay procedures, crown and bridge procedures or other procedures. The inserts can be assembled and configured to all provide practice on the same procedure or on different procedures and can be exchanged for other inserts once they are no longer reusable or because the user wants to train on a different procedure.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   The present application is a continuation-in-part of prior U.S. application Ser. No. 10/024,683 filed Dec. 18, 2001 and entitled DENTAL TRAINING DEVICE, now abandoned, which was a continuation-in-part of prior application Ser. No. 09/848,739 filed May 3, 2001 and entitled DENTAL TRAINING DEVICE, now U.S. Pat. No. 6,520,775. 

   BACKGROUND OF THE INVENTION 
   The present invention related to dental equipment, and more particularly, to teaching tools for the use of endodontic apical location equipment. 
   During certain dental procedures, the pulp of the tooth must be removed and other procedures must be performed on the root canal. Persons training to become dentists must learn how to properly remove such pulp and perform the other necessary procedures. Precise location of the root apex is vitally important for the correct endodontic treatment of a tooth. Pulp tissue is richly vascularized and innervated and is contained in the pulp cavity inside the tooth including in the pulp chamber and in pulp canals in tooth roots. The pulp canals are often referred to as root canals. If the endodontic procedure of extracting and cleaning the pulp tissue from a root pulp canal is performed at a length short of the apex, pulp tissue may remain in the canal. Failure to remove all pulp tissue may lead to infection and pain for the patient and necessitate additional surgery. If the endodontic procedure is performed beyond the length of the root apex, the reamer may penetrate into the periodontal ligament leading to pain and extreme sensitivity to the patient. Therefore, current endodontic procedures normally require the careful locating of the root apex at the base of the pulp canal before the reamer or other tools are used to enlarge the pulp canal. 
   Multiple methods are currently utilized to determine the location of the apex during an endodontic procedure on a live patient. One procedure is the use of x-ray radiographs of the tooth while a metal endodontic reamer is located in the root canal. This allows the dentist to visually compare the length of the metal reamer to the location of the end of the root to determine the location of the root apex. This method is often unreliable and not cost-effective. 
   A second method is to use an electrically aided apical position location. Certain electronic aids and methods of their use include those described in U.S. Pat. No. 5,759,159 to Masreliez, U.S. Pat. No. 5,211,556 to Kobayashi et al, and U.S. Pat No. 6,059,569 to Otsuka, all incorporated herein by reference. These patents describe apical position locators utilizing impedance measurements to determine the location of the apex that use electrical conductance. In the electrical conductance approach, an electrically-conductive probe is inserted into the root pulp canal and a second electrode is attached to the patient&#39;s body, such as by hanging a hook-shaped electrode from the patient&#39;s mouth. As the probe is inserted into the root pulp canal and advanced through the root pulp canal to the root apex, the electrical impedance between the probe and the electrode is continuously measured. The electrical impedance is greater when there is little conductance between the probe and the electrode, such as when the probe is in the pulp canal, and lower when there is greater conductance between the probe and the electrode, such as when the probe touches the tissue at the bottom of the pulp canal that is much more conductive than the pulp canal itself. Once the impedance lowers and reaches a predetermined range or value, the location of the apex is indicated and the depth of the probe is noted for future use with other instruments. The electrical approach using impedance for determining apex location is currently the preferred and standard technique used in endodontic practice and taught in dental schools. 
   Instruction in the use of electrical apical position locators has generally required practice upon live patients in need of endodontic treatment. Performing endodontic procedures on healthy teeth is unethical and represents dental malpractice. Endodontic patients are often in pain prior to seeing the dentist, and are usually apprehensive about the endodontic procedure and less than enthusiastic about serving as subjects in dental instruction on the use of apical position locators. The additional pain which may be encountered, or the mere potential for such additional pain, results in few such patients volunteering to allow students to perform the procedure. 
   The number of endodontic procedures that a dental student or a doctoral student in general dentistry performs on live patients is severely limited by the number of willing participants in need of such procedures. Dental students and general dentists would benefit from additional training and instruction in the use of apical position locators in a realistic setting. In turn, the endodontic patient would benefit from the additional training received by the practitioner. 
   Prior to this invention, no adequate surrogate for the live patient has been developed for instruction in the use of electrical apical position locators. U.S. Pat. No. 5,503,562 described a transparent endodontic inspection block which allows the dental student to simulate the cleaning out the root pulp canal. The student utilizing the inspection block could look through the side of the inspection block and locate the root apex. This invention is not designed to train apex location techniques and does not represent realistic conditions of endodontic treatment. U.S. Pat. No. 4,137,633, issued in 1979, disclosed a resilient mass located at the apex of a block of transparent material to simulate the tactile sensation of the periodontal membrane located at the apex of a natural tooth. Thus, prior devices permitted students to visually locate a simulated apex through the addition of a resilient mass located at the apex. However, no known prior devices have disclosed providing a simulation of a live tooth and human tissue to practice using an electrical apical position locator. 
   Additionally, during training to do such procedures, it is important to have the procedure simulated on an actual patient, as much as possible, so that the student can learn how to overcome problems of working in the patient&#39;s mouth. Therefore, it is also desirable to provide a training device that can be utilized for at least some of the student endodontic procedures and which simulates a live patient, as much as possible. 
   In addition to the need for a training device for use in teaching root canal procedures, it is also desirable to have such a device that can be used to teach other types of procedures such as how to treat dental decay and how to do crown and bridge procedures. Because training devices may be expensive for the student, it is preferable that the device allow the student to practice different types of procedures which preferably require somewhat different structure. Root canal procedures require real or artificial teeth having a root and with structure allowing electrical conductance. Crown and bridge work require a section of teeth wherein one or more is missing and real or artificial teeth can be modified to accept a bridge with a skin like structure over the gum, as it is important for the student to correctly interface the bridge with the skin. Dental decay procedures do not require a root or electrical conductance, but preferably utilizes real or artificial teeth that are mounted in such a manner so as to simulate the interaction of the teeth with each other and with ligament tissue that normally holds such teeth in place. Each of these and other procedures are preferably performed on separate or different practice units to allow the student the best range of training. 
   Furthermore, it is desirable that the different sections be modular so that a student can preform one, two or all procedures within a single assembly. For example, when working on one procedure, all the individual modular inserts in an assembly may be designed for a single procedure to provide multiple locations to practice or such can be changed to provide modular inserts for multiple procedures for practice or testing. Because the individual modular inserts can be easily changed, when one is used and is not reusable, it can easily be replaced by another without requiring that the entire assembly be discarded. 
   SUMMARY OF THE INVENTION 
   The present invention provides an improved device and method for the training of the use of an apical position locator. The invention uses a real or replicated tooth with a root and a root pulp canal (often referred to as a root canal) having an apex at the root tip. Real teeth with pulp in the root canals are available from a supply of such teeth removed from patients for other reasons or from cadavers. In the present invention a student practices on a tooth set in a hard medium which mimics the electrical impedance of human tissue so that an electronic apical locator may be used. In a first embodiment, the tooth is mounted in a single, rigid conductive medium which mimics the conductivity and impedance characteristics of human tissue. An alternative embodiment uses a first highly conductive medium wrapped around the root tip to cover the apex of the tooth which is then surrounded by a second rigid medium so as to set the tooth in a fixture containing the second medium. The second medium may be less conductive and holds the tooth suitably for manipulation training purposes. 
   An electronic apical position locator has one lead connected to an endodontic probe or reamer and the other to an electrode blade extending from the medium. When the reamer is inserted in the root canal and extended so that the reamer tip contacts the conductive medium at the root apex, the electronic circuit of the apical position locator is closed, the impedance is measured and the apex is appropriately indicated by the apical position locator. 
   In another embodiment of this invention, the tooth is mounted in a manikin jaw that simulates a working human jaw. Preferably, the manikin jaw has sockets at various locations that are located whereat various teeth would normally be found. Each tooth upon which the student is to train is mounted in an electrically conductive medium that has a lower impedance than the training tooth root canal and which desirably has approximately the conductance or impedance of tissue found around the natural live root apex. A highly conductive medium is preferably placed in a protective sleeve and a second medium or matrix is placed about the tooth within a sleeve and then allowed to harden. The sleeve is sized and shaped to be received in one or more of the sockets. Preferably, the sleeve is held in place by a pin, such as a thumbscrew or similar fastener, that also acts as an electrical conductor in contact with the conductive material in the sleeve and in turn is electrically connected to an electrode of an apex location apparatus. The entire matrix may be a highly conductive medium or a less conductive medium may be used externally relative to the sleeve. Further, if the pin connects directly with the highly conductive medium in the sleeve, the remainder of the matrix does not have to be conductive. 
   A more detailed understanding of the invention will be obtained from the following description of the preferred embodiments taken in conjunction with the attached drawings. 
   This invention provides an actual or replicated human tooth with an electrically equivalent replicated human tissue medium, especially in a human form manikin, to provide a realistic simulator for training in the use of an electrical apical position locator. Patient volunteers do not normally clamor for dentists-in-training to practice root canals upon them, so this invention allows the dental student the opportunity to practice in a realistic environment, preferably with real teeth having-pulp in the root canals thereof. The user may select a partially radiopaque electrically conductive medium, which allows the student to also simulate the determination of the location of the root apex through the use of an x-ray radiograph. 
   In yet another modification of the invention, the training aid is provided with modular inserts that mimic various portions of the jaw and which can be easily exchanged with other inserts that mimic the same portion of the jaw. In this manner, the inserts can include one or more units for training for particular procedures such that all of the assembled inserts may be for the same procedure or for different procedures. Each insert can be easily replaced by another for the same or a different procedure. 
   Different inserts may be advantageous for many different procedures. For example, the inserts may be especially designed to act as an instruction aid for root canal procedures, repair of dental decay procedures, for crown and bridge procedures or for other procedures. The root canal procedure inserts are preferably of the type described above with the added feature of providing a common electrical conductor for the entire insert support structure so that electrical conductance will be available whether none, one or multiple inserts are for root canal procedures. The dental decay procedure inserts preferably include structure to allow teeth to be mounted in a matrix that mimics the setting of live teeth relative to ligaments that support and hold live teeth, so the student more closely encounters the feel of working on live teeth, especially crowding by adjacent teeth and flexing under pressure. The crown and bridge procedure inserts preferably include an artificial skin layer that mimics a patent&#39;s skin, so that the student gains experience in mounting crowns and bridge relative to skin tissue. 
   OBJECTS AND ADVANTAGES OF THE INVENTION 
   Therefore, the objects of the present invention are: to provide a training aid for dental students comprising a holder or fixture for holding a tooth in a solid medium or material that is at least in part approximately as electrically conductive as non-boney tissue found in humans that surrounds teeth so as to simulate the electrical conductivity or impedance found in such tissue and thereby allowing a student to perform practice root canal procedures, including practice with an electrical apical position locator, without need for living patients; to provide such a training aid wherein the fixture is an independent container partially filled with solid electrically conductive medium or material that simulates the electrical conductivity or impedance of human tissue surrounding teeth; to provide an alternative embodiment of such a training aid wherein the fixture includes a socket in a manikin that simulates a human jaw structure; to provide such a training aid wherein the sleeve is sized and shaped to fit in such a manikin socket to allow easy removal and cleaning after the training session is complete; to provide an alternative manikin-training aid wherein teeth with a highly conductive media about the root tips thereof are molded directly into the manikin; to provide such a training aid wherein a thumbscrew is used as a pin to secure such a sleeve in a socket and wherein the thumbscrew also functions as an electrode for the apical position locator; to provide such a training aid that includes a set of modular training inserts wherein such inserts can be exchanged for similar or different inserts to form a training assembly; to provide such a training aid that provides such inserts wherein each insert is especially adapted to particular procedures, such as treatment of dental decay procedures, root canal procedures and crown and bridge procedures; to provide such training aid wherein all of the inserts in a final assembly may be selected for training on the same procedure or for different procedures to meet the needs of the student using the training aid; to provide a method of training aspiring dentists in endodontic procedures using the aforementioned training aids such that the students become skilled without having to practice on live patients; and to provide such training aids that are easy to use, comparatively inexpensive to make and especially well suited for the intended purpose thereof. 
   Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. 
   The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional view of a training aid in accordance with the present invention. 
       FIG. 2  is a cross-sectional view of a first alternative training aid. 
       FIG. 3  is a cross-sectional view of the first alternative embodiment of the training aid shown in connection with an electronic apex locator. 
       FIG. 4  is a perspective view of a second alternative training aid in accordance with the present invention, illustrating a training procedure being performed and with portions broken away to show internal detail thereof. 
       FIG. 5  is an enlarged cross-sectional view of a sleeve, tooth and highly conductive medium during a first step in assembly of the second alternative training aid. 
       FIG. 6  is an enlarged cross-sectional view showing a second step subsequent to the first step shown in  FIG. 5  in the assembly of the second alternative training aid. 
       FIG. 7  is an enlarged cross-sectional view of the second alternative training aid showing a third step in assembly thereof. 
       FIG. 8  is an enlarged cross-sectional view of the second alternative training aid fully assembled and shown in a fragmentary manikin as shown in  FIG. 4 . 
       FIG. 9  is an exploded perspective view of a third modified training aid according to the present invention having a plurality of modular inserts wherein each insert is utilized for training a student with respect to a different dental procedure. 
       FIG. 10  is a perspective view of the third modified training aid with inserts assembled. 
       FIG. 11  is a perspective view of the third modified training aid showing the assemblage being prepared for and during specific dental training procedures. 
       FIG. 12  is a fragmentary cross-sectional view of the third modified training aid, taken along line  12 — 12  of  FIG. 10 . 
       FIG. 13  is a fragmentary cross-sectional view of the third modified training aid, taken along line  13 — 13  of FIG.  10 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. 
   First and Second Embodiments 
   Referring to  FIG. 1 , the reference numeral  1  generally indicates a training device according to the present invention which is useful to create an effective simulation of a tooth in a patient, so that a student may practice using an electronic apical position locator. The training device  1  consists of a tooth  2  which may be an extracted human tooth or a replica, which is set in a fixture  3  and connected to an apical position locator  4 ,  FIG. 3 , as hereinafter described. In more detail, an illustrated exemplary tooth  2  is a pre-molar with two roots  10 , each with a root canal  11  ending at an apex  12  near the tip  13  of each root. Other tooth forms are equally suitable. In a live tooth, the root canal  11  is filled with nerve pulp tissue. Also, a live tooth is set into a periodontal ligament which surrounds the root  10  and acts as a barrier between the tooth root and the bone that holds the tooth. In a patient the periodontal ligament or tissue around the tooth is moist and electrically more conductive than the tooth, thereby enabling the use of an electronic apical position locator  4  which relies on the measurement of impedance to determine when the more conductive tissue is encountered and therefore when the apex is reached. When the measuring probe electrode approaches the apex, the magnitude of impedance or the phase angle of the impedance between the measuring probe and oral probe electrode starts to change. The detector identifies the apex when the designated range or the frequency of impedance is reached. 
   In the illustrated example, the tooth  2  is a “dead” tooth which has been extracted from a patient or cadaver and is not supported by a living periodontal ligament or other live conductive materials. As shown in  FIG. 1 , the tooth  2  is set in a container or fixture  3  which is selected for ease of manipulation by a student. Preferably, a single setting material  15  is selected which provides sufficient rigidity to support the tooth  2  during handling and during the practice of root canal procedures. Ideally, the selected material  15  should also replicate the range of impedance of live human tissue in order to provide an impedance in the range of the apex locator setting. Since there are many different types of apex locators on the market, a single conductive material having an impedance not in the range of live human tissue can also be used for some apex locators of simple design and it is foreseen that a conductive material could be selected for a specific locator. Generally, the selected material  15  should replicate the conductivity of live human tissue in order to provide an impedance generally matched to the impedance of live tissue. Because an electric apex locator of advanced design contains circuitry and components to measure the impedance of human tissue and then compare the impedance value to the impedance values obtained by a measuring electrode inserted into the root canal, a closer match of impedance between the material  15  and the circuit of the apical locator  4  in the locating of apex is normally preferred. A suitable range for the volume resistivity of the medium  15 ,  20  and  22  supporting the tooth  2  in the fixture  3  is in the range from 10 15  to 10 −3  ohm/cm. 
   To obtain a suitable support medium, conductive material is mixed with different binders. Such a binder can be plastic resin, polymer resin, plaster, stone, clay etc. Various types and concentrations of conductive materials in the binder have been conceived and include carbon, carbon fiber, graphite, silver powder, metal or metal coated fiber or powder or flakes, silicon, silicon dioxide, germanium, selenium, conductive polymer and others in slight to significant concentrations. If a radiopaque support medium can be tolerated, then a high metallic content or radiopaque chemical such as barium sulfate or stainless steel fibers or powder are usable with a binder. If radio transparency is needed, then metallic content is limited and carbon or other non radiopaque materials are increased to a proportion balancing strength, conductivity and human tissue impedance. The attribute of impedance matching is intended to bring impedance values into a range sensed by the circuit of the electronic apex locator. 
   A second embodiment of the present invention is shown in  FIGS. 2 and 3  and uses two conductive medium components. The second embodiment is essentially the same as the first embodiment described above except for a modification to the medium supporting the tooth and is thus numbered the same except for this medium. In particular, in the second embodiment, a first conductive medium  20  is applied to the root tip  13  to cover the apex  12 , generally in a ball about the root tip  13 . When applying the first conductive medium  20  to the root tip  13 , care is exercised so as not to pack the medium  20  into the canal  11 , but to merely cover the apex  12  as it intersects with the root  10 . The preferred material of the first conductive medium  20  is a water based or a highly conductive material. The first conductive material or medium  20  can be a mixture of water, alginate, agar, gum, clay or a highly concentrated carbon or metal powder that is a very good electrical conductor in plastics, especially acrylics, or a mixture with a calcium or sodium inorganic salt, such as calcium sulfate. 
   The tooth with its root tip coated with the first conductive medium is placed in a second conductive medium  22  which fills the fixture  3  and which is initially soft or even liquid. The second conductive medium  22  is preferably then set or hardened to form a solid support for the tooth  2 . Settling can be accomplished by allowing the medium to dry, where appropriate, allowing it to chemically set such as an epoxy or acrylic, heat setting the medium  22 , where it is capable of being heat set, or the like. The second medium  22  is preferably mixed with a conductive element as mentioned before, typically a resin type material, so that it can hold the tooth  2  in place for handling and practicing root canal procedures, after being hardened or set. 
   The first conductive medium  20  and the second conductive medium  22  may possess radiopaque material, if training utilizes radiographs to simulate use in a real patient. Such radiopaque material may include material such as metal fibers, metal-coated fibers, carbonaceous material, metallized glass or barium sulfate, as a substantial component of the medium  22  in sufficient amount to produce radiopaqueness. The first conductive medium  20  and the second conductive medium  22  may possess materials of differing radiopacity to simulate the different radiopacity of the periodontal ligament and the bone in a patient. 
     FIG. 3  shows the training device  1  in connection with an apical position locator  4 . To enable the training device  1  to be utilized with the apical position locator  4 , a measuring probe such as an endodontic reamer  25  is connected to the apical position locator  4  via leads  26  and a connector, such as an alligator clip  28 . The apical position locator  4  is connected to the conductive medium such as the second conductive medium  22  via lead  30  and a connector such as an alligator clip  32 , connected to an electrode or probe  34  set in second conductive medium  22 . In the illustrated example, apical position locator  4  indicates the closure of an electronic circuit when the endodontic reamer  25  contacts or almost reaches the conductive medium  20  at the apex  12 . Then the resistance or impedance of these materials are measured, compared and calculated based on the pre-set formula in the apex locator. A final reading will indicate reaching the apex by the tip of the dental reamer. Normally, the apical position locator possesses sufficient sensitivity that it can determine the distance between the tip of the endodontic reamer  25  and the apex  12  and the locator provides a visual readout of that distance. 
   In the practice of the invention, a tooth such as an extracted human tooth  2  is used to train a user by placing the tooth  2  into a container or fixture  3  and supporting the tooth  2  therein by a conductive medium, such as the single medium  15  shown in  FIG. 1 . Alternatively, a first conductive medium  20  can be molded around the root tip  13 , being careful not to enter the canal  11 . Next, the tooth  2  with first conductive medium  20  wrapped around the root  10  is placed in second conductive medium  22  in the fixture  3 . The second conductive medium  22  is allowed to set so that it firmly holds tooth  2  in place. The apical position locator  4  is connected to the endodontic reamer  25  and the probe  34  so that when the reamer  25  is placed in the root canal  11  and the reamer tip contacts the first conductive medium  20  or single medium  15  ( FIG. 1 ) at the apex  12 , the locator electronic circuit completes the measurement of electronic resistance or impedance and the apical position locator  4  so indicates. Importantly, the resistance of the conductive medium is selected so that the electronic apical locator measures the resistance. 
   Optionally, the training device may be utilized along with x-ray machines and radiographic film to simulate the verification of the location of the apex  12  through simulation of the relative radiopacity of the periodontal ligament and bone by utilizing differing levels of radiopaque materials in the first conductive medium  20  and the second conductive medium  22 . 
   Various forms of conductive media may be used as desired including thermoplastic resins, acrylic, polymers and plasters with fillers such as carbonaceous material or metal fibers or flakes. 
   Third Embodiment 
   Illustrated in  FIGS. 4 through 8  is a third embodiment of a dental training device in accordance with the present invention that is generally represented by the reference numeral  100 . The training device  100  has certain aspects that are similar to the devices that are illustrated and disclosed in the previous embodiments and reference is made to those embodiments for certain details such as materials of construction. 
   The training device  100  generally comprises a manikin  110  having at least one socket  111  and, unlike the previously disclosed embodiments, includes a sleeve  112  operably received in the socket  111  and within which a tooth  113  is mounted in a generally solid matrix  114 . 
   The manikin  110  is preferably a type of device which is sometimes also referred to as a typodent that is utilized in the training of dental students. The manikin  110  has an upper jaw or maxilla  120  and a lower jaw or mandible  121  that are mounted on a support frame  122 , such that the jaw  120  can be articulated with respect to the jaw  121  in a manner that is similar to that of a human jaw, so as to simulate a human jaw for purposes of training of a dental student. The jaws  120  and  121  have a plurality of real and/or simulated teeth  126  that are positioned about the facing surfaces of the jaws  120  and  121  in such a manner as to simulate the appearance of teeth in a typical human dental patient. The jaws  120  and  121  are constructed of a material that can vary, depending upon what is desired to be taught to the students, but which is typically a rigid or semi-rigid plastic that has the shape and appearance of the gums and mouth of a human. 
   As will be discussed below, the material of construction of the jaws  120  and  121  may in some cases be an electrically conductive material that has conductivity quite similar to the gums and mouth tissue of a human patient or may alternatively be constructed of a non-conductive material. The material of construction of the jaws may also be radiolucent or radiopaque depending on whether x-ray procedures are to be used. As is seen in  FIG. 4 , the upper jaw  120  of the present embodiment is hinged on the support frame  122  and is biased to a closed position by springs  128  wherein the teeth  126  of the upper jaw  120  engage similar teeth of the lower jaw  121 . This simulates a patient with a mouth that can be opened and in which a student must work to perform procedures using the device  100 . 
   The sockets  111  are provided in the jaws  120  and  121  at locations where it is desirable to provide training to a student learning endodontic procedures. In the illustrated embodiment such sockets  111  are provided in the lower jaw near the rear where a large molar would be normally located and which is illustrated by broken away portions in  FIG. 4 . Sockets  111  are also provided in other locations such as are illustrated in the upper jaw  120  where somewhat more forward teeth are normally located. A training procedure is illustrated in  FIGS. 4 to 8  with respect to an upper jaw socket  111 , such as is shown in  FIG. 4 . Each socket  111  is sized and shaped to receive a sleeve  112  snugly therein. Each of the sockets  111  has a shape that is somewhat in the form of a hollow truncated cone and is accessible from the rear of each jaw  120  and  121  opposite the teeth  126  (see  FIG. 4 ). 
   As is best shown in  FIGS. 5 through 7 , each sleeve  112  has a general truncated conical shape with a thin wall  129  and has a hollow interior so as to form a cavity  130  with an open upper end  131  and open lower end  132 . The cavity  130  has an interior surface  133 . The sleeve  112  is sized and shaped to receive a tooth  113  and combined form an insert  134 . Such an insert  134  is shown in phantom lines in  FIG. 8  prior to placement in the socket  111  wherein the insert is shown in solid lines. 
   As has been described with the previous embodiments, the tooth  113  is preferably a human tooth that has been removed from a live patient for some other reason or is a tooth that has been harvested from a cadaver. In certain instances where a human tooth is unavailable, an artificial tooth that is sized and shaped to mimic a real tooth may be used. Such a tooth  113  includes a pulp chamber  137  and at least one root pulp canal or root canal  138  that extends along each root  139  of the tooth  113 . Normally, such a tooth  113  would include pulp  141  intact in the root canals  138  and pulp chamber  137 . The root canals  138  containing the pulp  141  extend to an apex or tip  143  of each root  139 . 
   The practice tooth  113  extends outwardly from the sleeve  112  such that a crown  146  of the tooth  113  is exposed and the tooth roots  139  are located within the sleeve  112 . The tooth  113  is snugly and rigidly held in its associated sleeve  112  by the matrix  114 . In the present embodiment, the matrix  114  has two components  148  and  150 . 
   The first matrix component is a relatively good electrical conductor that is chosen to simulate the electrical conduction found in human tissue in the ligament and gum surrounding a live human tooth. The highly conductive matrix component  148  can be any of the materials that have been discussed in the previous embodiments for such a component. 
   In the present embodiment the highly conductive component  148  is a malleable or semi-solid material that is molded about each root tip  143 . Because the material is soft and can be stripped from the root  139  accidentally, a protector  149  is placed over the highly conductive component  148 . In the present embodiment the protectors are annular sleeves  151  that are placed over each tooth root  139 , as is shown in  FIGS. 5 and 6 . The highly conductive component  148  is specifically designed to provide good conductance at each root tip  143 . Each sleeve  151  is manually snugged against a respective root  139  and about the highly conductive component  148  to hold the latter in touch with a respective root tip  143 . It is foreseen that other forms and shapes could be utilized for the highly conductive component  148  such as a cup or the like and without a protector. 
   The second component  150  of the matrix  114  can be several different types of materials depending on whether or not it is desired for the component  150  to also be highly conductive or for conduction to be transferred from the highly conductive component  148  to the locating device described below through some other structure. Consequently, it is foreseen that the matrix component  150  can either be a highly conductive material similar to that of component  148 , a semi-high conductive material that would be useful in providing conduction between the component  148  and a locator or alternatively, may not be conductive at all. 
   It is important that the matrix component  150  be at least semi-solid and preferably rigid during usage of the device  1 , so as to support the tooth  113  in position while procedures are being performed on the tooth  113 . For this purpose, various thermally set materials or the like could be utilized wherein the component  150  is initially a resin or powder into which the tooth  113  can be initially pushed or embedded after which the component  150  is heat set and solidified. Alternatively the matrix component  150  may be a stick-type resin that forms a liquid when heated and which can be dispersed into the sleeve  112 , such as is illustrated in  FIG. 7 , and thereafter allowed to harden by drying, chemical reaction, heating with subsequent cooling or the like. It is foreseen that other types of matrix components may be used in accordance with the invention. For the purpose of dispersion, a heating gun  155 , such as a glue gun, distributes drops or a stream of conductive liquid or gel material  156  into the sleeve  112  around the tooth roots  139  which thereafter solidifies or hardens as matrix component  150 . 
   A pin  160  is utilized to secure the sleeve  112  in a respective socket  111 . While it is foreseen that in some instances, the matrix  114  could be placed in a socket directly without a sleeve  112 , such a sleeve  112  is preferred as same allows for quick change out and reduces the time that would otherwise be required to clean the hardened matrix out of the socket. 
   The illustrated pin  160  is a thumb screw that has a threaded shank  163  and flat head  164 . The pin  160  is received through openings  167  in the manikin jaws  120  or  121 , as is shown in  FIGS. 4 and 8 . The threaded shank  163  provides two functions. In particular, the shank  163  locks the sleeve  112  in position relative to a respective socket  111  and also provides a metallic conductor that directly engages the highly conductive component  148  when assembled, as shown in  FIG. 8 . The head  164  also provides two functions. The head  164  allows a grasping structure for a user to insert the pin  160  and further provides a surface that is comparatively shaped to receive an alligator clip  171 , as will be discussed below. 
   It is foreseen that the tooth  113  can be inserted into the matrix  114  in the sleeve  112  in a number of ways, but one alternative is shown in  FIGS. 5 to 7 . In particular, the crown  146  of the tooth  113  to be mounted is placed in an indentation  173  in a block  174  of wood, embedded in a putty-like material, or the like. The highly conductive matrix component  148  is placed over the root tips  139  and thereafter the root sleeves  149  are placed over the tooth roots  139  and the component  148 . Then the matrix holding sleeve  112  is placed over the lower part of the tooth  113  with the sleeve lower end  132  engaging an upper surface  175  of the block  174 . The liquid material  156  that forms the second matrix component  150  is then deposited in the sleeve  112  so as to preferably cover the root tips  143 , the conductive component  148  and the protectors  149 , so as to secure the tooth  113  in the sleeve  112 . The sleeve  112  with the tooth  113  secured therein is then placed in a selected socket  111  and the pin  160  is used to secure the sleeve  112  in the socket  111 . The pin  160  preferably also touches a respective highly conductive component  148  in which case the remainder of the matrix  114  that is component  150  does not have to be electrically conductive. If the pin  160  is not positioned to touch the highly conductive component  148 , then the matrix component  150  must also be electrically conductive. 
   After the sleeve  112  is placed in the socket  111 , a student  170  connects an apical position locator  180  to the device  100 . In particular the student  170  uses an elongate reamer or probe  181  that has a shaft  182  sized to extend through a selected root canal  138 . The shaft  182  is a conductive metal and is electrically joined by an alligator clip  184  attached to a lead  185  or the like to the main body (not shown) of the locator  180 . The alligator clip  171  with a lead  187  is attached to the pin head  164 , as is seen in  FIG. 4 . After opening the tooth crowns  164  by a well known process, the student then practices finding the bottom of the root canal  138  in the manner previously described. In an endodontic procedure, the finding of the apex of the root canal  138  is accompanied by removal of the pulp  141  and enlargement of the pulp or root canal  138  to the depth determined by the above described procedure. Thereafter, subsequent root canal procedures are performed. 
   It is foreseen that when a patient has a tooth that has a metallic filling or crown extending into or near the pulp chamber or root canal, it may be necessary to use a probe that is insulated over at least the portion of the shaft that would engage the filling or crown. For this purpose part of the shaft may be coated with nonconductive material. It is also foreseen that a hook, eye or the like may be joined to and extend-outward from the probe shaft to facilitate connection of the locator device and especially an alligator clip. 
   It is also foreseen the manikin may be constructed of conductive material as well as the entire matrix  114  in which case it is not necessary that the pin be conductive, but only that the locator lead hook onto or otherwise join with the manikin jaw somewhere therealong. It is also foreseen that the sleeve holding the tooth may be held in place by something other than a pin or set screw. For example, a cover hinged to the manikin or a moveable hook could be used to hold the sleeve in the manikin during training procedures. 
   It is foreseen that the highly conductive material may include a filler of conductive carbonaceous material, including furnace black, channel black, acetylene black, graphite fiber and carbon fiber; conductive fiber materials, including aluminum, nickel, copper, iron and stainless steel fibers; and metal coated fibers, including metallized glass, metallized graphite and metallized plastic fibers; conductive metal powders, including metallic flakes, powder and milled or ground metallized glass; and other conductive materials, including conductive organic polymers, glues, sponges, epoxies, paints, alginates and the like. A binder for the highly conductive component may be chosen from thermoplastic resins, including acrylic, polyvinyl chloride, polypropylene, polyethylene terephthalate, polystyrene, abs (acrylonitrite butodiene styrene resin), polyphenylene ether, polycarbonate, styrene and ethylene vinyl acetate; polymers, including bis-gma, TEGAMA and HEMA; and others, including plasters, yellow stone, clay and the like. 
   The following radiopaque materials may be added to some embodiments: barium sulfate and substantial concentrations of metal fillers such as nickel, stainless steel and the like. 
   It is foreseen that a conductive portion of the tooth holding matrix can also be a mixture of conductive materials including water, glycerine and other conductors, especially a percentage of from about 1 to 80% by weight in combination with a filler or gelatin selected from clay, silica, gum, agar, alginate and the like. Further, the conductive material is preferably water with sodium hypochlorite, EDTA (ethylenediaminetetraacetic acid), conductive aluminum compounds, conductive calcium and sodium salts, conductive carbonate compounds, conductive basic compounds and the like in a range from 1 to 80% by weight with the remainder being binder or miscellaneous fill. 
   The following examples are provided to illustrate the invention and are not intended to be limiting on the scope or interpretation of the claims: 
   EXAMPLE I 
   Highly conductive matrix components were produced in accordance with the invention having the following formulation by weight: 
   
     
       
             
           
             
             
             
           
         
             
                 
             
             
               Composition A 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
                 
               ethylene vinyl acetate 
               68% 
             
             
                 
               carbon powder 
               30% 
             
             
                 
               steel fiber 
                2% 
             
             
                 
                 
             
           
        
       
     
   
   
     
       
             
           
             
             
             
           
         
             
                 
             
             
               Composition B 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
                 
               flour 
               45% 
             
             
                 
               salt 
               15% 
             
             
                 
               water 
               35% 
             
             
                 
               oil 
                5% 
             
             
                 
                 
             
           
        
       
     
   
   The highly conductive matrix component Composition B was applied to roots of these teeth, as is shown in  FIG. 5  and a root sleeve of plastic tubing was placed about Composition B, as is shown in  FIG. 6 . Composition A was then placed about the tooth root in a sleeve, such as sleeve  112 , as is shown in  FIG. 7 , and a procedure was performed using an apex locator as described in the last embodiment to find the distance from the crown to each tooth root apex. Two other procedures were performed on each of the teeth to determine root length which were by x-ray measurement and by in vitro measurement. The results are provided in Table 1. 
   
     
       
             
           
             
             
             
             
           
         
             
               TABLE I 
             
           
           
             
                 
             
             
               Test Result: 
             
           
        
         
             
                 
               Root length 
               Root length 
               Root length by 
             
             
                 
               in vitro in mm 
               by x-ray in mm 
               apex locator in mm 
             
             
                 
             
             
               Anterior teeth 
               23 
               23 
               23 
             
             
               Two root bicuspid 
               20, 20 
               20, 20 
               20, 20 
             
             
               Three root molar 
               19, 19, 19 
               19, 19, 19 
               19, 19, 19 
             
             
                 
             
           
        
       
     
   
   EXAMPLE II 
   Matrix conductive components of compositions C and D were prepared and tests were performed in the same manner as in Example I. The Composition D was applied directly to each root apex and the Composition C was used to surround and support each tooth and around Composition D. 
   
     
       
             
           
             
             
             
           
         
             
                 
             
             
               Composition C 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
                 
               Clay 
               70% 
             
             
                 
               Carbon-coated fiber 
               30% 
             
             
                 
                 
             
           
        
       
     
   
   
     
       
             
           
             
             
             
           
         
             
                 
             
             
               Composition D 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
                 
               Agar 
               30% 
             
             
                 
               Salt 
               10% 
             
             
                 
               Water 
               55% 
             
             
                 
               Oil 
                5% 
             
             
                 
                 
             
           
        
       
     
   
   Table II illustrates the results of testing: 
   
     
       
             
             
             
             
           
         
             
               TABLE II 
             
             
                 
             
             
                 
               Root length 
               Root length 
               Root length by 
             
             
                 
               in vitro in mm 
               by x-ray in mm 
               apex locator in mm 
             
             
                 
             
           
           
             
               Anterior teeth 
               23 
               23 
               23 
             
             
               Two root bicuspid 
               20, 20 
               20, 20 
               20, 20 
             
             
               Three root molar 
               19, 19, 19 
               19, 19, 19 
               19, 19, 19 
             
             
                 
             
           
        
       
     
   
   EXAMPLE III 
   Matrix conductive components of compositions E and F were prepared and tests were performed in the same manner as in Example I. The Composition D was applied directly to each root apex and the Composition E was used to surround and support each tooth and around Composition F. 
   
     
       
             
           
             
             
             
           
         
             
                 
             
             
               Composition E 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
                 
               acrylic 
               70% 
             
             
                 
               carbon powder 
               30% 
             
             
                 
                 
             
           
        
       
     
   
   
     
       
             
           
             
             
             
           
         
             
                 
             
             
               Composition F 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
                 
               Gum 
               30% 
             
             
                 
               Salt 
               15% 
             
             
                 
               Water 
               50% 
             
             
                 
               Oil 
                5% 
             
             
                 
                 
             
           
        
       
     
   
   
     
       
             
             
             
             
           
         
             
               TABLE III 
             
             
                 
             
             
                 
               Root length 
               Root length 
               Root length by 
             
             
                 
               in vitro in mm 
               by x-ray in mm 
               apex locator in mm 
             
             
                 
             
           
           
             
               Anterior teeth 
               23 
               23 
               23 
             
             
               Two root bicuspid 
               20, 20 
               20, 20 
               20, 20 
             
             
               Three root molar 
               19, 19, 19 
               19, 19, 19 
               19, 19, 19 
             
             
                 
             
           
        
       
     
   
   EXAMPLE IV 
   Matrix conductive components of compositions G and H were prepared and tests were performed in the same manner as in Example I. The Composition H was applied directly to each root apex and the Composition G was used to surround and support each tooth and around Composition H. 
   
     
       
             
           
             
             
             
           
         
             
                 
             
             
               Composition G 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
                 
               epoxy 
               70% 
             
             
                 
               conductive sponge 
               30% 
             
             
                 
                 
             
           
        
       
     
   
   
     
       
             
           
             
             
             
           
         
             
                 
             
             
               Composition H 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
                 
               Glycerine 
               77% 
             
             
                 
               Salt 
                5% 
             
             
                 
               Water 
               15% 
             
             
                 
               Carbopol 
                3% 
             
             
                 
                 
             
           
        
       
     
   
   
     
       
             
             
             
             
           
         
             
               TABLE IV 
             
             
                 
             
             
                 
               Root length 
               Root length 
               Root length by 
             
             
                 
               in vitro in mm 
               by x-ray in mm 
               apex locator in mm 
             
             
                 
             
           
           
             
               Anterior teeth 
               23 
               23 
               23 
             
             
               Two root bicuspid 
               20, 20 
               20, 20 
               20, 20 
             
             
               Three root molar 
               19, 19, 19 
               19, 19, 19 
               19, 19, 19 
             
             
                 
             
           
        
       
     
   
   
     
       
             
           
             
             
             
           
         
             
                 
             
             
               Composition I 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
                 
               Ground Stone 
               60% 
             
             
                 
               Carbon Powder 
               40% 
             
             
                 
                 
             
           
        
       
     
   
   
     
       
             
           
             
             
             
           
         
             
                 
             
             
               Composition J 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
                 
               Alginate 
               60% 
             
             
                 
               Water 
               40% 
             
             
                 
                 
             
           
        
       
     
   
   
     
       
             
             
             
             
           
         
             
               TABLE V 
             
             
                 
             
             
                 
               Root length 
               Root length 
               Root length by 
             
             
                 
               in vitro in mm 
               by x-ray in mm 
               apex locator in mm 
             
             
                 
             
           
           
             
               Anterior teeth 
               23 
               23 
               23 
             
             
               Two root bicuspid 
               20, 20 
               20, 20 
               20, 20 
             
             
               Three root molar 
               19, 19, 19 
               19, 19, 19 
               19, 19, 19 
             
             
                 
             
           
        
       
     
   
   The test results for each of the Examples I to V indicate that locating root length apexes utilizing devices in accordance with the invention have essentially the same accuracy as direct measurement (which cannot be accomplished in a living patient) and x-ray. 
   It is foreseen that teeth may be imbedded in the matrix by several different methods. The matrix can initially be powder, soft, pliable or the like and the tooth pushed into the matrix. The matrix may be poured about the tooth as seen in the third embodiment. Furthermore, it is foreseen that the highly conductive component of the matrix may be located only about the tooth root and surrounded by a second component or the highly conductive component may completely fill a sleeve sized for insertion in a socket or a container, or the highly conductive component may be a layer having less conductive material above and/or below the highly conductive component, including a thin layer of matrix fixing material that forms a substantially solid layer of matrix near the top of the tooth. 
   As will be apparent to persons skilled in the art, various additional modifications, adaptations and variations of the foregoing specifically disclosed embodiment and method for training in the use of an apical position locator may be made without departing from the objectives and scope of the present invention. Various modifications and changes may be made to the embodiment disclosed herein by those skilled in the art and such are contemplated by the present invention and are to be understood as included within the spirit and scope of the appended claims. 
   Fourth Embodiment 
   Illustrated in  FIGS. 10 through 13  is a fourth embodiment of a dental training aid in accordance with the present invention and generally indicated by the reference numeral  200 . The fourth embodiment includes elements of the first three and reference is made to the first three embodiments for greater detail. 
   The dental training device  200  includes a tray or structural support  203 , three training inserts  204 ,  205  and  206  and a securing plate  207 . 
   The structural support  203  is generally in the shape of a human jaw and in conjunction with the inserts  204 ,  205  and  206  provides a user with the feel of working on a human. It can be either an upper or lower portion of the mouth and can be used separately or in combination with a second unit in a manikin of the type shown in  FIG. 4 . 
   The support  203  includes a peripheral wall  210  extending upward from a lower and generally flat base  211  to a contoured end  212 . A central and rearward portion  214  of the base  211  extends upwardly and has a pair of spaced and threaded bores  216  that extend downward vertically from a top thereof. The remainder of the base  211  is covered by a relatively thin metal conductive plate  220  that is somewhat crescent or horseshoe in shape and which preferably receives all of the training inserts  204 ,  205  and  206  thereon in touching relationship. The plate  220  includes a metal conductive ring  225  that extends through and protrudes outwardly from the support  203 . The plate  220  has an upper surface  228  that is below an upper surface  229  of the base portion  214 . 
   The support wall  210  has an interior facing aperture or slot  230  for each insert  204 ,  205  and  206  that also face the inserts  204 ,  205  and  206  respectively when placed on the support  203  and which are used for securing the inserts  204 ,  205  and  206  in the support wall  210  as described below. 
   The present embodiment includes three inserts  204 ,  205  and  206  although it is foreseen that two or more than three could be used in accordance with the invention. The illustrated inserts  204 ,  205  and  206  are designed to provide practice and instruction to a student training in dental procedures. 
   In the present embodiment, insert  204  is especially designed for training in repair of tooth decay procedures, insert  205  is designed for training in crown and bridge procedures and insert  206  is designed for training in root canal procedures. Each of the inserts  204 ,  205  and  206  are modular and can be replaced with other units that provide training for the same or different procedures. In this manner, the student can acquire inserts for a single aid  200  device that can be used multiple times to teach different procedures and can be assembled in such a manner, as shown, to allow training or testing on multiple procedures at the same time or a plurality of training sites for a single procedure. In particular, in some uses, all of the inserts may be for the same procedures. 
   The insert  204  includes a base structure  235  that simulates the right rear third of the lower jaw. It includes apertures, sockets or openings  238 ,  239 ,  240  and  241  for teeth  250  to be used in training for treating tooth decay. The openings  238 ,  240  and  241  are designed to receive a single tooth  250  each. The opening  239  is wider than the others and receives multiple teeth  250 , so that the teeth  250  therein can be set to simulate a close positioning. 
   A tongue  255  extends outwardly from the insert  204  and is shaped and sized to be received in one of the slots  230 . Each of the openings  238 ,  239 ,  240  and  241  extend vertically part way through the insert  204 . Glue or adhesive may be utilized to hold the tooth and a surrounding matrix  250  in the opening  238 . A bore  261  extends through the base  235  and allows the alternative use of screw to hold the tooth  250  in the socket or opening  238 . In use each of the openings  238 ,  239 ,  240  and  241  receive at least one tooth  250  for performing repair of dental decay procedures as described before. The insert  204  has an inward facing lip  257  near the bottom thereof for securing in place. A front  260  of the insert  204  has a recess  261  therein. Teeth  250  are placed in each of the openings  238 ,  239 ,  240  and  241  in the matrix  262  that gives slightly with pressure so as to simulate the ligaments that are attached to live teeth. Preferably, the matrix  262  is at least partly constructed of rubber, silicon or the like to provide some degree of flexure. It is foreseen that the top of the matrix  262  can be solid with the tooth  250  and only the bottom of a flexible material. 
   The insert  205  is designed for crown and bridge work and in the present embodiment simulates the portion of the jaw normally holding the front  6  lower teeth of the mouth with the intent to use the two outer teeth for supporting a bridge. In particular, openings  266  and  267  are provided which receive and hold artificial or real teeth which are then ground by the student to provide supporting pegs  270  and  271 , as shown in  FIG. 11 . The student prepares a bridge  275  with artificial teeth  276 ,  277 ,  278 ,  279 ,  280  and  281  that then set on and are adhered to the pegs  270  and  271  in a conventional manner. A drape  284  of polyurethane, silicon, rubber or the like extends over the insert  205  and simulates the flexibility and structure of gum tissue, since it is important for the student to carefully interact with gum in crown procedures. 
   The insert  205  also includes an outward facing tongue  290  that is positioned to fit in one of the slots  230  and an inwardly facing lip  291 . On opposite ends of the insert  205  are position outward extending pegs  293  that are sized and shaped to be received in respective recesses in inserts  204  and  206  such as recess  261  in insert  204 . 
   The insert  206  simulates the left side of the lower rear third of the jaw and includes six openings  300 ,  301 ,  302 ,  303  and  304  which are each sized to receive a tooth  308  and do extend to the bottom  307  of the insert  206 . Each of the openings  300 ,  301 ,  302 ,  303 ,  304  and  305  are sized and shaped to receive a unit such as unit  310  which includes a tooth  308  and a surrounding conductive media  311 . The units  310  are glued or otherwise affixed in the openings  300 ,  301 ,  302 ,  303 ,  304  and  305 . The teeth  308  are preferably real teeth having a root canal. The student performs root canal procedures on the teeth  308  in the manner described before. The top part of the media  311  does not need to be conductive, but the lower portion onto which the tooth  308  root canal opens must be conductive between the tooth  308  and the plate  220 . The material of the media  311  engages the plate  220  so as to provide a conductive path between the bottom of each tooth root and the ring  225 . The insert  206  has a tongue  318  and a lip  319  similar to like structure found on the insert  204 . 
   The securing plate  207  is sized and shaped to be secured to the base  211  using screws  324  set in apertures  325  that are received in bores  216  in the support  203 . The securing plate extends outwardly toward each insert  204 ,  205  and  206  so as to cover the lips  257 ,  291  and  319  and so as to secure the inserts  204 ,  205  and  206  in the support  203  when secured in place by the screws  324 . 
   In use the various inserts are used in the manner shown in  FIG. 11 . An electrode  330  attached by an alligator clip  331  to the conductive ring  225  when root cannel procedures are performed in any of the inserts  204 ,  205  or  206 . The inserts  204 ,  205  and  206  are changed out as needed for other procedures or when expended to start new procedures. 
   It is foreseen that each insert would have an inwardly directed extension plate that could be attached by a single thumb screw, by multiple screws or the like to the support  203  and could replace the plate  207 . Also, it is foreseen that an electrode could be attached to the plate  220  in a different manner than is shown which could replace the conductive ring  225 . 
   It is to be understood that while certain forms of the present invention have been illustrated and described herein, it is not to be limited to the specific forms or arrangement of parts described and shown.