Abstract:
A medical device and a method for therapeutic treatment within an oral cavity employ a control circuit for generating an electromagnetic field , the circuit including an electrical power source and being integrated in a prosthetic appliance shaped to fit onto a patient&#39;s dentition.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a medical device used intra-orally for therapeutic purposes.  
         [0003]     2. Description of the Related Art  
         [0004]     Electrical stimulation of various body tissues has been used for decades with documented success for repair and regeneration of bone, muscle, nervous tissue and epithelial tissue as well as increased efficacy of certain antibiotics cited in the literature.  
         [0005]     One method to produce electrical fields is by invasively placing electrodes into the bone with the cathode (negative pole) placed into the site of bone repair and the anode (positive end) placed in the nearby soft tissue.  
         [0006]     Non-invasive methods to produce electrical fields are by capacitive coupling (CC) and by inductive coupling (IC). IC produces electrical fields using pulsed, time varying PEMFs. This technique uses a single or double current carrying coil, which is driven by an external field generator which induces a secondary field in bone. A number of configurations can be used, both single pulse and pulse burst, the latter consisting of a series of pulses with frequencies of 1-100 pulses/sec. Depending upon amplitude, frequency, and wave-form configurations, time-varying magnetic fields of 0.1 to 20 gauss can be used, producing voltage gradients of 1-10 microvolts in the inductive search coil. Gauss is a unit used in measuring the repelling effect of a magnetic field.  
         [0007]     Selected, weak, pulsed electromagnetic fields (PEMFs) have been successfully used in more than 250,000 patients during the past 20 years without evidence of hazardous side effects. This surgically non-invasive technique has the capacity to trigger rapid angiogenesis, to improve early bone union and to reduce bone resorption. Each of these proven bioeffects has a rational basis for improving the ultimate fate of a bone graft. Their physical principles and mechanisms of action are sufficiently well documented to place them alongside phramaceutical agents as therapeutic adjuncts to bone grafting procedures. PEMF&#39;s have a rational role in minimizing the chance for a bone graft failure.  
         [0008]     Articles relating to bone stimulation of teeth, periodontal ligament, dental implants and intra-oral bone grafts are more limited. With orthodontics, PEMF have been shown to increase the rate of orthodontic tooth movement and bone deposition without unfavorable effects on the periodontal ligament. In vitro periodontal studies show PEMF stimulate osteoblast and fibroblast activity. In bone growth stimulation, it has been shown that an electrical charge, either direct or indirect, can promote osteogenesis and bone formation around dental implants as well as prevent ridge resorption after tooth extraction. PEMF stimulation has been found to be useful for the present invention as a result of earlier assessments and discussions of the current literature. PEMF in this context refers to the induction of voltage or current in tissues by an externally applied pulsating magnetic field.  
         [0009]     Several medical devices are currently on the market using PEMF principles for tissue stimulation. These devices have coils imbedded into adhesive pads similar to ECG leads. The coils are attached to the power source of the device similar in appearance to an older cell phone. The “ECG” leads are attached to the skin on either side of the area to be treated. Obviously, the size and design of these devices preclude their intra-oral use.  
         [0010]     European Patent Application No. 0,599,786, filed Apr. 7, 1993 by Enzo Lino Diodato, discloses a mouth internal device which generates a magnetic field in the oral cavity, which thereby induces an electrical field with “the result to stimulate in the tooth the accelerated growth of the dentine, with the aim of protecting the dental pulp in a series of pathological processes that can compromise its vitality.” 
         [0011]     Japanese Patent No. JP3007172, published Jan. 4, 1991 by Hashimoto et al., discloses a device which accomplishes “a therapy free from pain and inflammation by locating teeth between two permanent magnets facing each other, feeding a pulse current to a coil for generation of an electromagnetic field in pulse form, superposing this over a steady magnetic field from the permanent magnets, and applying this resultant field to the teeth.” 
         [0012]     These prior art devices have the disadvantage that, while being used internally, they must connect externally with a power source that powers the coil(s). This provides an awkward situation for the patient who must not only manage any discomfort of these prior art devices in their mouth, but must also deal with cables extending therefrom.  
         [0013]     Furthermore, the secure placement of these prior art devices within the oral-cavity, such that the intended area to be treated is appropriately within the generated fields, is difficult to achieve and the patient must struggle with remaining still during the treatment period. This places an undue burden on the patient since it is possible that treatment periods can range from several hours.  
       BRIEF SUMMARY OF THE INVENTION  
       [0014]     It is, accordingly, an object of the present invention to provide a novel and improved medical device for intra-oral use that incorporates the power source within the device itself, and allows the secure placement of such a device within the oral cavity.  
         [0015]     According to one aspect of the present invention, there is provided a medical device for therapeutic treatment within an oral cavity. The medical device comprises a means for generating an electromagnetic field for the therapeutic treatment. The means for generating an electromagnetic field includes an electrical power source to energize the means for generating the electromagnetic field. There is also a prosthetic appliance shaped to fit onto a dentition. The means for generating the electromagnetic field is integrated with the prosthetic appliance.  
         [0016]     According to another aspect of the present invention, there is provided a method for therapeutic treatment of an area in the oral cavity. The method comprising the steps of installing a prosthetic appliance to fit onto a dentition of a patient; and providing means for generating an electromagnetic field integrated in the prosthetic appliance, the means for generating the electromagnetic field including an electrical power source, and employing the electrical power source to energize the means for generating the electromagnetic field, whereby the electromagnetic field induces a therapeutic effect in the area. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     The invention will be more readily understood from the preferred embodiments thereof illustrated, by way of example, in the accompanying drawings, in which:  
         [0018]      FIG. 1  shows a perspective view of a medical device for intra-oral use according to one embodiment of the present invention;  
         [0019]      FIG. 2  shows a perspective view of an opposing pair of coils and a control unit of the medical device of  FIG. 1 ;  
         [0020]      FIG. 3  shows an exploded view of the control unit of  FIG. 2 ;  
         [0021]      FIG. 4  shows a diagrammatic view of pulsed magnetic field characteristics;  
         [0022]      FIG. 5  shows a diagrammatic view of the medical device of  FIG. 1 ;  
         [0023]      FIG. 6  shows a magnetic field produced by a circular coil of the medical device of  FIG. 1 ;  
         [0024]      FIG. 7  shows a diagrammatic view of a magnetic field at the center of two coils of the medical device of  FIG. 1 ;  
         [0025]      FIG. 8  shows a graphical view of magnetic field strength of the magnetic field of the coils of  FIG. 7 ;  
         [0026]      FIG. 9  shows a perspective view of a medical device for intra-oral use according to another embodiment of the present invention; and  
         [0027]      FIG. 10  shows a circuit diagram of the control unit of  FIG. 2 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0028]     Referring to the drawings and first to  FIG. 1 , there is shown a medical device indicated generally by reference numeral  10 , which comprises a prosthetic appliance, in this example a mouth guard  12 , and a control unit  14  and a coil assembly  16 . In other examples the prosthetic appliance can be a custom made prosthesis fabricated from thermoplastic or processed acrylic. The mouth guard  12  is adapted to fit onto and to conform to the dentition of a patient, and comprises a sheet of ethylvinyl acetate  11 , in this example, having an arch  13 .  
         [0029]     The coil assembly  16  is in the form of a saddle bag, in this example, and is arranged to straddle the area of treatment of the patient, and therefore the position of the coil assembly  16  along the mouth guard  12  varies from patient to patient.  
         [0030]     Referring now to  FIGS. 2 and 3 , the control unit  14  and the coil assembly  16  are shown apart from the mouth guard  12 . Electrical wires  18  electrically connect the coil assembly  16  with the control unit  14 . The electrical wires  18  provide a conduit for current pulses from the control unit  14  to the coil assembly  16  so that an electromagnetic field can be established, which is described in more detail below.  
         [0031]     The coil assembly  16  includes coils  34   a  and  34   b , which are joined together in series in this example, and which are arranged in a spaced apart and opposing manner. The coils  34   a  and  34   b  are imbedded into a water proof, plastic lamination  36  that can flex in the middle to allow the coils  34   a  and  34   b  to be placed on either side of the intended area of pulse electromagnetic field (PEMF) stimulation.  
         [0032]     Each of the coils  34   a  and  34   b  comprises, in this example, 200  windings of  39  gauge copper wire, and the inside diameter of the coils is  9   m m and the outside diameter is 1 mm. The coils  34   a  and  34   b  are made by wrapping wire around a removable central core which is, in this example, 9 mm in diameter. In other examples different dimensions of the coil are possible. Once wrapped, wire turns of each of the coils  34   a  and  34   b  are bonded together with an adhesive cement.  
         [0033]     Ends of the wire of the coils  34   a  and  34   b  are extended about 3 to 4 inches, in this example, to attach at one end to the control unit  14 . The coils are then removed from the removable core and cemented onto the plastic lamination  36 . The ends of the wire of the coils  34   a  and  34   b  for connection to the control unit  14  are twisted together to form the electrical wires  18 .  
         [0034]     As shown in  FIG. 3 , the control unit  14  comprises a housing  20 , an end cap  22 , a circuit board assembly  24  and a power source  26 . The housing  20  has receptacles  28  and  30  for receiving the power source  26  and the circuit assembly  24 , respectively.  
         [0035]     In this embodiment of the present invention, the power source  26  includes two  1 . 5  Volt AAAA batteries  40 , however other types of batteries can be used in other embodiments. The batteries  40  are adjacent each other with a negative pole of one of the batteries  40  being adjacent a positive pole of the other battery. A metal strip  32  connects the batteries  40  in series to form a  3  volt power source for the circuit board assembly  24  and the coils  34   a  and  34   b . There are lead wires (not shown) which extend from the batteries  40 , at an end of the batteries opposite the metal strip  32 , for connection with the control unit  14 . The two batteries  40  are shrink wrapped (not shown).  
         [0036]     Referring now to both  FIGS. 3 and 10 , the circuit board assembly  24  includes a printed circuit board  38 , an LED  42 , a switch  44 , a microcontroller  46  and a transistor  48 . The electrical wires  18  and the lead wires from the power source  26  are connected with the printed circuit board  38  such that electrical power from the power source  26  can be selectively applied to the coils  34   a  and  34   b.    
         [0037]     The circuit board assembly  24  is cemented onto a surface  50  of the power source  26 , and the combination is then received within the receptables  28  and  30  respectively. The control unit  14  is dipped into a waterproofing material. In other examples, the circuit board assembly  24  and the power source  26  can be affixed directly to the mouth guard  12  without first inserting them into the housing  20  and the end cap  22 .  
         [0038]     Referring again to  FIG. 1 , the mouth guard  12  is shaped to conform to the dentition of a patient, and the control unit  14  and the coil assembly  16  are attached with the mouth guard, according to the following procedure: 
    1. Take an accurate Alginate impression of the jaw of the patient, including the area of treatment. Ensure the impression is extended well into the buccal sulcus, especially in the treatment area.     2. Pour up the impression in dental stone.     3. Mold a thin sheet, e.g. twenty to sixty mil, of ethylvinyl acetate  11  onto the model using an OmniVac.     4. Fold the coil assembly  16  over the area to be treated and attach one of the coils  34   a  or  34   b  to the acetate sheet  11  using adhesive.     5. Attach the coil at the other end of the coil assembly  16  to the acetate sheet  11  onto the  10  opposite side of the arch  12 , ensuring that both of the coils  34   a  and  34   b  bracket the area to be treated.     6. Attach the control unit  14  to buccal aspect of the acetate sheet  11  on the side of the arch  12 . Ensure the control unit  14  lies deep in the buccal sulcus and the switch  44  faces buccally.     7. Make a cut into the acetate sheet  11  three millimeters on either side of the coil assembly  16  at right angles to the tangent of the arch  12 . Extend the cut into the buccal sulcus.     8. Make a cut into the acetate sheet  11  five millimeters on either side of the control unit  14  at right angles to the tangent of the arch  12 . Extend the cut into the buccal sulcus.     9. Trim the balance of the acetate sheet  11  up to the buccal sulcus.     10. Using a propane torch, gently heat the acetate sheet  11  remaining next to the coil assembly  16  on the buccal side until soft.     11. Fold the cut portion of the acetate sheet  11  back over the coil assembly  16  ensuring the fold is in the buccal sulcus.     12. Trim any excess of the acetate sheet  11  from the buccal sulcus.     13. Repeat for the lingual extension over the coil assembly  16  .     14. Repeat the same process for the extension over the control unit  14 .     15. Bond the cut portions of the acetate sheet  11  together, e.g. paint a coat of adhesive over the acetate sheet  11  or heat seal.     16. Mold a second thin sheet, e.g. twenty to sixty mil, of ethylvinyl acetate over the previous sheet onto the model using an OmniVac.     17. Trim off all excess from the second sheet allowing the margins to end in the buccal and lingual sulci.     18. Using a propane torch, run the flame over edges of the two sheets to meld the two edges together.    
 
         [0057]     Referring now to  FIG. 4 , the following are exemplary PEMF characteristics for the medical device  10 . However, other PEMF characteristics are possible. A waveform of the pulsed magnetic field is shown in  FIG. 4 . The overall duty cycle of the waveform ( FIG. 4 ) is 5%. Treatment duration may be varied. 
        Pulse amplitude (magnetic field strength)=10 Gauss     Pulse width 250 s (50% duty cycle)     Number of pulses per burst=20     Burst repetition frequency=10 Hz     Treatment duration=2 hrs per day     Treatment period 8 weeks        
 
         [0064]      FIG. 5  is a first level architectural design of the medical device  10 , illustrating a transducer  60  to produce the PEMF, an excitation circuit  62  to create the necessary current pulses to the transducer  60 , and a power source  64 .  
         [0065]     The coils  34   a  and  34   b  formed by insulated copper wire are chosen to produce the PEMF. The magnetic field of circular coils, for example, with a radius ‘a’ shown in  FIGS. 6 and 7 , at a distance ‘z’ along the coil axis is derived as follows. If the current flowing through a single turn coil is I, a magentic field dB is induced by the current element flowing in a small segment dl of the loop at a distance z away from the center of the coil. dB is given by:  
       dB   =           μ   0     ⁢   dl       4   ⁢   π   ⁢           ⁢     r   2         =         μ   0     ⁢   Iad   ⁢           ⁢   θ       4   ⁢   π   ⁢           ⁢     r   2               
 
         [0066]     The component of the magnetic field in the direction of the Z axis is:  
           dB   z     =       -   dB     ⁢           ⁢   cos   ⁢           ⁢   θ       ,       where   ⁢           ⁢   cos   ⁢           ⁢   θ     =     a   r           
 
         [0067]     Therefore, the magnetic field due to the entire coil in the direction of the z axis is:  
               B   z     =       ⁢     ∫     dB   z                   =       ⁢       ∫   0     2   ⁢   π       ⁢       -       μ   0       4   ⁢   π         ⁢       Iad   ⁢           ⁢   θ       r   2       ⁢     a   r                     =       ⁢       -         μ   0     ⁢     Ia   2         4   ⁢   π   ⁢           ⁢     r   3           ⁢       ∫   0     2   ⁢   π       ⁢           ⁢     ⅆ   θ                     =       ⁢       -         μ   0     ⁢     Ia   2         4   ⁢   π   ⁢           ⁢     r   3           ⁢   2   ⁢   π                 =       ⁢     -           ⁢         μ   0     ⁢     Ia   2         2   ⁢           ⁢     r   3                     
 
         [0068]     For an N-turn coil, the magnetic field becomes:  
           B   z     =     -         μ   0     ⁢     NIa   2         2   ⁢     r   3             ,       but   ⁢           ⁢   r     =         a   2     +     z   2           ,   therefore       
         B   z     =         μ   0     ⁢     NIa   2         2   ⁢       (       a   2     +     z   2       )       3   2               
 
         [0069]     As the transducer  60  must be totally imbedded into the mouth guard  12 , very thin insulated copper wire is needed to form the coils  34   a  and  34   b  to produce the magnetic field.  FIG. 7  shows the coils  34   a  and  34   b  placed at b mm away from the center on each side of the dental implant. Note that a typical titanium dental implant is 4 mm in diameter and 8 to 15 mm long. If the current in both of the coils  34   a  and  34   b  is equal (I) and flowing in the same direction, from equation (1), the magnetic field B at the center is equal to:  
             B   =         B   1     +     B   2       =       2   ⁢     B   z       =       2   ⁢         μ   0     ⁢     NIa   2         2   ⁢       (       a   2     +     b   2       )       3   2             =         μ   0     ⁢     NIa   2           (       a   2     +     b   2       )       3   2                       (   2   )             
 
 where B 1  and B 2 are the magnetic fileds due to coil 34   a  and coil  34   b  in  FIG. 7  respectively 
 
         [0070]     When each of the coils  34   a  and  34   b  has 200 turns (N=200) with a diameter of 10 mm (a=5 mm), and the coils are separated by 12 mm (b=6 mm). For non-ferromagnetic material, the permeability is approximately equal to that in free space, i.e., μ 0 =4π×10 −7  T.m/A. To produce a magnetic field of 10 Gauss (B=1 mT), using equation (2) above:  
       B   =             μ   0     ⁢     NIa   2           (       a   2     +     b   2       )       3   2         ⇒   I     =           (       a   2     +     b   2       )       3   2           μ   0     ⁢     Na   2         ⁢   B           
 
 and substituting the chosen values into the equation, the excitation current I is 76 mA. 
 
         [0071]     Table 1 shows the calculated magnetic field strength along the central axis of the setup in  FIG. 7  when I=76 mA. The magnetic field due to coil  34   a  alone, coil  34   b  alone and both coils at a distance of b 1  from the left coil are tabulated in the table.  FIG. 8  shows the plot of these magnetic fields at different locations along the center axis of the coils.  
                                                         TABLE 1                                   b1(mm)   Coil 34a   Coil 34b   Total (mT)                                        0   1.91   0.11   2.01           1   1.8   0.14   1.93           2   1.53   0.17   1.7           3   1.2   0.22   1.42           4   0.91   0.28   1.19           5   0.67   0.37   1.05           6   0.5   0.5   1           7   0.37   0.67   1.05           8   0.28   0.91   1.19           9   0.22   1.2   1.42           10   0.17   1.53   1.7           11   0.14   1.8   1.93           12   0.11   1.91   2.01                      
 
         [0072]     As the waveform duty cycle is  5 %, the average current consumption I avg  is therefore equal to 76 mA×5%=3.8 mA.  
         [0073]     Since the device is desired to be used for 2 hrs/day for an 8 week period, the minimum capacity of the power source supplying power to the device is therefore equal to (2 hr/day×7 day/wk×8 wk)×3.8 mA=426 mAhr.  
         [0074]     This is within the energy capacity of a lithium AAAA cylindrical battery (which has a typical capacity of 1250 mAhr and 1.5V output).  
         [0075]     Referring now to  FIG. 9 , wherein like parts to the previous embodiment have like reference numerals with an additional suffix “0.2“, there is shown a medical device  10 . 2  having a control unit  14 . 2  and a coil assembly  16 . 2  at different locations along a mouth guard  12 . 2 , in contrast to the medical device  10 , for treatment in another area of the dentition.  
         [0076]     As will be apparent to those skilled in the art, various modifications may be made in the present invention within the scope of the appended claims.