Abstract:
A gauge and a method for using the gauge, measures the Frankfurt Mandibular Angle (FMA) non-invasively, without the use of x-rays. The gauge has an upper bar that, in use, parallels the patient&#39;s porion-orbitale line. A downward bar depends from the upper bar and has an adjustably attached lower bar. The lower bar is adjusted to parallel the patient&#39;s gonion-menton line. Once the gauge is properly adjusted to the patient and locked into place, the user reads a measuring device on the gauge, which indicates the relative positions of the components of the adjusted gauge. These reading are then correlated, directly or indirectly, to the patient&#39;s FMA.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to measurement of the Frankfort Mandibular Plane Angle (FMA) and more specifically to the non-invasive, external measurement of FMA, without x-ray. 
     2. Description of the Background Art 
     The Frankfurt Mandibular Plane Angle is defined as the angle formed by the intersection of two extended lines: one drawn through the gonion and the second through the porion and orbitale. Traditionally, the FMA is determined by utilizing a lateral cephalometric radiograph, which is developed in an x-ray film processor, dried, labeled and then covered by an acetate sheet. The landmarks are marked, lines traced, and the FMA measured with a protractor. Most recently, charged coupled devices are irradiated in a similar fashion to the lateral cephalogram and the resultant image digitized. The FMA is then determined with the aid of a computer software program after the landmarks are identified. The major limitations and disadvantages of both of these techniques are that invasive x-rays irradiate most of the patient&#39;s head, and very costly, cumbersome equipment is required. Also, a skilled dentist, radiologist, or highly trained technician, who has had long experience in tracing these radiographs, must spend time discerning indistinct landmarks, tracing on the acetate coversheet, and “estimating” the FMA with a protractor. Specially shielded x-ray rooms are required when exposing dental x-rays, costly developing machines, and dangerous and harmful chemicals are required. Retakes of the x-ray must be done if the patient moves during exposure or if the head position or degree of mouth opening is not ideal. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to measure a patient&#39;s FMA without invasive procedures and without x-ray. 
     It is another object of the present invention to measure a patient&#39;s FMA without x-rays. 
     It a further object of the present invention to measure a patient&#39;s FMA without expensive special equipment. 
     These and other objects are achieved by a device that includes a frame having an upper bar and a downward bar extending from the upper bar at a known angle. The upper bar, when fitted to the patient, extends parallel to the patient&#39;s porion-orbitale line. The rear bar is fixed to the upper bar extends from the patient&#39;s porion to the patient&#39;s gonion. A lower bar is movably attached to the rear bar and, when fitted to the patient, extends parallel to and at the same height as the patient&#39;s gonion-menton line. Because the relationship between the fixed points of the bars and the fixed points of reference on the patient (porion, orbitale, gonion, and menton) and the dimensions and angular relationships between the various parts of the FMA gauge&#39;s frame are known, the FMA can be determined by reading a measuring device on the gauge. In some embodiments, this angular determination can be made directly from the measuring device. In other embodiments, the measuring device indicates the position of the lower bar, once adjusted to the patient, with respect to the downward bar. This relative position may then be correlated with the patient&#39;s FMA. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of an embodiment of the device according to the present invention. 
     FIG. 2 is a top view of the device shown in FIG. 1 
     FIG. 3 is a front view of the device shown in FIG.  1  and FIG.  2 . 
     FIG. 4 is an oblique view of a cost-reduced embodiment of a device according to the present invention similar to that shown in FIG.  1 . 
     FIG. 5 is a side view of the device shown in FIG. 4, after adjustment to fit the patient. 
     FIG. 6 is a front view of the device shown in FIG. 4, after adjustment to fit the patient. 
     FIG. 7 shows another embodiment of the present invention. 
     FIG. 8 shows the top bar of the gauge shown in FIG.  7 . 
     FIG. 9 shows the gauge of FIG. 7 when correctly aligned and adjusted on a patient. 
     FIG. 10 shows the gauge of FIG. 7 disassembled. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in FIG. 1, FMA gauge  10  includes a frame (typically trapezoidal) having upper bar  12 , rear bar  14 , front bar  16 , and lower bar  18 . Upper bar  12  extends at least from the porion to the orbitale of the patient. Upper bar  12  extends parallel to and typically at the same height as the porion-orbitale line. While upper bar  12  could be at height below or above the porion-orbitale line, having it at the same height better enables visual alignment of the gauge parallel to the porion-orbitale line. Additionally, this arrangement allows gauge  10  to be anchored at the porion by earpiece  11  (FIG.  2 ). 
     Rear bar  14  is fixed to and extends downwardly from upper bar  12 . Generally, rear bar  14  extend to at least the patient&#39;s gonion. Rear bar  14  may include a clear or cutout portion  20  which permits the user to visually align the rear bar.  14  with the patient&#39;s gonion. In the embodiment of FIG. 1, cutout  20  also serves as a slot allowing lower bar  18  to be upwardly or downwardly adjusted with respect to rear bar  14 . While FIG. 1 shows the use of cutout  20  and wingnut  21  to attach lower bar  18  to rear bar  14 , any method of attachment that allows lower bar  18  to be adjusted vertically and angularly with respect to rear bar  14  (so that the lower bar can be adjusted to extend parallel to and at the same height as an imaginary line between the patient&#39;s gonion and menton), and then locked into position, may be used. For example, lower bar  18  may be attached to rear bar  14  by quick-releasing spring clips fixed to lower bar  18 . 
     As with the attachment of lower bar  18  to rear bar  14 , the attachment of rear bar  18  to front bar  16  should allow lower bar  18  to be adjusted vertically and angularly with respect to rear bar  14  (so that the lower bar can be adjusted to extend parallel to and at the same height as an imaginary line between the patient&#39;s gonion and menton) and then locked into position. Thus, any attachment method suitable for attachment of lower bar  18  to rear bar  14  should be suitable for the attachment of lower bar  18  to front bar  16 . In the embodiment of FIG. 1, lower bar  18  and front bar  16  are attached using the same wingnut and cutout arrangement as used for rear bar  14  and lower bar  18 . Lower bar  18  also includes slots to simplify its alignment with the gonion-menton line. Optional support bar  24  is fixed to rear bar  14  and front bar  16 , and supports the frame of the gauge. 
     Although FIG. 4 shows that, in use front bar  16  of gauge  10  attaching to upper bar  12  forward of the menton, The position of front bar  16  with respect to the patient and rear bar  14  are, except for facilitating placement and handling of gauge  10 , not critical to the function of the device. Similarly, while FIG. 1 shows rear bar  14  and front bar  16  extending perpendicularly from upper bar  12 , the angle between upper bar  12  and the front and rear bars ( 14 ,  16 ) is not critical to the function of the invention. Instead, this invention only requires that the angular relationships and the distances between the parts of the frame are known sufficiently to allow determination of the angle between rear bar  14  and lower bar  21 . The device according to the present invention also benefits from a structure that allows the device to be stabilized with a known angular relationship to the orbitale-menton line and with the lower bar parallel to the gonion-menton line. 
     In the device of FIG. 1, stabilization of the device and proper orientation of the device with respect to the patient are aided by the earpiece  11 , handle  30  (FIG.  2 ), face bar  32 , nose piece platform  34  (FIG.  3 ), nosepiece slide  36 , universal joint  38 , nosepiece  40 , handle  42  (FIG.  2 ), and mandibular plate  44 . Typically, mandibular plate  44  is attached to lower bar  18  using the with the same fastening mechanism (such as wingnut  21  and bolt) using to attached lower bar  18  to front and rear bars  16 ,  14 . Therefore, the height and angle of mandibular plate  44  is adjusted simultaneously with that of lower bar  18  Handles  30  and  42  permit the user to more easily position device  10  with respect to the patient. Nosepiece platform  34  attaches nosepiece slide  36  to upper bar  12  so that nosepiece slide  36  extends toward the opposite side of the patient&#39;s head, essentially perpendicular to the device&#39;s frame, forward of the patient&#39;s nose. Nosepiece  40  is attached, at its stem, to nosepiece platform  34  by universal joint  38 , which includes a fastener (such as thumbscrew, wingnut, or the like) that can be easily tightened or loosened for facile positioning and locking of nosepiece  40 . Nosepiece  40  typically has a dumbbell-shaped end which, when properly adjusted, fits into the bridge of the patient&#39;s nose and stabilizes the gauge with respect to the patient. Handle  30 , is connected to earpiece  11  and upper bar  12  and facilitates the placement of earpiece  11  in the patient&#39;s ear. Handle  30 , attached to a portion of upper bar  12  that is essentially perpendicular to the frame, extends towards the opposite side of the patient&#39;s head and assists in adjusting the position of nosepiece  40 . Mandibular plate  44 , is typically attached to front bar  16  and supports the patient&#39;s mandible. Once properly fitted, earpiece  11 , nosepiece  40 , and mandibular plate  44  stabilize device  10  with respect to the patient, thus allowing accurate measurement of the FMA. 
     In the FIG. 1 embodiment, front bar  16  and rear bar  14  have measuring devices  26  and  48 , respectively, for indicating distance along the length of the bar. The measuring devices shown includes scale markings on the bars. Once device  10  is properly adjusted and aligned with respect to the patient, the scale marking at the location where the lower bar  18  intersects front bar  16  and the scale marking at the location where the lower bar  18  intersects rear bar  14  are read and noted. The difference between the markings is then determined. This difference is then entered into an FMA gauge conversion table, such as shown in Table 1, to give the FMA. Whether the scales are read at the forward or rear edges of their respective bars is of course irrelevant, provided that the conversion table is calibrated to the reading method used. If desired, the conversion table may be divided into three sections, one for low FMA, one for average FMA, and another for high FMA. 
     
       
         
               
             
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 FMA GAUGE CONVERSION TABLE 
               
             
          
           
               
                 Low FMA 
                 Average FMA 
                 High FMA 
               
             
          
           
               
                   
                 FMA in 
                   
                 FMA in 
                   
                 FMA in 
               
               
                 Difference 
                 degrees 
                 Difference 
                 degrees 
                 Difference 
                 degrees 
               
               
                   
               
             
          
           
               
                 10 
                 5 
                 39 
                 20 
                 65 
                 31 
               
               
                 11 
                 6 
                 40 
                 20 
                 66 
                 31 
               
               
                 12 
                 6 
                 41 
                 20 
                 67 
                 31 
               
               
                 13 
                 7 
                 42 
                 21 
                 68 
                 32 
               
               
                 14 
                 7 
                 43 
                 21 
                 69 
                 32 
               
               
                 15 
                 8 
                 44 
                 22 
                 70 
                 32 
               
               
                 16 
                 8 
                 45 
                 22 
                 71 
                 33 
               
               
                 17 
                 9 
                 46 
                 23 
                 72 
                 33 
               
               
                 18 
                 9 
                 47 
                 23 
                 73 
                 34 
               
               
                 19 
                 10 
                 48 
                 24 
                 74 
                 34 
               
               
                 20 
                 10 
                 49 
                 24 
                 75 
                 34 
               
               
                 21 
                 11 
                 50 
                 24 
                 76 
                 35 
               
               
                 22 
                 11 
                 51 
                 25 
                 77 
                 35 
               
               
                 23 
                 12 
                 52 
                 25 
                 78 
                 35 
               
               
                 24 
                 12 
                 53 
                 26 
                 79 
                 36 
               
               
                 25 
                 13 
                 54 
                 26 
                 80 
                 36 
               
               
                 26 
                 13 
                 55 
                 27 
                 81 
                 36 
               
               
                 27 
                 14 
                 56 
                 27 
                 82 
                 37 
               
               
                 28 
                 14 
                 57 
                 27 
                 83 
                 37 
               
               
                 29 
                 15 
                 58 
                 28 
                 84 
                 37 
               
               
                 30 
                 15 
                 59 
                 28 
                 85 
                 38 
               
               
                 31 
                 16 
                 60 
                 29 
                 86 
                 38 
               
               
                 32 
                 16 
                 61 
                 29 
                 87 
                 38 
               
               
                 33 
                 17 
                 62 
                 29 
                 88 
                 39 
               
               
                 34 
                 17 
                 63 
                 30 
                 89 
                 39 
               
               
                 35 
                 18 
                 64 
                 30 
                 90 
                 39 
               
               
                 36 
                 18 
                   
                   
                 91 
                 40 
               
               
                   
               
             
          
         
       
     
     Table 1 calculates the FMA using an assumed fixed porion-orbitale distance of 10. Of course the actual porion-orbital distance is irrelevant. Geometrically, the FMA can be determined from the measurements taken at front bar  16  and rear bar  14  provided that the frame is essentially planar, the distance between front bar  16  and rear bar  18  is known, the angle between front bar  16  and upper bar  18  is known, the angle between rear bar  14  and upper bar  18  is known, and the frame is in a known, specified position with respect to the porion-orbital line and the gonion. The trigonometric formula applied for Table 1 uses a predefined “orbital-porion” distance of 110 mm, in the following formula:          FMA   =     arctan                   (       OM   -   PG     OP     )         ,     in                   degrees   .                              
     From FIG. 1, its clear that the the FMA can be determined simply by knowing the angle formed by the bar paralleling the GM line and a line paralleling the OP line. Earpiece  11  and nosepiece  40  simply assist in assuring that the device is properly adjusted and stabilized so that the FMA may be measured. The device may be used with the anchoring provided by earpiece  11  and nosepiece  40 , although correct alignment and stability may be more difficult to achieve. Additionally, even upper bar  12 , or portions thereof (particularly the portions between the front and rear bars  16  and  14 ) may be removed, albeit at a potential reduction in stability and ease of alignment. As will be shown in embodiments discussed below, front bar  16  may also be removed if, rather than distance measurement along the front and rear bars  16 ,  14  are made, the angle between lower bar  18  and rear bar  14  is directly measured. Lower bar  24  functions only to aid handling during alignment and increase stability, and is optional. 
     Typically, device  10  of FIG. 1 is operated as follows: 
     1. The patient is seated upright, and the operator stands or sits to the right of the patient. After removing eyewear, hearing aides, and any interfering jewelry and pulling back the patient&#39;s hair, if necessary, the patient and operator orient themselves so that they are at approximately eye level. 
     2. The FMA Gauge is prepared by loosening the universal joint  38  just enough to pull the nosepiece  40  toward the front of the gauge; wing nuts  22  are loosened, allowing lower bar  18  to drop downward and forward; and a finger cot is placed over the earpiece  11 . 
     3. The patient or an assistant grips handles  42  and  30  and helps the operator to comfortably guide earpiece  11  into the right ear. The patient or assistant continues to stabilize the FMA Gauge while the operator adjusts the nosepiece  40 . 
     4. The earpiece automatically lines up the top of upper bar  12  with the top of the ear hole, corresponding to the portion. The operator palpates the patient&#39;s infraorbital notch and, while lining up the anterior aspect of upper bar  12  with the notch, fits the rubbery, dumbbell-shaped end of nosepiece  40  to the bridge of the nose and tightens the universal joint  40  by twisting the nosepiece adjusting knob  39 . The infraorbital notch corresponds to the orbitale. 
     5. Alignment of upper bar  12  is rechecked for location, fit, and comfort before proceeding to adjust lower bar  18 . 
     6. The patient is asked to swallow and relax the lower jaw, which is then placed into the desired evaluation position. The patient is requested to hold this position while lower bar  18  with attached mandibular plate  44  is raised to firmly contact the lower border of the mandible. 
     7. Wing nuts  22  are tightened to stabilize the lower bar  18  and mandibular plate  44 . 
     8. A pair of numerical values from the rulers on each of the bars  14 ,  16  is noted and recorded. In this particular example (using Table 1), the numerical values are derived from where the top of lower bar  18  crosses bars  14 ,  16 . An example of this is shown in FIG.  1 . The number from rear bar  14  is subtracted from the number from front bar  16 , and the numerical value of the difference is looked up on the FMA Gauge Conversion Table (Table 1). The corresponding Frankfurt Mandibular Angle (FMA) and the descriptive term (“High,” “Low” or “Average”) are then noted. 
     9. Repeat measurements are done simply by loosening the wing nuts and dropping down the lower bar  18 /mandibular plate  44  assembly. The patient is then allowed to relax for a moment, resume the desired jaw position, device  10  is readjusted, and another measurement is made. 
     10. Once satisfied with the repeatability of the measurements, the FMA Gauge may now be removed from the patient by reversing the procedure. 
     11. The finger cot is removed from the earpiece  11  and discarded. The FMA Gauge may now be washed and disinfected. 
     FIG. 4 shows a cost-reduced version of the FMA gauge of FIG.  1 . Frame elements upper bar  102 , rear bar  104 , lower bar  106 , and front bar  108  are analogous their counterparts in the FIG. 1 embodiment, and will not be further described. Also, support bar  109  and mandibular place  112  are analogous to their counterparts and need to be further described. The reduced cost embodiment of FIG. 4 lacks the stabilizing earpiece, and, rather than the nosepiece and associated components of the FIG. 1 embodiment, uses infraorbital indicator  110  to provide a reference point for alignment with the patients orbitale and support for stabilizing the device  100  during use. FIG.  5  and FIG. 6 show the device of FIG. 4 properly positioned on at patient. In this embodiment, the intersection of upper bar  102  and rear bar  104  provide a point of reference to align with the porion. If desired, however, a marking along the device, rather than an intersection of frame elements, may serve as the reference point for alignment with the porion. The operation and adjustment of the device shown in FIG. 4 is analogous to that shown in FIG.  1 . 
     FIG. 7 shows gauge  200  according to the present invention. Gauge  200  measures FMA directly, rather than via rulers and a conversion table. Analogous parts to the FIG. 1 embodiment are similar in form and function. As best shown in FIG. 8, upper bar  210  includes earpiece  212 , nosepiece  214 , nosepiece bar  216 , universal joint  218 , and infraorbital indicator  220 . When adjusted to the patient, infraorbital indicator  220  is aligned with the patient&#39;s orbitale (as shown in FIG. 9) and earpiece  212  fits into the patient&#39;s ear, wingnut  222  of universal joint  218  loosened and nosepiece  214  is adjusted so that its dumbbell-shaped end straddles the bridge of the patient&#39;s nose (see FIG.  9 ). 
     Downward bar depends from upper bar  210 , and extends to or below the level of the patient&#39;s gonion when gauge  200  is properly aligned with the patient. Slot  224  on downward bar  216 , together with longitudinal slot  226  of lower bar  228  allows for vertical and horizontal adjustment of lower bar  228  and attached mandibular plate  230  with respect to downward bar  216 . Mandibular plate  230  moves in unison with lower bar  228 , and, if desired, lower bar  228  and mandibular plate  230  may be a unitary piece. 
     Angulation indicator  232  is attached to lower bar  228  and mandibular plate  230  with wingnut  234 . Angular indicator  232  includes angular markings thereon. In use, wingnut  234  is loosened and angular indicator is set so that the “0” angle line is parallel to upper bar  210 . This alignment can be aided by line  236  which is fully within slot  224  of downward bar  216  when the “0” angle line is parallel to upper bar  210 . Gauge  200  is aligned with the patient as described above and mandibular plate  230 /lower bar  228  are adjusted so that lower bar  228  parallels the patient&#39;s gonion-menton line (see FIG.  9 ), typically by adjusting the device so that the mandibular plate is against the lower border of the mandible. The wingnut is then tightened. To check for correct adjustment, the patient may be asked whether he or she feels contact with the back and front of the underside of the lower jaw. The top bar is then securely held while the FMA is then read by noting the intersection of a mark (in this case longitudinal indicator line  238  with the angular markings on angulation indicator  232 . Repeated adjustments and readings may be taken to insure consistency and accuracy. As shown in FIG. 9, gauge  200  may be easily disassembled for storage and disinfection. 
     In all embodiments, the frame is typically made of a rigid material, such as a stainless steel or hard plastic, to reduce the possibility of inaccuracy due to flexing. Additionally, if desired, the device may be made of autoclavable material. Gauges made of autoclavable materials (e.g., stainless steel) may be desirable if use of the gauge during surgical procedures is envisioned. 
     Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.