Abstract:
A head positioning instrument is provided for accurately modeling the position of a patient&#39;s jaw for orthodontic treatment planning. The horizontal distance between a pair of reference points that are visible on an x-ray are measured. These reference points are then utilized to ensure that substantially true vertical and substantially true horizontal are reflected in a radiograph. The patient&#39;s lower jaw hinge is accurately located, and the upper jaw is located using a bite fork attached to the lower jaw hinge axis locator. The lower jaw hinge axis locator with the bite fork attached are removed from the head positioning instrument and transferred to an axis mounting stand for accurate reproduction. The patient&#39;s individual characteristics are accurately preserved throughout the transfer and modeling process, resulting in accurate correspondence between the model and radiograph.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to the field of orthodontics. More specifically, a head positioning apparatus to assist an orthodontist in accurately modeling the characteristics of a patient&#39;s upper and lower jaw, as well as their position relative to the hinge of the lower jaw, is provided. 
       BACKGROUND INFORMATION 
       [0002]    When planning or executing dental, orthodontic, or orthognathic treatment, accurate positioning of the upper and lower jaw are critical to optimizing the aesthetics, function, and stability of the stomatognathic system. An error of even a fraction of a millimeter can mean the difference between success and failure. However, presently available modeling systems fail to provide this level of accuracy. 
         [0003]    Traditional radiographs typically spread as they travel from their source, through the patient, and to the film, resulting in magnification and distortion of the resulting image. This magnification and distortion are eliminated by cone-beam computed tomography, allowing more accurate representation of a patient&#39;s current condition on the film. However, this technology does nothing to orient the image or represent true vertical and true horizontal on the radiograph, or to correspond the radiographic images to a model for use in planning treatment. 
         [0004]    Facebows are presently used to assist in locating the position of the maxilla (upper jaw) to the hinge of the lower jaw. However, presently available estimated facebows do not actually locate the lower jaw hinge, but are instead designed estimate the hinge position relative to a patient&#39;s ear canal. When presently available facebows are used, the hinge for the lower jaw is estimated to be about 15 mm from the ear canal. The models of the upper and lower jaws are therefore positioned based on an estimate of their position relative to the hinge, rather than a measured position with respect to the hinge. This estimate may or may not be sufficiently accurate for planning a given treatment. 
         [0005]    Accordingly, there is a need for a method of representing true vertical and true horizontal on an x-ray image of a patient&#39;s head. There is a further need for a more accurate method of locating the upper and lower jaw of an orthodontic patient with respect to the hinge of the lower jaw, and accurately transferring these positional relationships to a treatment planning model. Additionally, there is a need to provide accurate correspondence between an x-ray image of a patient and a treatment model of the patient in order to provide a means of accurate treatment planning. 
       SUMMARY 
       [0006]    The above-described needs are met by the head positioning instrument described herein. The head positioning instrument includes a pair of reference point locators that are structured to locate a pair of predetermined points which are selected to be easy to locate on an x-ray image, and provide a means to substantiate orientation of the radiographic image to substantially true vertical and substantially true horizontal. 
         [0007]    The head positioning instrument may also include a lower jaw hinge locator that is structured to be placed adjacent to a lower jaw hinge of the patient. A maxillary bite fork is structured to be attached to the lower jaw hinge locator in a manner that permits vertical and horizontal adjustment of the bite fork&#39;s position with respect to the lower jaw hinge locator. The assembly of the lower jaw hinge locator and bite fork may be removed from the head positioning instrument for producing a model that accurately represents the position of the patient&#39;s upper jaw, lower jaw, and jaw hinge relative to each other. 
         [0008]    These and other aspects of the invention will become more apparent through the following description and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a side perspective view of a frame for a head positioning instrument. 
           [0010]      FIG. 2  is a top and side perspective view of a forehead locator for the head positioning instrument of  FIG. 1 . 
           [0011]      FIG. 3  is a side perspective view of a tooth locator for the head positioning instrument of  FIG. 1 . 
           [0012]      FIG. 4  is a top plan view of a facebow for the head positioning instrument of  FIG. 1 . 
           [0013]      FIG. 5  is an exploded view of an adjustment arm and frame for a facebow of  FIG. 5 . 
           [0014]      FIG. 6  is a perspective view of the assembled components of  FIG. 5 . 
           [0015]      FIG. 7  is a top perspective view of a bite fork utilized with the head positioning instrument of  FIG. 1 . 
           [0016]      FIG. 8  is a side perspective view of a calibration instrument for the head positioning instrument of  FIG. 1 . 
           [0017]      FIG. 9  is a side elevational view of a forehead locator, facebow, and tooth locator for the head positioning instrument of  FIG. 1 . 
           [0018]      FIG. 10  is an environmental, side perspective view of the head positioning instrument of  FIG. 1 , showing a predetermined point on the patient&#39;s forehead being located. 
           [0019]      FIG. 11  is an environmental, side perspective view of the head positioning instrument of  FIG. 1 , showing the tip of the patient&#39;s front tooth being located. 
           [0020]      FIG. 12  is an environmental, side perspective view of the head positioning instrument of  FIG. 1 , showing the hinge of the patient&#39;s lower jaw being located. 
           [0021]      FIG. 13  is an environmental, side perspective view of the head positioning instrument of  FIG. 1 , showing the patient&#39;s upper jaw being located via a facebow with respect to the lower jaw&#39;s hinge. 
           [0022]      FIG. 14  is an environmental, front, side, and top perspective view of a facebow and bite fork of the head positioning instruments of  FIG. 1  mounted on an axis mounting stand. 
           [0023]      FIG. 15  is an environmental, side perspective view of an upper jaw and lower jaw model mounted within an articulator. 
       
    
    
       [0024]    Like reference characters denote like elements throughout the drawings. 
       DETAILED DESCRIPTION 
       [0025]    In the drawings, there is shown in example of a head positioning instrument. Referring to  FIG. 1 , a head positioning instrument  10  is shown. The head positioning instrument  10  includes a support frame  12  which in the illustrated example is structured to rest on a floor. The support frame  12  includes a base  14  having a plurality of feet  16 . The feet  16  are adjustable so that the support frame may be oriented in a substantially vertical position, thereby keeping the various components of the head positioning instrument  10 , described in greater detail below, oriented in a substantially horizontal position. Alternative support frames could be secured to a wall, or could depend downward from a ceiling. The support frame  10  includes three vertical members  18  extending upward from the base  14 . The illustrated vertical members  18  are secured at their top ends by a top brace  20 , and further secured together by an intermediate brace  22 . Although the illustrated braces  20 ,  22  are triangular, other structures may be utilized. A substantially vertical rod  24  is held in position by the brace  12 , and in the illustrated example is secured to the top support frame  20  at its upper end, and the intermediate support frame  22  in a lower portion of the rod  24 . Alternative examples of the support frame  12  could potentially eliminate the vertical members  18  and braces  20 ,  22 , and consist instead of a rod  24  and an alternative means to hold the rod  24  in a desired position relative to vertical. 
         [0026]    The head positioning instrument  10  includes a pair of reference point locators as well as a means for measuring at least a horizontal distance between the two reference point locators. In the illustrated example of a head positioning instrument  10 , the two reference point locators consist of a forehead locator  26  and a tooth locator  70  (described below). Referring to  FIG. 2 , a forehead locator  26  is slidably mounted on the rod  24 . The forehead locator  26  includes a main body  28 , which in the illustrated example includes a central portion  30  having a pair of arms  32 ,  34  extending therefrom. The illustrated forehead locator  26  defines an aperture  36  that is structured to receive the rod  24 . The forehead locator  26  includes a means of securing the forehead locator  26  in a desired position on the rod  24 , which in the illustrated example includes a rod  38  having a threaded portion  40  is received within a threaded hole  42  that intersects with and is substantially perpendicular to the aperture  36 . The opposite end of the rod  38  includes a knob  44  to facilitate turning of the threaded rod  38  so that it abuts the rod  24  and secures the forehead locator  26  in position, or is moved away from the rod  24  so that the forehead locator  26  maybe slid up and down the rod  24 . 
         [0027]    The forehead locator  26  includes a pointer  48 , which is an elongated member extending outward from the central portion  30  of the forehead locator  26 , terminating in a tip  48 . One or more forehead rests may also be provided. The illustrated forehead locator  26  includes a pair of forehead rests  50 ,  52 , each of which includes a threaded central rod  54 ,  56  passing through an aperture  58 ,  60  defined within the arms  32 ,  34 , respectively, of the forehead locator  26 . Each of the forehead rests  50 ,  52  includes a forehead stop  62 ,  64 , respectively, on either side of the pointer  48 . The opposite ends of the forehead rests  50 ,  52  includes a knob  66 ,  68 , to facilitate turning the forehead rests  50 ,  52  to move the forehead stops  62 ,  64  towards or away from the patient&#39;s forehead. 
         [0028]    Referring to  FIG. 3 , a tooth locator  70  is illustrated. The tooth locator  70  includes a housing  72  having a clamp  74  secured to its back surface. The clamp  74  includes a ring  76  that is structured to fit around the rod  24 . A threaded rod  78  engages a threaded aperture within the ring  76 , permitting the threaded rod  78  to engage the rod  24  when the knob  80  disposed at the end of the threaded rod  78  is turned. The tooth locator  70  may therefore be moved vertically along the rod  24 . The tooth locator  70  includes an elongated measuring member  82  having a tip  84  which may in some examples be covered with a disposable covering. The front of the housing  72  includes a display  86  which in the illustrated example is a liquid crystal display. The front of the housing  72  further includes an on/off button  88  and a zero button  90 . The housing  72  includes an appropriate microcontroller to enable a desired zero position for the tip  84  to be set using the zero button  90 , and for the horizontal distance of any positional changes of the tip  84  to be measured and displayed on the display  86 , in a manner which is well known to those skilled in the art of depth gauges, digital calipers, etc. 
         [0029]    The head positioning instrument  10  includes a lower jaw hinge axis locator, which in some examples may be a hinge axis facebow. Referring to  FIGS. 4-6 , an example of a hinge-axis facebow  92  is illustrated. The hinge-axis facebow  92  includes a central member  94 , and a pair of substantially parallel arms  96 ,  98  extending outward from each end of the central member  94 . A clamp assembly  100  is centrally located on the central member  94 . The clamp assembly  100  includes a clamp  102  including a ring  104  that is structured to fit around the rod  24  of the support frame  12 . The ring  104  defines a threaded aperture therein for receiving a threaded rod  106  having a knob  108  disposed at one end. The facebow  92  may be moved vertically along the rod  24  by loosening the knob  108 , and then secured in position by tightening the knob  108 . In a similar manner, the clamp assembly  100  defines an aperture  110  that is structured to receive a bite fork (described below) therein. Similarly, a knob  112  is turned to bring a threaded rod into engagement with a bite fork within the aperture  110 . 
         [0030]    Each of the arms  96 ,  98  is secured to the central member  94  by a joint assembly  114 ,  116 , respectively, that permits both longitudinal movement and angular pivoting of the arms  96 ,  98  with respect to the central member  94 . Referring to  FIGS. 5-6 , the joint assemblies  114 ,  116 , which are identical in the illustrated example, include a pivot block  118  and a U-shaped bracket  120 . The pivot block  118  secures the arm  96  (or  98 ) within a channel  119  defined therein, and utilizes a thumbscrew  122  to secure the arm  96  or  98  in place. The arms  96 ,  98  may therefore be extended or retracted by loosening the thumbscrew  122 , and then held in place by tightening the thumbscrew  122 . A channel  124  defined within the pivot block  118  is substantially perpendicular to the arm  96 ,  98 , and is structured to receive the central member  94 . A generally semicircular outer surface  125  is disposed opposite the thumbscrew  122 . 
         [0031]    The U-shaped bracket  120  includes a central portion  126  and a pair of arms  128 ,  130 . The arms  128 ,  130  define a channel  132 ,  134 , respectively, therethrough for receiving the central member  94 . A thumbscrew  136 ,  138  is utilized to secure the central member  94  within the channels  132 ,  134 , respectively. Loosening the thumbscrews  136 ,  138  therefore permits the joint assembly  116  to the moved along or removed from the central member  96 . Another thumbscrew  140  is disposed within the central portion  126 . When the joint assemblies  114 ,  116  are positioned on the central member  94 , the generally semicircular surface  125  is adjacent to the inner surface of the central portion  126  of the bracket  120 . Loosening the thumbscrew  140  thereby permits pivoting of the arm  96 ,  98 , and tightening the thumbscrew  140  secures the arm  96 ,  98  in a desired angular position. 
         [0032]    The ends of the arms  96 ,  98  opposite the joint assemblies  114 ,  116  includes pointers  142 ,  144 , respectively, each of which points towards the inside of the U-shape formed by the facebow  92 . The pointers  142 ,  144  may in some examples be adjustable so that they extend a greater or lesser distance into the U-shape formed by the facebow and secured by a setscrew, a threaded connection, or other means that will be obvious to those skilled in the art. 
         [0033]    Referring to  FIG. 7 , a bite fork  146  is illustrated. Suitable bite forks are available from various dental supply companies such as, for example, Panadent, Advanced Dental Designs, and SAM. The illustrated example of a bite fork  146  includes a substantially flat, generally U-shaped mouthpiece  148 . A generally horizontal rod  150  extends outward from the mouthpiece  148 , with the opposite end of the rod  150  being slidably secured within a clamping mechanism  152 . The clamping mechanism  152  also slidably secures a second, generally horizontal rod  154  that is substantially perpendicular to the rod  150 . A second clamping mechanism  156  is secured at the opposite end of the rod  154 . A substantially vertical rod  158  is slidably secured within the clamping mechanism  156 . The vertical rod  158  is structured to fit within the aperture  110  defined within the clamp assembly  100  of the facebow  90 . By adjusting the position of the rods  150 ,  154 ,  158  within the clamps  152 ,  156 , the position of the mouthpiece  148  with respect to the facebow  90  may be adjusted. 
         [0034]    In use, if not already done, the feet  16  of the support base  12  ( FIG. 1 ) are adjusted so that the rod  24  is a substantially vertical. Next, referring to  FIG. 8 , the tooth locator  70  is zeroed with respect to the forehead locator  26 . To accomplish this, a tri-square  160  is placed against the tip  48  of the forehead locator, and optionally secured in this position by a magnet  162  disposed on top of the main body  28  of the forehead locator  26 . The tooth locator  70  is adjusted so that the tip  84  is brought into contact with the tri-square  160 . If not already done, the on/off button  88  is depressed to turn on the tooth locator  70 . With the tip  84  in contact with the tri-square  160 , the zero button  90  is depressed, thereby defining this position as zero horizontal distance with respect to the tip  48  of the forehead locator. The final setup step, shown in  FIG. 9 , is to ensure that the arms  96 ,  98  of the facebow  92  are substantially horizontal, utilizing a level  164  to determine the angular position of the arms  96 ,  98 . If necessary, the thumbscrews  140  ( FIGS. 4-6 ) may be loosened so that the pivot blocks  118  within the joint assemblies  114 ,  116  may be pivoted to bring the arms  96 ,  98  into a horizontal position. At this point, the thumbscrews  140  are both tightened to secure the arms  96 ,  98  in this position. 
         [0035]    The initial step in locating the various features of a patient&#39;s jaw is to establish a predetermined point on the patient&#39;s forehead as a reference point, as illustrated in  FIG. 10 . A dot of barium paste or a metallic ball of approximately 1 mm diameter is placed on the patient&#39;s forehead. Either the barium paste or the metallic ball will easily be seen in an x-ray. The patient is asked to step forward towards the head positioning instrument  10 , keeping their head in a substantially vertical position, so that the forehead locator  26  may be adjusted vertically along the rod  24  to bring the tip  48  into contact with the barium paste or metallic ball. The forehead rests  50 ,  52  are adjusted so that the patient may comfortably rest their head against the forehead rests  50 ,  52 . 
         [0036]    Next, referring to  FIG. 11 , the patient is asked to smile, and the tooth locator  70  is adjusted so that the tip  84  is positioned against the tip of the patient&#39;s upper front tooth  166 . At this point, the horizontal distance between the predetermined point on the patient&#39;s forehead and the tip of the patient&#39;s upper front tooth  166  may be measured and recorded. Prior to or at this point, an x-ray of the patient may be taken. This x-ray may be taken using conventional radiography or using cone beam computed tomography. Cone beam computed tomography is preferred due to the minimal distortion of the radiographic image. Because both the predetermined position on the patient&#39;s forehead and the tip of the upper front tooth are clearly visible in the resulting x-ray, and because the support frame  12  has been positioned in a substantially vertical position, substantially true vertical and substantially true horizontal may be transferred and accurately represented on the x-ray image. 
         [0037]    The hinge  168  of the lower jaw is located by using an axiographic recorder or estimated by palpation of the lateral portion of the condyle. Once this is located and recorded, as shown in  FIG. 12 , the facebow  92  is moved vertically along the rod  24  until the facebow  92  is in the same horizontal plane as the hinge  168 . Next, this thumbscrews  122  are loosened so that the arms  96 ,  98  may be extended or retracted so that the pointers  142 ,  144  touch the hinge  168  of the lower jaw. At this point, the thumbscrews  122  are tightened. 
         [0038]    The location of the upper jaw with respect to the hinge  168  is determined as shown in  FIG. 13 . The upper and lower surfaces of the mouthpiece  148  of the bite fork  146  are covered with an impression compound that is known to those skilled in the art of orthodontics. The vertical rod  158  of the bite fork  146  is secured within the aperture  110  of the clamp assembly  100  of the facebow  92 . The rods  150 ,  154  are adjusted within the clamping mechanism  152  to bring the mouthpiece  148  of the bite fork  146  into the proper three dimensional position within the patient&#39;s mouth. At this point, when the patient closes their mouth around the mouthpiece  148 , the positions of the teeth within the upper jaw of the patient will be recorded within the impression compound. The position of the upper jaw relative to the hinge axis of the lower jaw  168  is now recorded in transferable form by the assembly of the facebow  92  and bite fork  146 . 
         [0039]    The facebow  92  and bite fork  146  are removed from the rod  24  as a single assembly, and transferred to an axis mounting stand  170  as shown in  FIG. 14 . Axis mounting stands are well known to those skilled in the art of orthodontics, and therefore are not described in great detail herein. Axis mounting stands that are useful with the head positioning instrument  10  are presently manufactured by Panadent, Advanced Dental Designs, and SAM. The vertical rod  158  of the bite fork  146  is vertically positioned in a location  172  on the axis mounting stand  170  designed for this purpose. The position of the assembly of the bite fork  146  and facebow  92  is then adjusted with respect to the axis mounting stand  170  so that the pointers  142 ,  144  of the facebow  92  are positioned adjacent to the hinge  174  of the axis mounting stand  170 . Upper jaw model  176  is then positioned on the axis mounting stand  170 , with its position determined by the impression compound on the mouthpiece  148  of the bite fork  146 . At this point, the positions of the upper jaw model  176  with respect to the hinge axis  174  are registered. 
         [0040]    Lastly, the upper jaw model  176  is secured in place using plaster in a manner familiar to those skilled in the art of orthodontics. The upper jaw model  176  is transferred to an articulator  180  and the lower jaw model  178  is related to the upper jaw model  176  using a centric relation wax bite. The techniques for transferring the upper jaw model  176  to the articulator  180 , as well as recording the centric relation bite and mounting the lower jaw model  178  on the articulator  180 , are known to those skilled in the art of orthodontics. Articulators  180  that are useful with the head positioning instrument  10  are made by Panadent, Advanced Dental Designs, and SAM. In selecting an articulator  180 , it is useful to select one that is compatible with the axis mounting stand  170  being used. The upper jaw model  176  is secured to the upper member  184  of the articulator. The lower jaw model  178  is secured to the base  186  of the articulator with mounting plaster in a technique familiar to those skilled in the art of orthodontics. With the transfer of the model to the articulator  180  accomplished in this manner, the hinge  182  of the articulator  180  will be in the same position with respect to the upper jaw model  176  and lower jaw model  178  as they were with respect to the hinge  174  of the axis mounting stand  170 . An accurate model of the patient&#39;s anatomy has now been produced. Pivoting the arm  184  of the articulator  180  will simulate jaw movement as it occurs within the patient. This model may be provided to a surgeon during the planning of surgery, to show both the current condition of the patient, as well as the desired changes to the patient&#39;s jaw structure. Because substantially true vertical and substantially true horizontal are represented by both the articulator and the x-ray image, and because of the accuracy with which the model was constructed utilizing the above-described procedure, the articulator and x-ray image accurately correspond to each other. The surgeon will therefore have accurate, detailed information about the surgery to be performed. 
         [0041]    The head positioning instrument  10  therefore provides a means of accurately reproducing the jaw anatomy of a patient in a model that can be utilized for treatment planning. The location of the jaw structure with respect to a fixed point on the patient&#39;s forehead ensures that substantially true vertical and substantially true horizontal are shown in the x-ray images, and reflected in the model. The head position on the radiographs and the jaw position of the articulator mounted models of the patient&#39;s teeth are coordinated to a high level of accuracy. The result is the ability to carry out highly accurate treatment planning and execution. During actual use of the head positioning instrument  10  in planning surgery, ideal results have been reported by the surgeon performing the surgery. 
         [0042]    A variety of modifications to the above-described embodiments will be apparent to those skilled in the art from this disclosure. Thus, the invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention. The appended claims, rather than to the foregoing specification, should be referenced to indicate the scope of the invention.