this object is achieved , according to the invention , by the bite device defined in claim 1 . advantageous embodiments of the invention are subject matter of the sub - claims . the invention improves on the prior art in that a bite device includes a holding member held in a directionally fixed position relative to the x - ray device , and a plate which is pivoted relative to the holding member and which has a bite piece on which the patient bites . the bite device also includes means for measuring the angle of deflection a between the plate and the holding member , which means for measuring the angle of deflection a are located in a zone of the bite device which is free from radiation during x - ray imaging . the zone involving x - ray irradiation can therefore be kept substantially free from metal . the invention is thus based on the idea of measuring the position of the occlusal plane of the patient relative to the device by determining the position of a plate disposed in the occlusal plane . for this purpose , the angle is measured between the plate and a holding member , which can be positioned relative to the x - ray device in fixed alignment . from this angle a signal can be derived which indicates the degree of inclination of the occlusal plane . it is advantageous for the means for measuring the angle of deflection a to contain one or more sensors located in the holding member . for example , the sensors might be in the form of a photoelectric sensor located in the holding member and adapted to register the position of an opening that is moved upwardly and downwardly in accordance with the pivotal motion of the plate . the bite device of the invention can conveniently include means for displaying the angular position of the pivoted plate . in a preferred development of the bite device , there are further provided driving means for vertical adjustment of the holding member and thus for pivoting the plate into a predetermined angular position . this makes it possible to adapt to the patient &# 39 ; s body size , and the patient can be constrained to adjust the inclination of his head to the inclination of the plate , so that a desired angular position of the patient &# 39 ; s occlusal plane relative to the x - ray device will be achieved . it is advantageous for the plate - swinging means to move the plate to the predetermined angular position automatically and to stop when the predetermined angular position has been reached . alternatively or additionally , provision may be made for said means to indicate that the predetermined angular position of the plate has been reached by emitting optical and / or acoustic signals . in a preferred embodiment of the bite device of the invention , the pivoted plate is connected to a rail within the holding member , which rail can be moved upwardly and downwardly and has an opening for indicating the position of the rail in the holding member . the bite piece of the bite device is preferably equipped with a replaceable protective sheath for hygienic reasons . alternatively , the bite piece can be in the form of a replaceable bite piece . the bite piece is preferably composed of a soft material , particularly a substantially radiolucent material . it has proved to be particularly suitable to fabricate the bite piece from closed - cell ethylene foam . the bite piece preferably occupies an angular range β of the mandibular arch , which is between 20 ° and 40 °, particularly 30 °. this substantially prevents any sideways tipping or tilting of the patient &# 39 ; s head . in an advantageous embodiment , the bite piece has on its upper surface and on its undersurface a bite groove to accommodate part of the dental arch of the patient &# 39 ; s upper and lower jaw respectively . the bite piece is preferably a unitary piece foldable about a folding edge . it preferably has on opposite sides a wedge - shaped projection and a complementary depression for the accommodation of said projection , to enable the bite piece to be removably attached to the pivoted plate . further advantageous embodiments , features , and details of the invention are given in the dependent claims , the description of embodiments , and the drawings . the invention will now be explained in more detail with reference to an embodiment and the drawings . only those elements are shown which are significant for comprehension of the invention . fig1 is a diagrammatic illustration of a panoramic x - ray system ; fig2 is a diagrammatic representation of the system for aligning the tomography zone of the x - ray device to the alveolar arch of a patient ; fig3 shows a perspective view of a bite device according to one embodiment of the invention , shown diagrammatically ; fig4 is a cross - section through the bite device of fig3 ; fig5 shows perspective views of an bite piece for a bite device according to one embodiment of the invention , shown ( unfolded ) diagonally from below in fig5 ( a ) and diagonally from above in fig5 ( b ); fig6 is a cross - section through the bite piece of fig5 , taken along line vi - vi ; and fig7 shows the bite piece of fig5 in the folded position , as attached to the bite device of fig3 . fig1 is a diagrammatic representation of a panoramic x - ray system 10 , in which a rotary unit 12 carries a radiation source 14 equipped with a shutter 16 , and a diametrically opposed detector camera 18 equipped with a shutter 20 . the beam of x - rays 22 emitted from the radiation source 14 transilluminates the jaw region of the head 24 of a patient and produces an image signal in detector camera 18 . this is directed to a control unit 26 for evaluation and display in the usual manner . rotary unit 12 is pivotally or hingedly mounted on an arm 11 which is mounted on a column 13 for vertical adjustable thereon . a drive 15 is provided to perform the vertical adjustment . in this way , the position of x - ray emitter 14 and detector camera 18 can be adjusted to the stature of the patient . it is essential , for obtaining a faultless , high - quality panoramic radiograph , for the tomography zone 30 ( fig2 ) to be in line with the alveolar arch 32 of the patient . fig2 depicts perfect spatial alignment of these two elements , this ensuring the production of a qualitatively good image . insufficient alignment can necessitate a repeat radiograph , resulting in increased x - irradiation of the patient and additional expense in terms of material and time . fig3 is a perspective view of a bite device referenced as 40 , according to one embodiment of the invention , shown diagrammatically , and fig4 is a cross - section through the bite device 40 of fig3 . bite device 40 has a holder 42 which is hinged to a thin plate 46 by means of a pivot 44 . the thin plate 46 is adjoined , at its end remote from pivot 44 , by an imaging zone 48 parallel to said thin plate . the imaging zone 48 has an opening 62 by means of which , in a manner to be described in more detail below , a replaceable bite piece 50 can be quickly and easily attached to the thin plate . on its upper surface and on its undersurface , bite piece 50 has occlusal grooves 64 and 66 respectively , which accommodate the dental arches of the patient &# 39 ; s upper and lower jaw respectively . this arrange - ment ensures that the thin plate 46 runs parallel to the occlusal plane of the patient when he bites on the bite piece 50 for taking the radiograph . the angle of deflection a of thin plate 46 is measured using a rail 54 capable of being moved upwardly and downwardly and connected to thin plate 46 in a region 56 , and adapted to extend vertically down the inside 52 of the holding member 42 . in its lower section , rail 54 is provided with a hole 58 . the vertical position of hole 58 is detected by two photodetectors indicated by arrows 60 . the angle of deflection of plate 46 can be deduced from said vertical position . by transferring the inclination of plate 46 to the movable rail , measurement of the angle of deflection α is carried out in a region of holder 42 which is far below plate 46 and is free from radiation . the x - irradiated region can thus be kept substantially free from metal . the bite device cooperates with a driving system 15 shown in fig1 such that rail 54 moves upwardly or downwardly and the thin plate 46 can thus be brought into any desired position . the deflection of thin plate 46 accompanying such vertical adjustment makes it possible to gently guide the patient &# 39 ; s head until it assumes the correct degree of inclination for the panoramic radiograph . vertical adjustment of plate 46 can be performed interactively by the operator . for example , the operator can press an adjustment button until the desired degree of inclination is attained . when a previously defined angular position , for example α = 100 °, which corresponds to an angle between plate 46 and the horizontal of 15 °, is attained , this can be indicated by means of optical and / or acoustic signals . alternatively , the drive can automatically move plate 46 into the predetermined angular position and stop when the desired position is reached . additionally , the angular position of the plate can be displayed for checking by the operator . the bite piece 50 shown in fig3 and 4 will now be described in more detail with reference to fig5 through 7 . fig5 shows , in fig5 ( a ) and fig5 ( b ), a per - spective view of the unfolded insert , shown diagonally from below in fig5 ( a ) and diagonally from above in fig5 ( b ). fig6 shows a cross - section through the bite piece taken along line vi - vi of fig5 ( b ), and fig7 represents the bite piece in the folded position , as attached to the bite device of fig3 . in the present embodiment , bite piece 50 is fabricated as a single piece of closed - cell ethylene foam , a soft and substantially radiolucent material . on its upper surface , bite piece 50 has occlusal grooves 64 and 66 adapted to accommodate part of the dental arch of the upper and lower jaws of the patient . bite piece 50 can be folded along a central folding edge 70 , defined by notches 72 on the undersurface and a central groove 74 on the upper surface of the insert . on its underside , bite piece 50 has a wedge - like tapered projection 76 which , when the insert is folded , slides into a complementary depression 78 located on the opposite side of the insert , this making for a stable but easily releasable connection . the flat imaging zone 48 of the bite device contains an opening 62 ( fig4 ) through which the projection 76 projects when the bite insert is attached , so that insert 50 is firmly attached to the thin plate 46 of the bite device once it has been folded together . after use , however , the insert can be unfolded with no great effort and thrown away for hygienic reasons . the insert shown in the embodiment illustrated in fig5 through 7 , has a width of 40 mm , occupies an angular region β of the dental arch of about 30 °. in order to accommodate for different jaw sizes of patients , bite pieces are also fabricated and used in other widths . the different widths can be easily distinguished by the user on the basis of different color markings or other labels . with this kind of bite piece , the position of the patient can be fixed with great accuracy but without discomfort for the patient .