The X-raying of the frontal teeth involves a further difficulty. Due to the anatomy of the palate the film, and consequently also the film support, will be pressed downwards which often leads to exclusion from the picture of the tissue regions around the teeth roots. When the frontal teeth of the lower jaw are X-rayed the tongue of the patient causes corresponding problems. For that reason conventional film supports can normally not be used in these regions.

The main object of the invention is to provide a dental instrument in which the problems above referred to are eliminated, meaning that once the patient has pressed his teeth against the bite block the latter will securely be retained in the position selected by the dentist. -

Other objects and advantages of the invention will appear .from the description and. the drawings which illust¬ rate three different embodiments .

Figure 1 is a perspective view showing an instru- ent according to the first embodiment.

Figure 2 is a cross-section taken along line II-II in Figure 1.

Figure 3 is a perspective view showing an instru¬ ment according to a second embodiment. Figure 4 shows the instrument of Figure 3 in a lateral view.

Figure 5 is a perspective view illustrating the third embodiment.

The instrument shown in Figures 1 and 2 substaπti- ally consists of a film support 1 with a groove or recess 2 for the film 3. Film support 1 is integral with a bite block. The device sofar described represents prior art. However, according to the present invention, the bite bloςk consists of two portions, hereinafter referred to as the upper portion 4 and the lower portion 5. The lower portion 5 is integral with the film support. Between block

A dental instrument for optimal positioning of anX-ray film support.

The present invention relates to a dental instru¬ ment comprising an X-ray film support connected to a bite block and, preferably, also an aligning rod. In prior art instruments of the type above defined the bite block is homogeneous and its top surface is parallel to its bottom. When a patient opens his mouth, the lower jaw swings around the jaw-joints. This means that an arbitrary point on the lower jaw substantially moves along a circular arc the radius of which equals the distance of the point from an axis through the jaw-joints. Consequently,, the farther back the bite block has to be located, the greater will be the aperture angle of the jaws. It follows that, when a bite block has been inserted between the upper and lower tooth rows of a patient and the latter has, obeying the iήstruc- tions of his dentist, again closed his mouth,only the rearmost teeth will contact the bite block whereas a ver¬ tical distance will be left between the block and the upper or lower teeth at the front edge o ^' f the block. The lack of contact between the bite block and all teeth overlying it means that it assumes anunstable position and may easily move in response to variations of the bite pressure exerted by a patient. Such movements lead to a displacement of the film support and hence of the film. As is understood, such a swinging movement of the bi-te block can occur both around an axis parallel to that of the jaw-joints and along a hori¬ zontal axis parallel -thereto.

The instability problem above referred to is aggra¬ vated in the following two situations. The one situation is when the rearmost molars are to be X-rayed. In order for the bite block to be received between the teeth the patient then has to open his mouth that much that the only contact between the teeth and the bite block will be at the rear edge of the latter. The second situation is when one f-r more teeth are missing, so that even when the frontal t-t-tii-. are to be X-rayed the bite block does not get sufficient

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portions 4 and 5 there is a shallow gap. Further, upper portion 4 and lower portion 5 are spaced from each other except centrally, where they are interconnected via a thin bridge portion 6. In the embodiment shown in Figures 1 and 2 film support 1, the lower block portion 5, bridge 6 and the upper portion 4 form an integral unit. However, block portion 4 is not connected to support 1 at its inner end - to the left in Figure 1.

The operation of the instrument above described is as follows. The narrow bridge _. 6 serves as a pivot, i.e. the two portions of the bite block may turn around it and, as has been indicated in Figure 2 , the corresponding angle is substantial. When a bite block according to the invention is introduced between the tooth rows of a patient and the latter bites into the block the two portions thereof will automatically assume such angular positions that each of them is parallel with a plane through the chewing surfaces of the adjacent tooth row or, in other words, each tooth row will in at least two points contact the adjacent bite block portion. Consequently, instead of the instable mount¬ ing position which, as has been explained above, exists in prior art instruments the film will be retained in the posi tion selected by the dentist before he leaves the patient during the film exposure. The corresponding advantage has several aspects. Naturally, the primary aspect is that the dentist knows that the region he intends to X*-ray will appear on the film. This avoids the need for repetitions of any given exposure. It should be appreciated that such re¬ petitions are not only time-consuming and costly but that, in addition thereto, most patients find them irritating and embarrassing. A second consequence of the stable position¬ ing of the film is a protection against movements which yields sharp and clear pictures.

In the embodiment according to Figures 1• and 2 at the end of bridge 6 remote from film support 1 there is

a sleeve 7 adapted to receive an -aligning rod 8.

In Figure 1 the instrument has been shown in the position it would assume during X-raying of teeth in the lower jaw. When teeth or tissues in the upper jaw are to be X-rayed, the instrument is rotated by 180 degrees so that the film 3 will instead be directed upwards.

There are two differences between the embodiment shown in Figures 3 and 4 and the one sofar described.

The one difference is that the film support 1 has two grooves 2 and 2a adapted to receive the film 3. As was the case in Figure 1, groove 2 is located in- a plane per¬ pendicular to planes through the top and bottom surfaces of the bite block. In contrast thereto, groove 2a is ob¬ liquely oriented relative to the first-mentioned plane. This means that, when groove 2a receives an X-ray film, the vertical distance between the upper and-lower edges of the film will be reduced which is advantageous when due to the anatomy conditions it is difficult to accommo¬ date a film having a greater height. Knowing the angle between grooves 2 and 2a the dentist may compensate for that angle by setting up the X-ray camera so that its focal axis will form the same angle with the aligning rod 8.

The second difference is that sleeve 7 is not inte- gral with the bite block. Ins.tead, the two portions 4 and 5 of the bite block do at their free edges opposite the film support have flanges 9 ^" and 10 engaging corresponding grooves in sleeve 7. This arrangement makes it possible laterally to move the sleeve along said flanges. Further, there is no counterpart to bridge portion 6 in Figure 2 meaning that the movable block portion 4 is connected to sleeve 7 only. Consequently, when sleeve 7 is in an ex¬ treme position as shown in Figure 3, the turning axis will be located at the one side of the block instead of cent- rally. The corresponding advantage is that the film can be brought into positions deeper back into the mouth than is ^SΕEΛ

possible when the aligning rod is centrally located which is valuable when the rearmost molars are to be X-rayed.

The instrument shown in Figure 5 has been supplemen¬ ted with wing-like lateral pieces 11 and 12 which may de- tachably be connected to bite block 4, 5. They extend the bite block in the direction of the tooth row which is of special value when front teeth are to be X-rayed. This is due to the fact that the film may now be positioned.so that the parallel technique rather than the bisecting- angle technique can be utilized. The side wings have flanges 13 protruding into the space between. block por¬ tions 4 and 5 and retained there by a snapping action.

It should be observed that the invention has many embodiments differing from those here described for exemplifying purposes only. The inventive idea resides in the realization that the bi-te block should be arranged so that its cross-section may vary between substantially rec¬ tangular and substantially wedge-shaped form, the corres¬ ponding principle being illustrated in Figure 2. There are several other ways in which such a deformation may be obtained. It should especially be pointed out that the "axis" around which portions 4 and 5 turn does not have to be a concrete portion of the instrument. Any bite block which is deformable as above described falls w'ithin the scope of the invention.

The bite block may, in a manner known per se, be pro¬ vided with markings making it possible for the dentist (by reference to one- or ^' more teeth) to ascertain that upon re¬ peated X-raying of one and the same portion of the jaw the film will always assume the same position so ^' that all ex¬ posures become completely mutually comparable.