Dentistry – Orthodontics – By device having means to apply outwardly directed force
Reexamination Certificate
2000-04-27
2001-10-09
Wilson, John J. (Department: 3732)
Dentistry
Orthodontics
By device having means to apply outwardly directed force
Reexamination Certificate
active
06299439
ABSTRACT:
The present invention relates to a suture expansion device comprising:
a central stretching screw support;
on either side of the stretching screw support, a right and a left fixing means support for fixing to the right and, respectively, the left section of the superior dental arch;
two stretching screws, which are parallel to one another, extend between the fixing means supports and are accommodated in screw passages made in the stretching screw support and threaded to match the relevant stretching screw;
wherein the stretching screws can be screwed in mutually opposed longitudinal directions out of the stretching screw support in order to push the right-hand and left-hand fixing means supports apart.
In the specialist field suture expansion is also referred to as ‘maxillary expansion’ or ‘palatal expansion’, both of which terms are frequently prefixed by ‘rapid’.
A suture expansion device of this type is disclosed in WO 94/26196. The suture expansion device known from this publication consists of a stretching screw support in the form of a cylindrical sleeve which is provided over virtually its entire length with a bore of large diameter provided with an internal thread and is provided at one end with a partition with a bore of small diameter, provided with an internal thread, therein. At one side a pin provided with an external thread extends from the outside through the small bore, which pin forms a first stretching screw, and at the other side a hollow pin with an external thread is screwed in from the outside, which hollow pin forms the second stretching screw. The cavity in the hollow pin is such that the first stretching screw fits in said cavity as it were in a telescopic manner. In the fully screwed-in position the first stretching screw and the second stretching screw are inserted one inside the other virtually completely in the sleeve-shaped stretching screw support. If the sleeve-shaped stretching screw support is now turned the stretching screws move outwards in opposing directions at either end as a result of their opposing threads. At their ends pointing away from the sleeve-shaped stretching screw support the stretching screws have fixing means supports in the form of U-shaped wires. The expansion length achievable with this suture expansion device is of the order of magnitude of 1.5 times the length of the suture expansion device in the fully screwed-in position. A significant disadvantage of this known suture expansion device is, however, that this device is insufficiently stable and rigid. Consequently, the jaws, or, more accurately, the right and the left portion of the superior dental arch, can also be pushed skew as well as, as intended, pushed apart. A further problem is that insofar as the device according to WO 94/26196 does have some rigidity and stability, this is provided only by the stretching screws, which has the associated risk of jamming.
The aim of the present invention is to provide a suture expansion device of the type with which the maximum expansion stroke has a length of the order of magnitude of approximately 1.5 (or possibly more) times the length of the suture expansion device measured in the expansion direction when the device is in the fully retracted position, which device is of particularly stable and rigid construction and is reliable in operation.
Said aim is achieved according to the invention in that for each fixing means support a guide system is provided that prevents rotation of the relevant fixing means support relative to the stretching screw support and guides movement of the fixing means support in the longitudinal direction of the stretching screw. The guide system provides the construction of the suture expansion device with rigidity and stability. The guide system ensures that while the fixing means supports are movable relative to the stretching screw support in the longitudinal direction of the stretching screws they in other respects remain fixed with respect to the stretching screw support.
Because two stretching screws which are effective in opposing directions are used, a relatively large expansion stroke can be achieved which will be in the order of magnitude of the sum of the lengths of the stretching screws.
To make the suture expansion device expand, the one stretching screw and the other stretching screw can be turned alternately, but it is also possible to unscrew first one stretching screw to its full extent and then the other stretching screw. In practice, incidentally, the expansion will take place gradually in the sense that the expansion increases by a predetermined extent per predetermined unit time. In this context it is possible, for example, to conceive an increase in the expansion of approximately 0.6 mm per day, an expansion step of approximately 0.2 mm, which can be achieved by, for example, unscrewing each expansion screw by 0.1 mm, being made in the morning, at midday and in the evening. If the screw threads are suitably chosen each screw can move out 0.1 mm on turning through 90°.
According to a preferred embodiment of the invention the stretching screws are freely rotatable about their longitudinal axes relative to the fixing means supports. By allowing the stretching screws to bear freely on the fixing means supports or at least keeping them freely rotatable about their own longitudinal axis relative to the fixing means supports, no moment will be exerted on the fixing means supports by turning the stretching screws and said fixing means supports will only be pushed outwards or, on screwing in, be able to move inwards, at least provided they are not restrained.
Although the guide system according to the invention can be implemented in a variety of ways, from the constructional, cost and reliability standpoint it is preferable if each guide system comprises at least one guide rod which is fixed by one end to the relevant fixing means support and which is accommodated in a guide passage in the stretching screw support such that it is slidable in the longitudinal direction. Such a guide system is compact and simple to produce.
With a view to, in particular, a robust, stable and rigid suture expansion device it is preferable according to the invention if each guide system comprises two of said guide rods, which are positioned some distance apart in a longitudinal direction running transversely to the left/right direction, and the stretching screws, viewed in said longitudinal direction, are located between the two guide rods. With this arrangement the guide rods provide the mutual stability and rigidity between the fixing means supports and the stretching screw support, whilst the stretching screws themselves are subjected to no or hardly any stress other than pressure, as a result of which, inter alia, jamming is largely prevented. Moreover, by positioning the stretching screws between the two guide rods it is possible largely to counteract the guide rods being able to jam in their guide passages in the stretching screw support as a consequence of forces acting transversely to the guide direction.
According to an advantageous embodiment, with this arrangement said longitudinal direction will run essentially parallel to the patient's palate when the suture expansion device is in the use position.
In order to obtain a suture expansion device which is is compact as possible in the fully retracted position and has as large as possible an expansion stroke in the fully expanded position, it is advantageous according to the invention if the stretching screws and guide systems extend from the right-hand to the left-hand fixing means support when the suture expansion device is in the retracted position. In order further to increase the compactness it is furthermore advantageous with this arrangement if the guide rod or guide rods and stretching screw belonging to the right-hand and left-land fixing means support respectively extend with their left-hand or right-hand end respectively into, or even through, the left-hand or right-hand fixing means support, respectively, when the device is in said
Wilson John J.
Young & Thompson
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