Dentistry – Orthodontics – By device having means to apply outwardly directed force
Reexamination Certificate
1999-12-17
2001-10-30
Wilson, John J. (Department: 3732)
Dentistry
Orthodontics
By device having means to apply outwardly directed force
Reexamination Certificate
active
06309213
ABSTRACT:
SPECIFICATION
The present invention is based on an expansion appliance having the features indicated in the preamble of Claim 1. An expansion appliance of this kind is known from WO96/28110. The known expansion appliance comprises two members the relative distance of which can be varied by means of a double spindle by means of which the two members, being guided in straight alignment by two parallel guide rods, can be driven away one from the other. The spindle does not act directly on the members but rather indirectly via compression springs. The springs are coiled springs that are tensioned as the spindle is rotated and that determine the expansion force. To this end, each of the two members accommodates a lengthwise displaceable, but non-rotatable nut which is engaged by one of the two threaded sections of the spindle that extend from an actuating section. The nut exhibits a flange. The spring is supported on that flange by one of its ends and on the end of an orifice in the respective member by its other end. By rotating the spindle, the nuts can be moved away from the actuating section of the spindle so that the springs are tensioned. The inherent tension force of the springs can then produce a change in tooth position in a patient's mouth, which comes to its end when the two members of the expansion appliance come to rest against the flanges of the two nuts. If the tooth position is then to be changed further, the two springs must be re-tensioned by rotation of the spindle.
The maximally possible expansion of the appliance is determined by the length of the threaded sections of the double spindle, while the expansion force is determined by the springs. This distinguishes such an expansion appliance from a non-resilient jackscrew of the kind disclosed by U.S. Pat. No. 5,167,500 as prior art, where the two variable-distance members are displaced directly by means of a double spindle having sections of oppositely directed threads, not by means of a spring in order to achieve high correction forces, such a jackscrew can always be expanded by no more than 0.25 mm. For a typical tooth correction with 4 mm of tooth movement, the patient must therefore visit the doctor 16 times in order to have the jackscrew readjusted, which is laborious and tiresome.
An advantage of the expansion appliance using a spring, as disclosed by WO96/28110, over the springlass jackscrew lies in the fact that due to its compressibility, it can be removed from and reinstalled in the dentition more easily, and not only by the doctor but also by the patient himself/herself. Although the springs of the expansion appliance known from WO/96/28110 are encapsulated in a recess in the two members, and the point of access to the recess is sealed by an O ring surrounding the spindle shaft, liquid food particles may still penetrate into the area of the springs, presumably due to a pumping effect which may occur not only during removal and reinstallation of the expansion appliance in the dentition but also when speaking and, especially, when chewing. The trapped food particles may then form hard depositions (tartar) which may cause the springs to become jammed, obstructed and blocked.
The present invention now has for its object to provide an expansion appliance which reduces the risk of food particles obstructing the expansion of the springs. The constructional measures necessary for this purpose, however, must not have the result to make the expansion appliance thicker than that known from WO96/28110, the space available in the mouth being small. The larger a foreign body, which is to be introduced into the mouth, the more will speaking be hindered, and the torque is so sensitive that it senses changes already in the range of a tenth of a millimeter. Consequently, the thickness of the expansion appliance may not be increased by protective measures for the springs.
This object is achieved by an expansion appliance having the features specified in Claim 1.
In the case of an expansion appliance using a double spindle, this object is further achieved by the features indicated in Claim 19. The dependent Claims 20 and 21 further provide, as means for achieving the object, an expansion appliance with a spindle that exhibits only one threaded section instead of two threaded sections.
In an expansion appliance according to the invention, contrary to that disclosed by WO96/28110, the springs do not enclose a threaded section of the spindle or a nut screwed onto the spindle, but have been shifted toward the guide rods. But contrary to the elastic expansion appliance disclosed by U.S. Pat. No. 5,167,500-A the springs are not arranged on a guide rod between the two members of the ole in the respective member of the expansion appliance, the end of that hole being closed. Each spring is, therefore, located in a chamber that is closed on the one hand by the walls of the respective member of the expansion appliance and, on the other hand, by the guide rod that is guided in the hole. This provides significant advantages:
The entire length over which the respective guide rod is guided in the member is available for sealing the space in which the respective spring is enclosed.
The gap between the guide rod and the wall in each section of the holes, in which the guide rod is guided, may be considerably narrower than the gap between the spindle and the edge of the opening giving access to the orifice in the member, and also much smaller than the gap between the nut and the wall of the orifice surrounding the latter.
A pumping effect, that may suck liquid food particles into the area of the springs, cannot occur.
The springs are tensioned only at the beginning of correction of the tooth position, when the expansion appliance is still absolutely clean. Thereafter, the spindle only serves to control relaxation of the springs. During the relaxation process, any depositions will, however, have a much less restricting effect that in the prior art, during re-tensioning of the springs.
If any liquid food particles should still penetrate into the gap between the guide rods and the wall of the respective hole in which they are guided, then they will be transported to the outside by the progressive expansion of the springs.
By having the springs shifted to the ends of the guide rods, no spring surrounding the spindle is needed. The expansion appliance according to the invention can, therefore, be made less thick than an expansion appliance according to WE96/28110. This is so because the springs provided at the ends of the guide rods may be made thinner without any problem. The resulting loss in spring force of the individual spring is more than compensated by the fact that springs, acting in parallel, are provided on both guide rods.
Contrary to a system with centrally arranged springs, the arrangement of springs on both guide rods prevents any tilting moments from occurring and provides well-balanced distribution of forces.
Seals are no longer required.
The guide rods and the sections of the holes in which the are guided exhibit, preferably, a cylindrical shape; this makes it possible to make the annular gaps between the guide rods and the sections of the holes, in which they are guided, especially narrow.
If the guide rods are guided over their full length at the beginning of the expansion process, then they develop the greatest sealing effect. Given the fact, however, that the length over which the guide rods are guided must not drop below a minimum value at the end of the expansion range if parallel guiding of the members is to be guaranteed, it has been found that the sealing effect is sufficiently good even in this state. This makes it possible to limit the length, over which the guide rods are guided, from the beginning and to design the holes in which the guide rods are arranged in such a way as to provide, between the sections guiding the guide rods and the end of each guide rod, a section whose interior width is larger than the interior width of the guiding section. This provides the advantage that a thicker portion, an enlargeme
Forster Bernhard
Kasper Horst M.
Wilson John J.
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