Dentistry – Orthodontics – By device having means to apply outwardly directed force
Reexamination Certificate
1998-09-29
2002-07-30
Manahan, Todd E. (Department: 3732)
Dentistry
Orthodontics
By device having means to apply outwardly directed force
Reexamination Certificate
active
06425758
ABSTRACT:
The present invention is based on an elastic expansion appliance having the features indicated in the preamble of claim
1
. An elastic expansion appliance of this kind is known from U.S. Pat. No. 5,167,500. The known elastic expansion appliance comprises two members joined to one another by two parallel guide rods, and a pseudoelastic coiled spring which is arranged between the two members. Each of the two guide rods is fastened at one of its ends in an orifice of one of the two members, and sits at its other end in a pertinent orifice of the opposing member, so that the two members can change the spacing between them by displacement along the two guide rods. The displacement can be effected by the coiled spring. The two members are intended either to be embedded in a plastic palate plate and/or to carry soldered-on or welded-on arms which respectively carry retention elements, clamps, or eyes which engage on teeth whose position is to be corrected, this occurring under the action of the spring. For this purpose, the elastic expansion appliance is installed into the dentition with the spring under stress, e.g. in the compressed state, and thereafter acts with the return force of the spring on the tooth or teeth whose position is to be corrected, the elastic expansion appliance being capable of expanding until the return force of the spring has declined to the point that it is no longer sufficient to correct tooth position. The magnitude of the correction which actually occurs thus results from the expansion which the spring performs until it has relaxed. If it is desired to change the magnitude of the correction, it is necessary either to change the distance ever which the elastic expansion appliance is initially compressed, and/or to replace the spring. Both are laborious and unsuitable for practical use. A further disadvantage is the fact that the preselected displacement travel is too great for the intended correction of the tooth position, which may become evident only in the course of the treatment. The physician performing the treatment can only ascertain this. However, if the patient comes in regularity for examination, it the patient does not do so, or does so ton late, the tooth position may already have been changed to such an extent that a countercorrection is necessary. This can be eliminated, however, by way of a jackscrew which is already disclosed in U.S. Pat. No. 5,167,500 as existing art and which displaces the two variable-spacing members not by way of a spring, but by way of a double spindle having sections threaded in opposite directions. In ardor to prevent excessive correction forces, a jackscrew of this kind 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. The came applies to the combined tension and compression screws according to Heller for sagittal movement of teeth.
An elastic jackscrew according to Hauser, disclosed in DE-824 632, allows for somewhat fewer readjustments than with a springless jackscrew. An elastic jackscrew of this kind is, however, more complex to manufacture than a springless (rigid) jackscrew.
It is the object of the present invention to indicate a way in which the progress of a tooth position correction can easily and reliably be kept under control.
This object is achieved by an elastic expansion appliance having the features indicated in claim
1
. Advantageous developments of the invention are the subject of the dependent claims.
According to the present invention, in order to adjust the distance over which the spacing of the two members of the elastic expansion appliance can be changed, a stop of variable length is provided for the spring and/or for one of the two members, the length of the stop being measured in the direction of the linear guidance means. By way of such a stop, the distance over which the spring can relax, and thus the distance over which the spacing of the two members can change, can be changeably predefined. In this fashion, the physician performing the treatment can specifically define, by visual inspection, how much tooth correction is to occur until the first examination. There are no deleterious consequences even if the patient does not arrive for an agreed-upon examination appointment, since correction of the tooth position automatically ends when the preset distance has been reached.
In an advantageous development of the invention, the length of the stop can be changed only in steps. This has the advantage that the length of the steps can be selected so that on the one hand sufficient treatment progress is attained, and on the other hand the step is not so large that an excessive, incorrect change in tooth position might occur. Misadjustments can be prevented by suitably selecting the step length. In the simplest case, the length of the stops can be changed in equal steps. It is also possible, however to conFig. the stops so that they can be changed in steps of unequal length. This has the particular advantage that longer steps can be set at the beginning of the treatment, while as the end of the treatment approaches, a shorter length can be selected for the steps; as a result, the treatment duration and the number of examinations can he decreased.
In an advantageous development of the invention, in order to constitute a stop that can be changed only in steps, provision is made for a stack of spacers, in particular plate-shaped, which are provided between the spring and one of the members, or between one of the members and an immovable stop. The spacers con easily be placed onto the linear guidance means which advantageously are guide rods, optimally perpendicular to the longitudinal direction of the linear guidance means, since they can then be removed without disassembling the elastic expansion appliance or destroying the spacers. In order to allow the spacers to be placed onto the linear guidance means perpendicular to their longitudinal direction, they advantageously have a laterally open recess into which the linear guidance means engage. This laterally open recess can be a slot into which the linear guidance means are inserted, one after another, when the spacers are slid onto the two linear guidance means in the direction of the plane spanned by said means. The spacers can also, however, be slid into the linear guidance means perpendicular to the plane spanned by said means, if the spacers have two slots provided at the spacing of the linear guidance means. Instead, however, it would also be possible to provide half-round recesses at opposite ends of the plate-shaped spacers, and clamp them with the recesses only between the linear guidance means. To ensure that they are securely held on the linear guidance means, they are advantageously snapped on, which is easily possible due to the inherent elasticity of a plate-shaped and, in particular, slotted spacer.
If the spacers are arranged between the spring and one of the members, then as the thickness of the spacer stank increases, given a predefined initial spacing between the two members, the stress on the spring becomes greater, and the distance over which the elastic expansion appliance expands in the course of the treatment is greater. If, on the other hand, the spacer stack is arranged riot between the spring and one of the members but between the member and an outer immovable stop, then as the thickness of the spacer packet increases the spring is also compressed more strongly, but at the same time the possible displacement travel is also limited. In this case, the elastic expansion appliance is used in such a way that at the beginning of the tooth correction the two members have a smaller spacing than would he determined by the spacers being used, i.e. at the beginning of the treatment, the member adjacent to the spacers is not in contact against the spacer stack, but rather is brought closer to the other member against the spring force, so that the po
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