Tensioning screw for orthodontic adjustment devices

A tensioning screw for orthodontic teeth straightening devices employed to adjust the situation and position of teeth along the curve of the jaw. The screw includes a nut and a threaded shaft that extends through it. An essentially resilient component (11) is disposed between the nut (6) and the shaft (2), at least on one side where the shaft enters or leaves the nut, and rests against the shaft's threads to prevent the shaft from undesired turning with respect to the nut.

BACKGROUND OF THE INVENTION 
The present invention concerns a tensioning screw for orthodontic teeth 
straightening devices. 
Tensioning screws of this type are known from the present applicant's U.S. 
Pat. No. 4,483,674. They are employed to adjust the situation and position 
of teeth or groups of teeth along the curve of the jaw. They include a nut 
and a threaded shaft that extends through it, tensioned between two points 
within the device. The effective length of the shaft is shortened during 
treatment to adjust the situation and position of the teeth. 
Such screws have proved effective in practice for this purpose. Still, the 
shaft will sometimes automatically turn backward, or even slowly out of 
the nut, due for example to the wearer's chewing motions. Attempts have 
been made to prevent this by using self-locking threads, but they are 
complicated to manufacture and make the screws more expensive. It also 
becomes almost impossible to screw the screw backwards when necessary, 
and, when one has been screwed in too tight, it must usually be discarded. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide a tensioning screw of the 
aforesaid type that will reliably prevent the shaft from turning backward 
out of the nut but that can be partly unscrewed and secured in that 
position without loss of function. 
This object, as well as other objects which will become apparent from the 
discussion that follows, are achieved, in accordance with the present 
invention, by providing an essentially resilient component squeezed 
between the nut and the shaft, resting against the shaft's threads, and 
generating there a tension essentially perpendicular to the length of the 
shaft. 
The resilient component can preferably be a ring or double loop in the 
shape of a figure eight resting against or enclosing the shaft on each 
side of the nut where the shaft enters or leaves it. 
The nut in one embodiment of the present invention has a projection on each 
side where the shaft enters or leaves it. The resilient ring or figure 
eight is introduced between the projections. The ring will accordingly be 
slightly squeezed and will press against the threads on the shaft, 
reliably securing them in position and preventing automatic backward 
rotation. 
The projections on each side of the nut can be in the form of pins, of 
strong wire perhaps, that secure the screw in the aforesaid orthodontic 
adjustment device. 
The resilient component in one very simple embodiment is in the shape of a 
figure eight, the two loops attached to each other along a web. The figure 
eight is positioned with the web more or less between, and extending along 
the circumference of each loop, each of which extends around the shaft. In 
this version, the web will rest against one side of the shaft and the 
loops against the other side. This embodiment requires no projections or 
pins extending out of the nut to secure the resilient component, although 
it may of course have one. It is in particular possible to secure to the 
nut at least one sleeve essentially paralleling the shaft and sliding 
along an arc of wire on the orthodontic adjustment device. The screw can 
accordingly be secured not only to clamps mounted on the teeth but also 
directly to the arc extending through the clamps.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The preferred embodiments of the present invention will now be described 
with reference to FIGS. 1-5 of the drawings. Identical elements in the 
various figures are designated with the same reference numerals. 
The tensioning screw 1 illustrated in FIG. 1 has an outside-threaded shaft 
2 with a head 3 provided with a slot 4 for a screwdriver. Between head 3 
and the threaded section is a slender neck 5 that can accommodate an 
unillustrated ligature wire as a fastening to one point on an orthodontic 
adjustment device. Shaft 2 engages and inside-threaded nut 6. Fastened to 
nut 6 and paralleling shaft 2 is a pin 7. As will be evident from the 
figure, pin 7 is inserted in a sleeve 8 and secured by laser or spot 
welding for example. Pin 7 could alternatively be secured directly to the 
circumference of the nut, by laser welding for example. The end of pin 7 
that points toward head 3 extends slightly beyond nut 6, constituting a 
projection 9. The other end of pin 7 extends considerably--as far, 
perhaps, as the shaft 2 is long--beyond nut 6, and can be inserted into 
the auxiliary tube of a molar band. The screw will accordingly also be 
attached to the band. The section of pin 7 on the side of nut 6 remote 
from projection 9 can be considered another projection 10 extending beyond 
the nut. 
A resilient ring 11 is now inserted tightly into the screw as illustrated 
in FIG. 2 between projections 9 and 10 and the threads on shaft 2. Ring 11 
extends between the projections on each side of pin 7 or sleeve 8. The 
hatched area in FIG. 3 represents the deformation in ring 11 once it has 
been inserted, the broken line indicating its original shape. The 
deformation of ring 11 forces it against the threads on shaft 2 and 
prevents the shaft from turning backward. 
FIG. 4 illustrates another embodiment of a screw 1 in accordance with the 
present invention, also with a shaft 2 with a head 3 and a nut 6. Nut 6 is 
provided with a sleeve 12 essentially paralleling shaft 2. Sleeve 12 can 
be slipped onto the wire arc of an orthodontic adjustment device that 
extends through clamps mounted on the teeth. 
The nut 6 in this embodiment has no projections on the side facing sleeve 
12. It employs instead a different kind of resilient component essentially 
in the form of a figure eight 11 as illustrated in FIG. 5. Figure eight 11 
has two loops 13 connected along a web 14 between them and extending along 
the circumference of each loop. Each loop 13 wraps around shaft 2 on 
opposite sides of nut 6 and accordingly rests snugly against the shaft's 
threads, preventing it from turning backward. As in the previous 
embodiment, however, it is till possible to turn shaft 2 in either 
direction in the threads inside nut 6. 
There has thus been shown and described a novel tensioning screw for 
orthodontic adjustment devices which fulfills all the objects and 
advantages sought therefor. Many changes, modifications, variations and 
other uses and applications of the subject invention will, however, become 
apparent to those skilled in the art after considering this specification 
and the accompanying drawings which disclose the preferred embodiments 
thereof. All such changes, modifications, variations and other uses and 
applications which do not depart from the spirit and scope of the 
invention are deemed to be covered by the invention, which is to be 
limited only by the claims which follow.