Patent Application
20090042164
The invention relates generally to orthodontics and more particularly to a tool for use in placing and removing small orthodontic bone screws for use in intra-oral orthodontic corrections.
As described in Balfour; et al. U.S. Patent Publication No. 20070122764, May 31, 2007, the contents of which are incorporated herein by reference, bone screws are now available for use for orthodontic anchorage. A bone screw of this type is designed to be inserted with a self-piercing and penetrating tip and self tapping locking threads in a single minimally invasive surgical operation. Once it is rigidly inserted into the host bone, standard orthodontic appliances can be attached to the exposed head of the screw. The orthodontic bone screw does not permanently integrate with the host bone, thereby allowing for removal at the completion of orthodontic treatment. A tool resembling a screwdriver is used to insert and later remove the screw.
The driver tool described in Balfour et al. has a tip end formed with a block shaped as a polygon in end view having side walls, ribs extending from selected side walls of the block and a centrally located cylindrical, tapered projection extending axially beyond the block; the block, ribs and projection sized to fit in the respective polygonal recess, cross grooves and cylindrical bored surface of the orthodontic bone screw. This tip end resembles the head of a Philips screwdriver. The end opposite the tip end is mounted in a driver handle sold by Ace Surgical.
A mechanism is provided to separate the driver tool from a bone screw to which it has been engaged for mounting in the host bone. The mechanism includes a threaded shaft on which the tip end is formed and a push-off driver sleeve having an internal thread is threadedly engaged to the thread on the threaded shaft. Upon rotation, the head of the bone screw to which the tip end is engaged, the push-off driver sleeve upon further rotation exerts a force against the head of the bone screw to move the tip end out of engagement with the bone screw.
Other bone screw drivers for orthodontics have taken the opposite approach to Balfour et al. and provided a socket on the tip that surrounds the head of the bone screw. The tool is essentially a miniature socket wrench. See, for example, the Aarhus System octagonal screwdriver marketed by American Orthodontics.
Neither of these approaches has proven free of problems. Tips resembling a Philips screwdriver release relatively easily when installation of the bone screw is done, but are not as secure as a socket tip, causing the bone screw to be installed off axis. Socket tips hold to the screw axis better, but are more difficult to release from the screw head, and the force needed to release the tip will render the anchorage less secure. Anything that causes the screw to wobble in place presents a problem from the standpoint of providing a secure anchorage. The present invention addresses these drawbacks.
An orthodontic driver tip according to the invention is configured for screwing and unscrewing an orthodontic bone screw. Such a driver tip includes an elongated inner rod having an enlarged diameter front tip portion with a frontwardly opening recess, which tip portion comprises at least two frontwardly extending resilient arms which define the frontwardly opening recess between them, and a rear connecting portion by which the driver tip can be removably secured to a handle. A sleeve is mounted on the rod rearwardly of the enlarged diameter front tip portion, the sleeve having a front end of lesser diameter than a maximum diameter of the arms of the tip portion. Suitable means are provided for releasably securing the sleeve against lengthwise movement along the rod when the sleeve is moved forward to a position wherein the arms are bent into engagement with the head of a bone screw disposed inside the front tip portion. One such means is a threaded connection between the sleeve and the rod, as described hereafter. In preferred embodiments the resilient arms are configured to engage the outer periphery of a predetermined type of bone screw head. For this purpose the arms extend forward from a front end portion of the rod and form a front end opening that is cylindrical or otherwise rounded, or polygonal. The arms are spaced from each other in the circumferential direction and this is visible as a set of gaps between the arms. In the case of a polygonal front end opening, each arm forms one side of an imaginary polygon, such as a triangle or hexagon for tips with three or six arms, respectively. In a preferred embodiment inner end portions of the arms extend from a front end of the rod at an angle forming a frustoconical surface, wherein the sleeve slides over and engages the frustoconical outer surface when the sleeve is moved forward to a position wherein the arms are bent into engagement with the head of a bone screw disposed inside the front tip portion.
The invention further relates to an improved bone screw for use with the driver tip according to the invention, and the assembly of the screw and driver tip when in use. The improved bone screw has a dual diameter head wherein a distal end portion has a smaller diameter or maximum width than a mid-portion adjacent to it. The front end opening of the tip fits over the distal end portion and ends of the arms engage flange or step formed by the mid-portion. This engagement prevents over-insertion of the tip and improves the holding power of the tip.
An improved orthodontic bone screw of the invention has a threaded body and a head at one end thereof, which head has a first radial flange proximate a distal end thereof and a second radial flange spaced from the first flange between the first flange and the threaded body. The second flange has a greater diameter than the first flange and presents a stop surface for the resilient arms facing the first flange. These and other aspects of the invention are further described in the detailed description that follows.
In the accompanying drawings, wherein like numerals denote like elements:
Referring to
Prior to use, rear connection portion 19 is inserted into a front socket of handle 20. Handle 20 may be any of a number of known designs wherein the driver tip assembly is inserted and locked in place, then released after use for cleaning. Handle 20 is of the type sold by Ace Surgical as part 454-19501 or -19001 and shown in the Balfour et al. patent application cited above. The user pulls back on a middle barrel section 26 and compresses an internal spring, which makes it possible for the detent such as a metal ball to freely enter and leave annular groove 21. When barrel section 26 is released, the spring then forces the handle mechanism back to the closed position and the detent is locked into groove 21, securing the driver tip 10. In another such handle marketed by Medicon, the barrel section is stainless steel and a sleeve ahead of the barrel section is pulled backward to release the driver tip. These and other similar mechanisms known in the art, such as a chuck for holding a drill bit, could be used to releasably secure the rear end of the driver tip 10 to the handle 20.
Tip portion 14 is configured for precise engagement with orthodontic bone screw 11. Bone screw 11 has a threaded body portion 31 as described in Balfour et al., and a head 32 including a pair of upper and lower annular flanges 33, 34 of like diameter, and a midportion 36 of reduced diameter with transverse holes 37 allowing attachment of orthodontic appliances. A spline drive recess 38 may be provided as part of screw 11, but is not needed in the present invention.
As shown in
It is known in the art to make bone screw heads that are hexagonal or triangular rather than cylindrical. For this purpose,
The means for securing the sleeve 13 relative to rod 12 and arms 16 may comprise a tongue and groove mechanism such as shown in
Although the invention has been described with regards to a specific preferred embodiments thereof, variations and modifications will become apparent to those of ordinary skill in the art. It is the intent that the appended claims be interpreted as broadly as possible in view of the prior art as to include all such variations and modifications.
This application claims priority of U.S. provisional patent application No. 60/961,931, filed Jul. 25, 2007.
| Number | Date | Country | |
|---|---|---|---|
| 60961931 | Jul 2007 | US |
