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Orthodontic force module

Orthodontic force module description/claims

This application is a divisional of U.S. Ser. No. 11/440,869, filed May 25, 2006.

The present invention generally relates to orthodontics and, more particularly, to an orthodontic force modules of the type used for palatal expansion and other applications.

Orthodontic palatal expansion is commonly carried out using a force module that is installed on the upper dental arch of a patient's mouth, the force module being connected to a palatal expander of a type commonly known in the art. The method of palatal expansion using expansion screws has become known in the art as “rapid palatal expansion” (RPE). Force modules used for this purpose must be tightened periodically to be effective.

Huge et al. U.S. Pat. No. 6,783,361, Aug. 31, 2004, describes an orthodontic mechanical force module having a jack screw whose rotation is controlled by a ratchet. In one embodiment, a pair of housings are interconnected with the patient in any appropriate manner, and are further rotatably interconnected with a rotatable spindle. At least one of these housings is also threadedly engaged with the spindle. A ratchet is associated with the spindle to selectively allow the spindle to rotate only in a direction that increases a magnitude of the treatment forces being exerted on the patient by changing the spacing between the pair of housings by a movement of at least one of the housings along the spindle due to its rotation. In an active position, the ratchet precludes the spindle from rotating in a direction that would tend to reduce the magnitude of the treatment forces being exerted on the patient.

The Huge et al. device, and also an appliance described in literature as the “RatchetRax” claim to provide bi-directional adjustment capability. The device of the present invention incorporates a mechanical locking device, unlike those of the previously mentioned devices, that allows bi-directional activation of the screw mechanism without a multitude of tools or augmented instruction to the user. The RatchetRax is bi-directional, but moves only one nut body to create the expansion. The great disadvantage inherent with movement of one nut body as opposed to both nut bodies is that the overall lateral size of the single body movement device must necessarily be twice as wide to effect the same amount of expansion or contraction. Appliance size is critical relative to accommodation in the mouth and to patient comfort and tolerance.

Bi-directional adjustability allows the mechanism to be employed not only as an expansion device (activation of the nut bodies apart from each other) but also as a contraction device wherein the bodies are purposefully installed in the patient screwed apart and then activated to bring them together, thereby delivering a closing force as opposed to an expanding or opening force. This is a common application of such force modules, i.e. to move teeth adjacent to an edentulous space together to eliminate the space and mitigate the need for a prosthesis. The most common applications of such force modules are expansion of the palate, expansion of the mandibular alveolus, contraction of teeth adjacent to an edentulous site, and contraction of the palate.

Screw de-activation (screw reverses direction after activation) has always been a challenge with expansion screws. In order to control screw reversal, most prior art mechanisms have incorporated some type of screw thread drag adjunct (lacquer coating, nylon bushing, etc.). These have sometimes been successful, but many times not. A popular device described in U.S. Pat. No. 6,482,001 suffered problems with screw reversal that could not be controlled. When an expansion device fails, its removal and replacement subjects the patient to the rigors of duplicating previous protocols. Additionally, after such expansion has begun and then fails, appliance removal is considerably more uncomfortable because the involved tissues are in a heightened state of irritability. Furthermore, clinicians experience aggravation over lost time, duplication of effort, and poor public relations that invariably result from patients and/or parents of patients exasperated about the inconvenience of repeated appointments and delayed treatment time. Locking the screw in place mechanically is the surest way to prevent screw reversal. The present invention inhibits screw reversal without requiring additional tooling and instruction.

An orthodontic force mechanism according to the invention includes an elongated jack screw having at a pair of end portions, at least one of which is threaded, and a central spindle section between the end portions, which spindle section has at least two radial holes therein. A pair of nut housings are mounted on the end portions of the jack screw, at least one of which is threadedly coupled to a threaded end portion of the jack screw. A lock mechanism is mounted on the central spindle section, which lock mechanism includes a spring-loaded detent configured to engage an end opening of each of the radial holes in the spindle section when such hole is in alignment with the detent, such that the spindle cannot rotate relative to the lock mechanism when the detent is inserted into a radial hole, and is free to rotate relative to the lock mechanism when the detent is clear of a radial hole. In a preferred embodiment, the radial holes comprise intersecting through holes. The detent can be moved out of engagement with a through hole using a tool inserted into that through hole from its opposite end, such that a distal end of the tool pushes the detent out of the through-hole, and the same tool can then be used to rotate the jack screw. For the reasons noted above, it is preferred that both end portions of the jack screw are threaded in opposite directions, with the nut housings are threadedly coupled to the end portions of the jack screw.

In a preferred embodiment, the lock mechanism according to the invention comprises a housing having an outwardly opening recess and a bearing surface in engagement with the jack screw. The spring is disposed in the recess and confined for compression between the detent and the housing. A guide rod is slidably disposed in guide openings in each of the nut housings, and the housing of the lock mechanism is secured to the guide rod such that the lock mechanism does not rotate relative to the jack screw when the jack screw is rotated in a manner effective to cause the nut housings to move toward or away from one another. For this purpose, the housing of the lock mechanism can be slidably supported on the guide rod, or the guide rod can be made integral with the housing, e.g. as projections extending in opposite directions. A pair of attachment rods extend from each of the nut housings, which attachment rods are configured for attachment to an orthodontic appliance to be installed in the mouth of a patient.

In an especially preferred embodiment, the openings of each through hole in the spindle section are configured to receive a coil-spring activated detent element oriented perpendicularly to the long axis of the jack screw either within the confines of a lock housing, thereby “locking” and “unlocking” according to compression or expansion of the encapsulated coil spring. The detent element/lock housing interface with lock-seats of the spindle section inhibit the spindle from spontaneously rotating in a direction that would decrease the magnitude of desired force, but that, in fact, will readily without adjunct tooling or instruction allow reverse rotation of the spindle according to the need and desire of the prescribing clinician. A force module such as described in Huge et al. provided with a tempered leaf spring locking mechanism is prone to breakage as a result of binding with the plurality of activating tools. In the “RatchetRax” device, if after partial activation and bowing of the leaf spring, the direction is reversed against the “bow” of the spring, a binding force can occur thereby causing the leaf spring to break. A sliding ball or cup locking arrangement of the present invention is activated by a coil spring as opposed to a leaf spring, which coil spring is protected from all outside destructive influences by virtue of its encapsulation within the confines of the lock housing thereby rendering it more protected and hence less sensitive to mechanical breakage. Furthermore, the nature of a coil spring as it functions through a cycle of expansion and contraction is not stressed and therefore not prone to break like a “bowed” leaf spring is if in mid-cycle the direction of stress is reversed.

The invention further provides a lighted wrench for use in tightening an orthodontic force module. Such a wrench includes a hollow handle, a battery disposed in the handle, a head connected to the handle by a pivot, an LED mounted on the head and connected to the battery by electrical connections such as wires, and a tool mounted on the head proximate the LED and extending forwardly therefrom. The tool has a reduced diameter tip configured to fit inside a hole in a jack screw forming part of an orthodontic force module. These and other aspects of the invention are discussed further in the detailed description that follows.

In the accompanying drawing, wherein like numerals represent like elements:

FIG. 1 is a perspective view of a force module according to the invention, with nut housings detached;

FIG. 2 is a perspective view of the force module of FIG. 1, with the nut housings threaded on;

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• Utility Patent

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