Elastomeric force module for orthodontic treatment

An orthodontic force module is made of an elastomeric material and includes one or more eyelet segments along with one or more connector segments coupled to the eyelet segments. The configuration of the eyelet segments and the connector segments is arranged so that a substantially constant cross-sectional area is provided throughout the working length of the force module. As a result, the resistance to elongation is substantially uniform throughout the working range of the force module and premature degradation and failure due to relatively high, concentrated stresses are avoided.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an elastomeric device that is used in the oral cavity during orthodontic treatment. More particularly, the present invention is directed to an elastomeric orthodontic force module that is useful for moving one or more teeth to desired locations along a dental arch, or for moving one dental arch relative to the other.

2. Description of the Related Art

Orthodontia is a specialized field within the general subject area of dentistry. Orthodontic treatment involves movement of malpositioned teeth to correct locations along the dental arch. In some instances, orthodontic treatment also includes movement of one dental arch as a unit relative to the other dental arch. Orthodontic treatment can result in improved occlusion as well as a more pleasing aesthetic appearance.

One type of orthodontic treatment involves the use of a set of components that are collectively known as “braces”. In this type of treatment, small slotted devices known as brackets are secured to the patient's anterior, cuspid and bicuspid teeth. An archwire is received in the slots of the brackets and forms a track to guide movement of the teeth to desired positions.

Ends of orthodontic archwires are often received in enclosed passageways of small devices known as buccal tubes that are connected to the patient's molar teeth. The passageways of buccal tubes help prevent the ends of the archwire from contacting the patient's soft tissue in the oral cavity, which might otherwise lead to pain and injury. More importantly, buccal tubes often serve as points of connection for components that apply forces in the oral cavity, since the molar teeth associated with the buccal tubes have relatively large roots. These large roots provide relatively stable anchorage against the applied forces so that the other teeth connected to the force components are moved as a result.

A number of options are available during orthodontic treatment for applying forces to teeth in order to move the teeth to desired positions. Oftentimes, the practitioner will use the inherent resiliency of the archwire to apply a force to one or more brackets and move the associated teeth as the archwire tends to return to its normal relaxed configuration. If desired, one or more loops, bends, twists or other configurations may be formed in the archwire by the practitioner in order to help guide movement of the teeth as desired.

In some instances, orthodontic treatment may include correction of the alignment of the upper dental arch with the lower dental arch. For example, certain patients have a condition referred to as a Class II malocclusion wherein the lower dental arch is located an excessive distance in a rearward direction relative to the location of the upper dental arch when the jaws are closed. Other patients have an opposite condition referred to as a Class III malocclusion wherein the lower dental arch is located in a forward direction of its desired location relative to the position of the upper dental arch when the jaws are closed.

Orthodontic treatment of Class II and Class III malocclusions is commonly undertaken by movement of the upper dental arch as a single unit relative to movement of the lower dental arch as a single unit. To this end, forces are often applied to each dental arch as a unit by applying force to the brackets or buccal tubes, the archwires, or attachments that are connected to the brackets, buccal tubes or archwires. In this manner, a Class II or Class III malocclusion can be corrected at the same time that the archwires and brackets are used to move individual teeth along the dental arch to desired positions relative to each other.

Correction of Class II and Class III malocclusions is sometimes carried out by use of a force-applying system known as headgear. Headgear often includes strapping that extends around the rear of the patient's head. The strapping is often connected to tension springs that, in turn, are connected to the buccal tubes, the brackets, or one of the archwires. Additionally, and as an alternative for correction of Class III malocclusions, the strapping may be connected by tension springs to a chin cup that externally engages the patient's chin. In either instance, the strapping and springs serve to apply a rearwardly-directed force to the associated jaw.

However, headgear is often considered unsatisfactory because it is visibly apparent. Headgear may serve as a source of embarrassment, particularly among adolescent patients who may experience teasing from classmates. The embarrassment can be somewhat reduced if the orthodontist instructs the patient to wear the headgear only at night. Unfortunately, such practice may lengthen treatment time since the desired corrective forces are applied during only a portion of each calendar day.

Consequently, many practitioners and patients favor the use of intra-oral devices for correcting Class II and Class III malocclusions. Such devices are often located near the cuspid, bicuspid and molar teeth and away from the patient's anterior teeth. As a result, intra-oral devices for correcting Class II and Class III malocclusions are hidden in substantial part once installed and eliminate much of the patient embarrassment that is often associated with headgear.

A variety of force modules are known for treatment of Class II and Class III malocclusions. U.S. Pat. No. 6,120,289 describes a force module in the shape of a flat spring that assumes a curved orientation along its length when the patient's jaws are closed. During use, the inherent resiliency of the module tends to urge the module toward its normally straight configuration and as a result move the associated dental arches relative to each other.

Other types of force modules for correction of Class II and Class III malocclusions include telescoping assemblies that may optionally include a spring. An example of an improved telescoping force module is described in applicant's U.S. Pat. No. 5,964,588. In devices of this general type, the dental arches are moved relative to each other by the force of a coil spring or by a dead stop when the piston reaches the bottom of the cylinder, or by a combination of both.

Orthodontic force modules made of an elastomeric material have also been used in the past to treat Class II and Class III malocclusions. Elastomeric force modules are connected between the dental arches and often used in tension to pull the jaws together. The tension applied by the module tends to pull the jaws together in a direction along a reference line that extends between the points of attachment of the force module.

A variety of elastomeric orthodontic force modules are known. Examples of such force modules include bodies having the shape of a large O-ring and chain-type modules made of a number of smaller O-rings that are integrally connected together. Other types of elastomeric force modules include “dogbone-shaped” modules having a central, elongated straight section and a round eyelet section connected to each end of the straight central section.

While the elastomeric force modules described in the preceding paragraphs are generally considered satisfactory by many orthodontic practitioners, there is a continuing need in the art to improve the force modules that are currently available. For example, it would be desirable to provide an improved force module that is more resistant to fracture at a given tensile load without increasing the overall stiffness of the module. To this end, many attempts have been made to find alternative elastomeric materials that would be suitable for use in the oral cavity as force modules. To date, however, few orthodontic force modules with alternative materials are available.

SUMMARY OF THE INVENTION

The present invention is directed toward an improved orthodontic force module having a shape that provides more uniform stress along its length during use. As a result, premature degradation of the material and breakage that might otherwise be due to high, concentrated stresses in certain areas are avoided. The force module of the present invention may be elongated to a relatively large extent without rupturing.

The orthodontic force module of the present invention provides a number of important advantages. For one thing, a force module that is less likely to break during the course of treatment helps reduce the likelihood that the overall treatment time will be extended since the desired corrective forces are continuously provided without interruption. Additionally, the relatively low stresses encountered by the force module of the present invention during use helps to increase the length of time that the module may be used before replacement is needed. The principles of the present invention may be used for the construction of any orthodontic force module, regardless of the composition of the elastomeric material.

In more detail, the present invention in one embodiment is directed toward an orthodontic force module that is made of an elastomeric material and has a longitudinal axis. The force module comprises an eyelet segment having an opening, a first section and a second section. The first section and the second section extend along respective paths located on opposite sides of the opening. Each of the first section and the second section has a certain cross-sectional area in directions perpendicular to its respective path. The force module also includes a connector segment coupled to the eyelet segment and having a certain cross-sectional area in directions perpendicular to the longitudinal axis of the force module. The total area of the certain cross-sectional areas of the first section and the second section is in the range of about 80% to about 120% of the cross-sectional area of the connector segment when the force module is relaxed.

Another embodiment of the present invention is also directed to an orthodontic force module that is made of an elastomeric material and has a longitudinal axis. The force module of this embodiment comprises an eyelet segment having an opening with a longitudinal axis that extends in a direction generally parallel to the longitudinal axis of the force module when the force module is relaxed. The force module also includes a connector segment coupled to the eyelet segment.

An orthodontic force module according to another embodiment of the invention is also made of an elastomeric material and has a longitudinal axis. In this embodiment, the force module comprises an eyelet segment having an opening, a first section and a second section. The first section and the second section extend along opposite sides of the opening. Each of the first section and the second section includes a substantially straight first portion and a substantially straight second portion when the force module is relaxed. At least one first portion and at least one second portion have a longitudinal axis that extends at an acute angle relative to the longitudinal axis of the force module when the force module is relaxed. The force module also includes a connector segment coupled to the eyelet segment.

An additional embodiment of the present invention is also directed toward an orthodontic force module that is made of an elastomeric material and has a longitudinal axis. The force module of this embodiment comprises an eyelet segment having an opening, a first section and a second section. The first section and the second section extend along opposite sides of the opening and have respective central axes. The force module also includes a connector segment that is coupled to the eyelet segment and has a central axis. The connector segment, the first section and the second section elongate to approximately the same extent when considered in directions along their respective central axes when a tensile force is applied to the force module in directions along the longitudinal axis.

These and other aspects of the present invention are described in more detail below and are illustrated in the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1is an illustration showing an exemplary use of an orthodontic force module20that is constructed according to one embodiment of the present invention. The force module20is installed in the oral cavity of an orthodontic patient undergoing treatment. The force module20in this example is arranged to correct a Class II malocclusion by urging the patient's lower dental arch in a forward direction relative to the patient's upper dental arch.

In more detail, a set of lower dental brackets22is secured to corresponding teeth of the patient's lower dental arch and an archwire24is placed in the slots of the brackets22. Ends of the archwire24are received in buccal tubes26(only one shown) that are mounted on the patient's lower molar teeth. Each of the lower buccal tubes26has a hook28that extends in a distal direction (i.e., in a direction away from the middle of the patient's dental arch).

Similarly, a set of upper orthodontic brackets30is secured to teeth of the patient's upper dental arch and an archwire32is placed in the slots of the brackets30. Ends of the archwire32are received in buccal tubes34(only one shown) that are mounted on the patient's upper molar teeth. In addition, one of the upper brackets30has a hook36that extends in a gingival direction (i.e., in a direction toward the patient's gingiva or gums).

The force module20is connected to the hook28as well as to the hook36. The length of the force module20is selected by the practitioner so that the force module20is in tension when the patient's jaws are closed. This tensile force tends to urge the lower dental arch in a forward direction relative to the upper dental arch in order to correct the Class II malocclusion over a period of time.

The force module20is shown in more detail in FIG.2. As illustrated, the force module20has a number of eyelet segments38that are integrally coupled together by connector segments40. When the force module20is in its relaxed, normal configuration, the eyelet segments38and the connector segments40are all aligned along a straight path that coincides with a central longitudinal reference axis42of the force module20.

Each of the eyelet segments38has a non-circular opening44that is in the general and overall shape of a parallelogram with four sides of equal length. Preferably, at least one and more preferably all of the interior corners of the parallelogram are rounded. Each of the openings44is elongated and has a longitudinal axis that coincides with the central references axis42of the force module20. The openings44are sufficiently large to receive a hook or other component of an orthodontic system, such as the hooks28,36depicted in FIG.1. Preferably, the outermost eyelet segments38located on opposite ends of the force module20are connected to small extensions that serve to reinforce the adjacent openings44where high contact stress is likely to occur.

The eyelet segments38also include a first section46and a second section48. The first section46and the second section48have respective central axes that extend along respective paths located along opposite sides of the corresponding opening44. Each first section46includes a substantially straight first portion50and a substantially straight second portion52that is integrally connected to the first portion50. Similarly, each of the second sections48includes a substantially straight first portion54and a substantially straight second portion56that is integrally connected to the first portion54.

The force module20is illustrated inFIG. 2in its normal, relaxed configuration. In this configuration, the longitudinal axes of the first portions50,54and the longitudinal axes of the second portions52,56all extend at an acute angle relative to the central longitudinal axis42of the force module20. Optionally, all of such acute angles are approximately equal. An example of a suitable angle is 20 degrees, although other angles are also possible.

As a result, the longitudinal axis of the first portion50is oriented at an obtuse angle relative to the longitudinal axis of the second portion52when the force module20is relaxed. Likewise, the longitudinal axis of the first portion54is oriented at an obtuse angle relative to the longitudinal axis of the second portion56when the force module20is relaxed. Preferably, adjacent ends of the first and second portions50,52are constructed to blend together to form a smooth curved configuration as shown inFIG. 2. Asimilar construction is provided for adjacent ends of the first and second portions54,56.

The connector segments40each have a central longitudinal axis that coincides with the central longitudinal axis of the force module20. In addition, the sides of the connector segments40lie in reference planes that are parallel to the central axis42. The connector segments40are of equal length in the embodiment shown inFIG. 2, although other constructions are also possible.

FIG. 2ais a cross-sectional view taken across one of the connector segments40in a reference plane that is perpendicular to the central axis42.FIG. 2bis a cross-sectional view of one of the second portions52, taken in a reference plane that is perpendicular to the central longitudinal axis of that portion. Cross-sectional views are not illustrated for the first portions50,54or for the second portions56, but preferably are all identical to the cross-sectional view shown for the second portion52in the illustrated embodiment.

Preferably, the cross-sectional area of the connector segment40as shown inFIG. 2is within the range of about 80% to about 120% of the total of the cross-sectional areas of the first section46and the second section48of the eyelet segments38. More preferably, the cross-sectional area of the connector segments40is within the range of about 90% to about 110% of the total of the cross-sectional areas of the first section46and the second section48of the eyelet segments38. Most preferably, the cross-sectional area of the connector segment40is approximately equal to the total of the cross-sectional areas of the first and second sections46,48and the cross-sectional areas of the first and the second sections46,48are approximately equal as mentioned above.

FIG. 3is an illustration of the force module20as it might appear when a tensile force is applied to its opposite ends in directions along the central axis42as represented by the arrows. As shown, the force module20elongates under tension. In particular, each of the eyelet segments38and each of the connector segments40elongate when a tensile force is applied to opposite ends of the force module20.

Advantageously, the percent of elongation per unit length of the first and second sections46,48in directions along their respective longitudinal axes is approximately equal to the percent of elongation per unit length of the connector segments40for a given applied tensile force. Such a relationship is possible because the total cross-sectional area of the first and second sections46,48is substantially the same as the cross-sectional area of the connector segments40. As a consequence, stresses are distributed uniformly throughout the force module20and relatively high localized stresses are unlikely to occur.

Moreover, and as can be appreciated by comparison ofFIGS. 2 and 3, the overall configuration of the eyelet segments38, including the angular orientation of the longitudinal axes of the portions50,56does not substantially change when the force module20is stretched from its normal relaxed configuration shown inFIG. 2to the elongated configuration shown in FIG.3. Such construction helps to ensure that the stress is substantially the same regardless of whether the force module20is initially relaxed when tensile forces are applied, or whether the force module20is somewhat elongated when additional tensile forces are applied.

The force module20may be made of any elastomeric material that is suitable for use in the oral cavity and has sufficient strength to provide the forces needed for the orthodontic application at hand without rupture. Elastomeric materials include a natural or synthetic polymer which at room temperature can be repeatedly stretched to at least twice its original length and which after removal of the tensile stress, will quickly and forcibly return to approximately its original length. Suitable materials include durable, set-resistant thermoplastic urethane elastomers such as Texin brand urethane no. 285 from Bayer Corporation. Examples of suitable stain-resistant elastomers are set out in applicant's U.S. Pat. No. 5,461,133, which is incorporated by reference herein. The force module20is an integral, one-piece construction that can be made by, for example, an injection molding process, a compression molding process or by die cutting or stamping a section of previously molded material.

A force module20aaccording to another embodiment of the invention is illustrated in FIG.4. The force module20aincludes a series of eyelet segments38aand a series of connector segments40athat are coupled to the eyelet segments38a.Each of the eyelet segments38ahas an opening44aalong with a first section46aand a second section48athat extend along opposite sides of the opening44a.

The connector segments40aare substantially the same as the connector segments40described above, except that the connector segments40aare somewhat shorter in directions along the longitudinal central axis of the force module20athan the length of the connector segments40in the same direction. Optionally, the connector segments40amay not be highly apparent to the eye. In that instance, the first section46aand the second section48aof one eyelet segment38amay appear to be directly next to the first and second sections46a,48arespectively of the adjacent eyelet segment38a.Other lengths may also be selected for the connector segments40aas desired.

Other features of the force module20aare essentially the same as the corresponding features of the force module20. As such, a detailed description of the similar features need not be repeated.

A force module20baccording to another embodiment of the invention is illustrated in FIG.5. The force module20bhas only two eyelet segments38band a single connector segment40bthat interconnects the eyelet segments38b.

Each of the eyelet segments38bincludes a first section46band a second section48bthat extend along opposite sides of an opening44b.Additionally, an end section58binterconnects the first and second sections46b,48b.The opening44bhas a longitudinal axis that coincides with the central longitudinal axis42bof the force module20b.

FIG. 5ais a cross-sectional view taken in a reference plane perpendicular to the central axis42bof the connector segment40b,looking along lines5a—5aof FIG.5.FIG. 5bis a cross-sectional view looking in a direction along a central longitudinal axis of the second section48band taken along lines5b—5bofFIG. 5. Asimilar cross-sectional view taken across the first section46bis not illustrated but is identical to the cross-section shown inFIG. 5b.

The total area of the cross-sectional areas of the sections46b,48btaken in reference planes perpendicular their respective longitudinal axes is approximately equal to the cross-sectional area of the connector segment40btaken in a reference plane perpendicular to the central longitudinal axis of the force module20. Such relationship can be appreciated by comparingFIG. 5atoFIG. 5b,since the cross-sectional area ofFIG. 5ais approximately twice the cross-sectional area ofFIG. 5b.

Optionally, the cross-sectional area of the end sections58bis larger than the cross-sectional area of the second section48bshown inFIG. 5b.Such construction serves to reinforce the end section58bto help resist fracture when the force module20bin connected to hooks, posts or other orthodontic components. Reinforced end sections similar to the end sections58balso may be used on the outermost eyelet segments of the force modules20,20aif desired.

As an additional option, and as illustrated inFIG. 5, the force module20bincludes a tab60bthat is integrally connected to one of the end sections58bby a molding gate. The tab60bis useful as a handle during installation for the force module20b.As an example, the opening44bof the free end of the force module20bmay be connected to an orthodontic component, and the tab60bmay then be used by the practitioner to stretch the force module20band guide the opening44bon the opposite end of the force module20bover a second orthodontic component. The tab60band the associated gate are then cut away from the remaining portions of the force module20band discarded.

Advantageously, the tab60balso serves as a location for display of information or identification markings. For example, and as depicted inFIG. 5, the tab60bmay bear the number “28” to indicate the installed length or working length of the force module20bin millimeters when the force module20bis in place. Preferably, the indicated length represents a length between the center of the openings44b.

Furthermore, the tab60bmay provide an overflow reservoir during an injection molding process. Provision of the reservoir assures that a solid knit in the material may be achieved when the adjacent eyelet segment38bis formed. Although not shown in the drawings, the elastomeric material in such an injection molding process is introduced into the mold cavity through a gate that is located on the opposite end of the force module20b,preferably next to the end section58band in alignment with the central axis42b.

Optionally, a number of force modules20bof varying lengths are provided in pairs on a single sprue for convenient storage, handling and delivery to the operatory. Other features of the force module20bare preferably the same as the corresponding features described in connection with the force module20.

FIG. 6is an illustration of an exemplary prior art force module80that is made by an injection-molding process. The force module80includes a number of circular eyelet segments82and a number of straight connector segments84that are coupled between adjacent pairs of eyelet segments82. The eyelet segments82and the connector segments84are arranged in series along a central longitudinal axis86.

FIG. 6ais a cross-sectional view of a connector segment84, taken along lines6a—6aof FIG.6and in directions parallel to the central axis86.FIG. 6bis taken along lines6b—6bof FIG.6and is a cross-sectional view of one of the eyelet segments82. The cross-section of the eyelet segment82represented inFIG. 6bis substantially the same along the entire circular length of the eyelet segments82, and is essentially identical to the cross-section of the connector segment84as shown inFIG. 6a.

FIG. 7is an illustration of another orthodontic force module80aaccording to the prior art. The force module80ais made by a die-stamping process, in contrast to the injection molding process used to make the force module80. The force module80aincludes a series of circular eyelet segments82athat are interconnected by connector segments84a.The cross-sectional views ofFIGS. 7aand7b,taken along lines7a—7aand lines7b—7bofFIG. 7respectively, illustrate the essentially identical cross-sectional configurations of the connector segments84aand the eyelet segments82arespectively.

FIG. 8is a fragmentary, somewhat schematic view showing a portion of the force module80aas it appears when a tensile force is applied in opposite directions along the central axis86aas indicated by the arrows. The dashed lines inFIG. 8represent the overall appearance of the same force module80awhen relaxed. As illustrated, the eyelet segments82ashift from a circular configuration to a straightened configuration with parallel sections on opposite sides of the now-closed eyelet opening when tension is applied.

FIG. 9is an illustration similar toFIG. 8, except that the tensile force applied to the force module80ais greater inFIG. 9than the tensile force applied to the force module80ain FIG.8. As shown inFIG. 9, the increased tensile force tends to elongate the entire force module80a,but greater elongation is observed in regions of the connector segments84ain comparison to the elongation of the eyelet segments82a.This characteristic of non-uniform elongation is due at least in part to the fact that the cross-sectional area across the two sections of the eyelet segment82ais twice as large as the cross-sectional area of the connector segment84a,as depicted byFIGS. 7aand7band indicated above. As a consequence, the connector segments84atend to elongate more than the eyelet segments82awhen a tensile force is applied.

Moreover, and referring again toFIG. 8, the initial elongation of the force module80aoccurs when the eyelet segments82aare collapsed. The force required to collapse the eyelet segments82ais typically smaller than the force required to elongate the connector segments84ato any appreciable extent. As a result, the force module80aprovides resistance to elongation at two different force levels: first, the force required to collapse the eyelet segments82a,and second, the force required to elongate the connector segments84aas shown inFIG. 9once the eyelet segments82ahave been collapsed. Such a characteristic may not be satisfactory in some orthodontic applications where a substantially uniform resistance to elongation is desired regardless of the preexisting amount of elongation.

The force modules20,20a,20bas described above can be used in a variety of applications. Exemplary uses include applications for Class II correction as shown for example inFIG. 1as well as applications for correction of Class III malocclusion. However, other uses are also possible. For example, the force modules of the invention can be used to close spaces that are present along one or more dental arches, such as may occur when a tooth is removed. To close spaces, the force modules may be connected between hooks, posts or other structures that are provided on brackets, on buccal tubes or on locations along a single archwire. The force modules may also be used for consolidation of a dental arch, wherein each bracket of a series of brackets along a single dental arch extends through a corresponding opening.

Those skilled in the art may recognize that a number of variations and additions are possible to the presently preferred embodiments described above and illustrated in the drawings. Accordingly, the present invention should not be deemed limited to the specific embodiments described in detail, but instead only by a fair scope of the claims that follow along with their equivalents.