GB2392844A

GB2392844A - Dental Appliance Retention Device

Info

Publication number: GB2392844A
Application number: GB0320885A
Authority: GB
Inventors: Gavin James Carmichael
Original assignee: EAST LANCASHIRE HOSPITALS NHS
Current assignee: EAST LANCASHIRE HOSPITALS NHS
Priority date: 2002-09-13
Filing date: 2003-09-05
Publication date: 2004-03-17
Anticipated expiration: 2023-09-05
Also published as: GB0221281D0; GB0320885D0; GB2392844B

Abstract

A device for incorporation in removable dental appliances to retain them in the mouth and resist the various forces that tend to displace them comprises a portion, such as a generally planar tag (1), which is retained in the body (4, 7) of the appliance, connected to a hollow tip (3) which is external to the body (4, 7) by a resilient, elongate limb (2). The hollow tip (3) of the device can serve as a mould or former for a counterpart lug (8) that may be created from light cured composite or other material directly onto the tooth the device is to engage. The hollow tip (3) may be shaped like a bowl or cup, or it may be like a split ring or collar which would make it more suitable for use in so called "fixed functional" orthodontic appliances. The device (1-3) is attached to the body (4, 7) of the appliance by bonding or by forming the material of the appliance body around the lug (1).

Description

DENTAL APPLIANCE RETENTION DEVICE

The present invention relates to a device to assist in the retention of removable dental appliances for patients with teeth shaped such that they render the application of 5 conventional retention devices ineffective.

Partial dentures are used to replace missing teeth and restore appearance and function.

They are normally made to be removable by the wearer for cleaning purposes.

Removable orthodontic appliances, more commonly referred to as braces, are used to 10 hold and/or move, teeth and other oral structures within the mouth to correct various irregularities of the dental arches and jaw relationships.

All removable dental appliances require some form of retention device to hold them in place during use. The known devices consist of individually formed clips or 15 clasps, usually either wrought from wire or cast in metal, although they can also be formed by the injection moulding of suitable resilient plastic materials, to engage in undercut areas on the teeth of each individual patient. These clips or clasps are then attached to some form of dental baseplate, usually made of acrylic plastic. This enables the baseplate to be retained in the mouth, either to support artificial teeth 20 during eating and speech or, to provide appropriate anchorage for other items, such as springs and traction screw devices, to act against other teeth to achieve movement and subsequent re-alignment. In all upper (maxillary) dental appliances there is also a requirement to overcome the effects of gravity in addition to any other loads that may be applied.

Some types of functional orthodontic appliance comprise upper and lower (mandibular) sections that act against each other to achieve correction of jaw relationships. This can create large displacing forces on the opposing sections that tend to unseat the appliances. Poor retention of these appliances can lead to patient 30 wear compliance problems resulting in failed treatments. In an attempt to overcome this problem some functional orthodontic appliances may also be "fixed" to the teeth

so that they can only be removed by an orthodontist for checks and adjustment. This "fixing" is usually done by means of stainless steel bands around the teeth with special attachments that can be difficult to fit and manage.

5 Many people, especially children, have teeth with very short clinical crowns that taper inwards from the gingival margin towards the occlusal or biting surface creating unfavourable contours for the successful construction of effective clasps. This can create major retention problems, particular in lower functional orthodontic appliances.

10 In the past there have been many attempts to overcome this problem by various means and those skilled in the art will be familiar with these methods. One method is to re-

contour the buccal or check surface of the tooth, usually a pre-molar or molar tooth, either by the addition of some form of dental composite material, usually light-cured, or by bonding on a preformed plastic component, to create an undercut shape prior to 15 the construction of an appliance. This enables the manufacturer of the appliance to fabricate a clasp or other form of retention for attachment to the baseplate at the appropriate place. Some orthodontic appliances are constructed by thermoforming a sheet of softened resilient plastic over a model of the recontoured teeth and this is then trimmed to act as both baseplate and clasping mechanism with other parts 20 optionally being attached to it after forming. An appliance of this sort, and its method of formation is described in WO00/32132. These appliances are vulnerable to damage and/or require special equipment to construct them.

It is an object of the present invention to obviate or mitigate one or more of the 25 problems outlined above.

According to the present invention a dental appliance is provided which comprises an appliance body and one or more devices for removably retaining the dental appliance on dentition, each device comprising a portion retained in the body and a tip portion 30 adapted for retaining the appliance on a lug on the dentition, the retained portion and the tip portion being connected by means of a resilient elongate limb, in which respect

the tip portion and at least part of the elongate limb are entirely external to the body of the appliance.

The retaining device may be pre-formed by injection moulding in a suitable resilient 5 plastic material. The device may comprise a generally planar tag, suitably of dovetail shape, connected to a hollow bowl shaped tip by the resilient elongate limb. The latter limb may be of ellipsoidal or D-shaped cross section and perpendicular to the tag although other sections and angles could be used.

10 In production of the dental appliance of the invention an appropriate number of such retaining devices would be incorporated in a manner familiar to those skilled in the art by means of bonding or embedding the tag into the body or baseplate of the appliance, usually where it extends over the occlusal or chewing surface of the teeth, although it could also be incorporated into the spaces created by missing teeth for use in a partial 1 5 denture.

In use of the invention the cavity in the tip of the device enables it to act as a mould or former for production of a lug on the surface of a tooth onto which the device is then to engage. In this way the surface of the tooth is re-contoured by provision of an 20 exact counter shape to the tip which is to engage thereon.

The hollowed tip of the device also usefully serves as a carrier or receptacle for any dental composite that may be used for the recontouring of the tooth. Thus, by implication, the hollowed tip provides an accurate measure for the quantity of 25 material require for lug formation.

The dental composite used may be of the type which is cured by application of light, for example ultraviolet light. Accordingly the tip of the device, or the whole device may be made of a material that allows sufficient light transmission to enable the 30 composite to be cured by directing a light source through the material of the retention device.

With a modified design of tip, for example in the form of a split ring or collar, the retention device could be incorporated into a so called "fixed" Functional orthodontic appliance that can only be removed by an orthodontist with appropriate instruments.

The present invention will now be described, by way of example with reference to the accompanying drawings, in which: Figure 1 is an isometric view of a preferred practical embodiment of a retention 10 device as used in a dental appliance in accordance with the invention; Figure 2 is a plan view illustration of a plurality of retention devices, as in Figure 1, incorporated into occlusal blocks formed in the baseplate of an orthodontic appliance in accordance with the invention; Figure 3 is an enlarged scale sectional view along line A-A of Figure 2 in the direction shown; and Figure 4 is a perspective view, to a smaller scale compared to Figure 1, of a modified 20 embodiment of a retention device which could be used in an appliance of the invention. Referring to Figure 1, a preferred embodiment of retention device comprises a generally planar tag 1 of dovetail shape connected to a hollow bowl shaped tip 3 by a 25 resilient elongate limb 2 of curved shape.

Figure 2 illustrates how a plurality of these retention devices 1-3 are applied to a lower section of a removable functional orthodontic appliance which comprises a body in the form of blocks 4 moulded onto a baseplate 7. In practice, at least four of 30 these retention devices 1-3 would normally be fitted to such an appliance with two on either side of the dental arch,. For clarity, only one device has been numbered with all

others corresponding. Each device is retained in the respective block 4 by means of its tag 1 (shown in dotted outline) so that at least a part of the limb 2 and the tip 3 extend outside the block 4 and the tip 3 lies with its hollow or bowl side placed against the buccal surface 5 of the tooth, as shown in Figure 3. The tip 3 fits over a 5 dome shaped lug 8 formed upon the buccal surface 5 of the tooth. This lug 8 is advantageously formed as a moulding of the bowl shaped cavity in the tip 3, as will be explained.

To construct the embodiment of the present invention shown in Figures 2 and 3 a 10 dental technologist would construct a plaster model of a patient's mouth and begin by positioning the retention devices shown in Figure 1 so that the hollow side of the tip 3 of each device was placed against the buccal surface 5 of a respective tooth 9 while the tag 1 was spaced above the occlusal surface 6 of the tooth 9 sufficiently to allow acrylic material to flow around the tag 1 during forming of the appliance and firmly 15 retain the tag 1 in the resulting acrylic block 4 after curing. During the forming of the blocks 4 the devices 1-3 would be retained on the dental model using dental wax in a manner familiar to those skilled in the art so that no acrylic material would be allowed to flow around the tip 3 and the elongate limb 2. After processing or curing of the acrylic the wax would be removed, eg with boiling water, to leave the tip 3 and the 20 limb 2 of each device clear of the acrylic. The appliance would then be trimmed to final shape and polished before being fitted in the patient's mouth.

After checking that the appliance fits, the orthodontist would treat the buccal surfaces 5 of the appropriate teeth with a suitable primer and then load each device tip 3 with a 25 suitable light cured composite or other material so that they are filled just over the level of the edges of the tip 3. The appliance would then be replaced in the patient's mouth and carefully seated so that the composite material in the tips 3 is pressed against the previously prepared buccal surfaces 5 of the teeth. A curing light of suitable frequency would then be applied and the composite material cured in the tips 30 3. After curing a dome 8 of the composite will have been formed on the buccal

surface 5 of each of the teeth that corresponds exactly with the bowl shape of the respective tip 3.

In order to remove the appliance from the mouth, the tips 3 on the ends of the 5 elongate limbs 2 must be sprung outwards from the buccal surface 5 of the teeth.

Thus in their normal unsprung condition the devices 1-3 resist vertical displacement of the appliance. Even if the buccal surfaces 5 of the teeth on both sides of the dental arch are converging towards the occlusal surface and, by implication, towards each other, the dome shaped lugs 8 formed by the devices will still create opposing 10 undercuts across the dental arch in all but the most extreme cases.

In other embodiments of the invention shown in Figure 1-3, as the devices could be added to the acrylic blocks 4 after the appliance had otherwise been made or to an existing appliance where conventional retention devices had failed. This may be done 15 by milling dovetail slots into the buccal aspect of the blocks 4 large enough to fit the tags or lugs 1 on the devices. The milled slots would then be filled with a light curing acrylic or cement and the baseplate fitted back onto the model or into the patients' mouth. The lug 1 of each device would be inserted into its respective slot so that the tip 3 of the device was resting in the correct position on the buccal aspect 5 of the 20 tooth. The light cured acrylic or cement would then be cured in situ using an appropriate curing light source. The counter dome 8 would then be created as previously described.

The foregoing is illustrative, not limitative, of the scope of the invention.

Although in the embodiment of the invention illustrated in Figures 1-3 the tip 3 of the device is hemi-spherical, it will be appreciated that other configurations of the tip could be provided in other embodiments. For example the tip could be formed with a hollow or recess of a different shape, perhaps angular or irregular in outline.

30 Alternatively, as shown in Figure 4, the tip could be made in the form of a split collar 13 so that it created and fitted onto a rivet shaped counter part projection and could

only be removed by an orthodontist using a specially shaped instrument. In yet another embodiment the tip of the retaining device could be shaped so that the resulting counter part projection was uncomfortable for the patient when the appliance was out of the mouth thereby encouraging the wearing of the appliance.

In the case of partial dentures the retaining device could readily be incorporated so that the elongate limb 2 lies near parallel with the occlusal surfaces of the teeth with the tag 1 embedded in the acrylic base plate and artificial teeth occupying the space left by the missing natural teeth in a manner familiar to those skilled in the art. In 10 other words, the shape of the limb 2 may vary, both longitudinally and in section, compared to the above-described illustrated embodiment. The material of the retaining devices may also vary, titanium or gold being possible, instead of plastic material.

Claims

1. A dental appliance comprising an appliance body and one or more devices for removably retaining the dental appliance on dentition, each device comprising 5 a portion retained in the body and a tip portion adapted for retaining the appliance on a lug on the dentition, the retained portion and the tip portion being connected by means of a resilient elongate limb, in which respect the tip portion and at least part of the elongate limb are entirely external to the body of the appliance.

2. A retaining device for use in the dental appliance of claim 1.

3. A device as claimed in claim 2 wherein the tip of the device has a cavity for retaining the lug.

4. A device as claimed in claim 3 wherein the cavity is bowl shaped.

5. A device as claimed in claim 4 wherein the bowl shaped cavity is substantially hemispherical.

6. A device as claimed in claim 3 wherein the tip comprises a split collar.

7. A device as in any of claims 2 to 6 wherein the whole device is formed from a resilient material

8. A device as claimed in claim 7 wherein the resilient material is a polymer.

9. A device as claimed in any of claim 2 to 8 wherein the tip is transparent to light.

10. A device as claimed in claim 9 wherein the tip is transparent to ultraviolet light.

11. A device as claimed in any of claims 2 to 10 wherein the arm is elliptical in 5 cross-section.

12. A device as claimed in any of claims 2 to 11 wherein the arm is D-shaped in cross-section. 10

13. A device as claimed in any of claims 2 to 12 wherein the retained portion has a dovetail shape.

14. A method of forming an attachment lug on dentition and of subsequent engagement and attachment of a removable dental appliance by said lug, said 15 method including the steps of providing a device comprising a resilient elongate connecting limb having at one end an attachment portion and having at its other end a tip with a cavity formed therein, bonding the attachment portion of the device to the dental appliance and using the tip cavity as a mould, in which respect the tip cavity is filled with a dental composite and the 20 composite is applied to the surface of a tooth and cured in-situ to form the lug whereby the tip is then releasably engaged.

15. A device for retaining a dental appliance upon dentition substantially as hereinbefore described with reference to and as illustrated by figures 1 and 3 25 or Figure 4 of the accompanying drawings.