GB2388030A - Orthodontic screw alignment device - Google Patents

Abstract

An apparatus for aligning a screw device relative to a dental model such that the screw device can be incorporated in an orthodontic appliance formed on the model. The apparatus comprises an elongate straight alignment member 20, for example a rectangular strip. The screw device is supported on a planar lug 22. A pair of clips 27,28 are supported on the alignment member 20, the clips 27,28 defining arms 32 between which the planar lug 22 may be received. The screw device comprises two bodies 23,24 intended to be secured to respective sections 37,38 of the orthodontic appliance and a screw rotatable 25 about a predetermined axis to adjust the spacing between the bodies 23,24. The lug 22 when mounted between the two arms 32 extending from the alignment member 20 is orientated such that the screw axis extends parallel to the length of the alignment member 20.

Description

2388030 À

ORTHODONCTIC SCREW ALIGNMENT DEVICE

The present invention relates to an apparatus for aligning a screw device relative to a dental model.

Single and double acting screw devices are incorporated in removable and, occasionally, fixed orthodontic appliances. Such appliances are often but incorrectly referred to as braces and are used to displace individual teeth or to achieve expansion or contraction, either segmental, lateral or sagital, of the upper and lower dental arches. Such screw devices have been commercially available for many years and, although there have been numerous variations in design, the general principal by which they achieve movement has remained unchanged. These devices are generally referred to as expansion or traction screws.

The known screw devices usually consist of a single or double acting screw extending between two bodies. When the screw is fumed the spacing between the two bodies is increased or decreased. The bodies and screw can be either metal or plastic. In use, the bodies are embedded in relevant sections of a dental plate such that the spacing between the sections of the plate can be adjusted. The sections are held in alignment by one or more guide rods passing through the assembly in a direction parallel to the screw thread.

Many orthodontic screws which are currently available have a common design feature in that the screw device is mounted on a lug which is usually made of a therrnoplastc material. The lug is generally planar and encases a portion of the screw on which a capstan is mounted and to which access is required to turn the screw after the device has been incorporated in an orthodontic plate. The lug encases the capstan during manufacture of the orthodontic appliance and is then removed before final finishing of the appliance, removal of the lug leaving the capstan exposed. Thus the lug supports the screw device during the manufacturing process, maintaining the screw device in an appropriate position whilst plate sections are moulded around it so that the two bodies of the screw device are embedded in separate sections of the completed appliance.

Thus the lug assists in the alignment of the screw device during construction and allows the screw device to be affixed to a model, usually with wax, prior to the

r. ,, 1 À application of the material from which the final plate is manufactured. Generally this i material is an acrylic resin which is moulded around both the screw itself and various I other wire components used for retaining the appliance on the teeth of the user. Some dental technicians cut a slot into the model into which an extended part of the screw lug can be placed so as to assist in supporting the lug in the appropriate position during the manufacturing process.

The correct positioning of screw devices for segmental, lateral or sagital movements is important and requires skill and experience if the rotation axis of the screw is to be correctly aligned in relation to the anatomical features of the jaw. The necessary skill levels are not always available in commercial dental appliance manufacturing facilities and it would be advantageous if the required skill level could be reduced to enable good quality appliances to be manufactured by relatively inexperienced technicians. The reason that a relatively high skill level is required is that the axis of the screw must be aligned in relation to at least two of the following variables: I. The line of the dental arch (sagital); 2. The upper palatal mid line (median suture line).

3. The occlusal plane of the arch (horizontal) in both the lateral and anterior/posterior directions.

It can also be difficult to hold the screw device in the correct position whilst attaching it to the model, prior to applying acrylic or wax around it.

Functional orthodontic appliances are used to correct various malocclusions (where the anterior/posterior relationship of the upper and lower jaws is incorrect). Some functional orthodontic appliances consist of upper and lower appliances working in cooperation with each other, through the medium of acrylic blocks formed over the occlusal (biting) surfaces of the posterior teeth and attached to dental plates, with the upper and the lower blocks meeting at a cooperating angle.

:: These appliances, usually known as twin block functional orthodontic appliances, rely on these cooperating angled faces of the opposing upper and lower sections to hold the upper and lower jaws in a predetermined anterior/posterior position relative to each other, whilst at the same time allowing both normal opening and closing of the mouth and lateral movement during mastication. The blocks act as guides during these movements.

Where a mid line expansion screw is fitted for example on the upper appliance, it is essential to align the cooperating faces of the upper posterior acrylic blocks with the rotation axis of the screw used to expand the upper appliance. The cooperating faces of the lower blocks will also be aligned with this axis given that those faces are parallel to the faces of the upper posterior acrylic blocks. Such aligrunent is essential so that, when the screw is rotated to expand the upper dental arch, there is no change in the anterior/posterior relationship between the upper and lower blocks. It can be difficult to achieve this alignment.

US Patent No. 4597738 describes an orthodontic device which includes an upper jaw thrust plate and a lower jaw thrustplate. These plates are connected to the teeth and are provided in the front teeth region with rods and slideways respectively, cooperating to effect a sagital displacement of the jaws relative to each other. This document describes various screw devices for expanding dental arches and a lug for supporting a screw device and an associated moulding plate. The described structure comprises a slotted plate through which the lug is inserted to provide an adjustable angle former for an inclined guide plane formed on the lingual surface of the lower section of the functional appliance. The inclined plane is laterally parallel to the long axis of the screw thread of the screw device. This arrangement has a number of disadvantages. Firstly the plate can only be applied to the particular screw device for which it was designed. Secondly it is only of sufficient dimension to create flat inclined surfaces immediately adjacent to the screw device. Thirdly it has no function in the alignment of the screw relative to the plate in which the screw is embedded.

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

According to the present invention, there is provided an apparatus for aligning a screw device relative to a dental model such that the screw device can be

:: c. f,: ':'.: r4e À incorporated in an orthodontic appliance formed on the model, comprising an elongate straight alignment member, a lug supporting a screw device, and means for connecting the lug to the alignment member, the screw device comprising two bodies intended to be secured to respective sections of the orthodontic appliance and a screw rotatable about a predetermined axis to adjust the spacing between the bodies, and the connecting means being such that connection of the lug to the alignment member causes the screw axis to extend parallel to the alignment member.

The invention also provides an apparatus for aligning a screw device mounted on a generally planar lug relative to a dental model such that the screw device can be incorporated in an orthodontic appliance formed on the model, the screw device including an expansion screw having an axis of rotation which is perpendicular to the plane of the lug, wherein the apparatus comprises an elongate straight alignment member which may be positioned on the model with its length extending parallel to an intended direction of expansion, and means mountable on the elongate member defining a slot for receiving and gripping the lug, the slot extending perpendicular to the length of the elongate member such that a gripped planar lug extends perpendicular to the elongate member.

The elongate member may be planar and may be formed for example from a rectangular plate. One of the elongate edges of the plate may be chamfered to enable it to be readily positioned on a dental model.

The elongate member and the lug may be connected by clips which can be pushed onto the elongate member. For example the clips may be U-shaped to define slots dimensioned to receive the elongate member. The clips may be simply spring-

biased to engage the elongate member or additional clamps or screws may be provided to provide further security.

The clips may define arms which extend perpendicular to the elongate member and define therebetween a slot which can receive a planar lug, thereby ensuring that the screw axis is aligned with the length of the elongate member.

The present invention makes it possible for a user to readily visually align the elongate member with a desired orientation relative to a dental arch, for example at right angles to the palatal midline. Once the elongate member has been so positioned, a lug can be mounted on the elongate member in the knowledge that the screw device

l . ( s carried by the lug will be aligned so that the expansion axis of the device extends in a direction parallel to the length of the elongate member.

The elongate member can perform a secondary function, that is providing a surface against which an active surface of a functional block may be formed, so as to ensure that the active surface is in a plane which extends parallel to the expansion screw axis An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic illustration of a model of an upper dental arch showing the position of the palatal midline of the arch and the location relative to that line of an expansion screw device which is intended to be incorporated in an orthodontic appliance split along the palatal midline; Figure 2 illustrates a dental model and a further screw device intended to be incorporated in an orthodontic appliance to be used for saggital movement of the dental arch; Figure 3 illustrates components of a conventional twin block appliance for advancement of the mandibular position; Figure 4 Illustrates components of an apparatus in accordance with the present invention; Figure 5 is a side view of a dental model of an upper dental arch showing the positioning of the embodiment of the invention illustrated in figure 4 on that model; Figure 6 is a view in the direction of the line 6-6 of figure 5; Figure 7 is a view in the direction of line 7-7 in figure 6; Figure 8 illustrates the embodiment of the invention shown in figure 4 positioned to assist in the location of a screw device for saggital expansion of a lower dental arch; and Figure 9 is a view on the line 9-9 of figure 8.

it should be noted that all retaining wires and clasps are not shown in the drawings, for the sake of clarity.

Referring to figure 1, this illustrates a dental model of an upper dental arch having a palatal midline represented by the line 1. In order to enable expansion of the dental arch, the dental model is to be used for the formation of an orthodontic appliance in which two plates or segments will be moulded on the dental model so as

c ( *: to form a plate assembly split along a plane corresponding to the palatal midline 1. A screw device has to be embedded in the orthodontic appliance so as to enable the two plate components to be moved apart. A conventional screw device is shown in figure 1 as comprising a first body 2, a second body 3, a screw 4, guide bars S. and a capstan 6. Rotation of the capstan causes rotation of the screw 4 which in turn forces the bodies 2 and 3 apart, the relative movement of the two bodies being guided by the guide bars 5.

A dental technician given the task of forming an orthodontic appliance of the type described with reference to figure 1 has to take great care to ensure that the axis of the screw 4 is perpendicular to the palatal midline plane so that as the two segments of the orthodontic appliance are moved apart as a result of rotation of the capstan 6 the expansion of the dental arch is in a direction perpendicular to the palatal midline plane. It can be difficult to correctly align the screw device in the required manner.

Referring to figure 2, this shows a dental model representing an upper dental arch, the model having been prepared to enable the preparation of an orthodontic appliance intended to achieve saggital movement of the arch. The intention is to produce an orthodontic appliance which is split into two segments with the boundary between the two segments being indicated by lines 7 and 8. A screw device comprising a first body 9, a second body l O. a screw I l a guide bar 12 and a capstan 13 to enable rotation of the screw l l has to be correctly positioned relative to the dental arch. The correct position is one in which the axis of the screw l l is parallel to the line of the dental arch viewed from the occlusal aspect and to the occlusal plane of the teeth viewed from a horizontal aspect As in the case of the circumstances represented in figure 1, it can be difficult for a dental technician to correctly position a screw device as required for the circumstances described in figure 2.

Referring to figure 3, this is a diagrammatic illustration of the principal components of one side of the upper and lower parts of a twin block appliance which is inserted between an upper dental arch 14 and a lower dental arch 15 and where the other side corresponds. The appliance comprises a first block 16 which in use is moulded into an appliance baseplate placed on the upper dental arch l S and defines an active surface 17 and a second block 18 which in use is moulded using the surface

À À À. À À <. .. À. 17 as a fonder into an apphance base-plate placed onto the lower dental arch 13 and defines an active surface 19. Generally the two surfaces 17 and 19 will be parallel to each other and perpendicular to the palatal midline. The fimction of the blocks is to hold the upper and lower jaws in a predetermined anterior/posterior position relative to each other while at the same time allowing both nonnal opening and closing of the mouth and lateral movement during mastication.

Functional blocks such as those illustrated in figure 3 are manufactured by dental technicians working on models of the upper and lower dental arches on which the blocks and the appliance base-plates to which they are attached are to be fitted. It can be difficult for a dental technician to ensure that the surfaces 17 and consequently 19 are correctly positioned so as to ensure that they are both perpendicular to the palatal midline.

Figure 4 illustrates components which make up an embodiment of the present invention and which can be used to facilitate the manufacture of orthodontic appliances in circumstances such as those described with reference to figures 1 to 3.

The illustrated device comprises an elongate straight alignment member in the form of a step 20 having a chamfered edge 21. A lug 22 supports a screw device comprising a first body 23, a second body 24, a screw 25, and guide bars 26. capstan (not shown) is provided on the screw 25 to enable its rotation relative to the bodies 23 and 24. After the screw device has been mounted in an orthodontic appliance comprising two plates or segments one of which has the body 23 embedded within it and the other of which has the body 24 embedded within it the lug 22 will be snapped off to provide access to the capstan so that the two plates of the orthodontic appliance can be moved relative to each other by rotation of the screw 25.

The lug 22 may be positioned in an appropriate orientation relative to the strip 20 by a pair of clips 27, 28. The clips 27 and 28 each comprise a U shaped body defining limbs 29 and 30. A slot 3 l is defined between the limbs 29, 30 into which the strip 20 may be inserted. Arms 32 extend from the U shaped bodies, the two clips 27, 28 being handed so that the two arms 32 can be pushed into contact with each other by sliding the clips 27, 28 towards each other along the strip 20. To facilitate the insertion of the lug 22 between the arms 32, the ends 33 of the arms 32 are turned

À.r # ,,. . out. To similarly facilitate the positioning of the clips 27, 28 on the strip 20, the ends 34 of the limbs 29 are turned out.

One use of the embodiment of the present invention shown in figure 4 will now be described with reference to figures 5, 6 and 7 which illustrate the positioning of an expansion screw device in an orthodontic appliance used for expanding an upper dental arch relative to the palatal midline. The palatal midline is represented by line 35 in figure 6. The surface of the palate is represented by line 36 in figure 7. The orthodontic device when moulded around the expansion screw comprises a first plate defined by a moulded body 37 and a second plate defined by a moulded body 38 as shown in figure 7.

In use, the components shown in figure 4 are assembled by mounting the clips 27, 28 on the strip 20, pushing the clips together so that the arms 32 are close together, and then pushing the lug 22 between the arms 32. The strip 20 is then positioned by the user on the dental model as best represented in figure 6. It is an easy matter for the user to visually inspect the dental model and to position the strip 20 so that it is perpendicular to the palatal midline 35. It is also a simple matter to position the lug 22 so that it is aligned with the palatal midline 35. Finally, it is a simple matter for the lug 22 to be moved between the arms 32 until the screw device is appropriately positioned with the lug 22 resting against the dental model. Once the components have been so positioned, the orthodontic appliance can be built up by moulding appropriate materials around the screw device in a conventional manner.

Once the moulding process has been completed, the moulded material can be cut along a plane corresponding to the palatal midline 35 and the lug 22 can be removed to enable access to the capstan which is used to rotate the screw 25.

Rotation of the screw will always result in relative movement between the plate components 37, 38 of the orthodontic device in a direction parallel to the direction in which the strip 20 was initially positioned on the denta] model. Thus, providing the technician appropriately positions the strip 22 relative to the dental model, the axis of the screw 25 will be appropriately positioned relative to the final product.

As described with reference to figures 5 to 7, the device shown in figure 4 can be used to correctly align an expansion screw relative to palatal midlines. It can also be used however to appropriately orient the active planar surfaces of a twin block

I...:.:

/ l À appliance of the general type illustrated in figure 3. The process is exactly as that described with reference to figures 5, 6 and 7 except for the fact that the final orthodontic appliance has blocks formed on the upper dental arch as part of the plate components 37 and 38 using the surface of the strip 20 in the moulding process.

Given that the dental technician can readily position the strip 20 so that it is perpendicular to the palatal midline the technician can be confident that the surface of a block moulded against the strip 20 will define a plane perpendicular to the palatal midline plane of symmetry of the dental arch.

Referring now to figures 8 and 9, this illustrates the use of the device shown in figure 4 to align err expansion screw for saggital movement of a lower dental arch.

Figures 8 and 9 show the strip 20 with the chamfered edge 21 resting in the occlusal fossae of the lower posterior teeth. The lug 22 is gripped between the arms 32 and supports the expansion screw. As shown in figure 9, the lug 22 can be manoeuvred between the arms 32 so as to appropriately position the screw device against the model of a dental arch. A body of material the surface of which is represented in figure 9 by the broken line 39 can then be moulded around the screw device. Once the noulded material has hardened the lug 22 can be snapped off to provide access to the capstan (not shown) mounted on the screw 25. The technician manufacturing the orthodontic appliance can be confident that the axes of the screw 25 and the guide bars 26 are parallel to the length of the strip 20. Thus, given that the elongate straight strip 20 can be easily visually aligned with the desired direction of expansion the expansion direction deemed by the direction of the axis of the screw 25 can be readily determined. Although in the embodiment of the invention illustrated in figure 4 the elongate strip 20 is fabricated from a simple plate of material it will be appreciated that other configurations of the elongate alignment member could be envisaged. For example, the alignment member could be a simple bar with circular cross section providing appropriate means are mountable on that bar to enable a lug carrying an expansion screw device can be supported in a configuration such that the expansion axis of the device is parallel to the bar. Of course, if the alignment member is a simple bar of circular cross section it cannot be used to mould a planar active surface of a block of a twin block appliance but it would be possible to mount components

/ r., I ( l defining such moulding surfaces on a simple bar to achieve the same effect as that achieved with the device described with reference to figure 4.

When the device illustrated in figure 4 is used to form an operational planar surface of a twin block device as described above the angle of the strip 20 may be adjusted to adjust the angle of the moulded surface. The height of the moulded surface can also be determined by reference to the width of the strip 20. For example a user could be supplied with a set of strips 20 of different widths so that, by appropriate selection of a strip of a particular width the length of the moulded active surface of a block of a twin block device of a given angle of inclination could be determined simply by ensuring that the moulded block extends to a height corresponding to the edge of the strip 20 furthest from the dental model upon which the device is positioned.

In the device illustrated in figure 4, the lug 22 is connected to the strip 20 by simple clips which are retained in position by spring action alone. It would of course be possible to provide locking screws or clamps so as to rigidly secure the clips to the strip 20 once they have been appropriately positioned on the strip 20.

In the use of the invention as described with reference to figures 5 to 7 it has been assumed that before the orthodontic device is moulded on the dental model the lug 22 is simply manocavred Into a position in which it rests against a surface of the dental model. In some circumstances, depending on the type of screw device being used, it may be necessary to cut away a portion of the dental model to accommodate art end of the lug remote from the strip 20. If this is necessary, the device as described with reference to figure 4 can be used to define a drill guide for the dental technician Simply by positioning the two clips on the strip 20 so that the arms 32 are spaced apart by distance corresponding to the drill diameter, the drill can be inserted between the two arms 32 and manoeuvred by the technician using the arms 32 as a guide so as to cut a slot of limited width in the correct position to receive a subsequently Inserted lug 22.

Claims (13)

::. À À ( À - e e CLAIMS

1. An apparatus for aligning a screw device relative to a dental model such that the screw device can be incorporated in an orthodontic appliance formed on the model, comprising an elongate straight alignment member, a lug supporting a screw device, and means for connecting the lug to the alignment member, the screw device comprising two bodies intended to be secured to respective sections of the orthodontic appliance and a screw rotatable about a predetermined axis to adjust the spacing between the bodies, and the connecting means being such that connection of the lug to the alignment member causes the screw axis to extend parallel to the alignment member.

2. An apparatus according to claim 1, wherein the elongate member is planar.

An apparatus according to claim 2, wherein the planar elongate member is rectangular.

4. An apparatus according to claim 2 or 3, wherein the elongate member has an elongate chamfered edge.

5. An apparatus according to any preceding claim, wherein the connecting means are clips which can be pushed on to the elongate member.

6. An apparatus according to claim 5, wherein the clips are U-shaped to define slots dimensioned to receive the elongate member.

7. An apparatus according to claim 5 or 6, wherein means are provided for clamping the clips to the elongate member.

8. An apparatus according to any preceding claim, wherein the connecting means define arms which extends perpendicular to the elongate member when the

! lo.. .. connecting means are mounted on the elongate member, the arms defining a slot adapted to receive the lug supporting the screw device.

9. An apparatus according to claim 8, wherein the arms defined by the connecting means are generally planar and extend parallel to each other and the lug is planar and when received between the arms is parallel to the arms.

10. An apparatus for aligning a screw device mounted on a generally planar lug relative to a dental model such that the screw device can be incorporated in an orthodontic appliance formed on the model, the screw device including an expansion screw having an axis of rotation which is perpendicular to the plane of the lug, wherein the apparatus comprises an elongate straight alignment member which may be positioned on the model with its length extending parallel to an intended direction of expansion, and means mountable on the elongate member defining a slot for receiving and gripping the lug, the slot extending perpendicular to the length of the elongate member such that a gripped planar lug extends perpendicular to the elongate member.

An apparatus according to claim l O. wherein the means defining a slot comprises two clips which define planar arms between which the slot is defined.

12. An apparatus according to claim 11, wherein the clips comprise U-shaped bodies which may be clipped onto a planar elongate member, the anus extending Tom the U-shaped bodies.

13. An apparatus for aligning a screw device relative to a dental model substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings.