WO2009141813A2

WO2009141813A2 - Typodont for demonstrating orthodontic occlusal problems and the correction thereof

Info

Publication number: WO2009141813A2
Application number: PCT/IE2009/000026
Authority: WO
Inventors: John Brown; Declan Millett
Original assignee: University College Cork, National University Of Ireland, Cork
Priority date: 2008-05-22
Filing date: 2009-05-18
Publication date: 2009-11-26
Also published as: WO2009141813A3

Abstract

The invention relates to a method of demonstrating use of an orthodontic removable appliance component, which method employs a typodont having an adjustable part (i.e. a tooth, teeth, palate) that is capable of simulating an orthodontic occlusal problem of the type correctable by a removable appliance component. The adjustable part being movable between a first position corresponding to the occlusal problem, and one or more second positions at least one of which is a corrected position, the method comprising the steps of positioning the adjustable part (i.e. a tooth) in the first position by means of a positioning means, applying the removable appliance component to the typodont, adjusting the removable appliance component to initiate correction of the occlusal problem; and repeating the last step to continue correction in a step-wise process. The positioning means is adjustable between a first state in which it exerts high resistance to movement of the adjustable part, and a second state in which it exerts lower resistance to movement of the adjustable part. The position means may be a deformable material which softens on heating.

Description

TYPODONT FOR DEMONSTRATING ORTHODONTIC OCCLUSAL PROBLEMS AND THE CORRECTION THEREOF

Technical Field

The invention relates to an adjustable typodont for demonstrating orthodontic occlusal problems, and the correction of such problems. The invention also relates to a method of demonstrating use of an orthodontic removable appliance component in correcting orthodontic occlusal problems .

Background to the Invention

A typodont is a model of the oral cavity including teeth, gingival (gums) and a palate. It is generally formed of acrylic and is used in dental schools to demonstrate the anatomy of the oral cavity to dental students. In many cases, one or more of the teeth in the typodont will be removable to allow the students remove and examine the tooth.

Orthodontics is a branch of dentistry concerned with growth of the face, development of the teeth and occlusion (bite) and the management of malocclusion (incorrect bites) . Some malocclusions may be corrected using removable appliance components (springs or screws) which are adjusted periodically over a period of weeks or months to correct the malocclusion. Ideally clinical orthodontics to undergraduate students require patients with malocclusions. To standardise teaching with equal exposure of each student to the same range of the same clinical problems which require upper removable appliance treatment, has proved impossible with the projected increase in dental student numbers this problem will become greater, the need for a simulated environment to treat and achieve competence with removable appliance therapy and to augment the clinical teaching experience. A system which allows the student to fit, adjust and record treatment by removable appliance components in a condensed time period.

It is an object of the invention to overcome at least one of the above problems .

Statements of Invention

The invention relates to a method of demonstrating use of an orthodontic removable appliance component, which method employs a typodont having an adjustable part (i.e. a tooth, teeth, palate) that is capable of simulating an orthodontic occlusal problem of the type correctable by a removable appliance component, the adjustable part being movable between a first position corresponding to the occlusal problem, and one or more second positions at least one of which is a corrected position, the method comprising the steps of:

(a) positioning the adjustable part (i.e. a tooth) in the first position by means of a positioning means;

(b) applying the removable appliance component to the typodont; (c) adjusting the removable appliance component to initiate correction of the occlusal problem; and

(d) repeating step (c) to continue correction in a stepwise process,

wherein the positioning means is adjustable between a first state in which it exerts high resistance to movement of the adjustable part, and a second state in which it exerts lower resistance to movement of the adjustable part. The term "high resistance" should be understood as meaning a level of resistance which approximates to the level of resistance exerted on a tooth in a clinical setting.

In one embodiment, the positioning means is a deformable material having sufficient rigidity to resist the force applied by the spring of the appliance when inserted onto the typodont and delay the movement, but also having sufficient resiliency to allow the tooth to move to its new position when it is adjusted into the second state. Ideally, the material is a thermoformable material that suitably exists in a hardened state at ambient temperature, and which softens when heated. Thus, heating the deformable material has the effect of softening the material, thereby allowing the removable appliance component effect movement of the adjustable part while the material is soft. A mixture of modelling and carding wax is an example of such a deformable material. Other examples will be apparent to those skilled in the art. Another example would be a material which changes its hardness in response to a different external cue, such as for example a material that softens upon hydration, upon applicatation of a chemical, or upon passing an electrical current through the material. In an embodiment in which the adjustable part is a tooth, the deformable material is, for example, placed around the tooth simulating part of the gingival. Alternatively, if the adjustable part is a palate formed in two parts that are movable relative to one another, the deformable material may be positioned as a filler between the two separated parts. In this context, the process involves a step of heating the material after each adjustment (step

(c)) to allow the removable appliance component make small adjustments to the movable part. In one embodiment, the means of heating is a water bath into which the typodont is immersed. In an alternative embodiment, the typodont may comprise a heating element that heats the deformable material. In either case, the process generally comprises multiple adjustments of the removable appliance component, each one involving a small adjustment followed by softening of the deformable material by heating, which allows a small movement of the movable part due to forces exerted by the removable appliance component. Small movements of the movable part are ensured by controlling the duration of the heating of the deformable material. In this manner, once heating is stopped, the deformable material will re-harden thereby limiting the extent of movement of the movable part .

In an embodiment of the invention in which the adjustable part is a tooth, the adjustable tooth (or teeth) may be suspended in a cavity formed in the typodont by a suitable retaining means such as a wire (as described below) . Typically, the cavity is dimensioned to allow movement of the tooth between a corrected position and one or more other positions including one or more positions simulating malocclusions .

This process of the invention has been found to accurately mimic the clinical situation where correction of an occlusal problem using a removable appliance component is an iterative process that generally involves a plurality of small step-wise adjustments. However, in a clinical situation, the time between each adjustment needs to be a matter of weeks or months to allow the appliance component effectively move the tooth. In contrast, with the method of the invention, the time period between adjustments can be a matter of minutes due to the ability to change the resistance of the positioning means rapidly (i.e. heating and softening of the deformable material) . Thus, the method of the invention effectively compresses the time required to demonstrate correction of an occlusal problem from a matter of months to a matter of hours.

The invention also relates to a typodont having an adjustable part that is capable of simulating an orthodontic occlusal problem of the type correctable by a removable appliance component, the adjustable part being movable between a first position corresponding to the occlusal problem, and one or more second positions at least one of which is a corrected position, the typodont including a cavity located adjacent the adjustable part that is suitable for receiving a positioning means capable of exerting varying resistance to movement of the adjustable part. The invention also relates to a method of demonstrating use of a removable appliance component which method employs a typodont of the invention and involves fixing the adjustable part into a position simulating a malocclusion, applying a removable appliance component, and changing the resistance of the positioning means to enable adjustment of the adjustable part by the removable appliance component, and repeating these steps in an iterative manner.

The adjustable part may be, for example, a tooth, teeth, a plurality of teeth making an arch, or a palate.

Where the adjustable part is a tooth, the cavity is typically dimensioned to allow movement of the tooth within the cavity simulating one or more occlusal problems. Suitably, the tooth is suspended within the cavity by retaining means capable of retaining the tooth within the cavity while allowing one or more movements that simulate occlusal problems. Thus, the retaining means may be, for example, a wire adapted to allow movement of the tooth between a correct position and a plurality of incorrect positions which simulate occlusal problems. A typodont having one or more teeth suspended in a cavity is referred to herein as a "final typodont". A typodont having a cavity without a tooth suspended therein is referred to herein as a "primary typodont". In one embodiment, the tooth is suspended on suspension means that typically engages a bore formed through the tooth. Generally, the suspension means is a wire, typically a rigid wire which maintains its shape while mounted on the typodont. Ideally, the bore is formed through the root of the tooth adjacent the apex of the root. Typically, the wire is mounted in the typodont perpendicular to a longtitudinal axis of the tooth and generally laterally through the tooth. Suitably, the wire is generally u-shaped. In a preferred embodiment of the invention, the bore is dimensioned for a tight but sliding fit on the wire. At least one end, and ideally each end, of the bore is suitably enlarged to allow a degree of play between the retaining means and the tooth in a non-vertical direction (i.e. lateral, pivoting movement or play or labial rotational movement or play about the wire) . However, the inner part of the bore is not enlarged, thereby preventing any substantial vertical movement of the tooth and the wire. This has been found to accurately mimic the clinical situation insofar as the tooth is suspended in a manner that allows a sufficient degree of movement to enable the tooth mimic most if not all occlusal problems. As the tooth is suspended on the wire, positioning the tooth such that it mimics a specific occlusal problem involves use of a position means such as positioning wax.

In one embodiment, the at least one cavity in the typodont extends through the typodont such that it is accessible from a rear of the typodont. This facilitates application of the positioning material (i.e. wax) around the repositioned tooth which typically is suspended on the retaining wire. Generally, when a tooth in the typodont is being positioned to simulate a specific occlusal problem, the typodont is placed in position in a final master mould which effectively positions the movable tooth to simulate the specific occlusal problem, and the positioning material is applied through the rear of the cavity around the tooth and sets around the tooth while the tooth is retained in the specific malocclusion position by the final master mould. In one embodiment of the invention, a plurality of teeth are mounted within the cavity on a suspension means (such as a wire) . Suitably, the at least two teeth are separated from each other by a spacer means, for example a circular disk of material having a bore for receipt of the suspending means. In one embodiment, a plurality of teeth

(for example, between four and eight teeth) simulating a upper or lower arch are mounted within the cavity.

Suitably, each of the teeth is adjustable. Ideally, the suspending means is also adjustable to allow correction of an arch contour problem. In this situation, the wire will be suitable deformable to allow correction of the arch contour problem.

In one embodiment of the invention, the typodont comprises a heating means, typically an electrical heating means, located in or adjacent to the cavity. The purpose of the heating means is to allow heating of the positioning means to enable a rapid change of the resistance to movement exerted on the adjustable part. The heating means may be, for example, an electrical element. When the adjustable part is a tooth, the heating means is generally located in the cavity, such that it can heat the deformable material that fills the cavity, thereby softening the material and allowing the tooth move within the cavity in response to pressure exerted by the removable appliance component.

Where the adjustable part is a palate, the typodont is generally formed in two parts (corresponding to opposite sides of the oral cavity) , which parts are connected means that allows relative movement of the two parts towards and away from each other. Thus, when separated, a cavity is located between the two parts. In use, the cavity may be filled with a positioning means (for example, a deformable material) that hardens and offers resistance to the movement of the two parts together. Heating of the deformable wax (for example, by means of a water bath or an electrical heating element located in or adjacent to the cavity, can effect softening of the deformable material to movement of the two parts together. Generally, this would be effected in an iterative manner, involving multiple adjustments thereby simulating a clinical situation.

The invention also relates to a final typodont comprising a primary typodont of the invention having tooth suspended within a cavity by means of a suitable positioning material such that it simulates a specific orthodontic occlusal problem. Typically, the positioning material is a deformable wax suitable for being manipulated to allow retro-fitting of the tooth, and adjustment of the tooth with respect to the model. Ideally, the re-positioned tooth is suspended in the cavity in the typodont by means of a suspending wire that engages a bore formed in the tooth.

The invention also relates to an intermediate master mould suitable for forming a primary typodont, the mould having cavities adapted for receipt of teeth such that the roots of the teeth extend proud of the mould, wherein the intermediate master mould is adapted to replace at least one tooth cavity with means for forming a cavity in the formed primary typodont, and wherein the at least one cavity forming means has dimensions larger than the root of the corresponding tooth to thereby enable the at least one removed tooth be repositioned in the primary typodont with a suitable positioning material (such as positioning wax) in a plurality of different positions simulating a plurality of orthodontic occlusal problems.

The invention also relates to a final master mould formed using the final typodont of the invention. The final master mould mimics the final typodont including the specific occlusal problem. Thus, during use of the typodonts of the invention, the final master mould may be used by a student to correctly position a tooth in the final typodont to simulate that specific occlusal problem.

The invention also relates to an orthodontic tooth movement simulation kit, the kit comprising a final typodont of the invention and, optionally, a final master mould of the invention corresponding to the final typodont. Optionally, the kit may also include a further component selected from the group consisting of: a suitable positioning wax; a temperature adjustable water bath; and one or more removable appliance components. In a preferred embodiment of the invention, the kit comprises: a final typodont of the invention adapted to simulate a specific orthodontic malocclusion; a final master mould of the invention corresponding to the final typodont; and a removable appliance for correcting the orthodontic malocclusion.

The invention also relates to a tooth having a bore formed through a root of the tooth, the bore being enlarged at one end, preferably each end, to allow movement of the tooth into one or more positions that simulate clinical occlusion problems. Thus, each end of the bore may be chamfered to allow the tooth, when suspended on a retaining means such as a wire, adapt a specific movement corresponding to clinical movement. For example, the disposition of the chamfering may allow some rotational play of the tooth about a longtitudinal axis of the tooth (labial movement) , yet prevent any vertical movement of the tooth. In such circumstances, the chamfering is generally disposed at least partly around a circumference of the apex of the tooth. Alternatively, the disposition of the chamfering may allow distal or medial movement of the tooth, while again preventing any significant vertical movement. In this circumstance, the chamfering is generally disposed parallel to a longtitudinal axid of the tooth.

The invention also provides an adjustable typodont suitable for performing the method of demonstration of the invention, the typodont comprising an adjustable part movable between a first position corresponding to the occlusal problem, and a plurality of second positions at least one of which is a corrected position. In one embodiment, the adjustable part is a tooth. In another embodiment, the adjustable part is the palate which, optionally is in two parts which are movable relative to each other to simulate adjustment of the shape of the palate. Positioning means typically control movement of the adjustable part. The positioning means is adjustable between a first state in which it exerts high resistance to movement of the adjustable part, and a second state in which it exerts lower resistance to movement of the adjustable part. One example of positioning means is a therformable material which softens upon heating. Other positioning means are envisaged such as, for example, a resiliently deformable material or a spring. Typically, the primary and final master moulds are formed of silicone. Typically, the typodont models are formed of wax or acrylic.

The invention also relates to a method of constructing a primary typodont suitable for demonstrating orthodontic occlusal problems, the method comprising the steps of providing a typodont formed from a deformable material such as, for example, wax, having at least one cavity formed in the typodont corresponding to at least one absent tooth, wherein the at least one cavity has dimensions larger than the root of the corresponding absent tooth to thereby enable the at least one absent tooth be repositioned in the primary typodont in a plurality of different positions simulating orthodontic occlusal problems.

Suitably, the cavity is formed such that it extends through the typodont. This enables access to the root of the tooth from a rear of the typodont. It also enables a suitable positioning material to be easily applied around the tooth from a rear of the typodont.

The invention also relates to a method of forming an intermediate typodont master mould (which is suitable for use in moulding primary typodonts) , comprising a step of forming a master mould using the primary typodont (including the at least one cavity) of the invention as a template.

The invention also relates to a method of forming a final typodont comprising a step of forming a primary typodont according to the method of the invention, or employing an intermediate master mould of the invention to form (cast) a primary typodont, and re-positioning the removed tooth into the corresponding cavity in the formed primary typodont using a suitable fixing means.

Suitably, the tooth is fixed in place in the primary typodont by retaining means (such as a wire) adapted to allow movement of the tooth between a correct position and a plurality of incorrect positions which simulate occlusal problems. In one embodiment, the tooth is suspended on a wire that engages a bore formed through the tooth. Ideally, the bore is formed through the root of the tooth adjacent the apex of the root. Typically, the wire is mounted in the primary typodont perpendicular to a longtitudinal axis of the tooth and generally laterally through the tooth. Suitably, the wire is generally u-shaped. In a preferred embodiment of the invention, the bore is dimensioned for a tight but sliding fit on the wire. At least one end, and ideally each end, of the bore is suitably enlarged to allow a degree of play between the retaining means and the tooth in a non-vertical direction (i.e. lateral, pivoting movement or play) . However, the inner part of the bore is not enlarged, thereby preventing any substantial vertical movement of the tooth and the wire. Suitably, the ends of the bore are chamfered in a manner that allows movement of the tooth is a specific orientation. Thus, for example, for a tooth which requires proclining the hole is chamfered mesially and distally at right angles taking care not to increase the size of the original hole (see fig. 20) . This allows the tooth to rotate around the long axis as the tooth proclines (fig. 21) . For a tooth which requires mesial or distal movement the hole is chamfered along the long axis of the tooth again taking care not to widen the size of the original hole (figs. 24 to 27) . This has been found to accurately mimic the clinical situation insofar as the tooth is suspended in a manner that allows a sufficient degree of movement to enable the tooth mimic most of not all occlusal problems. As the tooth is suspended on the wire, positioning the tooth such that it mimics a specific occlusal problem involves use of a position means such as positioning wax.

The invention also relates to a method of forming a final typodont master mould comprising a step of providing a final typodont according to the method of the invention, adjusting the re-positioned tooth to simulate a specific orthodontic occlusal problem, and employing the final typodont to form a final typodont master mould. Suitably, the re-positioned tooth is fixed in position by means of a positioning means such as positioning wax. The final master mould mimics the final typodont including the specific occlusal problem present in the final typodont. Thus, during use of the tooth simulation model the final master mould may be used by a student to correctly position a tooth in the final typodont to simulate that specific occlusal problem.

The invention also relates to an intermediate typodont master mould, and a final typodont master mould, obtainable by the method of the invention.

The invention also relates to a primary typodont, and a final typodont, formed by the method of the invention. Brief Description of the Figures

Fig. 1 is a picture of a silicone mould for producing illustrated teeth;

Fig. 2 is a picture of the teeth being placed in the mould;

Fig. 3 is a picture of the mould filled with modelling wax;

Fig. 4 is a picture of a wax typodont with all teeth in- situ;

Figs. 5 and 6 are labial and lingual views, respectively, of an upper central tooth trapped behind a lower incisor;

Fig. 7 is a picture of a primary typodent of the invention (with one tooth removed and a cavity formed;

Figs. 8 and 9 are a pictures of an intermediate silicone master mould of the invention formed using the primary typodont of Fig. 7;

Fig. 10 is a picture of an intermediate silicone master mould of the invention filled with acrylic resin;

Fig. 11 is a picture of the acrylic primary typodont of the invention removed from the mould;

Fig. 12 is a picture of the acrylic primary typodont of the invention showing the cavity corresponding to a removed tooth; Figs. 13 and 14 are pictures of the acrylic primary typodont of the invention with a tooth re-positioned in the correct position with positioning wax;

Figs. 15 and 16 are pictures of the acrylic primary typodont of Figs 13 and 14 with the tooth moved into a malocclusion;

Figs. 17 and 18 show the production of a silicone final master mould of the invention;

Figs. 19 to 23 show how a bore is formed in a tooth to enable the tooth simulate proclining correction;

Figs. 24 to 28 show how a bore is formed in a tooth to enable the tooth simulate distal or medial correction;

Figs. 29 and 30 show the rear of the acrylic primary typodont of the invention showing how the cavity is exposed on the rear of the typodont;

Fig. 31 is a picture of a tooth of the invention suspended on a wire prior to insertion into the primary typodont;

Figs. 32 and 33 illustrate the insertion of the tooth into the primary typodont to form the final typodont of the invention;

Fig. 34 shows the typodont of the invention with a removable appliance component in place prior to correction, and Fig. 35 shows shows the typodont of the invention with a removable appliance component in place after correction; Fig. 36 shows the result of the incorrect adjustment of the spring used in Fig. 35 where too much pressure applied to mesial of tooth causing a rotational effect malocclusion (anterior cross bite) ;

Fig. 37 shows the result of the incorrect adjustment of the spring used in Fig. 35 where too much pressure applied resulting in tooth being pushed too far forward;

Fig. 38 shows a typodont of the invention having an adjustable palate;

Fig. 39 shows a typodont of the invention having an adjustable palate and a plurality of adjustable teeth forming an arch; and

Fig. 40 shows the rear of a typodont according to an alternative embodiment of the invention having an heating element located in the cavity.

Detailed Description of the Invention

The typodont of the invention is employed to teach dental students how to use an orthodontic removable appliance component to correct dental malocclusions. The typodont has an adjustable part, for example a tooth, a plurality of teeth forming an arch, or an adjustable palate. In most cases, the adjustable part will be a single tooth, for example an incisor. In the latter case, the adjustable tooth will be suspended in a cavity in the part of the typodont simulating the gingival. Generally, the tooth will be suspended on a retaining means which will generally be a wire. To facilitate suspension, the tooth has a bore extending laterally through the apex of the root, the bore being dimensioned to receive the wire in tight but sliding fit. The fit may such as to allow some forwards and backwards pivoting movement of the tooth on the wire. In many cases, the ends of the bore will be chamfered to allow different movements of the tooth to simulate clinical movements. For example, the ends of the bore may be chamfered circumferentially around the apex of the root to allow some rotational play of the tooth about the longtitudinal axis of the tooth. Alternatively, the ends of the bore may be chamfered longtitudinally to allow some lateral play of the tooth.

The tooth is mounted in the cavity on the wire, and then the typodont is placed into a positioning mould which positions the adjustable tooth into a position simulating a malocclusion. The positioning mean, which in most cases with be wax, is then poured into the cavity through a hole in the rear of the typodont, and is allowed to set thereby fixing the tooth in the maloccluded position. The typodont is then ready to be used by the students to demonstrate correction of the malocclusion. First, a removable appliance component is applied to the typodont, and then adjusted to apply the correct force to the adjustable tooth. The typodont is then placed into a water bath for a fixed period of time to soften the wax. Softening of the wax allows some movement of the tooth. The wax quickly rehardens fixing the tooth in the slightly corrected position, and the student can then make further adjustments to the appliance component, and again place the typodont in the water bath to re-soften the wax and allow further iterative movement of the tooth. These steps are repeated every 15 to 20 minutes until the adjustment of the tooth position has been completed. The whole demonstration process may take a few hours, compared to a clinical demonstration which would take a matter of months .

In some cases, the typodont may include heating means, for example a heating element located in the cavity. The heating element is actuated to soften the wax, and obviates the need to place the typodont in a water bath at every step. The heating element include a socket located at the rear of the typodont, and may be operated by a battery or main electricity.

It is important to note that due to the chamfering of the tooth, a number of different movements of the tooth on the wire are possible. Thus, if the student does not correctly fit and adjust the removable appliance component, the position of the tooth may be adjusted incorrectly. Thus, the typodont of the invention provides an excellent tool for teaching dental students the correct use of an orthodontic removable appliance component, as well as a means for allowing a full demonstration in a matter of hours as opposed to a matter of months.

In the case of palate adjustment, the typodont can take the form two parts simulating opposite sides of the palate, which parts are interconnected by a sliding arrangement that allows movement of the two sides towards and away from each other. Such a typodont can be used to simulate correction of a narrow palate. In use, the two sides are placed in a positioning mould which positions the sides to simulate a narrow palate, and then wax is poured into the cavity between the sides. Once the wax is hardened, a suitable removable appliance component is positioned by the student, and then adjusted to begin the process of widening the palate. To allow movement of the sides, the wax is heated, either by means of a water bath, or by an electrical heating element positioned in or adjacent to the cavity. These steps are then repeated in an iterative manner until the student feels that the adjustment is complete.

In a different embodiment, the typodont may comprise an adjustable palate, and one or more adjustable teeth. For example, as described below, the typodont may include an adjustable palate, and a plurality of adjustable teeth simulating an adjustable arch. In this case, the suspending means may be for example an elongated wire upon which six or eight teeth are suspended. The wire will be suitably arched to simulate an incorrectly formed arch in which the teeth are crowded. Such a typodont may be used to simulate correction of a narrow arch and crowding, and to allow the student correct the palate and arch and ensure that the vertical position of the teeth in the arch is not adjusted. It is preferable that the teeth suspended on the wire are separated by spacers. The spacers maintain the gap between the roots and therefor maintain the vertical position of the teeth which simulate the tooth movement.

Construction of Orthodontic Tooth Movement Simulation Model Acrylic teeth are produced from a silicone mould (fig. 1). A wax model is produced from a silicone master mould (fig.2) . Teeth with roots are trimmed, polished and placed in the silicone mould (fig. 2). Pink Modelling Wax is melted and poured into the silicone mould and allowed to solidify (fig. 3) . The wax model with the plastic teeth (typodont) is removed (fig. 4 ) .

The typodont (fig. 4) is then used to carve, shape modify to create a scenario. The scenario described is for an upper central tooth trapped behind the lower incisors (fig. 5 & 6) . A ^λZ' Spring appliance will be used to correct the malocclusion. Some are simple scenarios while others are more complex.

The central tooth is removed from the wax typodont and the wax is carved and shaped to create a cavity to allow tooth movement to take place (fig. 7). This is a primary typodont. A silicone mould is constructed (fig. 8) . This silicone mould will be used to produce the acrylic primary typodont models. Teeth are then placed into the master silicone mould for producing acrylic primary Typodont models (fig. 9) .

Acrylic denture resin is then poured into the silicone mould

(fig. 10) and then placed in a pressure pot to cure. The acrylic model is removed from the silicone mould (fig.11), trimmed and polished (fig. 12) . The cavity into which the adjustable tooth will be suspended is clearly visible in Figure 12.

The removed tooth is then placed into the cavity in the acrylic model in its normal position and waxed into place (fig.13 & 14). It is easier to start with the tooth in its ideal position and then create the malocclusion, in this case a tooth behind the lower centrals. The wax is then softened and the tooth moved into the malocclusion (tooth behind the lower incisors) . It is extremely important to maintain the tip of the roots position when moving the tooth into the malocclusion. This will be the fulcrum point on which the tooth rotates (figs. 13 to 16) . The details of how the tooth is suspended in the cavity is explained in more detail below.

The tooth is secured into position and waxed up to reproduce the desired malocclusion. A silicone mould is then made as shown in figures 17 &18.

Preparation of adjustable tooth

To allow the tooth to mimic the movement by orthodontic appliance treatment a lmm hole is drilled through the tooth. This allows the tooth a tight but sliding fit on the suspending means, which in this case is a wire. The position of this hole is determined by the desired tooth movement. Removable appliances only tilt or tip teeth so the hole is drilled near the apex of the root.

Proclining: For a tooth which requires proclining the hole is chamfered mesially and distally at right angles taking care not to increase the size of the original hole (figs. 19 to 21) . This allows the tooth to rotate on the wire around the long axis as the tooth proclines (figs. 22 and 23) .

Mesial / Distal Movement: For a tooth which requires mesial or distal movement the hole is chamfered along the long axis of the tooth again taking care not to widen the size of the original hole (figs. 24 to 25). This allow lateral pivoting movement of the tooth on the wire (figs. 26 to 28) .

Inserting Tooth into Model

The prepared tooth is now ready to be positioned in the

Acrylic Typodont model (fig. 29) . As shown in Fig. 29 and 30, the cavity in the typodont extends through to the rear of the typodont. A flat ^ΛU' shaped piece of 0 ^• 7mm wire is measured and inserted into the slot in the tooth (fig. 31). Two slots are cut into the base of the acrylic model adjacent the cavity (fig. 30) in line with the roots of the rest of the teeth. The wire is inserted into the two slots as shown in Fig. 32, with the adjustable tooth being suspended in the cavity and projecting through the cavity in the front of the typodont (Fig. 33). A small amount of acrylic is poured into the slot and allowed to set. The acrylic model is placed in the master silicone mould to position the adjustable tooth into a position simulating a malocclusion, and the positioning means (wax) is poured into the cavity from the rear of the typodont to fix the tooth in the desired position. This is the final typodont. Fig. 34 shows the typodont with a removable appliance component fixed in place prior to treatment, while Fig. 35 shows the the typodont with the removable appliance component fixed in place after treatment. Fig. 36 shows the result of the incorrect adjustment of the spring used in Fig. 35 - too much pressure applied to mesial of tooth causing a rotational effect malocclusion (anterior cross bite) . Fig. 37 shows the result of the incorrect adjustment of the spring used in Fig. 35 - too much pressure applied resulting in tooth being pushed too far forward malocclusion.

Referring to Fig. 38, there is illustrated a typodont of the invention for use in simulating correction of palate malocclusions. The typodont comprises two parts that are connected in a sliding arrangement for movement together and apart. In use, the parts are positioned to simulate a malocclusion, and the cavity between the parts is filled with wax which hardens fixing the parts in place. Use of the typodont is described above.

Referring to Fig. 39, there is illustrated an alternative typodont in which both the palate, and a plurality of teeth simulating an arch, are adjustable. In this system, the malocclusion to be corrected is a narrow palate, and crowding. The adjustable teeth are mounted on an elongated wire which follows the arch of the teeth. Each of the adjustable teeth are separated by spacers which function to retain the position of the apex of the root, and main the vertical position, of the teeth during adjustment. The cavity is also elongated to allow access of the positioning/fixing wax to all of the teeth and to the cavity between the two parts of the palate. In use, the student will use a removable appliance component to widen the palate in an iterative process, while also straightening the arch contour to relieve crowding of the teeth.

Referring to Fig. 40, there is illustrated a typodont according to an alternative embodiment of the invention. In this embodiment, the typodont includes a heating element located within the cavity which can be used to heat and soften the wax. The typodont also includes an electrical socket (not shown) electrically connected to the heating element. This embodiment of the typodont obviates the need for placing the typodont into a water bath, and is acapable of heating and softening the wax more quickly than the water bath.

Tooth Movement Simulation System (Kit)

The system consists of the following:

• Final Silicone Master Mould.

• Orthodontic Removable Appliance.

• Acrylic Tooth Movement Simulation Model (Final Typodont) (fig. 33) .

The silicone mould is used to produce dental stone models on which the removable orthodontic appliance is made. The same silicone mould is used for refurbishing the Tooth Movement Simulation Model (Typodont) . A mixture of 3 sheets of pink Modelling wax and one full strip of carding are melted in a pot and poured into the hole in the acrylic model. This combination of wax seems to reproduce the tooth simulation and can be used at 50° C which is a reasonable safety level of temperature. When the wax has solidified the Typodont model is removed. The orthodontic appliance is constructed from the model produced from the master silicone mould.

The student checks the design to see if it corresponds with the prescription. He then removes the appliance from the white plaster model and does a quality check of the standard of work which he has been given. The next stage is a simulation exercise. The appliance is fitted onto the typodont which is his simulated patient's upper jaw. He checks the fit of the baseplate, clasps, etc, on his model of the patient' s oral cavity and does any necessary adjustments .

After all the checks have been completed and the student is satisfied with the fit of the appliance, he then adjusts the active part of the appliance - in this case the ^s%' spring - to move the upper central incisor forward. The spring is adjusted approximately 1 to l^»5mm which simulates 3Og to 5Og of force to move the tooth, the maximum force required to move a tooth. To achieve this movement the typodont is placed in a heated water bath at 50⁰C initially for 15 minutes and then at 10 minute intervals until the tooth reaches its desired position. This sequence can simulate 3 to six months of clinical treatment in 2 to 3 hours.

It will be appreciated that the invention is not restricted to the correction of the position of teeth, but may also be applied in the correction of palate problems, such as for example, widening of the palate. An example of a typodont model employed for simulating palate widening is shown in Fig. 38 and generally comprises a typodont model in two halves, each half being mounted on a connector for sliding movement towards and away from each other to simulate palate widening. The gap between the half typodont is filled with a deformable wax that softens upon heating. The use of this typodont model is similar to that described above for demonstrating correction of a tooth malocclusion. The invention is not limited to the embodiments hereinbefore described which may be varied in construction and detail without departing from the spirit of the invention.

Claims

1. A method of demonstrating use of an orthodontic removable appliance component, which method employs a typodont having

! an adjustable part that is capable of simulating an orthodontic occlusal problem of the type correctable by a removable appliance component, the adjustable part being movable between a first position corresponding to the occlusal problem, and one or more second positions at least

) one of which is a corrected position, the method comprising the steps of:

(a) positioning the adjustable part in the first position by means of a positioning means;

5 (b) applying the removable appliance component to the typodont;

(c) adjusting the removable appliance component to initiate correction of the occlusal problem; and

(d) repeating step (c) to continue correction in a step- wise process,

2. A method as claimed in Claim 1 in which the positioning means is a deformable material having sufficient rigidity to resist the force applied by the spring of the appliance when inserted onto the typodont and delay the movement, but also having sufficient resiliency to allow the tooth to move to its new position when it is adjusted into the second state.

3. A method as claimed in Claim 2 in which the deformable material is a thermoformable material that suitably exists in a hardened state at ambient temperature, and which softens when heated.

4. A method as claimed in Claim 2 or 3 in which the deformable material is a mixture of modelling and carding wax.

5. A method as claimed in any preceding Claim in which the deformable material is one which is capable of changing its hardness in response to an external cue selected form the group consisting of: hydration; applicatation of a chemical; or passing an electrical current through the material .

6. A method as claimed in any preceding Claim in which the adjustable part is selected from the group consisting of: a tooth; teeth; a plurality of teeth forming an arch; and a palate.

7. A method as claimed in Claim 6 in which the adjustable part is a tooth or teeth, and wherein the deformable material is placed around the tooth or teeth simulating part of the gingival .

8. A method as claimed in Claim 6 in which the adjustable part is a palate formed in two parts that are movable relative to one another, and wherein the deformable material is positioned as a filler between the two separated parts.

9. A method as claimed in any preceding Claim in which the process involves a step of heating the material after each adjustment (step (c) ) to allow the removable appliance component make small adjustments to the movable part.

10. A method as claimed in any preceding Claim in which the means of heating is a water bath into which the typodont is immersed.

11. A method as claimed in any of Claims 1 to 9 in which the typodont comprises a heating element that heats the deformable material.

12. A method as claimed in Claim 12 in which the heating element is located within or adjacent to the positioning means .

13. A method as claimed in any preceding Claim in which the adjustable part is a tooth, wherein the adjustable tooth (or teeth) are suspended in a cavity formed in the typodont by a suitable retaining means, and wherein the cavity is dimensioned to allow movement of the tooth between a corrected position and one or more other positions including one or more positions simulating malocclusions.

14. A method as claimed in Claim 13 in which the retaining means is a wire, and wherein the tooth or teeth comprise a bore for engaging the wire.

15. A typodont comprising an adjustable part that is capable of simulating an orthodontic occlusal problem of the type correctable by a removable appliance component, the adjustable part being movable between a first position corresponding to the occlusal problem, and one or more second positions at least one of which is a corrected position, the typodont including a cavity disposed adjacent k to the adjustable part that is suitable for receiving a positioning means capable of exerting varying resistance to movement of the adjustable part.

16. A typodont as claimed in Claim 15 in which the adjustable part is selected from the group consisting of: a tooth; teeth; a plurality of teeth making an arch; and a palate.

17. A typodont as claimed in Claim 16 in which the adjustable part is a tooth, and wherein the cavity is dimensioned to allow movement of the tooth within the cavity simulating one or more occlusal problems.

18. A typodont as claimed in any of Claims 15 to 18 in which the tooth is suspended within the cavity by retaining means capable of retaining the tooth within the cavity while allowing one or more tooth movements that simulate occlusal problems .

19. A typodont as claimed in Claim 18 in which the tooth movements are selected from the group consisting of: labial movement; and medial/distal movement.

20. A typodont as claimed in Claims 18 or 19 in which the retaining means is a wire adapted to allow movement of the tooth between a correct position and a plurality of incorrect positions which simulate occlusal problems.

21. A typodont as claimed in any of Claims 15 to 20 in which the tooth is suspended on suspension means that engages a bore formed through the tooth.

22. A typodont as claimed in Claim 21 in which the suspension means is a wire.

23. A typodont as claimed in Claim 22 in which the wire is mounted in the typodont perpendicular to a longtitudinal axis of the tooth and generally laterally through the tooth.

24. A typodont as claimed in any of Claims 18 to 24 in which each end of the bore is suitably enlarged to allow movement of the tooth on the retaining means in a non-vertical direction.

25. A typodont as claimed in Claim 24 in which the bores are chamfered to allow a movement of the tooth on the retaining means selected from the group comprising: labial movement; and distal medial movement.

26. A typodont as claimed in any of Claims 15 to 25 in which the at least one cavity in the typodont extends through the typodont such that it is accessible from a rear of the typodont.

27. A typodont as claimed in any of Claims 16 to 26 in which a plurality of teeth are mounted within the cavity on a suspending means .

28. A typodont as claimed in Claim 27 in which at least two of the plurality of teeth are separated from each other by a spacer means.

29. A typodont as claimed in Claim 27 or 28 in which a plurality of teeth simulating a upper or lower arch are mounted within the cavity.

30. A typodont as claimed in Claim 29 in which the suspending means is adjustable to allow correction of an arch contour problem.

31. A typodont as claimed in Claim 15 and in which the adjustable part is a palate, wherein the typodont is formed in two parts corresponding to opposite sides of the oral cavity, which parts are connected by connecting means that allows relative movement of the two parts towards and away from each other.

32. A typodont as claimed in any of Claims 15 to 31 in which the typodont comprises an electrical heating element located in or adjacent to the adjustable part or cavity.

33. A typodont as claimed in Claim 32 wherein when the I adjustable part is a tooth, the heating means is generally located in the cavity, such that it can heat the deformable material that fills the cavity, thereby softening the material and allowing the tooth move within the cavity in response ^'to pressure exerted by the removable appliance 5 component .

34. An intermediate master mould suitable for forming a primary typodont, the mould having cavities adapted for receipt of teeth such that the roots of the teeth extend

) proud of the mould, wherein the intermediate master mould is adapted to replace at least one tooth cavity with means for forming a cavity in the formed primary typodont, and wherein the at least one cavity forming means has dimensions larger than the root of the corresponding tooth

5 to thereby enable the at least one removed tooth be repositioned in the primary typodont with a suitable positioning means in a plurality of different positions simulating a plurality of orthodontic occlusal problems.

35. An orthodontic tooth movement simulation kit, the. kit comprising a typodont according to any Claims 15 to 33 and a positioning mould capable of receiving the typodont and correctly positioning the adjustable part in a position simulating an orthodontic occlusal problem.

36. A kit as claimed in Claim 36 and including a further component selected from the group consisting of: a suitable positioning wax; a temperature adjustable water bath; and one or more removable appliance components.

37. A tooth having a bore formed through a root of the tooth for receipt of a retaining means, the bore being dimension for a tight but sliding fit on the retaining means, the bore being enlarged at each end to allow non-vertical movement of the tooth on the retaining means into one or more positions that simulate clinical occlusion problems.

38. A tooth as claimed in Claim 37 in which each end of the bore is chamfered.

39. A tooth as claimed in Claim 38 in which the chamfering is disposed at least partly around a circumference of the apex of the tooth (labially) to enable labial movement of the tooth relative to the retaining means.

40. A tooth as claimed in Claim 38 in which the chamfering is disposed parallel to a longtitudinal axis of the tooth (medially/distally) to allow distal/medial movement of the tooth relative to the retaining means.

41. A tooth as claimed in any of Claims 37 to 40 and being a natural or synthetic tooth.