WO2024010523A1

WO2024010523A1 - Artifical jaw for orthodonitic simulation

Info

Publication number: WO2024010523A1
Application number: PCT/SG2023/050466
Authority: WO
Inventors: Xu Jie Luke GOH; Yue Xuan Chantel LOH; Hugo Jean Guillaume BOURGUIGNON; Fang Yu Tracy SHEN; Jo Hanan LAU; Ching Chiuan YEN; Kelvin Weng Chiong FOONG; Sze Yin LEO
Original assignee: National University Of Singapore; National University Hospital (Singapore) Pte Ltd
Priority date: 2022-07-05
Filing date: 2023-06-30
Publication date: 2024-01-11

Abstract

Disclosed is a method for fabricating an artificial jaw member. The method includes 3D printing a simulated jawbone such that the simulated jawbone comprises an inner material, outer shell at least partially encasing the inner material, and one or more tooth recesses, the outer shell being harder than the inner material, forming a sensor in each said tooth recess and an output connector in electrical communication with each said sensor, and providing a tooth in each said tooth recess.

Description

ARTIFICAL JAW FOR ORTHODONITIC SIMULATION

Technical Field

The present invention relates, in general terms, to an artificial jaw for use, among other applications, in simulated orthodontic procedures. In particular, the present invention relates, but is not limited to, an artificial jaw for use in simulations of orthodontic mini screw placement.

Background

In orthodontic treatment, mini screws are used as temporary anchorage devices. Mini screws assist with complex movement of teeth - in situations where it is not possible to use the surrounding teeth as a stable support for the forces applied by a brace, a mini screw can move a tooth without affecting the position of surrounding teeth. In addition, bone porosity in the jaw varies across individuals due to factors such as age, so the technique and strength required to insert a mini screw differs from patient to patient.

Due to a lack of training opportunities, mini screw insertion by novice dentists has a high reported failure rate. Common risks due to improper insertion include root damage, neurovascular damage and screw fracture.

It would be desirable to overcome or alleviate at least one of the abovedescribed problems, or at least to provide a useful alternative.

Summary

To address the above problems with the prior art, this disclosure provides a realistic device or system to simulate the experience of inserting a mini screw prior to performing that insertion procedure on a real patient. With sufficient

training, practitioners will gain the confidence and experience necessary to safely insert orthodontic mini screws.

Disclosed is a method for fabricating an artificial jaw member, comprising :

3D printing a simulated jawbone such that the simulated jawbone comprises an inner material, outer shell at least partially encasing the inner material, and one or more tooth recesses, the outer shell being harder than the inner material; forming a sensor in each said tooth recess and an output connector in electrical communication with each said sensor; and providing a tooth in each said tooth recess.

Also disclosed is an artificial jaw member, comprising: a 3D printed simulated jawbone comprising : an inner material; outer shell at least partially encasing the inner material, the outer shell being harder than the inner material; and one or more tooth recesses; a sensor formed in each said tooth recess; an output connector in electrical communication with each said sensor; and a tooth disposed in each said tooth recess.

Advantageously, embodiments of the artificial jaw use materials selected based on simulated bone densities - the resistance applied to a mini screw during insertion into bone of an artificial jaw in accordance with the present disclosure may therefore simulate or replicate the resistance experienced when a mini screw encounters actual bone.

Advantageously, embodiments provide a sensing system with a conductive surface. This systems can detect when a screw encounters the conductive surface, an alert (e.g. light or sound) is triggered to inform the user that the

screw has encountered "root" material corresponding to the root of a tooth in the artificial jaw.

Advantageously, embodiments involve an artificial jaw formed from materials of different densities and/or more radiopacities, such that they are differentiable on an X-ray. This enables a practitioner (e.g. clinician or student) to check the position of a mini screw after placement (insertion). In practice, incorrect placement will be undetectable by a patient since they'll be under local anaesthetic when the screw is inserted.

Brief description of the drawings

Embodiments of the present invention will now be described, by way of nonlimiting example, with reference to the drawings in which:

Figure 1 illustrates a method for fabricating an artificial jaw member in accordance with present teachings;

Figure 2 is an illustrative cross-section of part of an artificial jaw formed by the method of Figure 1 ;

Figure 3 is an illustration of orthodontic mini screw placement;

Figure 4 is a photo of a real world procedure corresponding to the illustration in Figure 3;

Figure 5 shows the positions of two mini screw heads with attached coil springs (connectors) to intrude the molar tooth 500;

Figure 6 illustrates problems with placement of mini screws in a jaw;

Figure 7 is a schematic depiction of variation in bone density;

Figure 8 is a series of X-ray images of artificial teeth of an artificial jaw; and

Figure 9 is a series of X-ray images showing radiopacity of materials usable in producing an artificial jaw in accordance with present teachings.

Detailed description

The invention is an orthodontic mini screw insertion simulator in the form of an artificial jaw (herein interchangeably referred to as an "artificial jaw member" unless context dictates otherwise). The simulator is designed to accurately replicate the experience of inserting a mini screw into a patient's jawbone. The simulator can therefore be used to provide dental students and practitioners with a training platform for practising mini screw placement. Some embodiments of the simulator utilise 3-dimensional (3D) printing to mimic various jawbone densities, recreating lifelike material strengths that reproduce the 'hand-feel', required force and mini screw angulation for successful insertion. The simulator can thus be used effectively to prepare the user to perform the procedure (mini screw placement) in vivo.

Aside from "hand-feel", some embodiments of the artificial jaw use materials of different densities for different structural members (e.g. jaw, teeth, gum) and provide a sensor or detection system. These embodiments can make evident via an alert, during practice of a procedure, when the practitioner has incorrectly placed the mini screw.

Figure 1 illustrates a method 100 for fabricating an artificial jaw member in accordance with present teachings. The method 100 involves: 3D printing a simulated jawbone with tooth recesses (102), forming a sensor in each tooth recess (104) and providing a tooth in each tooth recess (106). A tooth may be provided in each recess by separately forming teeth (i.e. forming teeth

separately from the jawbone) and inserting each into a respective recess, or by forming the teeth into the tooth recesses.

Figure 3 shows an example of placement of a temporary anchor device 300 attached to a connector 302 that supports a tooth 304 neighbouring a void (missing tooth) 306. Figure 4 shows insertion of a real orthodontic mini screw 400 into the jawbone 402 of a patient, to secure a similar connector to support a tooth around a void 404. Thus, the artificial jaw member produced by method 100 can be used in planning a specific procedure, with a 3D printed artificial jaw member, tooth recesses and teeth being designed based on the mouth of a specific patient. In other embodiments, the artificial jaw member can be used in training for orthodontic mini screw placement more generally. Figure 5 then shows the position of two minscrew heads with coil springs (connectors 504) attached to a molar tooth 500 to intrude tooth 500 in the jaw 506.

Figure 6 illustrates various mini screw placement issues, such as encountering a tooth (image (a)), encountering a nerve (image (b)) and fracture of the mini screw (image (c)) due to, for example, over-tightening.

With reference to Figures 1 and 2, step 102 (3D printing a simulated jawbone), involves printing a simulated jawbone 200. To properly mimic a real jawbone, the artificial jawbone 200 comprises an inner material 202 (lighter material) and outer shell 204 (darker material between outer surface 210 and inner surface 212) at least partially encasing the inner material 202. The outer shell 204 is formed from a harder material than the inner material 202.

The jawbone 200 comprises a plurality of tooth recesses 208 (broken line). The tooth recess 208 is a recess or depression in the outer shell 204 in which a tooth sits when formed in or inserted into the jawbone 200. In Figure 2, the tooth recess also extends into the inner material 202. While only one tooth recess 208 is indicated, each tooth 206 sits in a recess the closely conforms to the shape of the portion of the respective tooth 206 that is within the material of the

jawbone 200.

The simulator may use any 3D printing technique. For example, 3D printing step 102 may involve using Fused Deposition Modelling (FDM) 3D-printing to create specific 3D printed infills or structures to simulate the bone densities in the mouth. Figure 7 depicts jawbone density variation based on porosity of the material of the jawbone - densest to lightest (700 to 706) - and corresponding simulated materials showing a greater amount of internal structure (matrix or lattice structure) for simulating the denser material and less internal structure for lighter material (708 to 714 being simulated densest material to simulated lightest material).

In some embodiments, there may be an outer layer to hide or disguise the internal structure. In other embodiments, no such outer layer is provided.

The internal structure of the simulated jawbone 200 may take any suitable form. For example, forming the internal structure may involve forming the inner material 202 to have a gyroid structure. The internal structure may vary across the artificial jawbone member 200, and may involve using curated infills to simulate jawbone densities found in the mouth. By simulating bone density types, orthodontists and training dentists can experience screwing into bone before trying it on a real patient to provide a realistic experience even with a simulator model.

The main 3d printed infill structure (i.e. the inner material 202, where the outer material may comprise a denser structural material or a solid material) is a gyroid structure. This is due to gyroids having equal strength in all directions. Other structures can be used such as a regular, square lattice, a solid foam or other structure - e.g. a porous structure - though the spacing between structural members is ideally very small to reduce redirection of the mini screw during placement (insertion). Two 3D printing filament materials were also utilized to vary the hardness of the simulated bone, Polylactic acid (PLA) and

Acrylonitrile butadiene styrene (ABS). In Figure 7, 708 and 710 comprise PLA with 1mm line distance between gyroid structures, and 2mm distance, respectively, and 712 and 714 use ABS with 1mm and 1.33mm line distance, respectively. The cortical plate was simulated by adjusting parameters for surface layer thickness in the slicing software (Creality/Prusa).

With further reference to Figure 1, step 104 comprises forming a sensor in each said tooth recess and an output connector in electrical communication with each said sensor. Sensors may be formed by inserting one or more wires into the tooth recesses such that impacting or severing a wire will result in a change in electrical properties along the wire (e.g. current leakage or lost signal), adding piezoelectric sensors into the recesses before inserting or forming to teeth therein, and connecting an output of the piezoelectric sensors to the output described herien. In the embodiments shown in Figure 8, sensors are formed in each said tooth recess by applying a conductive coating to each tooth recess.

The conductive coating can be any appropriate material. In Figure 8, a carbon coating is used as shown in X-ray from the side (image (a) - carbon coating with teeth formed from wax and inner material 202 density of 40% - i.e. 60% void space) and front (image (b)). However, it is difficult to distinguish the conductive coating from surrounding material. Using a Nickel coating as shown in image (c) makes the conductive coating 800 much more readily visualised by post procedure X-ray evaluation. Image (c) also shows an output connector in the form of wire 802, with a Nickel conductive coating and wax teeth (barely visible). The output connector 802 provides a common electrical connection between all the conductive coatings and an output. In other embodiments, more than one wire or connector may be used to connect to the output. The output is not shown but will be understood by the skilled person to comprise a processor or micro -processor that measures an electrical property along wire 802 (e.g. capacitance or current) and determines based on a change in the electrical property that a mini screw has encountered the wire or conductive coating during mini screw placement. The detection system may, for example, use the

capacitive sensor capabilities of an Arduino micro-processor, running on the capacitive sensor library found on the Arduino ecosystem

In this instance, the conductive coating is therefore a capacitive coating.

Figure 8, image (d) shows a carbon coating and plaster teeth, again with the wire clearly visible to connect the coating to an external micro-processor. Both images (c) and (d) use a 40% infill density.

Various materials can be used for the conductive coating applied into the tooth cavity, depending on application and budget. The radio-opaque option useful for post-Xray examination is 841AR (Super Shield Nickel Conductive Paint) that has been diluted in 1ml of thinner for ease of application. The cheaper option that is radiotransparent is 838AR (Total Ground, Carbon Conductive Paint) also diluted in 1ml of thinner for ease of application. A thin metal wire (802) is threaded through the teeth to maintain good electrical connection between the detection surface and the Arduino.

Making the precision of mini screw placement visible to the trainee and instructor through the root contact detection system (i.e. contact with the conductive coating or other sensor) and providing differential density materials between the teeth and jaw bone, provides a simulation experience that enhances a practitioner's ability to reproduce the mini screw placement procedures in the clinic. These features also enable materials to be distinguished by X-ray and alerts to be raised in the event of improper mini screw placement, and thereby permit instructor feedback that promotes better procedural precision in subsequent practices.

Mini screws are usually placed between the roots with a tolerance of 1 to 2mm on both sides of the screw - therefore, the feedback provided by the sensor is critical to help users develop the precision required to avoid damaging the vital structures in the jaw during the procedure. The conductive surface is applied to

the cavities of the teeth (i.e. tooth recesses) and is turned into a capacitive sensor capable of detecting for "touch" when a screw encounters the coating surface. When a screw contacts the conductive surface, a light and/or sound output from the processor or micro-processor indicate that the screw has impacted a "root" of a tooth. The screw detection system provides a means to quantify the success of the mini screw insertion since orthodontists must insert these mini screws between the roots of the teeth. If they fail to do so and instead screw into the roots of the teeth, the system will alert them that their insertion has gone wrong so they can adjust accordingly.

Per step 106, a tooth is provided in each said tooth recess. Each tooth may be formed separately and installed in a respective tooth recess, or formed in the tooth recess itself. In the latter case, a tooth may be formed by flowing material around the wire (connector) in the tooth recess. The teeth may be casted into the cavities of the roots of the teeth after the conductive coating has been applied. Forming a tooth directly in each said tooth recess in this instance comprises flowing a radiopaque material into each tooth recess and forming the tooth from the radiopaque material. Relatedly, flowing a radiopaque material into each said tooth recess can include flowing a mixture of wax and plaster into each said recess. A special hybrid blend of plaster and Paraffin wax is used to produce a composite that behaves like wax (low melting point, fast cure time, extremely viscous when molten) but also exhibits radio-opaque properties of plaster. The plaster behaves as a radio-opaque material as shown in Figure 8, image (d), while wax is translucent as shown in Figure 8, image (c). Other methods for casting or fabricating teeth may also be used, as may other materials and combinations thereof.

Distinct differentiation of tooth density from bone density is observable from an X-ray as shown in Figure 8, image (d), with appropriate material selection. The denser (more radiopaque) tooth 804 is formed from a mixture of wax and plaster. The differentiation in tooth/bone densities on the X-ray film is an important feature which replicates the actual radiographic environment. After

placement of the mini screw in a jaw, a clinician will take an X-ray to check the position of the mini screw. As mini screw placement is carried out under local anaesthesia, an incorrect insertion and placement of the mini screw will not be detected by the patient unless an X-ray is taken thereafter.

Figure 9 shows various tooth and coating materials, to illustrate varying radiopacity. Relevantly: image (a) is a side X-ray of wax teeth in a simulated jawbone, with carbon conductive coating; image (b) is a side X-ray of hybrid plaster/wax teeth in a simulated jawbone, with Nickel conductive coating; image (c) is a side X-ray of wax teeth in a simulated jawbone, with Nickel conductive coating; image (d) is a side X-ray of hybrid plaster/wax teeth in a simulated jawbone, with carbon conductive coating; image (e) is a side X-ray of plaster teeth in a simulated jawbone, with carbon conductive coating; and image (f) is a side X-ray of hybrid plaster/wax teeth in a simulated jawbone, with carbon conductive coating and an inserted mini screw. In each case, the infill (material in the tooth) is 40% (of the volume of the tooth).

In Figure 10, material compositions for the teeth are tested. In image (a), the left sample 1000 is a 100% wax sample and the right sample is an 8: 1 1002 wax:plaster ratio sample. Image (b) shows samples with ratios of 2: 1, 1 : 1 (1004, 1006, respectively) and image (c) shows a sample with a ratio of 4: 1 (1008). A 2: 1 ratio was found to have the least shrinkage and was readily useable.

In some embodiments, to better replicate the appearance of a natural jaw, a gum layer (not shown) may be formed over at least part of the simulated jawbone. This at least partially obscures the structure of the simulated jawbone. Material for forming the gum may be any appropriate material. For example, silicon (Smooth-on Inc. Dragon Skin™ 20/30) and dyed silicon colorants (Smooth-on Inc. Silc-Pig) may be used to produce the gum and give it the opacity and colour of gum.

It will be appreciated that many further modifications and permutations of various aspects of the described embodiments are possible. Accordingly, the described aspects are intended to embrace all such alterations, modifications, and variations that fall within the spirit and scope of the appended claims.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

Claims

1. A method for fabricating an artificial jaw member, comprising:

2. The method of claim 1, further comprising forming a gum layer over at least part of the simulated jawbone.

3. The method of claim 1 or 2, wherein providing a tooth in each said tooth recess comprises forming a tooth directly in each said tooth recess.

4. The method of claim 3, wherein forming a tooth directly in each said tooth recess comprises flowing a radiopaque material into each said tooth recess and forming the tooth from the radiopaque material.

5. The method of claim 4, wherein flowing a radiopaque material into each said tooth recess comprises flowing a mixture of wax and plaster into each said tooth recess.

6. The method of any one of claims 1 to 5, wherein 3D printing the simulated jawbone comprises forming the inner material to have a gyroid structure.

7. The method of any one of claims 1 to 6, wherein forming a sensor in each said tooth recess comprises applying a conductive coating to each said tooth recess.

8. The method of claim 7, wherein forming the conductive coating comprises forming a capacitive coating.

9. The method of any one of claims 1 to 8, wherein forming the output connector comprises connecting a wire between the sensor in each said tooth recess.

10. The method of claim 9, wherein providing a tooth in each said tooth recess comprises flowing material around the wire.

11. An artificial jaw member, comprising : a 3D printed simulated jawbone comprising : an inner material; outer shell at least partially encasing the inner material, the outer shell being harder than the inner material; and one or more tooth recesses; a sensor formed in each said tooth recess; an output connector in electrical communication with each said sensor; and a tooth disposed in each said tooth recess.

12. The artificial jaw member of claim 11, further comprising a gum layer formed over at least part of the simulated jawbone.

13. The artificial jaw member of claim 11 or 12, wherein the outer shell has a hardness substantially equivalent in hardness to a cortical bone of a human jaw, and the inner material has a hardness substantially equivalent in hardness to a cancellous bone of the human jaw.

14. The artificial jaw member of any one of claims 11 to 13, wherein each tooth is formed from a radiopaque material.

15. The artificial jaw member of claim 14, wherein each tooth is formed from a mixture of wax and plaster.

16. The artificial jaw member of any one of claims 11 to 15, wherein the inner material has a gyroid structure.

17. The artificial jaw member of any one of claims 11 to 16, wherein each sensor comprises a conductive coating applied to each said tooth recess.

18. The artificial jaw member of claim 17, wherein the conductive coating is a capacitive coating.

19. The artificial jaw member of claim 18, wherein the output connector comprises a wire connected between the sensor in each said tooth recess.

20. The artificial jaw member of claim 19, wherein the wire is embedded in each said tooth.