1. Using Advances in 3D Printing to Improve
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Using Advances in 3D Printing to Improve
Dental Education
B. M. Welch MS; P. Yaman DDS, MS; J.B. Dennison DDS, MS; S. O'Grady
University of Michigan School of Dentistry
YOUR
PHOTO
ABSTRACT
METHODS
TITLE: Using Advances in 3D Printing to Improve Dental Education
Objectives: Design a more accurate artificial tooth by using advances in 3D printing to create remarkably accurate anatomy and to simulate the durometer difference between the enamel/dentin and dentin/pulp interfaces. Methods: Extracted human teeth were placed in agar, Micro-CT scans were performed to produce DICOM files. DICOM files were imported into the software program MIMICS® and thresholding operations were performed to create digital masks of the enamel, dentin, and pulp. The digital masks underwent smoothing and Boolean subtraction operations. The digital masks were combined to create a single .stl file, which was uploaded into the software program 3-Matic®. Using 3-Matic® the foramina in the root apices were sealed, solid wax was assigned as the print material for the pulp mask, and a 2-micron wax sphere matrix was introduced into the dentin mask. The .stl file was sent to a 3D printer manufactured by 3D Systems© and a translucent proof-of-concept tooth was printed from Visijet® M3 Crystal Acrylic Polymer and Visijet® S300 Paraffin Support Wax. Results: An artificial tooth with excellent internal and external anatomy was produced. Furthermore, by using novel advances in 3D printing, such as incorporating support wax internally, a significant and detectable durometer difference was achieved. Conclusions: This research encourages further advances in 3D printing and artificial tooth manufacturing. Different materials and printers can be used to manipulate features such as hardness, color, and texture. The incorporation of support wax, which is not normally inside a 3D printed part, changes the density of the plastic and provides a significant and detectable difference in durometer between the enamel/dentin and dentin/pulp interfaces. With a very low production cost per tooth, this methodology may provide the most cost effective and anatomically accurate way of producing an artificial tooth for dental education and research to date.
1. Human teeth free of carious lesions and restorations were isolated and scanned via Micro-CT.
2. Teeth were stored in a mixture of 50% Glycerin:50% Ethyl Alcohol in order to maintain moisture and prevent desiccation.
3. The teeth were suspended in agar and Micro-CT scans were completed.
4. The Micro-CT scans yielded DICOM (Digital Imaging and Communications in Medicine) files.
5. DICOM files were converted to STL (STereoLithography) files.
6. Using commercially available 3D editing software, density thresholding was performed in order to distinguish the enamel, dentin, and pulp.
7. Digital masks were created for each tissue type and each mask underwent smoothing and Boolean subtraction operations.
8. The masks were combined to create a single STL file.
9. Using various features within the 3D editing software, the foramina in the root apices were sealed and solid support wax was assigned as the print material for the pulp mask. The closing of the foramina allowed for retention of the support wax internally while external support wax was melted away and discarded.
10. A 2-micron wax sphere matrix was introduced into the dentin mask in order to create a detectable durometer difference between the representative enamel and dentin interfaces.
11. The single STL file was printed on a Pro3500 HD 3D printer manufactured by 3D Systems© and a translucent proof-of-concept tooth was printed from Visijet® M3 Crystal Acrylic Polymer and Visijet® S300 Paraffin Support Wax.
12. Knoop Hardness Testing.
Fig. 1 3D Translucent image of artificial tooth comprised of 3 digital masks: Representative Enamel, Dentin Wax Matrix, and Solid Wax Pulp Chamber.
INTRODUCTION
Fig.2 Cross-section 3D image of an .stl file depicting the solid wax pulp chamber and the wax sphere dentin matrix.
The selection of artificial teeth available to the dental education sector is limited. Dental students traditionally use Ivorine® teeth in their typodonts while learning how to perform preparations and restorations. This material was chosen for its ability to be carved or drilled into and has been used for well over 100 years. The Ivorine® teeth produced today lack many of the key internal and external structural features present in human teeth. Ivorine® teeth contain no vasculature, no representative dentin, no representative pulp, and no texture or hardness differences internally, all of which are structural features present in a living human tooth. Dental students must imagine and estimate where pulp chambers and dentin layers are located when working with Ivorine® teeth. Artificial teeth with layers which have color differences, dentin layers, and pulp chambers do exist. However these artificial teeth are routinely made through injection molding or other manufacturing processes that lack robustness and are not capable of creating a continuous cured interface between layers. The layers are either secured together with heat or another chemical agent such as an adhesive. These layers are prone to chipping and fracturing. Advances in 3D printing can eliminate these layers which chip or fracture because as the polymeric material is dispensed it is immediately light cured and polymerized. Additionally the ability to incorporate internal features is possible through creative workarounds such as incorporating the support wax which is normally discarded during the 3D printing process.
RESULTS
CONCLUSION
An artificial tooth with excellent internal and external anatomy was produced. Using novel advances in 3D printing, such as incorporating support wax internally, a significant and detectable durometer difference was achieved. Representative Enamel = 24.5 KHN (mean value), Dentin Wax Matrix = 17.8 (mean value), and Solid Wax Pulp Chamber = 7.8 KHN (mean value).
Advancements in 3D printing will undoubtedly change the way artificial teeth are manufactured. These advancements will have applications far beyond the manufacture of artificial teeth geared towards the dental student in pre-clinic. These advancements can be applied to teeth meant for dental prosthesis and clinical application as well. Advancements such as creating matrices within the 3D printed part or the internal incorporation of support wax or other materials provides a mechanism in which biological components such as growth factors and/or antimicrobial agents may be delivered. Different materials and printers can be used to manipulate features such as hardness, color, and texture.
*Research reported in this publication was supported by The University of Michigan School of Dentistry.
Fig. 3 Proof-of-Concept 3D Printed Artificial Tooth.