3D Printing for Education and Training in Endodontics

Current and future possibilities with printed model teeth

Gregory S. Jacob, DDS

In recent years, three-dimensional (3D) printing has been mentioned throughout the media as a huge opportunity for industrial manufacturing and prototyping. Now, recent advances in this technology also present an opportunity to expand pre-graduate and post-graduate endodontic education and bench practice.

Also referred to as “additive manufacturing,” 3D printing is the process of joining plastic or metal materials in incremental and successive planar layers to build 3D objects from computer data files. In 3D printing, manufacturing data files may be created by designers using commercial CAD/CAM programs specific for the design of an industrial product or developed from 360° computer scans of physical items. Special 3D printing equipment is then programmed and tasked to deposit and bond light-cured, heated, or molten materials layer by layer (Figure 1). These materials fuse together into one solid piece while accurately forming the shape and size of the item to be printed (Figure 2).

Different 3D printing perspectives may be selected. For example, the subject item may be built in layers from side-to-side, from the bottom up, or from top to bottom. Each successive layer is laid down with precision until the full item is built to completion. The completed printed product is then removed from the printer and finished. Because each computer data file is a permanent record of the object being printed, it is possible to produce multiple copies of the same item when desired.

CT Scans and Printing Applications for Dentistry

One important application of 3D printing in dentistry is recreating digital scans of full or partial arches into durable plastic model casts without the use of impression materials poured with stone. Also, some newer software programs help technicians digitally design a fixed or removable partial denture framework or crown restoration that is then printed out in full form as a wax pattern for direct casting.

This printing also offers promise in endodontic bench exercises using micro-computed tomography (micro-CT) scans from actual natural teeth. CT scans are commonly used in implantology to help study mandibular and/or maxillary bone quality, optimal implant location, and other factors in planning implant procedures. These scans can be viewed through tissue at about 0.5-mm slices. However, micro-CT technologies can provide even higher resolution scans for imaging separate tissue specimens in as little as 0.5-micron slices (0.0005 millimeters) from subjects. Micro-CT scanners are currently available as self-contained desktop units for in vitro tissue scanning at research laboratories (Figure 3). Because of the resolution they can offer, it is possible to non-destructively scan and view disinfected extracted teeth in great detail complete with internal pulpal and canal spaces. Figure 4 shows a micro-CT scan view of an extracted third molar translated into the popular .STL (stereolithography) 3D scan file format. Figure 5 and Figure 6 show additional views of the same tooth from the perspective of other software “reader” programs specifically developed for visualizing micro-CT scans. It is worth noting these and other reader programs are available free of charge and can be easily downloaded from the appropriate websites.

Printed Model Teeth for Endodontic Bench Exercises

At this time, it may not be feasible to expect 3D printer equipment to recreate a molar tooth in the 0.0005-mm resolution of micro-CT scans. To date, 3D printers can print plastic materials (eg, ABS, polycarbonate) with characteristics similar to dental acrylic. Materials can be printed at a resolution of approximately 20 microns (0.02 mm) for consistent and precise production of tooth models.

The tooth scan examples in Figure 4 through Figure 6 are shown as printed tooth models in Figure 7 and Figure 8. When sectioned lengthwise in the occlusal-apical aspect, the model tooth features visible pulpal and canal spaces (Figure 9). Similarly, it is interesting that while not yet fully developed for ideal radiography, the printed tooth model’s polycarbonate material shown in Figure 10 reveals a slight discernable outline of pulpal and canal space when radiographed under low exposure times. Thus, with expected continued development of printing material and incorporation of radiopaque materials, it may be feasible to conduct radiographic evaluation during an instrumentation exercise to simulate clinical conditions. Additionally, some modern 3D print materials have other characteristics to accommodate medical/dental procedures such as biocompatibility and sterilization by autoclave.

3D printing can begin from just about any perspective of a scan, such as from the apex of a tooth up towards the occlusal, from buccal to lingual, etc. If tooth models can be printed from the occlusal surface down to apical areas, this somewhat simulates natural tooth formation, as the tooth germ of the occlusal aspect first appears in development and leads in the apical growth of root structure. In this way, the printing of a tooth may be stopped at any desired stage of root formation and the result may simulate an open apex. Hence, there now exists the ability to practice on model teeth that have open apices often found in the developing permanent teeth of children. Encounters with such actual cases may not always be common in daily practice and bench exercises with such model teeth may improve and update clinical skills in treating children or where periapical surgery is needed.

Bench practice of instrumentation with various printed teeth would help discover and improve clinical skills in entirely new educational settings. This contrasts with the current use of extracted teeth for such practice exercises. Unlike with a limited and inconsistent supply of available extracted teeth, multiple model tooth copies can be printed from any pre-selected micro-CT scan with uniformity and in any quantity desired to share among dentists and dental students. New standardized exercises with printed model teeth can be developed for a live venue such as a classroom or webinar, or may be distributed under independent or group self-study educational correspondence programs. Much like extracted natural teeth now used in bench instrumentation, model teeth may be mounted in acrylic or plaster or be handheld. For example, a future journal article may present a new endodontic technique. Subscribers may be able to order model teeth printed from scans of those demonstrated in the article. Now it is possible for bench practice on the same tooth by journal readers to better learn these new techniques just as presented in the article. Completed model teeth may then be returned to course proctors for final evaluation and comments.

Another possibility is to maintain a library of tooth micro-CT scans that feature different and controlled levels of complexity in internal anatomy and/or any variation of root size and formation. In this case, students or instructors may order printed model incisor teeth that contain one or multiple canals, mandibular molars with four to five canals, premolars with three roots, etc. Endodontic courses can now be conducted under controlled or desired levels of difficulty to help course attendees advance together as a group in gaining new skills, experience, and confidence.

Yet another benefit of creating model teeth from actual scans is that 3D printers can be programmed to adjust proportionality of sizing and partial sectional views in printed models. This also presents a new possibility for improving patient education. Several firms already provide a wide variety of dental models for patient education, demonstration, specialized dental procedure training techniques, and other applications. 3D printing may help these firms build upon their existing product lines and distribution networks with 3D printed models. Informational value of printed models may actually expand patient awareness for better understanding and appreciation for the benefits of suggested dental procedures. Figure 11 depicts a 3D computer scan image of half a tooth for 3D printing in a sectional view to depict pulpal areas. Physical models of a tooth in cross section, when properly used, provide patients with a tool to better visualize disease and treatment for better understanding and care acceptance. With 3D printing, a tooth scan file can now be printed at 200% (Figure 12) or greater of actual size and with special variations in printed patterns of material layers (Figure 13). Larger models can help staff and dentists better explain care procedures for informed consent. Similarly, a scan file printed at 90% of actual size can introduce an intentional challenge when practicing instrumentation at the bench. This can lead to the learning of new skills and methods for matching these challenges.

Making Printed Tooth Models Available

Once a desired micro-CT scan is chosen, dentists, students, and dental schools may have the scan data file sent electronically to a commercial 3D printing service (also referred to as a “rapid prototyping service” or “service bureau”) equipped with high-capacity industrial 3D printers for hire. These service firms are increasing in number throughout the United States and some operate on a 24-hour basis and/or have capabilities to produce model teeth on short notice within a few hours of receiving scans electronically.

Production of model teeth appears to be cost effective, and price discounts may be offered in quantity orders. As of November 2015, costs for producing four life-size printed molar models from the micro-CT scan shown in this article are approximately $20.00 each excluding any shipping and applicable taxes.

As mentioned earlier, dental laboratories are increasingly adopting 3D printing technologies, and many may already have suitable 3D printers in-house that create digital casts. Since this equipment is already in regular use, technicians may also be capable of printing model teeth in a timely manner that is cost effective.

Future Possibilities

The usefulness and contribution of 3D printing has yet to be fully realized in dentistry and especially in endodontics. Furthermore, as computer software advances in dental laboratory technology, it is only reasonable to assume that there will be an ability to modify or even create variations in micro-CT tooth scans for adding levels of desired complexity and/or conditions such as to imitate pulp stones, internal/external resorption, dens-in-dente, and more. This may possibly be done by integrating micro-CT scan data with CAD/CAM software for designing digital alterations into the scan. Hence, 3D printing may soon help create new and almost limitless variations of model teeth to help both clinicians and students learn, improve, and advance in the science and art of endodontics.

Disclosure

Gregory S. Jacob, DDS, has no relevant conflicts of interest to disclose.

Acknowledgments

Micro-CT scans of molar using SkyScan 1172 Micro-CT System are provided courtesy of Raj Manoharan, Micro Photonics Inc., Allentown, Pennsylvania. CTvox and DataViewer freeware programs provided courtesy of Micro Photonics Inc., Allentown, Pennsylvania. MiniMagics viewer freeware by Materialise, Plymouth, Michigan.