3. Discussion
In this technical note, we have described the manufacturing of a cost-effective 3D-printed model for temporal bone training. This model has recently been validated for educational purposes.6The model costs ~5 USD to manufacture and the printer used can be acquired for <300 USD. This enables most departments to start in-house production of 3D-printed models, providing an effective and inexpensive alternative to commercially available models.
Even though 3D-printed models are perceived to have an important role in the future temporal bone training curriculum9 it should be noted that 3D-printing is not just “plug-and-play”. In-house production requires material and time along with know-how on 3D-printing as maintenance of the printer is pivotal.
We chose to use Material Extrusion based 3D-printing technology as it is inexpensive, easy to use and effectively reproduces the air cells in the mastoid bone, unlike other more advanced print technologies where unconsolidated residual material easily entraps.4 To avoid melting and agglomerating when drilling, we chose a filament with a high load of chalk filler. However, this filament is very fragile and easily breaks during the printing. To avoid this, we made some minor modifications to the printer, installing a direct filament drive and replacing the standard nozzle with a Ruby nozzle. These modifications are cost-effective and easy to install. In addition to the standard brass nozzle, the Ruby nozzle has a ruby gemstone at the tip of the nozzle enhancing durability. A standard nozzle (~5 USD) gets worn out after approximately five prints whereas the Ruby nozzle (~60 USD) can last more than 50 prints, reducing the need for replacement and maintenance. Installing the direct filament drive is easy, takes 1–1.5 hours and does not require major printer modifications. Alternatively, investing in a printer with direct drive installed as a standard (e.g. the ~1000 USD Prusa i3 MKS3+, Prusa Research, Czech Republic) would remedy this issue. However, the design of the Prusa i3 hot end is more compact and complicates cleaning and maintenance. Although any of the suggested printers, without any modifications, is suitable for printing temporal bone models, we recommend using the Ender-3 Pro with the suggested modifications (total price of ~450 USD) for the lowest cost, lowest need for maintenance, and highest rate of successful prints compared with out-of-the box 3D-printers.
While the presented model closely replicates temporal bone properties, post-processing steps are necessary to represent important soft-tissue structures. Consequently, the dura and sigmoid sinus are represented by colored silicone layers and the facial nerve by a yellow wire. In the current iteration of the model, the chorda is not represented and the lateral semicircular canal and ossicles are printed in the same material as the remaining bony parts and therefore lack specific visual cues. The ossicles are inadequately replicated due to the print resolution; more accurate representation would require a higher resolution printer.10 In addition to solving these problems, reducing the need for post-processing steps would enable mass-production. This would likely require the use of more advanced and costly print technologies.
Altogether, the presented workflow is suited for a relatively small in-house production (for example larger training centers). Nevertheless, in-house production of an inexpensive and effective 3D-printed model for temporal bone training is feasible and enables training institutions to manufacture their own models to provide ample training opportunity.