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.