Table 1 Overview of methods employed to address considerations for temporal bone model design and fabrication

Model Material and Colour

To have the model safe for drilling by high-speed surgical drills that produce fine particles.

Construct the model with material safe for high-speed drilling that produces fine particles.

To have the model mimic the normal colour of the bone, reducing glare from Operating Theatre lighting.

Dye resin to a colour tint which minimises glare.

Considerations at Specific Anatomical Regions

Mastoid air cells

To achieve differential demarcation of the Koerner Septum relative to the adjacent mastoid air cells.

Use fine detail slice-by-slice segmentation methods in addition to HU threshold method segmentation of key areas of the mastoid air cells.

To achieve appropriate density of mastoid air cells.

To prevent print failures due to “cupping” i.e., formation of pools of uncured resin which prevent successful printing.

Orientate the model in a manner to prevent “cupping”.

Tympanic Cavity Ossicular chain

To model small sized and thin anatomical structures e.g., ossicles and tympanic membrane.

Use multiplanar reconstructions to suitably orientate the ossicular chain to allow for easier fine detailed segmentation.

To mitigate impact of supports obstructing the key anatomy of the tympanic cavity.

Use manual support placement techniques to minimise support density and touchpoint size at key anatomical structures of the ossicular chain and along surgical corridors in the tympanic cavity.

To model the course of the tympanic segment of the Chorda Tympani nerve which is not visible on CT.

Model the expected course of the Chorda Tympani nerve based on known anatomical landmarks.

To model the appearance of the skull base boundary structures during otological surgery i.e., the dura of the middle cranial fossa, the transverse and sigmoid sinuses.

Use silicone to model the tympanic membrane, dura and dural venous sinuses.

Facial nerve

To maintain the demarcation and integrity of the facial nerve canal from the adjacent bone.

Use CAD Modelling techniques to demarcate the walls of the facial nerve canal as well as place resin drainage holes that allow flushing through it using millifluidic printing techniques.

To prevent uncured resin from depositing inside instead of draining through the thin facial nerve canal.

Inject coloured silicone through the facial nerve canal to differentiate it from normal bone.

Cochlea

To model the detailed anatomy of the cochlea in order to facilitate cochlear nerve implant simulation.

Use detailed fine slice-by-slice segmentation methods to delineate the turns of the cochlear as well as the modiolus.

To simulate the round window niche as a surgical landmark.

Use CAD modelling techniques to place demarcating features at these niches.

Semicircular canals

To prevent uncured resin from depositing inside the small channels instead of draining through them.

Use CAD modelling techniques to enlarge as well as place resin drainage holes within the channels which allow flushing through them using milli-fluidic printing techniques.

Consider the orientation of the semicircular canals during model orientation.