Extra Auricular Prosthesis Fabrication

Extra Auricular Prosthesis Fabrication:
The process of manufacturing an extra-auricular prosthesis, including the ear, nose, or facial segment, involves thorough selection of materials and precise mixing of silicone to achieve an anatomically correct and lifelike appearance that will last. Silicone elastomers are used because they are biocompatible, flexible, and can simulate natural skin tones and textures. Mixing silicone is an important step since it will define the final aesthetics, strength, and resilience of the prosthesis.

Step 1: Silicone Material Selection
Medical-grade RTV (Room Temperature Vulcanizing) Silicone is used for facial prostheses.
The most commonly used silicones are PDMS-based materials.
Shore A hardness is chosen according to the anatomical site and patient requirements (usually 10-30 Shore A for soft tissue areas).

Step 2: Preparation of Work Area and Materials
A clean, dust-free environment is maintained to avoid contamination.
Wear gloves and protective eyewear to prevent direct skin contact with silicone parts.
Components to gather:
Base silicone material
Catalyst/curing agent
Intrinsic color pigments
Fumed silica or thixotropic agents, if required for texture
Mixing tools (spatula, glass slab, electronic scale, measuring cups)
Vacuum chamber for bubble removal

Step 3: Mixing Base Silicone and Catalyst
Weighing Components
Silicone materials are mixed in a ratio as per the manufacturer’s instructions, which is usually 10:1.
Proper curing requires accurate weighing using an electronic scale.
Adding Catalyst
Mix the catalyst evenly into the base silicone with a folding motion to minimize air entrapment.
Stir slowly but thoroughly to avoid introducing bubbles.

Step 4: Pigmentation for Lifelike Appearance
Intrinsic Coloring
Pigments such as silicone-based colors, oxide pigments, or artist-grade oil paints free of water-soluble components are used.
Colors are added in small increments and mixed thoroughly to match the patient’s skin tone.
Reference photographs or direct skin comparison aids in achieving natural shades.
Layering Method

Different tones can be layered to mimic the translucency of natural skin.
Adjustments are made by adding red, yellow, brown, or blue hues for undertones.

Step 5: De-Airing (Vacuum Degassing)
Vacuum mixing (placed in a vacuum chamber for 2-3 minutes) removes air bubbles introduced during mixing.
This step ensures the consistency of silicone is smooth, evenly consistent and does not have weak spots.

Step 6: Adjusting the Consistency
Add thixotropic agents (such as fumed silica) to adjust your viscosity, if needed for sculpting or layering a thicker material.
If desired, plasticizers may be added for soft areas for more flexibility.

Step 7: Curing and Setting
Mixed silicone is poured into the prosthetic mold and allowed to cure at room temperature for 6 to 24 hours or accelerated through heat curing (40-60°C for 1-2 hours, depending on the requirements).
A post-cure step further increases the mechanical strength and durability.

Final Steps
Once cured, the prosthesis is trimmed and surface textured, and extrinsic painting is added for realism.
A matte finish or surface sealer is added for durability.
Proper mixing of silicone is critical to achieve a realistic, durable, and comfortable extra-auricular prosthesis tailored to the patient’s needs.