Cases

A 30-year old male had lost his right external ear in a traffic accident (see figure 1). In such cases, the treating specialist can choose between two common treatments. He can opt for surgical reconstruction, which poses a challenge to the surgeon due to  the complexity of the human ear’s shape and size. Another option is to design an auricular prosthesis, which usually offers a  better morphologic result. However, the final outcome always depends closely on the maxillofacial technician’s artistry and skill. In the following case, the researchers opted to design a prosthesis using advanced CAD/CAM techniques.

The researchers began the design process by taking a head spiral CT scan of the patient. The CT data were imported to  Mimics, where the patient’s ear and face were easily reconstructed in a detailed 3D image. These reconstructions were then imported to Materialise’ Magics software. Magics allowed the researchers to mirror the intact ear easily over the midline of the face onto the deficient side (see figure 2). The mirrored image would serve as a basis for the ear prosthesis. It could easily be moved in any direction on the deficient side of the face until it fi t the patient’s physiognomy flawlessly.

However, scarring on the deficient area meant the mirrored image was not a true match for the deformed side. Some margins would turn out to be redundant and the scarring might protrude onto the prosthesis. The solution was SensAble FreeForm, which the surgeon used to smooth the mirrored image and sculpt the redundant margin. The image then underwent a Boolean operation, which enhanced its smoothness, ensured it did not contain any holes and fit it precisely to the deficient side of the patient’s face. The ease and speed of this process surprised even the researchers.

When the design of the prosthesis was ready, the researchers exported their image to a Kynergy Mechatronics Zippy-I rapid prototyping machine. Using laminated object manufacturing (LOM), the team created a paper model of the ear, on which a silicon cavity block was formed via vacuum casting. With the addition of an elastomer to the cavity block, the final ear prosthesis was made.

A calibrated dose of pigment was added to the elastomer so that it would match the patient’s skin tone (see figure 3).

Applying the latest techniques in medical imaging and rapid prototyping (see figure 4), the authors were able to develop a new CAD/CAM method for the design and manufacturing of custom ear prostheses. Thanks to Mimics’ high level of accuracy, the researchers were confident that the prosthesis’ final design was a perfect fit for the patient’s physiognomy. Its shape, dimensions, anatomic contour and color were so meticulously defined based on the patient’s physiology that it blended in without a flaw. The development of this approach means that a maxillofacial technician is no longer necessary for manufacturing an ear prosthesis.