Technical Note
Facial Rehabilitation
Rapid development of auricular prosthesis using CAD and rapid prototyping technologies

https://doi.org/10.1016/j.ijom.2007.07.013Get rights and content

Abstract

External ear defects can be corrected by surgery, but this may not be feasible for personal or medical reasons. Reconstructive solutions are a good alternative, but rely on the artistry and availability of the anaplastologist. A semi-automated methodology using computer-aided design (CAD) and rapid prototyping (RP) technologies was developed for auricular prosthesis development, and demonstrated in a real-life case. The correct geometry and position of the prosthesis were ensured by stacking the computed tomography scan images of the contralateral normal ear in reverse order, and joining them using a medical modelling software program. The CAD model of the remnant portion of the defective ear was subtracted from the model of the mirrored contralateral ear, using a haptic CAD system, to obtain the final geometry of the prosthesis. Polymer models were fabricated in RP systems, and used for making a corresponding mould. Medical grade silicone rubber of the appropriate colour was packed into the mould to fabricate the final ear prosthesis and fitted to the deficient side of the patient using medical grade adhesive. The computer-aided methodology gave a high level of accuracy in terms of shape, size and position of the prosthesis, and a significantly shorter lead time compared to the conventional (manual) technique.

Section snippets

Background information

Reverse engineering or 3D digitizing14 can be used to capture the morphology of deficient and normal ears3, as well as casts made by impression[1], [10]. Some blind spots (undercuts) result in missing data patches and need to be manually ‘stitched’, but the latest CT/MRI systems combined with medical modelling software can yield correct anatomical details15, and have been successfully used for the ear region[5], [8]. CT-scan data is also useful for prosthesis positioning18, CNC machining11 and

Computer-aided prosthesis development

The procedure involves five steps: (i) CT-image data acquisition for deficient and contralateral ears, (ii) reconstruction of the corresponding 3D models using medical modelling software, (iii) design of the missing ear using a haptic CAD system, (iv) fabrication of prosthesis master using RP system and (v) fabrication of the final prosthesis using a mould made from the master (Fig. 2). The steps are described for the case of a patient (male, 19 years) with congenital absence of the right ear (

Discussion

This work demonstrated how high accuracy in morphology and positioning can be achieved by finer CT scanning (0.63 mm slice thickness) coupled with the reverse stacking approach (to mirror the contralateral normal ear), if there is reasonable facial symmetry presented by the patient, as in this case. The haptic CAD system eased the design (to match the morphology of the deficient side), and smoothing of the final auricular prosthesis model. The use of RP technology enabled accurate reproduction

Acknowledgements

We acknowledge the assistance of Dr. K. Balabsubramanian and Mr. Nirmal Panda of Non Ferrous materials Technology Development Centre, Hyderabad in 3D model reconstruction from CT scan data. We would like to thank Ms. Mona Sharma, IIT Bombay, for assisting in FreeForm modelling. We would like to thank Dr. K.P. Karunakaran, Indian Institute of Technology, Bombay, for allowing the use of the FDM RP system, and Dr. P.B. Joshi, Maharashtra Institute of Technology, Pune, for allowing the use of the

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