The involvement of Product Engineering in facial prosthetic rehabilitation: construction of prostheses by means of Reverse Engineering and Rapid Prototyping

In the field of maxillo-facial rehabilitation, facial disfigurements after tumor ablative surgeries and deformities due to Treacher Collins Syndrome necessitate the replacement of the missing volumes of the patient’s face with customized prostheses anchored to craniofacial implants. The option to make implant supported facial prostheses should be the last choice for patients, and plastic surgeons should do whatever is possible to restore defects with skin and cartilage. Sometimes local and general condition of patients does not allow a correct plastic surgery, and these are the only cases that warrant facial prostheses. This paper describes a selection of case studies applying a costumized procedure which implements innovative prototyping technologies together with conventional silicone processing procedures. The design of such facial prostheses involved both mechanical engineers and medical departments producing a mutidisciplinary solution and making evidence of results on real cases. The procedure is basically composed of three main steps. The first reverse engineering step is based on 3D laser scanning of the defective regions of the patient’s face and 3D reconstruction of the relative digital models. Then a Computer Aided Industrial Design approach is followed to project customized prostheses and develop relative molds and substructures. An “Ear & Nose Digital Library” based on digitalized anatomic models is used to design nasal prostheses and auricular prostheses when controlateral ear is not available (bilateral defects). These kinds of defects do not allow digital reconstruction of missing volumes based on virtual mirroring of the healthy side of the face. After this step, a rapid prototyping system is employed to manufacture molds and substructures for bar anchoring by Fused Deposition Modeling (FDM) of plastic material. Finally, conventional silicone processing is used to obtain the definitive prostheses containing relative substructures and based on the designed and prototyped molds. Each case report is presented together with the results achieved in terms of time requirement, cost, and level of patient discomfort