Three-Dimensional, Computer-Assisted, Three-Layer Models of the Face

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Recent advances in three-dimensional printing technology in plastic surgery have been described.1 The technology has also been reported to be beneficial for replacing soft tissues.2 We have used realistic three-dimensional, computer-assisted, two-layer elastic models of the face.3 The surface layer is composed of polyurethane and the inner layer is composed of silicone, representing skin and subcutaneous tissue. The model enables residents and young doctors to understand three-dimensional design and flap movement and to simulate operations on face-like organs with a complicated three-dimensional structure. We have improved the model to make it more realistic.
The new model has one more layer representing bone. We made a realistic three-dimensional, computer-assisted, three-layer model for a 19-year-old male patient with multiple facial bone fractures (Le Fort I, II, and III) caused by a motorbike traffic accident (Fig. 1). This model was used by a young doctor to help in the operation for facial bone fractures.
From the face Digital Imaging and Communications in Medicine data of the patient’s computed tomographic scan, volume rendering was performed and stereolithographyic data with external surface information were generated with the use of a Digital Imaging and Communications in Medicine manager. The mold data were calculated from the stereolithographic data (Fig. 2).
To make the mold, we used salt granules with a particle size of approximately 30 µm, consisting of sodium chloride (80 percent), hygroscopic material (15 percent), and bonding agent (5 percent). The smooth salt granules were applied and laminated with the use of a three-dimensional inkjet printer.4 The facial bone model was made by the same method from the computed tomographic stereolithographic data. Next, polyurethane, which is made by mixing polyols (70 percent) and isocyanate (30 percent), was applied several times inside the mold until the thickness reached 1 mm. The mold for the external surface was combined with the facial bone model. After the hardening of polyurethane, silicone was poured between the mold and the bone model. The silicone was made by mixing a silicone base with a catalyst (100:8). The silicone was hardened in an oven at 100°C for 1 hour. Then, the outer mold was broken and the surface layer of the polyurethane was washed. A resident doctor practiced simulation surgery using this model to study the operation for multiple facial fractures.
Integrated life-size solid models of bone and soft tissue for cleft lip and palate of infants have been reported.5 The models have a polished transparent surface through which the bone’s surface can be seen. Simulation surgery cannot be performed because they are solid. Our new model is composed of two elastic layers and one hard layer, representing skin, subcutaneous tissue, and facial bones. It does not have a muscle layer, but various methods of approaching the fracture lines can be tried, and osteotomy can be simulated from the simulated incisions and flaps. Finally, suturing is possible.
We must make the model more realistic. We hope to use these models for teaching methods of approaching fracture lines and for the reduction of typical facial fractures in seminars and clinical clerkships.
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