Computer production of facial epitheses

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BACKGROUND

Rehabilitation in individuals with facial defects requires complex technological stages of treatment and further psychoemotional adaptation [1, 2]. The loss of part of the face may be due to oncological diseases, congenital defects, gunshot wounds, specific lesions of the maxillofacial region, and suicide attempts [3]. Additionally, according to the World Health Organization, a child with a facial defect is born every 3 minutes.

Surgical interventions in the maxillofacial region may cause patients to experience disruption of vital body functions, such as breathing, digestion, speech production, etc., which reduces the overall quality of life and aggravates the psychosomatic status of the patient. As a result, the social adaptation of patients worsens, and their ability to work is lost [4–7].

The main rehabilitation method of such patients is maxillofacial prosthetic repair. Face epitheses are used to replace facial defects and restore vital functions of the body. Improved appearance leads to social adaptation of the patient and normalization of his/her quality of life [8].

The technological process of producing face epitheses includes several surgical, orthopedic and dental stages. A coordinated work of all participants and comprehensive treatment planning are required to achieve a successful and guaranteed treatment [5, 6].

Currently, face epitheses are manufactured according to analog algorithms. At the start of the orthopedic stage of rehabilitation, silicone impressions are obtained from the wound surface; this alone already causes extreme discomfort to the patient. The subsequent stages of producing a plaster model of the defect and the creation and individualization of the final prosthesis take several weeks [9, 10].

The traditional methods of producing epitheses use platinum-based silicones. When mixing the two components, the silicone is polymerized, which should show an elastic and durable structure with a Shore A hardness of 10–30 [11–13].

The use of digital technologies in the manufacture of facial prostheses is limited by the lack of software for three-dimensional (3D) modeling of defects and material for making an epithesis with the required physical and mechanical properties. Additive production of facial epitheses revealed in other studies are non-demanded and inaccessible owing to the complexity of the technological process itself and economic inaccessibility of equipment for everyday dental practice [14, 15].

Thus, postoperatively, the patient is forced to live with a disfigured face until the epithesis is manufactured. Suicide attempts have been reported in such patients who could not withstand the psychoemotional stress. The fast and high-quality production of immediate facial prostheses the patient can use while waiting for the final design has not been fully studied. Further study is warranted to search for a method for direct rehabilitation of patients with facial defects using digital technologies for modeling and producing epitheses.

This study aimed to develop a 3D modeling technology for additive production of immediate facial epitheses.

MATERIALS AND METHODS

In the present study, the primary task was to develop a specialized 3D software for modeling facial epitheses. The program functionality should allow for virtual modeling of missing parts of the face (i.e., the ear, eye, nose, or orbit). In creating a digital platform, with recommendations from IT specialists, the following programming languages were used: C++ for writing the software core, writing UI/UX interaction modules, and interaction with the Windows operating system; C# for comprehensive assembly of the entire project; Python for automated assembly of virtual library modules; OpenGL HSLS as a shader language for graphic visualization of objects; and C for creating functions for interaction with shaders that require high speed.

The software being developed was expected to integrate 3D models of facial parts (i.e., the ear, nose, eye, or orbit) of various shapes and sizes for subsequent automatic adaptation of virtual epitheses to the wound surface, with the possibility of manual correction of the final virtual model. Hence, 287 computed tomographic (CT) images measuring 15×15 cm were analyzed, whereas 50 images of male and female patients of various ages with intact facial parts of various shapes and sizes were selected.

The development of the technology was aimed at manufacturing direct facial epitheses without preliminary obtaining silicone impressions from the wound surface. Writing the program code enables automatic conversion of the CT image of the patient’s head from the.dicom to the.stl format for subsequent virtual modeling of epitheses.

RESULTS

Considering the specified functional requirements, the 3D software “Phoenix 3D” was developed.

The use of this 3D program for modeling defects avoids invasive approaches to prosthetics and allows coordinating with the patient regarding the shape of future structures. In cases of a replacement, the built-in library of structures with a database ensures manufacturing of the prosthesis even without the patient’s presence. Moreover, the advantages of the technology include the fact that the prostheses can be manufactured on the day of surgery to remove part of the face while restoring completely lost functions and ensuring rapid social adaptation.

The technology is unique owing to the complete automation of all processes necessary for the manufacture of facial epitheses. Obtaining silicone impressions from the wound surface of the face is not required. To ensure the process of epithesis modeling, a CT image of the patient’s head should be exported in the.dicom format. Then, the 3D model is automatically converted into the.stl format (Fig. 1).

 

Fig. 1. Conversion of computed tomography data into .stl format in the developed program.

 

The 3D program includes a virtual 3D database of the ears, noses, orbits, and zygomatic bones of patients of different ages and sexes. This enables the specialist to select the most adaptive part of the face to compensate for the defect. Following the analysis of 50 CT images of patients with intact parts of the face, the ears, eyes, nose, and orbits were selected separately to create a virtual digital library and for further integration into the Phoenix 3D software (Fig. 2).

 

Fig. 2. Virtual library of nose models of the Phoenix 3D program.

 

After converting CT images into the.stl format, the defect boundary is marked using the built-in editing tools, and the desired face model is selected from the virtual library. The Phoenix 3D program places automatically a virtual model of the epithesis in the defect area, considering the presence of undercuts and topography of the prosthetic bed tissues (Fig. 3).

 

Fig. 3. Automatic adaptation of the virtual nose model to the tissues of the prosthetic bed in the Phoenix 3D program.

 

Then, specialists manually make corrections to the design using built-in editing tools. Further, a 3D virtual model of a part of the face is exported in.stl or.obj format, with subsequent production using additive or subtractive technologies (Fig. 4).

 

Fig. 4. Appearance of a patient with a nose defect of oncological origin before and after prosthetics with a temporary epithesis made by 3D printing using the proposed technology.

 

DISCUSSION

In recent years, in addition to the annual increase in the number of patients with oncological diseases of the maxillofacial region, the number of patients with shrapnel and gunshot wounds to the face caused by local wars and conflicts has increased. Thus, rehabilitation of such patients is extremely relevant.

Traditional orthopedic rehabilitation methods and the production of facial epitheses are complex and long-lasting processes. Postoperatively, in this category of patients, a sharp decrease in the quality of life, decline of the basic vital functions of the body, and poor social adaptation are noted.

Direct facial prosthetics in the postoperative period was previously impossible owing to the lack of the necessary digital modeling technologies and structural materials for additive or subtractive production methods. The manufacture of temporary or permanent facial epitheses using digital technologies is critical to improve the social and functional living conditions of patients.

A specialized computer program has been developed for 3D modeling of prostheses for patients with midface defects based on combined facial scanning and computed tomography data (Computer program. S.V. Apresyan, A.G. Stepanov, Program for 3D modeling of facial epitheses; registration number (certificate) 2023663490, dated 07/04/2023). Instead of obtaining analog impressions using plaster or silicone material, this technology uses a special 3D facial scanner. The developed program comprises a virtual 3D database of the ears, noses, orbits, and zygomatic bones of patients of different ages and sexes. This enables the specialist to select the most adaptive part of the face to compensate for the defect. Built-in modeling tools are useful in personalizing the 3D model of a part of the face, considering the structural features of the human maxillofacial region. The finished 3D model of a part of the face can be exported in various formats or sent directly to production using additive technologies.

CONCLUSION

The developed 3D modeling technology for additive manufacturing of temporary facial epitheses enables manufacturing a facial prosthesis on the day of surgery. Clinical testing of this technology has confirmed its efficiency. However, its further implementation into clinical practice requires more clinical randomized studies.

ADDITIONAL INFORMATION

Funding source. This study was not supported by any external sources of funding.

Competing interests. The authors declare that they have no competing interests.

Authors’ contribution. S.V. Apresyan — curation of research, development of a program for modeling facial epitheses, preparation and writing of the text of the article; A.G. Stepanov — literature review, collection and analysis of literary sources, development of a program for modeling facial epitheses, preparation and conduct of clinical trials, writing and editing the article; A.P. Zrazhevskaya — literature review, collection and analysis of literary sources, formation of a database of virtual data, statistical data processing; V.K. Suonio — literature review, collection and analysis of literary sources, formation of a database of virtual data, statistical data processing. All authors confirm that their authorship meets the international ICMJE criteria (all authors have made a significant contribution to the development of the concept, research and preparation of the article, read and approved the final version before publication).

About the authors

Samvel V. Apresyan

Peoples’ Friendship University of Russia named after Patrice Lumumba

Email: dr.apresyan@mail.ru
ORCID iD: 0000-0002-3281-707X
SPIN-code: 6317-9002

MD, Dr. Sci. (Medicine), Associate Professor

Russian Federation, Moscow

Alexander G. Stepanov

Peoples’ Friendship University of Russia named after Patrice Lumumba

Author for correspondence.
Email: stepanovmd@list.ru
ORCID iD: 0000-0002-6543-0998
SPIN-code: 5848-6077

MD, Dr. Sci. (Medicine), Associate Professor

Russian Federation, Moscow

Anastasia P. Zrazhevskaya

Peoples’ Friendship University of Russia named after Patrice Lumumba

Email: dr.azrazhevskaya@gmail.com
ORCID iD: 0000-0002-1210-5841
SPIN-code: 2449-2914
Russian Federation, Moscow

Valeria K. Suonio

Peoples’ Friendship University of Russia named after Patrice Lumumba

Email: valerijasuonio@ya.ru
ORCID iD: 0000-0002-4642-6758
SPIN-code: 6079-4490
Russian Federation, Moscow

References

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