Introduction to 3D printing and surgical planning

Introduction to 3D printing and surgical planning

History of 3D printing

The first 3D printers were constructed in the 1980s (1981 – Hideo Kodama – photopolymer printing, 1984 – Charles Hull – invention of stereolithography, 1988 – Scott Crump – FDM technology, plastic fiber printing). Since then, 3D printing processes have evolved in many ways and the technology as a whole has grown significantly. The recent expansion of 3D printing followed after several major patents  from the 1980s expired, making 3D printing much more available today. Companies that started the technology in the 1980s grew from small start-ups, which were considered by only few people as important, to multimillion-dollar corporations (STRATASYS, EOS, 3D systems and many others). There is a huge variety of advanced 3D printing technologies making it possible to print from a variety of materials, and development is exponentially advancing.

 

3D printing in medicine

As in many other areas, 3D printing has found widespread use in healthcare. Because each person is individual and unique, 3D printing as a way to create custom-made individualized products has a very clear application in healthcare. No other CAD / CAM manufacturing method offers so many possibilities of making any object architecture and so many combinations of different materials with different properties. An interesting area of ​​3D printing is also its application in the relatively newly established branches of regenerative medicine and tissue engineering. In recent years and literally months, many of the unthinkable milestones in biological tissue regeneration have been reached. 3D printing plays a key role in these sectors, and its utilization and collaboration with advances in biochemical, pharmacological and other medical sciences such as genetics, histology or molecular biology are expected to allow whole organ regeneration over the next decades. The use of 3D printing in healthcare is truly extensive and it is difficult to find a medical discipline where it wouldn’t offer innovative applications. For dental medicine, the area of ​​3D printing is particularly interesting, whether it is used in prosthodontics, endodontics or implantology, or also for planning surgical interventions in our associated discipline – maxillofacial surgery.

 Surgical planning in maxillofacial surgery

In surgical disciplines, where operations are often performed on complex anatomical structures, the use of 3D printing is an excellent supportive aid for healthcare professionals. It can be used to prepare surgical tissue models that are evaluated preoperatively. The surgeon has a better chance to get acquainted with the operated structure in advance, to assess it visually and haptically and to prepare for the procedure. This structure can be divided in various cross-sections, either virtually before printing or additionally physically as a printed model, and it is possible to examine a complex internal anatomy thereon. If appropriate materials are used, the surgical procedure can be carried beforehand on the printed structure, which is important in the case of preparations for complex operations and in the case of education and training of various procedures. The printed structure can also serve as a communication tool for the doctor and the patient.

The basic prerequisite for the use of these techniques is to obtain specific 3D data based on 3D radiodiagnostic examinations and surface scanning techniques. To obtain a virtual 3D computer model of anatomical structures, 3D X-ray, such as MSCT (Multi-slice computed tomography) or CBCT (Cone-beam computed tomography), is most commonly used in the field of maxillofacial surgery. To a lesser extent, MRI examination or 3D ultrasound is also used. In Maxillofacial Surgery and Dentistry, surface scanning is also used today, especially with intraoral scanners or laboratory scanners (Trios, iTero, Medit, Kodak) that generate a 3D file by reflecting light from surface of scanned structures. The use of face scanning techniques and the interconnection of these data with the other modalities mentioned are expected to increase in the future too.

The 3D structure, obtained from these diagnostic modalities (mostly in DICOM format), is generated by software (f.e. Anatomage, Blue Sky Bio, 3DSlicer, ITK-SNAP). Subsequently, the generated 3D file (most often in STL format) is appropriately modified (removing of artifacts, removing of not needed areas, smoothing, etc.) in 3D modeling software (f.e. Materialize mimics, Blender, Meshmixer) and then processed into a format that is readable by a particular 3D printer. To put it simply, we edit and combine the object that we get from the slices generated from 3D CT into a single model and then virtually cut it into layers again, so that the 3D printer can physically print  those layers on top of each other. Thus, in the 3D printing process, the object is produced by bonding layer by layer. This layer transferring process is common for all types of 3d printers. Thanks to this principle, it is possible to create objects with very complex geometries, which is unique among other production processes. These four important steps in model fabrication – software segmentation (usually from DICOM format), fine-tuning and editing the model, virtual slicing of the model for 3D printing and printing itself – also determine the dimensional accuracy and level of detail on the printed object. Any potential error in these steps results in inaccuracy.

At the end of this process, a model is printed that is used to prepare the operation for the operation team, to evaluate and possibly test the procedure and prepare the surgical aids. As part of the software analysis of the 3D printed anatomical structure, it is also possible to prepare surgical operating templates that are important for physical perioperative guidance of the procedure. They can be used to precisely guide the incision on the hard tissues at a predetermined location, depth and a predetermined angle, to precisely insert the implants, or to precisely guide the resection of the hard tissue. It is also possible to prepare various tools in advance according to the 3D printed model, such as a reconstruction plate in the case of large resective operations. These devices such as reconstruction plates or titanium hard tissue replacements can be made manually on the 3d printed structures or they also can be produced directly using 3D printing.

Biovoxel technologies provides printing of plastic organ and tissue structures.