Читать книгу Digital Dentistry - Группа авторов - Страница 16

Conventional two‐dimensional (2D) imaging modalities usually have several limitations such as image distortion, magnification, superimposition of anatomical structures, and lack of three‐dimensional (3D) information for diagnosis and planning. In this context, 3D imaging modalities such as cone beam computed tomography (CBCT), intraoral and facial scanning systems provide 3D digital images for dentistry [1–3]. CBCT imaging allows for visualization and assessment of bone structures with high diagnostic accuracy and precision. For CBCT images, the professional needs to understand image acquisition parameters, since the quality of the image affects the quality of the work in digital dentistry. There are several CBCT acquisition parameters, such as field of view size (FOV), peak kilovoltage (kVp), milliamperage (mA), and voxel size. Each of these parameters has an influence on CBCT quality [2–5].

Intraoral and facial scanning can capture 3D patient images that can be used for digital treatment planning systems (Figure 1.1). The software will then develop a digital representation of the 3D object surfaces available, which will be automatically converted into 3D images composed by wireframe models.

Any 3D images can be rendered and edited in the 3D space, before being converted and saved in a specific file format [5]. As discussed in the next chapter, three file formats are commonly used in digital dentistry: OBJ, STL, and PLY. These files are based on the geometric reconstruction of objects by vectors, triangles or polygons, considering their positioning in a 3D space. After all data is ready, it is possible to store the shape of a model and other details such as color or texture.

Figure 1.1 Three‐dimensional objects imported in different coordinates of the 3D space (screen capture of MeshMixer software, Autodesk). Note that the fixed bridge is closer to the screen than the molar crown. The dynamic grid is used to orientate the spatial disposition of the 3D objects.

Three‐dimensional images can be manipulated in various ways, depending on the characteristics of the software. For example, with DICOM and STL files, using the CAD software one can plan and perform digital surgery of dental implants and wax‐up of future prostheses. After digital planning, the implant surgery guide, temporary crowns, and definitive crowns can be printed with additive manufacturing devices or milled by subtractive manufacturing devices [5, 6].