Jul/Aug 2017
Volume 38, Issue 7

Peer-Reviewed

Digital Imaging and Prosthetic-Driven Implant Planning: Efficient, Accurate, and Reliable Treatment

Bryan T. Harris, DMD; Li Chen, BDS, PhD; and Wei-Shao Lin, DDS

Implant-supported and -retained restorations have been widely accepted as predictable treatment modalities for partially or fully edentulous patients. Proper implant position and angulation facilitates the construction of an optimal restoration and is critical for its long-term success. The continuous technological evolution in digital imaging and prosthetic-driven implant planning allows clinicians to surgically place implants more accurately, predictably, and efficiently.

Conventional Vs. Digital Workflows

Advancements in 3-dimensional (3D) imaging and computer-aided design/computer-aided manufacturing (CAD/CAM) technology have significantly altered the conventional workflow of prosthetic-driven implant planning.1 Conventional prosthetic-driven implant planning is a model-based workflow that begins by recording the intraoral and extraoral conditions of the patient with impressions made of irreversible hydrocolloid or elastomeric material, and continues with occlusal record registration and even facebow transfer. Clinical photographs are taken for further facial and dental esthetic evaluation. Diagnostic waxing or denture teeth arrangement can be performed and used to fabricate the radiographic template. During cone-beam computed tomography (CBCT) imaging, the radiographic template should be present intraorally to transfer the prosthetic plan to the 3D volumetric imaging data in digital imaging and communications in medicine (DICOM) file format. The radiographic template can then be manually modified to the desired surgical template.

A fully digital, model-free prosthetic-driven implant planning pathway works differently from the conventional one. The goal of this digital pathway is to create a virtual model of the patient, beginning with CBCT imaging2 and intraoral scanning.3 The DICOM files generated by CBCT imaging and standard tessellation language (STL) files generated by intraoral scanning can be imported to the implant planning software. By superimposing the DICOM and STL files, the remaining dentition, surrounding intraoral soft tissue, and underlying craniofacial hard tissue can be visualized in great detail in a single virtual entity. Digital waxing or virtual teeth arrangement can be performed in this single virtual entity to subsequently determine prosthetic-driven implant planning.

A CAD/CAM surgical template can then be milled or 3D-printed based on the approved surgical plan.4 The CAD/CAM surgical template is used in conjunction with computer-guided surgery and can incorporate metal sleeves and special surgical instruments to fully control accurate drilling depth and angulation during implant surgery.5 In many cases, the digital pathway can significantly reduce the number of clinical visits and eliminate the need for a time-consuming, laboratory-fabricated radiographic template.6 All the digital diagnostic data can be collected in a single visit and electronically transferred to the dental laboratory with great efficiency.

State-of-the-Art Digital Imaging

Contemporary imaging technologies make it possible to digitize and virtualize the anatomy of an actual patient. During prosthetic-driven implant planning, it is essential that clinicians have knowledge of craniofacial hard and soft tissue, the remaining dentition and surrounding soft tissue, and the corresponding occlusion. In complicated cases, the extraoral facial profile can be supplemented as optional diagnostic information to simulate facial changes that would result from the proposed treatment.

CBCT

CBCT has been widely installed and routinely used in dentistry. Compared with conventional fan-shaped computed tomography (CT) devices, CBCT delivers a lower dose of radiation, equivalent to 20% of that of conventional medical CT.7 The accurate and consistent 3D imaging produced by CBCT is critical for implant treatment planning, especially when implants will be placed in esthetic regions or around vital anatomical structures.

To facilitate fully digital prosthetic-driven implant planning, the DICOM file produced by CBCT imaging is often merged with the STL file produced by intraoral scanning to create a virtual entity. This endeavor involves segmenting the DICOM file; separation of the maxillary and mandibular dentition with a plastic bite fork or a cotton roll during CBCT imaging will make segmentation easier.8 Scattering, which is due to existing metallic restorations, will make the merging process of the DICOM and STL files difficult and reduce accuracy.9 When intensive scattering is expected, an alternative solution is to design and fabricate a CAD/CAM radiographic template with radiopaque fiducial markers distant from the metallic restorations. These markers on the template will be fixed intraorally during CBCT scanning and will provide guidance when the DICOM and STL files are superimposed.

Surface Scan

In a fully digital workflow, a virtual diagnostic cast can be created by either making a digital impression directly with intraoral scanners, or scanning the irreversible hydrocolloid or elastomeric diagnostic impression with laboratory scanners or CBCT imaging. The digital data acquired through various instruments is usually converted into standard STL file format so that the data can be processed with different implant planning software. Some intraoral scanning systems include in-office design and milling, while others are designed for data acquisition only.10 Other factors to consider are whether the system is an open or closed system, and whether it uses powder, offers full-color capabilities, and performs full-arch scanning. Compared with conventional irreversible hydrocolloid or elastomeric diagnostic impression, digital intraoral scanning is more efficient for clinicians and technicians. The accuracy and reproducibility of intraoral digital impressions of dentate arches have been intensively investigated and validated.11

Facial Scan

In certain clinical cases, 3D facial scanning systems can be advantageous. Various facial scanners are being used to acquire 3D facial volumetric data to facilitate the treatment planning process. Examples of 3D facial scanning systems include the FaceScan (3D-Shape GmbH, 3d-shape.com), which is a structured light scanner, and the 3dMDface System (3dMD, 3dmd.com), which is based on stereophotography technology. Both systems allow the capture of 3D facial volumetric data in natural head position (NHP) and output 3D virtual facial models with real color texture in very short time. NHP is clinically repeatable and considered to be the most natural physiologic position of the head.12

Prosthetic-Driven Implant Planning and Computer-Guided Implant Surgery

Both conventional and digital planning workflows should be performed with the same concept of prosthetic-driven implant treatment. Based on the analysis of the current problems of the patient, a treatment option is proposed, and digital waxing can be developed to fulfill the esthetic and functional requirements. During this phase, the facial proportion and profile, the lip–teeth relationship, and the esthetic desires of the patient should be carefully considered. Implant position will be determined by the digital waxing and available bone volume. For the patient in need of full-mouth rehabilitation, a 3D virtual facial model can be integrated with digital dentition and bone to create virtual imaging of the patient to simulate the outcome of the final treatment. For example, the impact of teeth morphology and position change on the facial appearance of the patient can be shown. Such a digital workflow has been shown to provide better communication among patient, technician, and clinician.13

When the implant position and angulation is determined during the virtual implant planning process, this information can be transferred to the actual implant placements in a computer-guided implant surgery approach. Techniques have been developed to facilitate the transfer, including real-time navigation systems (dynamic) and CAD/CAM surgical templates (static). A dynamic navigation system is designed to guide the placement of dental implants in real time by a computer. Motion tracking technology is the key to the system; it tracks the positions of both the drill and the patient during osteotomy and implant placement. With the 3D position information, the computer instantaneously calculates and displays the virtual position of the instruments and implants.

Several navigation systems are available on the market but they have not yet gained popularity among clinicians, possibly because the systems are difficult to use and relatively high in cost. A recent study concluded that the dynamic guided system tested was at least as accurate as static guides and was a significant improvement over freehand implant placement.14 Although upgraded systems have been developed recently, further study on accuracy and consistency is still needed.

CAD/CAM surgical templates have been more widely used and well documented. A CAD/CAM surgical template can be supported by teeth, mucosa, bone, mini-implants, or a combination of these to realize the computer-guided implant surgery approach. The types of support used have a significant impact on accuracy. A bone-supported guide shows lower accuracy when compared with other types of supports, while a surgical guide supported by mini-implants provides high accuracy in implant positioning.15 A recent study showed that implant placement facilitated with a CAD/CAM surgical template could achieve higher precision and accuracy in implant position and angulation than implant placement without surgical guide templates.16 Another study found that the computer-guided implant surgery approach was more accurate than the conventional approach.17 With the computer-guided implant surgery approach, the most inaccuracy occurs in the vertical direction (depth of the placed implant) and there is less inaccuracy in the mesial-distal or buccal-lingual directions.17

Conclusion

Current digital imaging, digital prosthetic-driven implant planning, and computer-guided implant surgery technology have dramatically changed dental implant treatment, moving the conventional workflow into a digital one. More efficient, accurate, and reliable implant placement can be achieved with current and continuous technology advancement.

About the Authors

Bryan T. Harris, DMD
Associate Professor and Director
Advanced Education in Prosthodontics
Department of Oral Health and Rehabilitation
School of Dentistry
University of Louisville
Louisville, Kentucky

Li Chen, BDS, PhD
ITI Scholar, Division of Prosthodontics
Department of Oral Health and Rehabilitation
School of Dentistry
University of Louisville
Louisville, Kentucky
Attending faculty
Department of Prosthodontics
Peking University School and Hospital of Stomatology
National Engineering Laboratory for Digital and Material Technology of Stomatology; and Beijing Key Laboratory of Digital Stomatology
Beijing, China

Wei-Shao Lin, DDS
Associate Professor and Director
Division of Prosthodontics
Department of Oral Health and Rehabilitation
School of Dentistry
University of Louisville
Louisville, Kentucky

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