Key points
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Intraoral scanning and/or model scanning can be combined with cone beam computed tomography to accurately design and plan surgical guides for implant placement.
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Three-dimensional printers have become more compact and affordable to allow in-office printing of surgical guides.
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Dynamic navigation can be used for implant planning and real-time guidance of the drill and implant placement.
Introduction
Dental implant placement ideally should be restoratively driven, with respect to the design and position of the definitive prosthesis. Conventional panoramic radiography performed with the patient wearing a radiographically visible template does not provide three-dimensional (3D) anatomic information, much in the same way that surgical templates made from diagnostic casts do not address underlying anatomic structures. Although they try to direct bone entry and drill angulation, traditional surgical guides allow a wide range of implant positioning errors that can be detrimental to the functional and esthetic demands of the definitive implant prosthesis. This freehand placement using laboratory-fabricated conventional pilot drill stents is less accurate than implant placement using a navigation system. There are now 2 types of navigation system available to oral and maxillofacial surgeons: static guidance and dynamic guidance. Use of these navigation systems during implant placement allows increased placement accuracy compared with freehand placement, regardless of the experience of the surgeon.
Computer-aided implant planning
The introduction of cone-beam computed tomography (CBCT), digital intraoral scanning, and computer-aided design (CAD)/computer-aided manufacturing (CAM) technologies has led to the rapid development of multiple computer-aided implant planning platforms. All of these platforms require data acquisition to be uploaded into the software before their use. A digital workflow starts with the data capture in the oral and maxillofacial surgery office.
Data acquisition
Cone-beam computed tomography
CBCT has become an integral diagnostic tool in oral and maxillofacial surgery, particularly in implant dentistry. CBCT allows 3D digital radiographic data from the patient to be conveniently acquired by the oral and maxillofacial surgeon in the office setting. The CBCT data are acquired in a Digital Imaging and Communications in Medicine (DICOM) format. This DICOM data alone, in conjunction with implant planning software, has made it possible to create a virtual 3D model of the proposed treatment area, and to have a laboratory fabricate a CAD/CAM static stent to perform guided implant surgery. The accuracy of these implant surgical guides fabricated by CBCT DICOM data alone is subject to CBCT scan quality. One of the limitations with producing implant surgical guides using DICOM data alone is the relative lack of hard and soft tissue detail, which can be overcome with the addition of an intraoral or model scan of the patient.
Dual scan protocols
CBCT-generated surgical guides may be fabricated by a dual scan protocol. The dual scan protocol is used primarily for full arch reconstruction.The first CBCT scan is taken with the patient’s denture in the mouth, seated with a bite registration that may be comfortably bitten into. It is important that a well-fitting prosthesis is used for the scan. Before scanning, radiopaque fiducial markers (gutta-percha or metal balls) must be randomly applied to the denture to be used during the CBCT scan fusion. Ideally, the scan is taken with the occlusal plane of the prosthesis oriented parallel to the axial slices. Immediately after the first CBCT scan is obtained, a second scan of the prosthesis itself is performed. The denture should be positioned in a similar orientation to the scan, taken with the patient wearing the prosthesis. This dual scan protocol allows the clinician to merge the prosthesis CBCT to the patient CBCT. The data from these DICOM sets are used to compute the surface of the patient’s bone and the surface of the denture when loaded into the implant planning software, allowing the oral and maxillofacial surgeon to accurately treatment plan and create an accurate bone and soft tissue–supported static surgical guide ( Fig. 1 ).
Model scanning elastomeric impressions
Elastomeric impression materials have been very successful over the years and have good dimensional stability and accuracy. Laboratories often pour a physical impression and then scan the stone model into a box scanner to start the digital manufacturing workflow. These laboratory scanners have little research describing their accuracy; however, some have been shown to perform better in complete arch trueness compared with the last generation of intraoral scanners. Scanning an impression or model from an elastomeric impression gives the clinician the ability to create a Standard Tessellation Language (STL) file, which, when merged with the DICOM data from a CBCT scan, can be used for virtual implant planning and eventual surgical guide fabrication. It is a simple way to enter patients with conventional impressions into a digital workflow ( Fig. 2 )
