Implant surgical procedures have more or less remained the same since the introduction of osseointegrated dental implants. Briefly, implant placement surgery involves the use of a full-thickness flap elevation and a sequential series of drills with increasing diameters under profuse irrigation to create a precise osteotomy site in the bone for the placement of a dental implant (see Chapter 75). The site is prepared, and the implant positioned to avoid important anatomic structures, such as the inferior alveolar nerve, sinus cavities, and teeth, and to optimally support and emulate the planned prosthetic tooth replacement(s). Proper implant position is important for optimal function and esthetics.
Clinicians determine implant positions based on presurgical diagnostic imaging, study models, and the use of a diagnostic wax-up of the planned tooth replacement(s). The actual or final position of the implant(s) results from the surgeon’s interpretation of diagnostic information and his or her ability to translate that information to the patient at surgery. Most often, the surgical “guide” between the diagnostic information and the patient is an acrylic stent, fabricated by a laboratory technician that may or may not have precise guide channels for implant positioning. Consequently, inaccuracies in the stent fabrication and movement of the stent during surgery, as well as variations in the use of the stent during surgery, can lead to imprecise implant positioning.
• Computer-imaging software used preoperatively to “simulate” the implant position(s) into a virtual patient, that is, a three-dimensional (3D) computer image of the patient’s jaw created from the computed tomography (CT) scan data.24
CAIS is the most sophisticated and perhaps the most promising of these technologies because it has the greatest potential to reduce surgical time, minimize surgical invasiveness, and result in a more precise translation of implant planning to the actual surgical procedure.23 CAIS immediate mapping has the advantage of an immediate chairside procedure, which can be performed without CT scan images. Understandably, CAIS is also the technique that requires the greatest amount of preparation and coordination of the patient, image data, and surgical instrumentation. This chapter provides a conceptual overview of the techniques and terminology used in CAIS.
Computerized navigation surgery evolved from early applications in neurosurgical procedures and continues to evolve today with applications in many surgical specialties.17,19 Clearly, the advantage of using a computer to assist surgery is the precision that it offers. There is also a real-time safety control obtained with multiple imaging sources facilitating a minimally invasive approach to surgical procedures. As in medicine, 3D imaging is used in dentistry to facilitate presurgical planning and to guide the surgical placement of dental implants. This allows precise positioning while avoiding injury to nearby important anatomic structures. Several different approaches to computers have been used in dental implant surgery, from simple imaging software to visualize the implant positions in a 3D virtual patient to more complex, simultaneous image monitoring and instrument navigation used to perform surgery.6
The use of CAIS requires precise and continuous coordination of the patient, the image data, and the surgical instrumentation. Therefore CAIS requires an accurate alignment (identification and registration) of the patient with the patient’s image data (contact probe or ultrasound 3D mapping CT scan data) and a system of tracking the precise movements of the surgical instrumentation (e.g., handpiece, drills) in relation to the actual patient. A variety of systems have been developed to acquire and register image data and to coordinate and track movements. These methods are described in the following sections.
1. Data acquisition. The patient is scanned for image data acquisition (e.g., CT scan) with fiducial (artificial) radiographic markers (e.g., stent with markers or intentionally placed pins or screws into jaw) or anatomic (natural) markers such as teeth or bony landmarks. If fiducial markers are placed in a stent, the patient must have it in place when scanned.
2. Identification. The anatomic or fiducial markers will be identified with a probe tracked by the system. If markers were incorporated into a radiographic stent, the stent will again be placed in the mouth and the markers identified by hand with a probe tracked by the stereovision system.
3. Registration. After identification of the predetermined markers, the software will indicate the best localization or “match” on the arch between the image data and the patient. If registration is not validated, matching can be improved with additional points. An invalidated registration may be caused by an improper initialization or CT scan data.
4. Navigation. Ultimately, the operator will be able to visualize surgical instrument navigation (movement). The drilling instruments will be guided to a target point of impact with a 3D spatial orientation.
5. Accuracy. Sustained accuracy procedures are critical during surgery and should prove reliability in regard to the system’s overall accuracy. This sustained accuracy procedure will be done through contact of the drill on the handpiece with selected teeth, by visualization of markers, which can be viewed by the stereovision system, or repositioning of the radiomarker stent.
1. Preparation for 3D mapping data acquisition. A removable attachment (bracket or similar device) is stuck on a nonmobile tooth to support infrared markers for a 3D real-time tracking of the patient position. If no teeth are available, a mini implant can be placed to hold a bracket. Any other tool with its tracking device will be localized, in real time, with the patient position. These tools and patient position will generate data in the same referral time and 3D space.
a. Anatomical 3D contouring with a contact probe or a similar device. Tracking cameras are scanning in an infrared light environment, while reflecting markers (rigid body) are connected to a contra angle through a rigid mount. The contact probe can be a regular drill and its tip will draw lines to contour teeth surfaces or a bone socket in case of extraction. Because a 3D mapping is recorded at the same time as the patient is positioned, the inaccuracy is limited to the maximum deviation (0.3 mm) of the camera’s tracking systems.
b. 3D Ultrasound bone and root contour acquisition. An ultrasound probe depth provides a bone surface mapping, point by point, with a maximum deviation of 0.2 mm for 10 mm of soft-tissue thickness. With this technology of 3D bone and soft-tissue mapping there is no need to match images.
4. Accuracy. Sustained accuracy procedures are easily performed in a 3D mapping real-time system by a contact on a tooth or a bone surface. In case of discrepancy the system can be reset rapidly to provide a real time safety.
CT scans and the more-recent cone-beam CT (CBCT) scans are widely used for 3D patient imaging (see Chapter 73). Factors that must be considered when deciding to use a CT scan include radiation exposure, limitations in accuracy, and the possibility of diffracted images as a result of metallic restorations. The evolution of scanner technology (spiral CT scan, CBCT scan) has made it possible to reduce the radiation dose to the level of a conventional panoramic radiograph while maintaining adequate diagnostic quality for preoperative implant planning.9
Similar to implant planning using conventional diagnostic methods, radiographically identifiable markers are important for CAIS. However, unlike conventional planning, in which orientation and simulation of implant positions are related to the planned prosthetic crown positions, CAIS markers must relate the image data to the actual patient anatomy. In other words, the position of the surgical instrumentation (and ultimately the implant) must be related to the scan image data of the patient’s jaw morphology. Thus it is critically important to scan the patient with markers that are identified in the scan and correlated to the patient at surgery. Markers can be anatomic markers, such as teeth or specific bony landmarks, or artificial markers (fiducial), such as small tacks or screws that are secured in the bone.
Chairside real-time synchronization between 3D images (contact probe and ultrasound) and patient position allows a real-time accuracy and, in case of mismatch, the ability to perform a new chairside 3D acquisition at any time during the procedure. This accuracy depends on a rigid body tracking system with a maximum deviation around 0.3 mm without artifacts or deviations that can occur with CT scan or CBCT. An ultrasound surface mapping4 will not provide internal structure images, except root contours and the sinus floor. However, the distance from the alveolar crest to the nerve canal can be evaluated on 2D X-ray, transferred precisely to the extracted 2D image from a 3D mapping image. If needed 3D X-ray images can be superimposed on the ultrasound or probe mapping.8,22