Guided dental implant surgery through dynamic navigation is evidence based, has undergone significant change, and literature supported with accuracy comparisons to freehand and static guide placement. Workflows and technological explanations with review of 2 prominent dynamic navigation systems in use today are explained. After a review of accuracy studies and technique considerations, the reader can appreciate the benefit of image-guided dental implant drilling and placement.
Key points
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Dynamic navigation can drill bone, place a root form implant into bone with accuracy, and be a model-less workflow.
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Implant placement protocols such as dynamic computer-aided implant surgery (static computer-aided implant surgery/dynamic computer-aided implant surgery/mental navigation) are widespread, and survival rates compare.
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Dynamic navigation developed in dentistry to help clinicians obtain a more accurate match between implant placement and the preoperative plan.
Introduction/Background
Implant placement protocols such as dynamic computer-aided implant surgery (static computer-aided implant surgery [sCAIS], dynamic computer-aided implant surgery [dCAIS], and mental navigation are widespread and survival rates compare. Movement from freehand to partially or fully guided dental implant surgery with the possibility of guided prosthetics has become a reality. In the early days of implant dentistry, freehand techniques with analog restorative procedures were the only practical options available. Gradually, cone beam imaging was introduced, and it revolutionized dental implantology progressing from being an examination/planning tool at first to eventually morphing in to becoming useful for computer-aided surgery/prosthetics. With the invention and vision for better hardware, better software, optical scanners, and the ingenious fortitude of achieving dentists, scientists, and our corporate partners, it has become clear and the opinion of many that guided dental implant surgery can improve safety, provide optimal implant tridimensional (3D) positioning, decrease morbidity, and offer better control of prosthetic outcomes. In dentistry, static-guided surgery was first and then dynamic surgery appeared. Dynamic navigation (DN) developed in dentistry to help clinicians obtain a more accurate match between implant placement and the preoperative plan. This study reviews the latest advances in dental implantology placement and restoration strategies.
Discussion
Data Acquisition, Planning, and Design
The introduction of cone beam computed tomography (CBCT) digital imaging and communications in medicine (DICOM) data sets in to dentistry along with 3D implant planning software, coupled/merged with various scanning technologies, can be referred to as data acquisition. Modern data acquisition can include physical records, digital records ranging from cone beam scanning to include intra/extraoral scanning, face scanning, jaw motion, and photogrammetry. Digital technology with implant planning software can provide outstanding outcomes with proper training and experience. Optical scans or other data obtained can be merged with cone beam data (CBCT), intraoral scanning (IOS),or extraoral scanning (EOS) leading to prosthetically driven treatment planning, a cornerstone of modern treatment planning, surgery, and restoration. Various scanning protocols have been introduced, based on patient presentation, to acquire the appropriate data to plan cases, execute surgery, and to restore the patient with digital workflows. Moreover, computer-aided design (CAD) with computer-aided manufacturing (CAM), with both milling and fabrication, is common in modern dental practice, both in restoration fabrication and in surgical guidance design (static, dynamic, and robotic).
Cone Beam Resolution and Field of View
There are no strict guidelines on cone beam resolution for guided surgery. Many sources often cite implant planning with a 200 μm detector slice thickness, while exceeding a layer of 1,000 μm may result in considerable inaccuracies. High-quality imagery is advised for improved performance. Emery and colleagues in 2016 utilized a 0.3 voxel resolution to compare postoperative position to preoperative position of implants. Field of view (FOV) is selected to be no larger than necessary following as low as reasonably achievable (ALARA) principles, and to avoid lag in computer data processing. A recent study showed for sCAIS, a small to medium FOV was not different in accuracy from a larger FOV. Utilizing a sCAIS approach, a quadrant scan without scatter with an IOS that merges may work for sCAIS design in best case scenario. As for dCAIS, a full dentition FOV is better. For dCAIS, an arch FOV is a reasonable choice because being able to secure a patient tracker contralaterally while drilling ipsilaterally, and to be able to register spread out anatomic coordinates being the considerations with imaging size selection.
Prosthetically Driven Treatment Planning
Placing dental implants according to functional, esthetic, and prosthetic requirements is referred to as prosthetically driven treatment planning. Planning and placing dental implants in proper position facilitates better hygiene, adequate componentry space, knowledge of implants and abutments to stock, better screw channel location, better emergence profiles, improved esthetics and hygiene, and occlusal design. Virtually planning the prosthesis with implants/components in the software allows for matched outcomes in both surgery and restoration. Optimal position should be a treatment goal since it facilitates restoration and maximizes esthetics. Vital to understanding, clinicians plan osteotomies, not implants.
Guided Surgery for Biologic Reasons (mm/metrics)
A plethora of implant-to-adjacent structure metric distances is supported by literature. Improper implant positioning clearly has bearing on biologic outcomes. Monje and colleagues conducted a clinician’s survey and concluded implants placed too buccally can contribute to peri-implantitis. Canullo and colleagues concluded peri-implantitis can be surgically triggered by malpositioned implants. Metrics that are well known include Spray stating 1.8 mm of facial bone beyond the implant periphery serves to prevent future bone loss. Recommendations by Tarnow advise an inter-implant distance of 3 mm to avoid peri-implant loss and achieve inter-implant papillae. Tarnow also demonstrated proximal contact to implant platform depth metrics for papilla forming metrics and literature also supports a minimum of 1.5 to 2.0 mm distance of implant to tooth for interproximal bone maintenance. In his radiographic retrospective analysis, Tarnow concluded a 3 mm minimum metric for inter-implant distance in the esthetic zone. This horizontal metric, at the inter-implant shoulder, can reduce crestal bone loss. Smith and colleagues showed implant-to-tooth distances of 2 and 3.5 mm fared better in preventing adjacent decay, compared to the horizontal distance of 6 mm or more to an adjacent tooth demonstrating a 40% increase in caries. Smith and colleagues further concluded a 4 mm horizontal placement threshold be considered safe for implant-to-tooth distance. In support of these recommendations, parallax error in freehand mental navigation can be avoided with guided surgery, for molar implant replacements to help prevent adjacent proximal, cervical, and root caries. Moreover, esthetic outcomes can be predictably achieved with guided surgery coupled with preplanned knowledge that bone augmentation may not be necessary.
Another consideration to guide surgery rests on determining case complexity. Colombo and colleagues in 2017 described a simple case as having 7 mm bone width/9 mm height and complex cases as having bone width of less than 7 mm with height between 7 to 9 mm. Interestingly, his commentary stated that more complex cases were treated with guided surgery. Furthermore, he stated that there were not any failure differences between conventional freehand and guided groups. Because surgery can also be stressful for the clinician, mental anxiety can be considered a clinician’s biologic metric. Anxiety can simply be defined as “fear of the unknown”; therefore, having a plan and the use of guided surgery can decrease mental anxiety through preplanned outcomes.
Turning our focus to image-guided surgery (IGS), we have another computer-based method to guide surgical outcomes to control how we cut or make holes in bone for various treatment planning needs. Recently, in the dental field, DN was introduced to endodontics for guiding nonsurgical and surgical applications. In oral and maxillofacial surgery, DN is utilized to guide where to osteotomize bone for various surgical procedures. DN is used extensively in implantology to prepare osteotomies and to fully guide placement of dental implants. Our focus will be centered around IGS with the application of drilling osteotomies and placing dental implants.
Equipment/Explanation: Image-Guided Surgery/Dynamic Navigation
While many software companies have come and gone, surviving companies are in next-generation development because of their proven efficacy and accuracy. IGS requires a rigidly affixed tracker to be separately attached to the patient and to the surgical handpiece. Under camera optics, handpieces are calibrated and the patient’s anatomy is physically registered. Accuracy touch point system checks are also performed under optics with a probe or calibrated drill tip. The affixed pattern array or sensors transmit 3D position information from the overhead camera, which allows the computer to instantaneously calculate and display the virtual position of the instruments relative to the stored image of the patient’s hard CBCT anatomy. This process is similar to global positioning system (GPS) transportation, like a satellite tracking movement against a stored map. DN is described as real-time, optically guided, computerized camera tracking of the operator’s handpiece/drill. This kind of IGS was coined as “dynamic,” as the constant changes in the operative field are reflected live on the visual monitor. DN allows for real-time verification of position accuracy allowing clinicians to adapt or change their surgical planning during surgery. There is no need for a specific set of drills or instruments, and the surgeon’s perception of the drilling sequence and implant placement, unlike a surgical guide , DN does not affect haptic feedback bylimiting tactile perception.
A DN system’s proprietary software can be utilized to virtually plan implant positions in the patient’s skeleton so that physical surgical guidance of a handpiece with drill bit can occur to both drill and perhaps also to place an implant at the software’s preplanned position, angle, and depth into bone. Third-party software can also be used to plan, if DN system compatible, and simply exported to the DN system. This method of planning can sometimes offer advantages. Similar to all computers, the software controls the hardware. Currently available DN systems include X-Nav, Navident, DENACAM, and others. The software allows hardware such as cameras to track calibrated markers firmly attached to the patient and to a handpiece with incredible processing speeds. The surgical handpiece and patient-tagged positional information are relayed to the proprietary navigational software found inside the computer’s hardware to compute and provide drill tip position on the display screen, along with handpiece/drill angulation related to the patient’s hard tissue arch anatomy. Simultaneously superimposing that over the software’s virtual CBCT with the virtual implant osteotomy plan. In computer-guided dental implant surgery, one arch is typically treated at a time. However, if the opposing arch is also being treated during the same surgical session, a simple recalibration process is necessary. This involves recalibrating the tagged handpiece and the opposing arch’s patient tracker, which is securely attached with a tracer probe or fiducial. This quick step registers the opposing arch’s CBCT hard anatomy data to the surgical equipment and plan, ensuring accurate implant placement. A physical to virtual match, in real time, occurs to track the drilling and cutting of bone to “drive” the plan. The information is displayed and watched on the computer monitor. Noteworthy, computed tomography/ computer-aided navigation is not new, as DN has been used for decades in spinal surgery, orthopedics, ear nose & thorat (ENT), and other disciplines. Robodent introduced DN in the early 2000s, developed by Lueth and Bier, at Humboldt University. In the beginning, because most private practices did not have CT scanners, it was not feasible because of cost, concerns with accuracy, and many dental clinicians lacked training in digital technologies. CT scanning evolved with the cone beam shape containing isotropic voxels and then with competition and costs declining of CBCT machines, running tandem with improvements occurring in DN; these 2 circumstances allowed for DN to reestablish itself (pg. 330 Nicolas GC Fahey textbook “Guided Surgery”).
Importantly, DN of the osteotomy can be a model-less workflow. Model-less workflows can happen by use of a CBCT machine, optical scanning, photogrammetry, or other scanning protocols along with a DN system or third-party planning software to plan and export to live dynamic surgery. Moreover, DN lends itself to advanced digital restorative workflows to complete the final restoration. DN can be used to place dental implants for implant-supported dentures, single or multiple fixed implant restorations, including full arch protocols. DN has not been Food and Drug Administration (FDA) cleared for various remote-form anchorage implants including pterygoid, transnasal, transsinus, or zygomatic form implants. In addition to drills, DN can also be used to guide piezo saw tips.
Calibration, Registration, and Accuracy Checks Summarized
Calibration and registration are critical processes with DN setup and usage. However, accuracy touch point checks with DN are the cornerstone of safe navigational guided surgery outcomes. Accuracy checks are the physical to virtual link during all navigational operations and must not be underutilized and interpreted as correct with objectivity and subjectivity. Scoring and displays occur with X-Nav registration processes. An orange radial-diametric “sphere of accuracy” symbol is displayed, along with also including disparity scores upon registration, recommended to be less than ±1.0, while spread scores are also displayed and encouraged to be as large as possible, preferably greater than 14, but not necessary. Scanning and planning, calibration of tools, registering anatomy, calibrating the drill measurement, performance of system accuracy checks, in that order, are the workflows for DN to proceed to live surgery to drill and to place the implant. Modern DN offers a significant advantage by employing direct anatomical or biological registration. This approach surpasses traditional indirect methods that rely on synthetic devices or fiducials worn when making CT scans. Direct registration ensures accurate alignment with the patient’s unique anatomy, enhancing precision and minimizing errors (refer to Figs. 1–17 for detailed illustrations).
