Computer-Guided Planning and Placement of Dental Implants

The goal of dental implant therapy is the accurate and predictable restoration of a patient’s dentition. These goals are best achieved when all members of the surgical and restorative team are working together on diagnosis, planning, and reconstruction. The recent introduction of new 3-dimensional (3D) diagnostic and treatment planning technologies in implant dentistry have created an environment for the team approach to the planning and placement of dental implants, according to a restoratively driven treatment plan. The team can now start with the end result, the planned tooth, and then place an implant into the correct position according to the restorative plan. The accurate and predictable placement of implants according to a computer-generated virtual treatment plan is now a reality, transferring the virtual plan from the computer to operative treatment. Third-party proprietary implant software and associated surgical instrumentation, in combination with 3D imaging technologies, has revolutionized dental implant diagnosis and treatment. This development has created an interdisciplinary environment in which communication between the team members leads to better patient care and outcomes.

Historical overview

Standard dental diagnosis involves evaluating and diagnosing patients using 2-dimensional radiographic images (ie, periapical, bitewing, panoramic, and cephalometric radiographs). Clinician acceptance of the limitations of these technologies was required in the evaluation of actual 3D problems, because few options were available. Oral and maxillofacial surgeons, because of their hospital training, have long used computed tomography (CT) scans for the 3D evaluation of facial trauma and pathologic lesions. These CT evaluations were commonly viewed in 2 dimensions as axial or reformatted frontal or coronal slices through the area of interest of a patient’s anatomy, viewed as sheets of printed films or on a computer screen. The remainder of the dental community had little if any exposure to 3D image evaluation.

The first medical-grade helical CT scanners were all slower, single-slice machines, typically based in hospitals or private radiology facilities. Today’s medical multislice CT scanners are capable of performing an upper and/or lower jaw scan in a few seconds. However, radiation exposure, the lack of familiarity and training among dentists, the size and cost of the machines, and the perceived cost-benefit ratio in patient care made them inappropriate for a dental office setting. In 1998, with the development and introduction of the New Tom 9000 (Quantitative Radiology, Verona, Italy), cone-beam volumetric tomography (CBVT/CBCT) was introduced to the dental community . Although the early machines were large, the advantages were that they produced good 3D images at lower radiation doses . The newer machines of today have a much smaller footprint and are small enough to fit into a dental office. The disadvantages were that although the radiation was less than medical-grade CT, it was larger than conventional dental radiographs and because of the reduced radiation, the images produced had somewhat less definition than medical CT. Medical-grade CT remains the gold standard for accurate 3D diagnosis . Adaptive statistical iterative reconstruction (ASIR) software has recently been reported to allow up to a 50% reduction in radiation dose in medical CT scans, without diminishing image quality . There are different average deviations and percentage error measurements for all CBCT scanners .

In the late 1980s articles discussing the use of Dentascans to evaluate the bone of the maxilla and mandible in preparation for placement of dental implants began to appear in the professional literature . Columbia Scientific (CSI) introduced the 3D Dental software in 1988. This software converted CT axial slices into reformatted cross-sectional images of the alveolar ridges for diagnosis and evaluation. In 1991, a combination software named ImageMaster-101 was introduced by CSI, which added the ability to place graphic dental implants on the cross-sectional images. The first version of Sim/Plant was introduced by CSI in 1993. This software allowed the placement of virtual implants of exact dimensions, on CT images, in cross-sectional, axial, and panoramic views. In 1999 SimPlant 6.0 was introduced, adding the creation of 3D reformatted image surface-rendering images to the software . Soon after Materialise (Leuven, Belgium) purchased CSI in 2001, the technology for drilling osteotomies to exact depth and direction through a surgical guide was introduced. SimPlant was designed as an open system to perform osteotomies for the placement of straight-walled implants from all implant manufacturers. It was not designed for the final placement of implants to depth, through a surgical guide, or for tapered implant systems. NobelBiocare (Zurich, Switzerland) introduced the NobelProcera/NobelGuide technology in 2005. This technology was introduced as a complete implant planning and placement system, for both straight-walled and tapered NobelBiocare implants. Instrumentation was developed to create osteotomies of accurate depth and direction, as well as the ability to place implants flaplessly, to accurate depth, through a guide. The system was designed for typical postimplant insertion treatment (cover screws or healing abutments), immediate loading of implants, and the fabrication of partial-arch or full-arch restorations before implant placement. In 2011, NobelClinician, a completely redesigned upgrade of the NobelGuide software, was introduced. Software from other manufacturers, such as EasyGuide (Keystone Dental, Burlington, MA, USA), Straumann coDiagnostiX (Straumann, Basel, Switzerland), VIP Software (BioHorizons, Birmingham, AL, USA), Implant Master (IDent, Foster City, CA, USA), and others are now available as well. Other implant manufacturers have developed instrument trays for the guided placement of their implants using the SimPlant software for implant planning (ie, Facilitate [AstraTech Dental, Molndal, Sweden], Navigator [Biomet 3i, Palm Beach Gardens, FL, USA], ExpertEase [Dentsply Friadent, Mannheim, Germany]).

General technology concepts

Using CT/CBCT scanners, the visualization of the height and width of available bone for implant placement, soft tissue thicknesses, proximity and root anatomy of adjacent teeth, the exact location of the maxillary sinuses, sinus septae, and other pertinent vital structures such as the mandibular canal, mental foramen, and incisive canal are possible . Variations and aberrations of normal anatomy are also easily visualized. Once images are imported into proprietary software programs (SimPlant, NobelClinician, and so forth), the clinician can then virtually plan treatment for the placement of implants according to an individual patient’s anatomy and case plan. The type and size of the planned implant, its position within the bone, its relationship to the planned restoration and adjacent teeth and/or implants, and its proximity to vital structures can be determined before performing surgery on a patient . Surgical drilling guides can then be fabricated from the virtual treatment plan. These surgical guides are used by the clinician to place the planned implants in the same positions as those of the virtual treatment plan, allowing for more accurate and predictable implant placement and reduced patient morbidity .

All of the current systems have similar restorative and surgical protocols. Upper and lower arch impressions are made, and a bite registration is obtained. Poured models are mounted on an articulator. Guided surgery requires reverse planning. The prosthodontist or restorative dentist first creates an ideal restorative treatment plan, determining the planned tooth position by creating a diagnostic wax-up that indicates the exact anatomy and position of the teeth to be replaced. This ideal diagnostic wax-up is then incorporated, by a dental laboratory, into an acrylic prosthesis, referred to as a radiographic guide, scan prosthesis or scan appliance. Depending on the system to be used, this scan prosthesis can be a partial or full denture ( Figs. 1–3 .) Most systems, other than NobelClinician, require that the planned restorations contain a 20% to 30% barium sulfate mixture in the acrylic to allow for radiopacity of the planned restorations in the CT/CBCT images. NobelClinician uses a double-scan technique with a hard acrylic scan prosthesis and gutta percha markers as reference points, with no barium sulfate. According to the individual system protocols, the CT/CBCT scan is then taken with the patient wearing the scan prosthesis. The CT scan DICOM (Digital Imaging and Communication in Medicine) images are then imported into the various proprietary software programs (SimPlant, NobelClinician, EasyGuide, and so forth). The software programs are then used to virtually place implants into their ideal position related to the planned restoration and the underlying bony anatomy ( Figs. 4–6 .) The digital treatment plan is then downloaded to the manufacturer for fabrication of a surgical guide ( Figs. 7–9 ). The surgical guide is used, with implant-specific drilling instrumentation, to precisely place the implants in the positions, depths, and angulations as planned virtually.

Fig. 1
NobelGuide Radiographic Guide, fully edentulous. Modification of a patient’s well-fitting existing denture.

Fig. 2
SimPlant radiographic barium stent, partially edentulous.

Fig. 3
EZ Guide radiographic appliance, partially edentulous.

Fig. 4
NobelGuide virtual treatment plan, fully edentulous.

Fig. 5
SimPlant virtual treatment plan, partially edentulous.

Fig. 6
EZ Guide virtual treatment plan, partially edentulous.

Fig. 7
NobelBiocare NobelGuide fabricated from treatment plan in Fig. 4 .

Fig. 8
SimPlant SurgiGuide fabricated from treatment plan in Fig. 5 .

Fig. 9
EZ Guide fabricated from treatment plan in Fig. 6 .

Many CT-guided implant planning technologies require radiopaque fiducial reference markers to be placed in the scan prosthesis that the patient wears during the CT/CBCT scan. The software uses these reference markers to virtually position the scan appliance, and with it the parameters of the planned restoration(s), to the patient’s jaw. The accurate assessment of these geometric markers can be difficult for some CBCT scanners and has the potential to add error into a precise planning system, ultimately leading to inaccurate fitting of surgical guides and error in implant placement. It is advisable to make every effort to investigate which CBCT scanners have high levels of accuracy or to use medical CT scanners when using these technologies .

General technology concepts

Using CT/CBCT scanners, the visualization of the height and width of available bone for implant placement, soft tissue thicknesses, proximity and root anatomy of adjacent teeth, the exact location of the maxillary sinuses, sinus septae, and other pertinent vital structures such as the mandibular canal, mental foramen, and incisive canal are possible . Variations and aberrations of normal anatomy are also easily visualized. Once images are imported into proprietary software programs (SimPlant, NobelClinician, and so forth), the clinician can then virtually plan treatment for the placement of implants according to an individual patient’s anatomy and case plan. The type and size of the planned implant, its position within the bone, its relationship to the planned restoration and adjacent teeth and/or implants, and its proximity to vital structures can be determined before performing surgery on a patient . Surgical drilling guides can then be fabricated from the virtual treatment plan. These surgical guides are used by the clinician to place the planned implants in the same positions as those of the virtual treatment plan, allowing for more accurate and predictable implant placement and reduced patient morbidity .

All of the current systems have similar restorative and surgical protocols. Upper and lower arch impressions are made, and a bite registration is obtained. Poured models are mounted on an articulator. Guided surgery requires reverse planning. The prosthodontist or restorative dentist first creates an ideal restorative treatment plan, determining the planned tooth position by creating a diagnostic wax-up that indicates the exact anatomy and position of the teeth to be replaced. This ideal diagnostic wax-up is then incorporated, by a dental laboratory, into an acrylic prosthesis, referred to as a radiographic guide, scan prosthesis or scan appliance. Depending on the system to be used, this scan prosthesis can be a partial or full denture ( Figs. 1–3 .) Most systems, other than NobelClinician, require that the planned restorations contain a 20% to 30% barium sulfate mixture in the acrylic to allow for radiopacity of the planned restorations in the CT/CBCT images. NobelClinician uses a double-scan technique with a hard acrylic scan prosthesis and gutta percha markers as reference points, with no barium sulfate. According to the individual system protocols, the CT/CBCT scan is then taken with the patient wearing the scan prosthesis. The CT scan DICOM (Digital Imaging and Communication in Medicine) images are then imported into the various proprietary software programs (SimPlant, NobelClinician, EasyGuide, and so forth). The software programs are then used to virtually place implants into their ideal position related to the planned restoration and the underlying bony anatomy ( Figs. 4–6 .) The digital treatment plan is then downloaded to the manufacturer for fabrication of a surgical guide ( Figs. 7–9 ). The surgical guide is used, with implant-specific drilling instrumentation, to precisely place the implants in the positions, depths, and angulations as planned virtually.

Fig. 1
NobelGuide Radiographic Guide, fully edentulous. Modification of a patient’s well-fitting existing denture.

Fig. 2
SimPlant radiographic barium stent, partially edentulous.

Fig. 3
EZ Guide radiographic appliance, partially edentulous.

Fig. 4
NobelGuide virtual treatment plan, fully edentulous.

Fig. 5
SimPlant virtual treatment plan, partially edentulous.

Fig. 6
EZ Guide virtual treatment plan, partially edentulous.

Fig. 7
NobelBiocare NobelGuide fabricated from treatment plan in Fig. 4 .

Fig. 8
SimPlant SurgiGuide fabricated from treatment plan in Fig. 5 .

Fig. 9
EZ Guide fabricated from treatment plan in Fig. 6 .

Many CT-guided implant planning technologies require radiopaque fiducial reference markers to be placed in the scan prosthesis that the patient wears during the CT/CBCT scan. The software uses these reference markers to virtually position the scan appliance, and with it the parameters of the planned restoration(s), to the patient’s jaw. The accurate assessment of these geometric markers can be difficult for some CBCT scanners and has the potential to add error into a precise planning system, ultimately leading to inaccurate fitting of surgical guides and error in implant placement. It is advisable to make every effort to investigate which CBCT scanners have high levels of accuracy or to use medical CT scanners when using these technologies .

Indications for use

Because of its precision and accuracy in implant placement, an argument could be made for the use of CT-guided implant surgery in almost all cases. As with anything in medicine, a cost/time/benefit determination must be made by the clinician, based on the circumstances of an individual case. In certain cases the increased patient and treatment planning time, the additional expense, and the additional radiation exposure to the patient may outweigh the clinical benefits. The authors have found that these technologies are most beneficial to the patient and the dental team in the following clinical circumstances.

  • Three or more implants in a row

  • Proximity to vital anatomic structures

  • Problems related to the proximity of adjacent teeth

  • Questionable bone volume

  • Implant position that is critical to the planned restoration

  • Flapless implant placement

  • Multiple unit or full-arch immediate restorations, with or without extractions and immediate placement

  • Significant alteration of the soft tissue or bony anatomy by prior surgery or trauma

  • Patients with physical, medical, and psychiatric comorbidities.

Conventional surgical guides to aid in implant positioning have been used in implant dentistry for many years. Guides of these types can be simple (ie, vacuform shells with the buccal or palatal/lingual facings of the planned restorations) or more complex (ie, dental laboratory–fabricated guides with 2-mm drill holes or metal tubes). The problem in their use is that there is no correlation in these appliances between the planned restoration and the underlying bony anatomy. This anatomic relationship can be predictably established and considered before surgery only with the use of 3D visualization and the use of computer-guided implant surgical guides.

The fabrication of a surgical guide, used in implant treatment, is determined by the patient’s anatomy and local references, such as the numbers and locations of teeth in the arch to be treated or in the opposing arch. Fewer anatomic references are present for the predictable accurate placement of implants as the length of the edentulous area increases. In a fully edentulous case, all local references are lost other than the soft tissue ridge and palate. Bone and soft tissue loss from periodontal disease and atrophy, long-term denture wear, and sinus pneumatization can make it difficult to predictably use a traditional surgical guide.

In cases for which 3 or more implants in a row are planned, concepts of implant spacing and angulations, implant parallelism in all dimensions, proximity of implants to anatomic structures, and relationships between implant positions and the planned restorations are all significant considerations for the clinician. CT/CBCT-guided surgery allows for the ideal placement of multiple dental implants according to the planned restoration(s), the relationships of implants to surrounding anatomy, and principles of ideal prosthodontic implant positioning and spacing ( Figs. 10–13 ).

Fig. 10
Lower right mandible, 3 implants in a row, virtual treatment plan.

Fig. 11
Three implants in a row, NobelGuide in place. Note Implant Mounts with attached implants placed to depth.

Fig. 12
Final posteroanterior radiograph. Note implant parallelism, different diameters and lengths, and spacing corresponding to the implant site and the planned restorations.

Fig. 13
Final individual restorations, 3 implants in a row.

Differences in x-ray machines and radiographic techniques commonly lead to distortion of anatomic structures on conventional 2-dimensional images, such as elongation, shortening, stretching, and contraction. Accurate 3D evaluations and measurements of the relationship between a planned implant and the position of the mental nerve, inferior alveolar nerve ( Figs. 14 and 15 ), nasopalatine/incisive nerve ( Fig. 16 ), maxillary sinuses, and nasal floor ( Fig. 17 ) are best visualized, evaluated, and measured using CT-generated images. In cases for which there are questions of nerve or sinus proximity related to the patient’s available bone, implants are most accurately placed using computer-generated surgical guides. These technologies minimize potential patient morbidities.

Fig. 14
Severe atrophy of posterior mandible, implant placement planned lingual to the inferior alveolar nerve.

Fig. 15
Three-dimensional reformation of Fig. 14 . Note appearance of proximity between implant and inferior alveolar nerve in lateral view.

Fig. 16
Implant placement planned in close proximity to enlarged nasopalatine canal.

Fig. 17
Severe maxillary atrophy. Implant planned in the anterior nasal spine, in close proximity to the nasal floor.

All proprietary implant planning software has the functionality to isolate the roots of teeth adjacent to the edentulous areas to aid in the accurate placement of implants between and adjacent to tooth roots in the planned sites. Some software will use virtual dots or lines to outline tooth roots ( Fig. 18 ), whereas others have the ability to alter the software’s sensitivity to Hounsfield units or isovalues to virtually remove bone from around tooth roots (known as segmentation) ( Fig. 19 ). These technologies are most beneficial when implants must be placed in tight spaces because of close root proximities, or when tooth roots are in extremely divergent or convergent relationships.

Jan 23, 2017 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Computer-Guided Planning and Placement of Dental Implants
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