Computer‐assisted implant surgeries have revolutionized modern implantology, optimizing final results. Evidence indicates that the computer‐assisted dynamic surgery method has greater accuracy and precision compared to the static method (currently most used) and this, in turn, is superior to the conventional technique (freehand). In short, the more superior the results of a technique, the more complex and expensive it is.
6.1 The Concept of Prosthetically Driven Surgical Planning
Regardless of how the implant installation surgery will be carried out, correct and accurate reverse planning must be performed and strictly adhered to during the surgical stage. As a result, the number of problems related to the lack of proper three‐dimensional positioning of the installed implants also increases significantly. On the other hand, recent technological evolution has brought advantages and solutions that favor the adequate preparation and development of the professional.
Technology has revolutionized dental practice quickly and irreversibly. For implantology, specifically, it has brought more security, speed, and predictability to treatments. Computers and software, working together, provide dentists with tools to help, both for diagnosis and for the surgical and restorative phases of a dental implant treatment. As discussed in Chapter 2, a three‐dimensional (3D) virtual patient can be created for planning dental treatments and surgeries noninvasively. In this context, digital workflow allows for sharing treatment plan data immediately with a network of other professionals, enhancing communication among patients, dentists, and dental technicians .
In the field of oral rehabilitation, digital 3D or two‐dimensional (2D) facial analyses such as digital smile design were found to be beneficial for predicting the final esthetic result. In this context, several methodologies for working with facial images of the patient during virtual treatment planning have been described in the literature [2–4]. Integration of DICOM® files from CBCT and STL files from intraoral scans (IOS) enables concomitant use of data from hard and soft tissues during virtual surgical and prosthetic planning . Among the advantages of the aforementioned methodology are virtual wax‐up tools for easy adjustment of teeth shape, size, and position along with enhanced prosthetically driven virtual implant planning [2, 4].
6.2 Static Image‐Guided Implant Surgery
The advent of treatment with dental implants has been one of the most important changes in the field of dentistry since 1983. Since then, treatment with dental implants has become one of the most predictable ways to replace lost teeth.
As a result, the number of problems related to the inadequate 3D positioning of the installed implants also increased significantly. On the other hand, recent technological developments have brought advantages and solutions that favored the preparation and proper development of the professional. Technology, as it has been doing in practically all areas of various human activities, has also revolutionized dental practice quickly and irreversibly. Computers and softwares, working together, provide dentists with tools, both for diagnosis and for the surgical and restorative phases of a treatment with dental implants.
Currently, two main methods are available for obtaining orientation of the ideal three‐dimensional positioning of dental implants during the transoperative period of computer‐assisted implant surgeries: surgery through the use of stereolithographic guides, known as static computer‐assisted implant surgery (s-CAIS), or real‐time image browsing surgery known as dynamic computer‐assisted implant surgery (d-CAIS). The latter method uses optimized continuous tracking of surgical instruments, which are equipped with infrared light emitters. Computed tomography data are still needed, as are reference markers that are used to compare the images to the actual surgical field. On the other hand, stereolithographic guides favor the reliable transfer of the surgical plane from digital images to the real surgical field. For this purpose, guided perforation models are used, helping the surgeon to obtain a satisfactory implant installation, together with prediction of the final result of the prosthesis, as well as good conditions related to soft tissue handling, emergence profile, and final morphology of the implant. In certain cases, implants can be loaded at the same surgical placement visit using esthetics or immediate loading systems.
6.2.1 Dual CBCT Scanning Technique
Guided surgery originally was indicated for full‐arch cases with guides supported by the mucosa for edentulous patients. At the time guided surgery was proposed, intraoral scanners were not widely available and software for implant planning was limited because the only format that was accepted to work with was CBCT. Therefore the only digital exam needed for guided surgery was CBCT.
Dual CBCT scanning refers to the acquisition of two exams. The first is the CBCT of the patient wearing the tomographic guide and the second is the CBCT of the tomographic guide only. Both CBCTs will be merged in the software to proceed with implant planning.
Once the alignment of both exams is complete, a 3D model of the tomographic guide is generated. This mesh will be used as a base for the surgical guide, which means that all the surface of the guide that will be in contact with underlying mucosa will be copied from the tomographic guide.
The alignment of both CBCTs can be achieved by placing gutta‐percha markers in the tomographic guide. Most software programs use gutta‐percha markers to align both CBCTs automatically. A total of five gutta‐percha markers is recommended, all of them in the flange, one anterior below the frenal notch and two posterior in each side of the tomographic guide.
In order to improve the quality of the CBCT of the tomographic guide. and the resulting surgical guides, we recommend the following.
- The thickness of the tomographic guide must be at least 3 mm to avoid holes in the surgical guide.
- The extent of the tomographic guide must be wide enough to stabilize the surgical guide during surgery.
- At least five gutta‐percha markers should be used.
- The tomographic guide must be well adapted to the mucosa. If a denture is used as a tomographic guide, it should be realigned prior to the scan to improve its adaptation and thickness.
188.8.131.52 Tomographic Guide
Fabrication and Scanning
Clinically the tomographic guide follows all steps of a denture fabrication. It starts with the wax rim to determine the correct VDO in CR, the occlusal planes and all proportion lines to guide the tooth mounting. After the tooth mounting, a consultation is needed to verify adaptation, stability, occlusion, and esthetics. Because the alignment of the teeth will be used as a reference for implant planning in the software, all teeth must be in the position desired for the final prosthesis.
The wax rim with the tooth mounting will be duplicated in translucent acrylic to make the tomographic guide and after finishing and polishing, the gutta‐percha markers are placed.
Preparation for First CBCT (Scan of Patient Wearing the Tomographic Guide)
The patient wears the radio‐guide and final adjustments are made. A silicone roll or wooden sticks can be used to stabilize the guide with occlusion during CBCT exam. Lip retractors and/or cotton rolls are also recommended to better identify the contour of the prosthesis since acrylic and soft tissue may look similar in CBCT plane cuts.
Preparation for Second CBCT (Scan of the Tomographic Guide Only)
During acquisition of the tomographic guide’s CBCT, a radiolucent base such as sponge or polystyrene may be used to support the guide. This technique will provide a clean 3D model, minimizing mesh errors.
The dual scanning technique has been used for decades in guided surgery planning. The analogue step of this technique is the fabrication of the tomographic guide to achieve a prosthetically driven implant planning. Nowadays this step can be done digitally with the acquisition of new digital exams including photographs, intraoral scanning and facial scanning.
A virtual 3D facially driven wax‐up can be incorporated into the full‐arch project and all the implant planning and guides design can use the initial wax‐up as a reference. This approach will reduce the consultations needed to create the tomographic guide, leading to just one consultation to determine the VDO and do all exams. This means time reduction for the treatment.
6.2.2 Using Combined CBCT and Intraoral Scans
184.108.40.206 Virtual Waxing
In order to carry out digital planning of the ideal position of an implant to be installed for rehabilitation of an edentulous patient, we must first determine the positioning of the prosthetic restorations (Figure 6.1).
In this way, 3D images of STL files, obtained by intraoral scanning, can be used for development of a digital prosthetic plan or tools existing in the virtual planning software for implant surgeries or, preferably, the use of specific CAD software for restoration simulations of prosthetic restorations.
Such virtual wax‐ups, created by software programs, will guide the best positioning of the implants, which in turn will support the planned prosthetic rehabilitations.
220.127.116.11 Virtual Implant Surgery Planning Software
In today’s market, there are several software programs dedicated to image‐guided surgical planning. Each has specific strengths and weaknesses. Most of these programs are third‐party (i.e., not developed by the TCFC manufacturer), such as SimPlant® (Materialize Dental Inc.), Invivo5TM (Anatomage), NobelClinicianTM (Nobel Biocare), OnDemand3DTM (Cybermed Inc.), virtual implant placement software (BioHorizons, Inc.), coDiagnostiXTM (Dental Wings Inc.), Blue Sky Plan® (BlueSkyBio), Implant Studio® (3Shape), and ExoPlan® (Exocad), among others. Among the software options developed by CBCT scanner manufacturers that offer tools for planning dental implants are Galileo (Sirona Dental Systems, Inc.), Tx STUDIOTM (i‐CAT), and NewTom (NewTom).
Currently, almost all implant surgery planning software enables the communication (merging) of DICOM images with intraoral scanning STL files. Likewise, not all implant planning software enables digital visualization of prosthetic components when planning virtual implants.
After the virtual wax‐up and subsequent virtual planning of the 3D positioning of the implants, the surgeon may decide to proceed with bone reconstruction surgeries (grafts) if detecting, by virtual planning, the impossibility of installing the implants in a good position.
It is also at this time that the dimensions and characteristics of the implants, such as type (conical or cylindrical), thickness, and length, are chosen.
Alignment of Tomographic Images and Scans
Most modern implant planning software is capable of merging intraoral scan STL files with images from DICOM files (Figure 6.2). In this procedure, the geometries of key structures are automatically recognized. The resulting images and files can be used not only to define soft tissue contours and prosthetic teeth, but also to fabricate stereolithographic models and surgical guides.
With this technology, implants and abutments can be virtually preplanned, based on virtually combined soft and hard tissue information, which facilitates the immediate loading and restoration of implants in selected cases.
Professionals working in implantology should always bear in mind that the ultimate goal of installing dental implants is to support a final prosthetic restoration. In other words, the patients are looking for teeth and not implants, and a restorative mentality must always be maintained.
Surgical Guide Design
A surgical template is essentially a transfer tool, whose objective is to transfer the diagnosis and planning of surgical and prosthetic treatment from the software to the patient, during the implant installation surgery.
Precise surgical guides, produced using CAD‐CAM technology, require a very careful treatment plan. The basis of surgical guide design starts with a well‐conceived prosthetic design, taking into account the patient’s needs, desired esthetics, and functional results.
The surgical guide will enable the clinician to perform the surgery with maximum precision, transferring the design carefully conceived during the planning phase to the patient’s mouth.
There are numerous techniques, software, and procedures that have been developed to carry out the entire process of virtual implant and prosthetic planning. The main initial imaging requirements are:
- CBCT DICOM dataset
- intraoral surface scan dataset (STL files)
- virtual planning of implant positions.
Combining this set of tomographic data, intraoral scanning, and virtual implant planning with specific software (e.g., in a single file) will provide all the necessary information for preparation of the surgical guide.
Most dedicated and specific software programs for the virtual planning of implant surgeries have tools that enable the virtual creation of the surgical guide and ensure that the STL drawing of the surgical guide is then saved and exported to a CAM device (Figure 6.3), which will then produce the surgical guide that will be used transoperatively in order to transfer the chosen position prior to the implant.
Surgical guides are usually in the form of acrylic plates and are designed to fit into the patient’s oral cavity during surgery. Most surgical guides have small metal objects called “sleeves” inserted in the exact place where the implant is to be inserted, in order to guide the direction of implant perforation, as well as limit the maximum depth that the implant must reach physically in the bone.
Surgical guides must contain openings, called “inspection windows,” at different points of their structure, through which the surgeon can assess the correct seating of the guide during the operation.
There are three categories of guides, according to the type of intraoral support used during the transoperative period, which is extremely important to achieve stability and precision.
- Teeth‐supported guides, which use the remaining teeth to anchor the surgical guide in place.
- Guides supported on the mucosa, which will receive support only in the soft tissues.
- Bone‐supported guides, which will necessarily be fixed in direct contact with the bone.
Mucosal and bone‐supported guides must always be used in conjunction with fixation pins directly inserted into bone to help stabilize the guide.
Overall findings conclude that mucosa and teeth‐supported guides provide more reliable support.
Preparation of the Surgical Guide
The CAD‐CAM fabrication process can be performed via additive 3D printing processes, such as rapid prototyping (RP), or subtractive fabrication (computer numerical control [CNC] machining; milling).
Subtractive fabrication is a generic term for various controlled machining and material removal processes that start from solid blocks, bars, plastic rods, metal or other materials, which are molded by material removal through cutting, milling, drilling, and grinding.
The construction data produced with the CAD software is converted into milling tracks for CAM processing and finally loaded into a milling machine. This typically involves computation to control the CNC milling process, including features such as sequencing, milling tools, and tool motion direction and magnitude.
Due to the anatomical variations of dental restorations, milling machines often have different sized drills. Milling accuracy is within 10 μm. There are three‐, four‐, and five‐axis milling devices.
A three‐axis device has degrees of motion in three directions of the orthogonal plane. Thus, the mill waypoints are uniquely defined by the X, Y, and Z coordinates. The advantages of these devices are short milling times and simplified control via the three axes. As a result, such machines are generally less expensive than those with four or five axes.
With a five‐axis milling device, in addition to the three spatial dimensions and the rotating tension bridge (fourth axis), there is also the ability to rotate the milling spindle (fifth axis).
Three‐dimensional printing enables the fast and automated fabrication of physical objects directly from computer‐drawn, virtual 3D design data without a significant planning process related to part features and geometry.
This technology was initially configured to increase the speed of prototype fabrication in the manufacturing industry. Recently, it has also been used for different applications in the fields of medicine and dentistry.
Additive 3D printing techniques that can be used to produce a surgical guide include SLA, digital light projection (DLP), jet printing (PolyJet®/ProJet®), and direct laser sintering (DLMS)/selective laser sintering (SLS). To produce the surgical guide, the STL file of the guide should be imported to a slicing software, as previously discussed in Chapter 3. An adequate and resistant light‐cured resin should be used to fabricate the guide (Figure 6.4).
In relation to the two types of manufacture of surgical guides mentioned (additive and subtractive), there is evidence that those produced by additive methods have better adaptation to the seating surface and its support.
The surgical guide tested in the mouth to confirm its correct adaptation must undergo chemical disinfection, through submersion in an alcoholic solution at 80% for a period of 15 minutes or chemical sterilization using ethylene oxide, depending on the material used to make the guide. The process of chemical sterilization by ethylene oxide involves high temperatures, which can cause distortions and dimensional changes in the guide.
The anesthetic blockade of the region of interest is performed, always controlling the volume of anesthetic liquid injected into the submucosal region, because with the change in the volume of the mucosa, it may be difficult or even impossible to adapt and settle the surgical guide, especially in cases of fully mucosa‐supported guides. The fully muco‐supported surgical guides or those with bone support, after being adapted with the aid of occlusion indexes, must be fixed using anchorage pins (see Chapter 7).
It is noteworthy that guided surgery is not synonymous with “flapless” surgery. What determines whether a surgery should be “flap or flapless” (open or closed) is the width of the band of keratinized tissue in the region chosen as the impact point for implant insertion. Therefore, if there is enough keratinized tissue, the surgery can then be flapless.
Once the surgical guide fits with stability, the osteotomy sequence for the preparation of the implant sites can be started, using the specific order of drills of the implant system and model chosen (Figures 6.5 and 6.6). The same guide can also be used to place the dental implant (Figures 6.7 and 6.8). All the above‐mentioned steps are illustrated in the case report below.