8
Guided Surgery for Placing Immediate Implants using Standard Osteotomy Preparation or Osseodensification
Arndt Guentsch
Introduction
Successful immediate implant placement (IIP) and provisionalization requires optimal three‐dimensional (3D) implant positioning to achieve adequate primary implant stability and allow for an esthetically pleasing and stable implant restoration. Outcomes of IIP can be affected by patient‐ and implant‐dependent factors as well as by the level of expertise of the clinician. Patient‐dependent factors include the length, diameter, and sagittal position of the tooth root, the proclination and concavity of the labial bone, and the available alveolar bone width and height. Implant‐dependent factors to consider are shape, length, and diameter [1]. Guided implant surgery (GIS) improves the accuracy of implant placement [2–4] for both experienced [5] and novice clinicians [6]. While it is a useful complement to conventional surgery, GIS does not replace surgical experience, skill, and knowledge of anatomy [7]. However, proper implementation of GIS methodology can increase the level of agreement between the planned and definitive 3D implant positions thus enhancing esthetic outcomes [8].
Compared with pilot drill‐only guided techniques, fully guided surgical procedures, with their higher degree of guidance, can result in more accurate reproduction of the digitally planned implant position into the final post‐surgical position [4, 9, 10]. It allows accurate 3D implant placement based not only on bone availability [11] but also on the ideal prosthesis position [12], increasing the predictability of a favorable emergence profile with ideal soft tissue esthetics [13].
Amorfini et al. [14] compared soft and hard tissue outcomes following freehand versus fully guided surgery in replacing maxillary anterior teeth with single dental implants. They concluded that fully guided surgery delivered more optimal esthetic outcomes with better soft tissue results over time. The high accuracy between planned and final post‐surgical implant positions can make guided surgery the ideal procedure for immediate placement with immediate provisionalization and even immediate “loading”. Additionally, fully guided surgery ensures short intraoperative and provisionalization times with lower incidences of intra‐ and postoperative complications [14].
Malpositioning of dental implants is one of the main reasons for future unfavorable bone and/or soft‐tissue changes [15], can present a restorative challenge, might result in compromised esthetic results [16], and can hinder cleaning which may lead to future peri‐implant inflammation and even implant failure [17]. Indeed, Romandini et al. [18] identified implant malpositioning as the main risk factor for peri‐implant soft‐tissue dehiscence followed by thin peri‐implant phenotype. Possible immediate surgical complications arising from malpositioning can include nerve damage, perforation of a cortical plate, or even damage to adjacent teeth [19]. By combining digital technology, precise planning and real‐time guidance, guided implant placement enhances the success and efficiency of “immediacy” while minimizing patient discomfort and overall treatment times.
Digital Workflows in Implant Dentistry
Digital technology is omnipresent in today’s dental practice and found its way into implant dentistry with the introduction of digital workflows through diagnosis, treatment planning, and computer‐assisted surgery. The use of surgical stents to translate implant positioning from treatment planning casts [20], allowing the surgeon to determine optimal fixture positioning [21], was introduced in the 1990s. This cast‐based technique was driven by ideal final prosthetic positioning. Clinicians relied on two‐dimensional radiographic imaging techniques to evaluate critical anatomical structures and manual palpation to assess alveolar ridge dimensions. However, the use of two‐dimensional imaging was a limitation, increasing risk of complications such as damage to vital structures due to superimpositions and both under‐ and over‐estimations of their locations and dimensions [22, 23].
With time, 3D imaging modalities created for dentomaxillofacial applications were introduced as a replacement for conventional computed tomography (CT) [24]. Cone beam computed tomography (CBCT) allowed for volumetric jawbone scans with a reduction in radiation and cost as well as greater accessibility to practicing dentists. This technology has given the clinician the ability to evaluate potential surgical sites and to plan the placement of dental implants in three dimensions accurately prior to booking surgeries. It can also be used for computer‐aided design (CAD) and computer‐assisted manufacturing (CAM) to plan for the optimal restoration by overlaying collected information onto the patient’s CBCT file [25].
There are three different main approaches with CAIS (computer‐assisted implant surgery) based on digitally planned implant positions: (i) designing a static surgical guide and using it as a template to direct drills during osteotomy preparation with or without placing the implant through the guide [26]; (ii) using virtual navigation systems with cameras to monitor the 3D position of the operator’s handpiece in relationship to the site while performing the osteotomy [27]; or (iii) robotic systems where controlling the drilling process is devolved to a computer program [28, 29]. While the latter two approaches might be technologically more advanced, they have yet to show clinical superiority over static surgical guides [30]. In fact, robot‐assisted implant surgery has shown less accuracy than static computer‐assisted surgery in a bench test study, with multiple violations of the recommended 2‐mm safety margin at the implant tip [29].
Low costs for planning and digitally producing static surgical guides [31] makes this approach a user‐friendly tool to facilitate accurate implant surgery while mitigating surgical risk [32]. Appropriate digital workflow includes: (i) proper diagnosis and case selection; (ii) data acquisition; (iii) virtual treatment planning including guide design; (iv) guide production; and (v) CAIS (Figure 8.1). The design and production of an immediate provisional or individualized healing abutment based on the virtual implant position also can be implemented in this described workflow.
Figure 8.1 Digital workflow in guided implant surgery. Tx, treatment.
Data Acquisition
Planning for optimal 3D implant positioning will be based on the radiographic information provided by pretreatment CBCT. However, the surgical guide and the registrations for dynamic or robot‐assisted surgery rely on digital impressions of the actual intraoral situation. The CBCT provides detailed 3D radiographic images, allowing for the assessment of bone density, neighboring anatomic structures, and potential challenges (see also Chapter 2). Previous dental procedures, including existing restorations and prior implants, can produce scatter and beam‐hardening artifacts which decrease the diagnostic quality of the images. However, changes to the scanning settings and patient positioning can lessen these artifacts. CBCTs do have limitations in precisely differentiating soft tissues [33]. However, using lip retractors or placing cotton rolls in the vestibule, especially in the area of interest and adjacent to edentulous areas, can help later to align the optical scan information with the CBCT [34]. The patient should also bite on additional occlusally located cotton rolls posteriorly, it being important that the patient is not in actual occlusion during the CBCT scan. The visible structures in both the CBCT and optical scan data sets are the teeth which function as clinical markers. Having a clear outline of crown shapes will later reduce potential errors in merging these data sets. The field of view (FoV) should be limited to the dental arch or sextant in question and extend apically to just beyond the inferior border of the orbits in maxilla or inferior border of the mandible in a mandibular scan. A voxel size of 0.3–0.4 mm is adequate to provide CBCT images of acceptable diagnostic quality for implant treatment planning [35]. Most available implant planning software require a set of single file Digital Imaging and Communications in Medicine (DICOM) data for 3D reconstruction.
Intraoral Surface Scan (IOS)
Soft and hard tissue intraoral anatomy is captured using: (i) a traditional dental impression followed by extraoral digitalization using an optical scanner; (ii) pouring a cast and digitizing the cast with a laboratory scanner; or (iii) direct intraoral use of a scanner. This information is apprehended in digital Standard Tessellation Language (STL) file in Object (OBJ) or Polygon (PLY) file format. The latter file format stores color information in addition to 3D anatomy.
Recent enhancements of commonly available intraoral scanners and software now allow intraoral scans to be as accurate as conventional dental impressions [36]. The intraoral scanner systems create 3D models by “stitching” multiple captured images together [37]. The scanning strategy in taking the digital impression, (i.e. how the full arch is captured with an intraoral scanner) has a significant impact on accuracy of the collected data. Scans should start from the occlusal surface of the most posterior tooth of the right or left side of the jaw and move along the occlusal surfaces towards the anterior teeth, which can be captured with an alternating labiolingual movement and continued onto the occlusal surfaces until the most posterior tooth of the contralateral side is reached. The scan is then completed with capturing of all buccal and oral surfaces [38, 39]. The quality of this digital impression will impact subsequent alignment with the CBCT. Double‐imaging or missing segments of the intraoral scan, or a low quality of physical models when they are digitized in the dental laboratory, will affect surgical guide fit or the registration with dynamic or robot‐assisted implant systems. Drying the scan area and avoiding direct illumination with operatory light can optimize the scan quality.
Virtual Treatment Planning
A plethora of implant planning software is available commercially. When deciding on a particular software, the clinician should consider that it: (i) is open to allow seamless import of DICOM and STL, OBJ or PLY files from different sources and the unrestricted export of the planned surgical guide as an STL file; (ii) provides check stops for the clinician when artificial intelligence (AI) tools are being used to confirm or adjust AI‐supported planning steps; (iii) allows for a digital wax‐up to simulate the future restoration and has an import and export function for CAD files; (iv) has an open and frequently updated database of implants, sleeves, and abutments; (v) includes a virtual tooth extraction tool or has the capability to edit the STL mesh, this being especially helpful when planning immediate implant cases; and (vi) provides a case export or exchange tool for communication with the dental laboratory or other providers.
While there might be nuances in the planning steps depending on the software being used, the following describes the common main steps in virtual implant planning:
- Data manipulation:
- Importing the CBCT (DICOM files) into the software.
- Setting the occlusal plane, panoramic curve, and segment teeth in the CBCT.
- Importing STL, OBJ or PLY files of the jaw and merging them with the CBCT data.
- Performing virtual tooth extraction or punch STL mesh.
- Wax‐up and 3D implant positioning:
- Importing the digitized wax‐up, doing a virtual wax‐up or using an existing crown as orientation.
- Selecting implant and positioning accordingly.
- Guide design:
- Selecting the guidance sleeve depending on the guided system being used, implant diameter, and space availability.
- Designing the guide and exporting it as an STL file for guide production.
Most of these steps, including segmenting the teeth in the CBCT, tracking neurovascular canals, setting the panoramic curve, aligning the optical impressions with the CBCT, and performing a virtual extraction of an existing tooth or root can be prepared with the assistance of AI tools [40].
Data Manipulation
The CBCT data are imported into the planning software as DICOM files (set of single files), allowing the software to construct a 3D image of the maxilla or mandible or both. For proper viewing of the CBCT, most software allows adjustment of the patient coordinate system in all three dimensions to have a leveled occlusion in the sagittal, coronal, and axial planes. The panoramic curve is set typically through the center of the teeth (pulp chambers are good landmarks for orientation) following the natural arch of the dentition. This will impact the rotation around the planned implant position. Lastly, the CBCT data need to be prepared for registration with the 3D intraoral scan file formats (STL, OBJ, or PLY). Since the teeth are clinical markers visible in both radiographic and optical scans, they must be segmented in the CBCT. This creates a 3D mesh of the teeth that can be merged with the 3D mesh of the optical scan. In mandible, the intra‐alveolar nerve (and if desired, any accessory blood vessels) can be tracked and marked to provide a safety feature. This virtual segmentation process allows for the differentiation of anatomical structures from one another. It also can help in reducing image distortions affected by motion artifacts and scattering [41]. Some or all of these preparative steps can be automated depending on the sophistication of the software (Figure 8.2a–d). However, any intelligent features in the planning software do not replace a critical review of the 3D image and clinical judgement of the surgeon.
After these preliminary steps have been completed, CBCT information about the socket condition needs to be carefully assessed to determine if sufficient bone volume is available to allow immediate implant placement (see Chapters 1 and 2 for more detail). The status of the facial bone wall plays a crucial role in esthetic outcomes and long‐term success. CBCT scans can be used to assess the condition of the buccal plate, although metal artifacts or root canal fillings can sometimes obscure the images. Detecting thin bone structures has also shown to have a low reliability [42]. Additionally, the facial bone wall can be damaged during the extraction procedure itself. Consequently, a definitive evaluation of the facial bone should be conducted after the tooth extraction to ensure proper management and treatment.
Clinical studies have shown that when the buccal plate is less than 1 mm it is more susceptible to significant vertical crestal resorption. In such cases, particulate bone grafts placed into the requisite buccal gap between implant and buccal plate may not be completely contained. This can lead to incomplete bone fill, exposure of the rough surface of the implant crestally, and gingival recession of the peri‐implant mucosa. Therefore, it is important to carefully evaluate the thickness of the facial bone and consider appropriate treatment options to prevent these complications (see also Chapters 4 and 6) [43].
Registration of Cone Beam Computed Tomography and Intraoral Surface Scan
A critical step that can influence the accuracy of implant placement is the registration of the intra‐oral surface scan (IOS) with the CBCT data [44]. The two data sets must be perfectly aligned in the same coordinate system. The implant position is planned based on the CBCT, but the surgical guide (or the registration with dynamic‐ or robot‐assisted systems) is planned based on the intraoral surface scan (IOS) [27]. Any misalignments between CBCT and IOS will be translated into the clinical situation and will result in deviation between the planned and postoperative implant positions [44]. The quality of the IOS, the appropriate FoV of the CBCT, the distribution of teeth, and the number of dental restorations (metal or zirconia artifacts) can impact the quality of the registration process. The FoV must be sufficiently large to provide an optimal number and distribution of registration points, making a medium or large FoV the first choice for virtual implant planning. When enough well‐distributed teeth are visible in a smaller FoV CBCT, the registration with the digital intraoral scan appears to be within clinically acceptable limits for guided surgery, but greater errors in the precision of optical scan registration happen with small compared with large FoV [45].
Registration of the CBCT and IOS files can be performed either manually or automated by relying on a “best‐bit” algorithm which aligns shared features in both 3D surfaces, aiming to identify the optimal alignment between the two data sets. The teeth as clinical markers must have an appropriate triangulation to enable the alignment of the two data sets. Common references in both data sets need to be selected to start the superimposition. It is recommended to spread reference points over four areas bilaterally to achieve the highest precision [45]. Dental restorations can create artifacts which disturb the segmented tooth surfaces. This can lead to misalignments of the data sets, and the number of deviations tends to increase with more restorations (Figure 8.3a,b) [44].
In the absence of sufficient tooth numbers or distribution, as in edentulous cases, fiducial radiopaque markers are necessary when the CBCT is taken. The fiducial marker‐based registration can also be considered when four or more highly radiopaque full‐coverage restorations limit the available potential reference points or when the accuracy of the registration cannot be confirmed visually [46].
Virtual Tooth Extraction
The surgical guide is designed based on the surface outlines of the optical scan. The virtual guide has a 3D file format, and its software will not allow the closed mesh of the guide to penetrate the mesh of the digital model of the scanned arch; otherwise, the created surgical guide would not seat onto the teeth in the physical world. For immediate implant cases when the crown of a non‐restorable tooth is still physically present, that tooth will also be present in the digital model and will therefore be a barrier for any surgical guide elements, such as sleeves and sleeve holes. To make the surgical site accessible for the guide design, the tooth (or teeth when multiple implants are planned) needs to be virtually extracted. A sophisticated software may offer this virtual extraction feature as a tool in which an algorithm removes the segmented tooth from the STL file of the digital impression and automatically marries the segmented extraction socket with the IOS (Figure 8.4a,b).
Figure 8.2 (a) The teeth and other anatomical structures such as bone need to be segmented. (b) The patient coordinate system is to be aligned. (c) The panoramic curve must be defined. (d) The mandibular canal and mental foramina must be identified for implants in the mandible.
Figure 8.3 (a) Radiographic and optical surface scan data must be perfectly aligned to allow proper translation from the virtual planning to the clinical situation. (b) Any misalignment will result in inaccuracies since the guide is planned based on the intraoral scan. If the automatic alignment results in a mismatch, the user must manually align.
Figure 8.4 (a) The hopeless tooth is selected in a virtual tooth extraction tool. (b) The software removes the segmented tooth from the intraoral scan Standard Tessellation Language file and uses the socket from the segmented bone to connect it with the intraoral scan.
If such a feature is not offered, alternative tools such as punching the STL file in an open‐source program such as Meshmixer® (Autodesk Inc., San Fransisco, CA, USA) might help to overcome the challenge to remove the crown from the STL file at the implant site. Taking a conventional impression and trimming the diagnostic cast to remove the crown, followed by digitizing that modified model and importing it into the implant planning software, where it can be aligned with the digital impression, is also an option.
Wax‐up
Planning the ideal implant position applies a backward planning concept and is driven by the planned future restoration design [26]. The possibility to virtually plan the implant position under functional aspects and depending on the quantity and quality of available bone and soft tissue, allows for esthetically driven implant planning [8]. If the crown is still present in an immediate implant case, it can orient the proper angulation of the planned implant. In case of a fractured crown or a misaligned tooth position, a digital wax‐up directly in the planning software or imported from a CAD software can help to determine the prosthetically driven optimal implant position and angulation (Figure 8.5a–c).
Three‐Dimensional Implant Positioning
The existing root provides an excellent orientation for the optimal 3D implant position and angulation in immediate implant cases. The sagittal/radial tooth root position dictates the entry point of the initial osteotomy into bone [47]. When the root is located centrally in the ridge with more than 2‐mm buccal bone thickness (class I‐A), the initial osteotomy entry point is suggested to be at the root apex. When the root axis is located centrally but the buccal plate is less than 2 mm in thickness (class I‐B) or the root axis is inclined facially (class II with thick or thin buccal plate or class III, the coronally segment is inclined facially), the initial entry point of the osteotomy should be at the palatal wall, in the lower third from the socket apex (Figure 8.6).
If a screw‐retained restoration is planned, the implant must be angulated in a way that the screw access channel is palatal to the incisal edge [1]. However, with some new implant designs (see Chapter 12) and individualized abutments [48] which accommodate for angular deviations, the implant axis can be aligned with the root axis. Furthermore, with the use of angulated prosthetic screws, the screw access can be moved to a more favorable position to compensate for a less than ideal implant placement.
Figure 8.5 (a) The existing crown. (b) A digital wax‐up in the implant planning software. (c) Alternatively, a physical wax‐up can be digitized using an intraoral or lab‐scanner and imported into the planning software. As a next step, an appropriate implant can be selected from a database that provides an up‐to‐date multitude of implant options.
Figure 8.6 Ideal three‐dimensional implant positioning: The distance to adjacent teeth is at least 1.5 mm at the crest level. The gap between buccal plate and implant should be ideally > 2 mm to allow proper bone grafting. The socket configuration determines the initial osteotomy entry and is in most cases in the lower third from the apex.
Virtual simulation of the future implant position allows consideration of critical anatomical entities, such as the relationships to important anatomical structures (nerves, blood vessels, adjacent roots, nasal floor, maxillary sinus), the bone quantity (horizontal and vertical), and the contour and amount of soft tissue [49]. The length and diameter of the implant is limited by these critical anatomical structures, and, if need be, choosing a narrower diameter and/or tapered implant may reduce the risk of implant exposure and accommodate for proximity to the nasopalatine canal if the immediate implant is planned for a maxillary central incisor. This also can result in more available buccal and lingual bone volume surrounding the implant [50]. A smaller diameter implant can also increase the probability of being able to combine immediate implant placement and provisionalization with a straight screw‐channel, screw‐retained restoration [1] if that is the desired treatment plan. Measurement tools in the planning software can be used to determine clinically relevant distances such as: (i) the final width of the gap between implant and buccal socket wall; (ii) the depth of the implant platform in relation to the crestal bone level; (iii) the remaining apical bone for implant stability; (iv) the distance to adjacent teeth or implants; and (v) the soft tissue thickness (distance from gingival outline of the intraoral scan and the outer surface of the buccal plate in the CBCT), which is relevant in planning whether or not to include additional soft tissue grafting. Digital measurements of soft tissue thickness may supplement the clinical assessment of gingival phenotype estimated with a periodontal probe (assessing whether the probe is visible or not when placed in the facial gingival crevice). It is known that sites with a thin soft tissue phenotype are at higher risk in developing gingival recession after immediate implant placement which can negatively impact the final and long‐term esthetic outcome [16].
When the desired implant position has been determined, the user can then select an appropriate guidance sleeve that matches the implant.
Guide Design
The accuracy of CAIS using static guides is impacted by several factors: (i) the sleeve height [51, 52]; (ii) the implant platform‐to‐sleeve distance [3, 53]; (iii) the height of the surgical key [51, 54]; (iv) the extension of the guide [55, 56]; (v) the crown coverage of the guide [57]; and (vi) the presence or absence of teeth to support the surgical guide [58–60].
Sleeve Selection
When surgical guides are used, the operator has the possibility: (i) to use the guide for both the osteotomy and implant insertion through the guide sleeve; (ii) to use the guide only for the osteotomy, placing the implant free‐hand; or (iii) to use the guide only for the pilot drill, performing the remaining drilling sequence and implant insertion freehand [61]. Using a guide for the pilot drill delivers more accurate implant positioning than performing the implant surgery totally free hand, but it is still less accurate than option one [3]. The inner diameter of the pilot sleeve should match the diameter of the pilot or initial implant drill of the surgical system used.
As indicated, the osteotomy needs to be performed fully guided and the implant placed through the guide to the preplanned depth to achieve the highest accuracy, especially when immediate loading with a prefabricated custom healing abutment or immediate restoration is planned [8].
Implant companies are using different approaches for fully guided surgery by modifying how the drills are guided while performing the osteotomy. All systems require a tube or sleeve cylinder of a defined diameter and height to house the drills. The mesial–distal dimension between the teeth adjacent to the implant site and the interproximal bone levels will determine a suitable diameter for the sleeve cylinder. The sleeve height is typically specific to the implant system. The shorter the sleeve height is, the lower the guidance of the drill will be, resulting in greater angular deviation [62]. The optimal sleeve height seems to be around 5 mm. If the sleeve is shorter, the accuracy of implant placement significantly drops. More than 5‐mm sleeve height does not improve the accuracy and might in fact rather limit access to the surgical site.
The distance from the sleeve to the future implant platform also has an impact on the accuracy of guided surgery [3, 51, 53]. When the sleeve is closer to the implant platform, the accuracy is greater [3, 63]. The distance should be between 2 and 4 mm. If the sleeve is too close to the implant platform, the sleeve will interfere with bone or soft tissue, yet a sleeve too far (> 4 mm) from the implant platform results in increased drilling distances. Longer drilling distances lead to greater deviations from the planned position [51]. Tapering the base of the sleeve housing might help to prevent interference with the gingival margin and crestal bone in immediate implant cases.
If the implant planning software allows exporting a calibration matrix, the ideal offset of the cylinder tube to house the sleeve can be determined. A matrix with incremental offsets can be printed or milled, and the best fit of the sleeve can be tested. This step is especially important when a sleeveless guide is planned. In this sleeveless technique, the drill handle or the shank drill is directly placed into the cylinder tube removing the tolerance that exists between a sleeve and the guide supposedly improving accuracy [64].
Basic Design Principles
Surgical guides rest in the mouth on anatomical structures. Guide support can be any of tooth‐supported, mucosa‐supported, bone‐supported or pin‐supported [26]. Tooth‐supported guides deliver the highest accuracy [65]. Depending on the clinical situation, a combination of different guide support options, so called “hybrid support”, is appropriate and indicated to improve guide stabilization. Inadequate guide stabilization can be a factor for intraoperative complications [66].
The number and location of teeth that support the surgical guide will impact the accuracy of guided surgery. Having at least four teeth supporting a guide is recommended and can result in the same level of accuracy as using a full‐arch guide [56]. If the implant location is in the anterior maxilla, the guide should extend bilaterally to the bicuspids for appropriate guide stabilization. If the implant location is for a bicuspid, the guide should extend at least to the canine of the contralateral side. Adding a crossbar to the guide can improve its stiffness and intraoperative stability [67].
The surgical guide should also cover crowns at least to the height of contour [57]. Reduced crown coverage can result in rocking of the guide. In the guide design process, the digital model of the arch is positioned according to the desired insertion direction. The software will then automatically block out any undercuts which might impede the path of insertion of the guide.
Workflow for Guide Design
The steps in designing the guide are commonly: (i) selecting the digital model that serves as the basis of the guide; (ii) defining the desired insertion direction of the guide; (iii), selecting the bearing surface on teeth and/or mucosa or bone (requires bone windows in the digital model); (iv) setting the material thickness (2–3 mm) and tolerance of fit (≤ 0.25 mm); (v) planning “inspection windows” to allow intraoperative verification of the seating and fit of the guide; (vi) labeling the guide and setting an orientation marker; and (vii) exporting the guide in STL‐format for guide production (Figure 8.7) [68].
Figure 8.7 (a) Define the insertion direction. (b) Select the guide supporting teeth according to the design principles. (c) Set the material thickness and offset. (d) Plan inspection windows. (e) Label and set orientation marker. (f) Export Standard Tessellation Language file of guide for production.
Some software will allow for the design of an “open frame” guide where bearing supports are strategically distributed. More common is the closed guide design, which requires inspection windows to confirm the fit of the guide visually before and during the surgery. The inspection windows should be placed bilaterally to the implant site and otherwise be distributed such that the seating of the guide can be confirmed. However, too many inspection windows can weaken and destabilize the guide and may lead to its fracture [8].
Guide Production
The STL file of the surgical guide needs to be imported into a CAM software that allows users to prepare the designed guide for production. In general, the surgical guides can be: (i) milled using computer numerical controlled machining as subtractive method from a prefabricated block; or (ii) 3D printed as additive fabrication using biocompatible resins (Figure 8.8) [69]. No statistically significant differences were found for trueness and precision of surgical guides either milled or 3D printed [70].
Three‐dimensional printing includes a variety of technologies capable of creating physical objects by sintering powder or polymerizing liquid materials layer by layer in cross‐sections from digital designs [69]. Consumer‐level 3D printers can produce surgical guides with a similar accuracy to high‐end, professional 3D printers, but with reduced costs [71]. Seven categories of additive manufacturing technologies have been distinguished by the American Society for Testing and Materials, including: (i) vat photopolymerization (stereolithography); (ii) material jetting; (iii) material extrusion; (iv) binder jetting; (v) powder bed fusion; (vi) sheet lamination; and (vii) direct energy deposition [72]. 3D polymer printing technologies (vat photopolymerization, material extrusion, and material jetting) are mainly used for printing surgical guides [69]. The laser speed, intensity angle, building directions, number of layers, shrinkage, position of the support structures (Figure 8.9a,b) post processing, sterilization and storage can have an effect on the accuracy of these surgical guides [55, 69, 73].
Figure 8.8 The Standard Tessellation Language file of the guide is prepared in a computer‐aided design software for stereolithographic three‐dimensional printing. The yellow objects are the support structures that can be easily removed after printing.
Figure 8.9 (a) Interference of support structures with the sleeve tube or the intaglio surface of the designed guide can result in inaccuracies during the surgery. (b) The support structures should insert away from the sleeve tube so the sleeve can later be properly seated.
The post‐production instructions specific to the material and the 3D printer need to be followed. Fresh out of the printer, the surgical guide needs to be cleaned of residual resin liquid or powder and light cured to reach maximum material strength [74]. Uncured resin is typically removed by washing in an ultrasonic bath with a solution recommended by the manufacturer (such as isopropyl alcohol or other detergents). Inserting the sleeve after the washing and before the final ultraviolet polymerization has shown advantages in daily practice. The light curing time and magnitude of light is very specific and must comply with Food and Drug Administration requirements [75]. Supports are removed and the surface of the guide polished. The surgical guide is then sterilized. Again, the product instructions must be followed to reduce inaccuracies and avoid micro cracks in the material [55]. Storing the guides between 30 and 90 days after their manufacture does not change the intaglio accuracy [76].
Guided Implant Surgery
Guided implant surgery using surgical stents, also described as static CAIS, has been shown in numerous studies to be more accurate in translating the planned implant position to the actual delivered implant position than freehand implant surgery [2, 3, 9, 10,29–31, 58, 62, 63, 65, 66,77–85].
Guided surgery systems are based on different design concepts. The drills: (i) can have vertical stops, use drill handles that have an inner hole with a diameter that is specific to the diameter of the respective drill, and have an outer dimension that matches the sleeve cylinder in the guide; (ii) have a drill shank of compatible diameter with the inner diameter of the sleeve cylinder to allow for drill‐body guidance; or (iii) have a surgical key attached that matches the inner diameter of the sleeve cylinder (key on drill). The latter two approaches are considered keyless and do not require a drill handle (Figure 8.10a–c) [62].
When using drill‐handle systems, the implant drill is guided through the drill keys inserted into the sleeve cylinder, whereas in key‐on drill systems and drill‐body guidance systems, the drill is directly stabilized through the surgical guide. Holding a drill key might be considered an ergonomic disadvantage over keyless systems as the operator needs to hold the key manually, but drill‐handle systems have higher accuracy compared with shank‐modified drills, at least in in‐vitro studies [62, 80]. The perceived ergonomic disadvantage can be bypassed in using a sleeveless guide where the drill handle is stabilized in the cylinder tube, which has an inner diameter matching the outer diameter of the drill handle (plus a predetermined offset). In‐vitro studies have shown that such a sleeveless approach can be more accurate in fresh extraction socket sites [64, 86].
Figure 8.10 (a) Examples of guided surgery systems using (a) drill‐handles, (b) shank drills, or (c) have the surgical key attached to the drill.
Whatever guided surgery system the clinician decides to use, it is of utmost importance that they are familiar with the design principle, potential limitations, and factors that can impact the accuracy of implant placement. All guided surgery systems are not the same and different systems result in different levels of accuracy [62]. The surgeon should acknowledge controllable factors to avoid implant mal‐ positioning to take full advantage of guided protocols. These controllable factors are discussed earlier in this chapter and include but are not limited to errors associated with the data acquisition, the specific scanner and method of scanning used, errors associated with merging scanned files with the CBCT scan, errors in planning, errors using different surgical guide fabrication methods, and errors associated with intraoperative techniques. All these potential errors might be in the sub‐millimeter range; however, if they accumulate, implant placement errors can exceed 1–2 mm at the platform level while angulation errors can exceed 8 degrees, which will lead to violation of the 2‐mm safety space at the implant tip [87].
Guided surgery and IIP add an additional level of complexity since, in many cases, the hopeless tooth is partially or completely still in situ. This prevents checking the fit and seating of the guide preoperatively. The clinician should stick to a well‐established digital workflow that has been proven to be effective in partially edentulous cases. Additionally, the extraction of the tooth may change the anatomical situation in a way that was not simulated in the virtual planning phase, and the clinician should have the expertise to recognize and modify the surgical plan accordingly.
Guided surgery can improve the accuracy of placing implants in prosthetically correct 3D positions in the esthetic zone, and the fully guided approach (full drilling sequence and placing the implant through the guide) is more accurate than using a surgical guide only for the pilot drill [9]. A systematic review and meta‐analysis by Tattan et al. [2] has shown that guided surgery provides clinical advantages over conventional implant placement methods, such as freehand or partially guided implant placement, as long as the clinical situation allows the stabilization of the surgical guide and an unhindered drilling sequence is followed. This is especially important with fresh extraction sockets. Any modification from a complete drilling sequence in fresh extraction sockets can lead to higher deviations from the planned position [64].
In general, guided surgery in healed sites is more accurate than in fresh extraction sockets [86]. However, guided surgery is still an advantage for achieving predictable immediate implant placement [48] with good esthetic outcomes [14]. One of the factors that needs to be taken into consideration is that implants in extraction sockets may have a tendency for facial drift. This can be minimized when the implant is placed through the surgical stent under guidance. The macro design of the implant also impacts the accuracy of immediate implant placement. A deep‐threaded, tapered macro design appears to reduce the facial drift and is more advantageous than an implant that has a shallow‐threaded parallel macro design when placed through the guide [86]. The inclination of bone can also influence the angulation of dental implants [88]. Higher bone inclinations result in greater deviation of the initial implant drill. The entry point for the initial drill in most maxillary sockets is in the palatal wall with a high inclination (except for class I‐A, where the entry point is at the root apex). The clinician must be conscious of this as the first drill will set the implant axis and control potential deviations.
Immediate Implant Placement with Customized Provisional or Healing Abutment
A full digital workflow allows providers to not only place the implant under guided conditions but also to indirectly prefabricate a custom restoration or healing abutment using CAD/CAM technology (Figure 8.11a–c) [89].
Figure 8.11 (a) The implant position is exported as Standard Tessellation Language. (b) The temporary restoration is designed in computer‐aided design software. (c) Milled or three‐dimensional printed transitional crown.
The custom restoration is designed based on the 3D position of the implant. It is therefore of upmost importance that the preparation of the implant bed be performed fully guided and the implant placed through the guide until the planned depth is reached. The implant connection needs to be aligned according to the planned position to insert the prefabricated custom healing abutment or immediate provisional restoration (Figure 8.12a–p) [48].
With IIP, the failing, hopeless, and non‐restorable tooth might have undergone excessive restorative attempts until the decision to extract was made. To stabilize the tooth or root, a provisional restoration, ideally using an adhesive technique and composite resin material, can minimize the risk of fractures during the tooth extraction.
After the proper diagnosis is made and all necessary clinical parameters have been documented (see Chapters 1, 2 and 3), intraoral scans of both jaws, a bite registration, and a CBCT of the relevant jaw need to be acquired for CAD/CAM production of a surgical guide and provisional abutment or restoration. The treatment planning steps for guided immediate implant placement are explained in detail above. Once the ideal 3D position of the implant is determined, these records are exported as an STL file with a virtual implant analog to a prosthetic design software in which the individualized healing abutment or custom provisional restoration can be planned. An STL file of the restoration or healing abutment will be sent for production using milling or 3D printing. On the day of surgery, the provider has the surgical guide for fully guided surgery and the indirect fabricated provisional restoration or custom healing abutment at hand, which shortens the time for surgery and provisionalization and increases patient satisfaction. A prerequisite of this protocol is the compatibility of laboratory and guided surgery systems to guarantee that the restoration accounts for the 3D position of the implant [89]. Sufficient primary stability of the implant must have been achieved to consider loading the implant immediately [90].
Immediate Implant Placement with Guided Osseodensification
“Osseodensification” is a relatively new universal additive bone instrumentation method for dental implant placement [91, 92]. It uses specially designed burs that induce a time‐dependent hydrodynamic wave ahead of the point of contact. The densifying burs use cancellous bone plasticity, creating an osteotomy via autografting bone into the trabecular spaces [92]. Biomechanical and histological studies have demonstrated that osseodensification leads to a bone spring back towards the implant body, which increases the bone‐to‐implant contact by 70% on the day of surgery. This effect enhances the primary stability measured by insertion and removal torque [92–97]. A retrospective analysis of 211 placed implants, including 126 immediate implants, suggested that osseodensification may accelerate implant rehabilitation treatment periods and provide higher success and survival rates than conventional methods [98].
Immediate implant placement is not the only indication for an osseodensification protocol. The efficacy of osseodensification to produce alveolar ridge plastic expansion allows for implant placement into narrower ridges with adequate amounts of trabecular bone without creating dehiscence [99–101]. The increase in bone plasticity also facilitates upper and lower molar septum expansion and immediate implant placement in posterior regions [102]. The hydraulics created by the densifying burs, which are used in counterclockwise (CCW) mode, facilitate compaction autografting in both lateral and apical directions, resulting where needed in efficient indirect elevation of the maxillary sinus floor and membrane and crestal sinus grafting with local autogenous bone or allograft or alloplastic bone substitutes [103–107].
Osseodensification can be performed guided using a universal guided surgery system (identify system and source) with open sleeves for sufficient irrigation to facilitate the required hydraulic pump effect [63]. Surgical keys are attached to the burs to allow for the luxation needed and are used in incremental steps to deliver accurate and predictable implant placement [62]. Since these densifying burs are universal and not implant specific, the guided workflow for immediate implant placement does not include placing the implant through the guide. The implant is placed freehand.
Figure 8.12 Immediate implant and indirect prefabricated immediate temporary restoration. (a) Hopeless upper left lateral incisor. (b) Intraoral scan of the same area. (c) Virtual tooth extraction. (d) Actual situation after atraumatic extraction. The fit of the guide is confirmed. (e) The implant osteotomy performed fully guided according to the surgical protocol. (f) The depth and axis of the preparation is confirmed. (g) The implant is placed guided and its connection aligned with the orientation marker (highlighted orange). (h) The actual implant position corresponds to the planned position (i and l) and the gap between implant and buccal socket wall grafted with bone material (j and k). The lower row depicts the baseline situation (m), the designed temporary (n) and the delivered temporary restoration (2 days postoperatively) (o) according to the digital plan (p).
The digital workflow for IIP with osseodensification is in general as already described. The chosen implant diameter must be slightly wider in mesial–distal direction than the tooth apex to ensure adequate initial stability. After the optimal 3D position is determined, the user selects the open sleeve of the universal guided surgery system from the sleeve data bank in a size that is smaller than the crestal part of the extraction socket (typically size M for IIP). If the software does not include these sleeves, the user can add them to most software as custom sleeves that match the required outer sleeve parameters. In any guided IIP case, the sleeve is not supposed to interfere with the crestal bone of the extraction socket or the interproximal bone of the adjacent teeth. Since the universal guided system for osseodensification offers different sleeve sizes, the clinician can choose the size which best matches the clinical situation and select a sleeve‐to‐platform distance that is coronal of the crest level. The sleeve‐to‐platform distance, together with the implant length, determines the final key length of the guided system (e.g. a 3‐mm distance and a 10‐mm implant length require a 13‐mm key). The surgical keys are available in different lengths (3–15 mm), enabling the clinician to work in incremental steps to achieve the highest accuracy. This also provides flexibility in creating osteotomies of different depths depending on the ridge height and allowing for controlled, guided sinus floor elevation. Figure 8.13 illustrates a case where the immediate implant protocol was combined with a slight elevation of the sinus floor with local autogenous bone.
The surgical guide is, of course, designed according to the design principles already mentioned. An inspection window is placed at the buccal‐facing opening of the C‐shaped sleeve. This allows for sufficient visualization and water/saline irrigation during the osteotomy [108].
Figure 8.13 Guided osseodensification for an immediate implant. (a) The upper‐right second premolar was determined non‐restorable. (b) A provisional filling helps to stabilize the tooth. (c) During the atraumatic extraction. (d) The extraction socket is cleaned. (e) The seating of the guide confirmed. (f) The surgical key is attached via a gauge to the densifying bur for guided osseodensification. (g) The keys are used in incremental steps until the final depth is achieved. (h) When the osteotomy is completed, the socket is loosely filled with bone graft material. (i) Densified. (j) The implant is inserted free‐handed. (k) One finger stabilizes the buccal plate. (l) The implant was placed as planned. (m) A healing abutment seals the bone graft material and allows for (n) soft tissue healing (3 months postoperatively). The implant was restored with a screw‐retained crown (o). (p) The buccal view shows stable gingival tissue. (q) The planned implant position requires a slight elevation of the sinus floor. (r) The three‐dimensional implant position shows a > 2 mm gap between implant and buccal wall, and 2 mm apical retention for the implant. (s) The postoperative radiograph shows a proper implant position and a bump where the sinus floor was elevated through autografting via osseodensification. (t) The radiograph at time of crown insertion shows stable crestal bone levels.
IIP protocol for guided osseodensification includes: (i) flapless, minimally traumatic extraction; (ii) meticulous seating of the surgical guide; (iii) assembling the 2.0‐mm drill with a gauge and an attachment key which matches the sleeve size diameter and implant length; (iv) using the densifying burs in osseodensification mode (800–1500 rpm, CCW, with copious irrigation) through the guide until the vertical depth is reached; (v) completing the osteotomy through the guide with sequential densifying burs according to the implant diameter; (vi) loosely filling without compaction the osteotomy with a well‐hydrated suitable allograft; (vii) densifying the allograft with the bur that is one size smaller than the last bur used for the final socket preparation (150–200 rpm, CCW, no irrigation) through the guide; and (viii) removing the guide and placing the implant. The implant should receive a customized healing abutment or temporary crown that covers and protects the bone graft sufficiently.
Mandibular second premolars are the most commonly missing teeth [109], with a prevalence of 2.4–4.3% [110]. The persistence of a primary second molar in patients with agenesis of one or two second premolars in a permanent dentition without morphological deviations can be an acceptable, semipermanent solution for the patient [111]. However, when the persistent deciduous tooth fails due to root resorption or caries, an immediate implant in the interradicular bone is a feasible treatment option [112, 113]. An implant‐supported crown in the second premolar site results in more esthetic outcomes than a tooth‐supported reconstruction [114].
A persisting primary tooth provides a good orientation for the future 3D IIP. Since persistent primary second molars have widely separated roots, the interradicular bone provides a good bony implant housing, but the implant needs to be placed deep enough, using the interradicular bone of the adjacent teeth for orientation. The selected sleeve should not interfere with the buccal and lingual crests or interproximal bone of the adjacent teeth. The septum of a persistent deciduous tooth can be at the level of the interproximal bone and might need an osteoplasty to facilitate appropriate subcrestal immediate implant placement and to allow for seating of the surgical guide. Instead of using traditional subtractive implant drills, which remove the better part of the available septum and expose the implant surface mesially and distally, densifying burs can preserve the available bone and achieve higher primary stability.
The guided osseodensification protocol includes (Figure 8.14a–t): (i) separating the deciduous tooth buccal–lingually, without compromising septal integrity, and extraction; (ii) confirming full seating of the surgical guide (perform osteoplasty only of the septum without compromising the lingual and buccal crest level if the sleeve interferes with the septum); (iii) assembling the densifying burs and starting guided osseodensification; (iv) using the densifying burs with small increment increases to expand the septum and increase bone plasticity; (v) removing the guide and placing the implant subcrestal (approximately 4 mm from the gingival margin of the adjacent teeth); and (vi) adding a customized healing abutment or transitional crown.
Figure 8.14 Guided osseodensification with septum expansion for an immediate implant. (a) A persistent lower‐right primary molar in an adult patient shows external resorption and caries. (b) Due to the divergence of the roots the tooth was segmented and (c) the parts extracted separately. The height of the septum (d) suggested the need for a minimal osteoplasty (e) of the septum peak (green circle in d). (f) The fit of the surgical guide was confirmed. (g–j) The osteotomy was prepared under preservation of the available bone with densifying burs. The keys of the guided system were used in incremental steps to achieve highest accuracy. (k) The implant was placed free‐hand and (l) the sockets filled with bone graft material. (m) The socket was sealed with a direct individualized healing abutment, which protected the bone graft and allowed for soft tissue healing (n). (o) The final restoration after 2 years in situ. The lower row shows radiographic images (p) from baseline, (q and r) of the virtual implant planning, (s) immediately post surgery, and (t) 2 years after the final restoration was delivered.
Conclusions
Computer‐assisted implant surgery can be of benefit in placing immediate dental implants in ideal, prosthetically driven 3D implant positions. The best outcomes are those where both osteotomy creation and actual implant insertion are all achieved with carefully designed and created surgical guides. As with placement with dental implants generally, using osseodensification burs will help to stabilize IIPs sufficiently to allow immediate provisionalization.
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