Читать книгу Fundamentals of Implant Dentistry - John III Beumer - Страница 15

CHAPTER 5

Digital Technologies and Implant Dentistry

Jaafar Abduo | Karl Lyons | Kumar C. Shah | Benjamin M. Wu Robert F. Faulkner | Basil Al-Amleh

While implant dentistry has provided a variety of alternative treatment options for our patients, few advances have had an impact on the concepts of diagnosis, treatment planning, communication, and fabrication of prostheses as much as digital technologies.1 The incorporation of digital technologies within implant dentistry has been largely driven by the desire for simpler, predictable, and esthetic implant restorations. Digital technologies of today have altered the concepts of diagnosis, treatment planning, prosthesis design, and the overall treatment workflow. Further, these technologies have had a significant impact on treatment duration and prosthesis material selection options. They have also enhanced the communication among the different members of the treating team and the patient. Today, the paradigm shift and the acceptance of digital technologies in implant dentistry have been furthered by the continuous refinements of the digital devices that make them more ergonomic, versatile, accurate, and affordable for dental practices. One example is the modern software programs that are user friendly and simple to use, even by operators with minimal digital background. The industrial standards of the digital devices ensure greater control of treatment planning, virtual evaluation, and prosthesis quality. In addition, the parallel development of more novel materials that can only be produced by digital technologies has increased the popularity of these systems.2,3 In contrast to traditional dentistry, digital dentistry is rapidly evolving, and there will continue to be significant improvements in the near future.

Despite all of these advancements, digital technologies are not without limitations, and they will not replace the fundamentals of sound surgical and prosthodontic knowledge and skills. This is because the technology alone may not be able to provide the anticipated patient outcomes. This chapter explains the many digital technologies that are available to us to provide prosthodontic treatment that incorporates dental implants.

Merits of Digital Technologies in Implant Dentistry

The merits of incorporating digital technologies within implant treatment can be summarized as follows: (1) facilitating diagnosis and treatment planning, (2) improving communication, (3) simplifying treatment protocol, (4) enhanced prosthesis fabrication and materials, and (5) tracking treatment over time.

Diagnosis and implant treatment planning

Digital technologies have allowed for better visualization of the dentition and the future implant sites. Combining 3D radiologic imaging with intraoral tissues outlines the clear relationship of the existing hard and soft oral tissues and the future implant site. Digital scanning of the dental arch and occlusal relationship can be followed by a digital wax-up of the future implant restoration, from which the planning clinician can easily determine the dimension and orientation of the implant (Fig 5-1). The virtual dental arch can receive a virtual implant and restoration, which will clearly illustrate the impact of the future of implant placement on the design of the prosthesis and the anticipated esthetics prior to the actual treatment. The process is also very efficient and less time consuming than using conventional wax-ups and planning tools. In addition, all the planning steps are reversible and do not negate the ease of treatment planning modifications. In addition, the need for any adjunctive treatment, such as grafting, can be determined and justified (Fig 5-2).

Fig 5-1 Digital diagnostic wax-up for a prosthodontically driven implant treatment plan.

Fig 5-2 Digital workup allows virtual visualization of the bone volumes and anatomical structures for proper implant treatment planning.

In comparison, the conventional wax-up and planning involves modifying the diagnostic cast with wax, which is time consuming and requires technical skill and material manipulation. Judicious use of digital technologies for implant planning allows the treating clinicians to opt for the most conservative treatment options, and in some cases, the invasiveness of the surgical intervention can be reduced with appropriate implant positioning.4 However, soft tissue deficits are readily represented with conventional wax-ups, which cannot be done with digital equivalents.

Communication with implant team members

Digital data is easily stored and transferred to other members of the team in various locations in real time, which immensely improves the communication and transference of diagnostic and planning information. The planning information can also be outlined and easily conveyed to the patient and the dental technician, which enhances understanding and the visualization of the proposed treatment. Instead of observing a dental cast, a 3D image can be displayed and enlarged for the patient that clearly shows the amount of remaining bone and the planned future implant site. With the aid of contemporary manufacturing tools, such as milling and printing, it is possible to produce models of patient bone and final planning that further enhance the team communication during the management of more challenging cases. In addition, from the agreed implant planning, a provisional or prototype prosthesis can be reliably produced and, if approved, can be accurately replicated into a definitive prosthesis5 (Fig 5-3; see chapter 8, sections entitled “Monolithic Zirconia Prostheses” and “Immediate Loading—CAD/CAM method” and chapter 10, section entitled “Procedures for monolithic zirconia fixed prostheses”).

Fig 5-3 An immediate load conversion prosthesis designed digitally and milled out of PMMA. (a) The digitally designed prosthesis engaging a digitally designed prosthesis orientation template (see Fig 8-68 for details). (b) The immediate load prosthesis secured to the prosthesis orientation template, on a milled replica of the bone contours of the mandible. (c) The milled PMMA provisional prosthesis secured intraorally to the prosthesis orientation template. (d) The completed immediate load provisional prosthesis secured to the implants.

Simplifying treatment protocol

In multiple aspects of implant dentistry, digital technologies have simplified the treatment protocols, including diagnosis and treatment planning. This is because digital technologies provide enhanced visualization of patient anatomy, improved surgical management, reduced numbers of treatment steps and patient visits, a simplified impression procedure, a more reliable prosthesis design and fabrication, and potentially increased cost-effectiveness.6–9

The substitution of conventional impressions with digital impressions may improve patient comfort and reduce the clinical time. In addition, the use of impression material is avoided, which may also improve the patient experience. Currently, digital impressions of linear quadrant-sized defects are sufficiently accurate to fabricate definitive prostheses. However, full-arch digital impressions still lack the consistent accuracy needed to fabricate definitive complete-arch implant prostheses (see section entitled “Digital impressions”).

Currently, the most commonly discussed digital tool in implant dentistry is the surgical guide that is produced according to the implant digital plan (Fig 5-4). Digital surgical guides are used to completely or partially control and guide the implant placement to the planned virtual position.10–12 The prosthesis design can then be optimized digitally and produced via milling or printing, thereby avoiding multiple error-introducing steps such as waxing, casting, and polishing.13–15

Fig 5-4 (a) Digitally designed fully guided surgical template used in the patient shown in the previous figure. It is designed to engage a foundation template. (b) Milled surgical template. The drill sleeves are made of zirconia. (c) Surgical template secured to the foundation template intraorally.

Enhanced prosthesis fabrication and material usage

Digital technologies provide the clinician with an increased number of viable options to restore implants. Digitally produced prostheses have been shown in several studies to have adequate durability and accuracy.16,17 This has been attributed to fewer fabrication steps, reduced human intervention, and less reliance on experienced dental technicians. The implementation of industrial manufacturing techniques has allowed for production of implant frameworks and prostheses from a variety of materials, including polymethyl methacrylate (PMMA; Fig 5-5), alternative metal alloys to noble metal alloys such as cobalt-chromium alloys, as well as titanium and zirconia (Fig 5-6). Although frameworks and prostheses with metal alloys can be produced using conventional methods, their conventional production is technique sensitive, and the produced prostheses have been reported to have a compromised fit.18 Alternatively, milling these metal alloys from a digital file will overcome many of the problems of conventional casting. Alongside the advancement in digital technologies, modern ceramic materials such as zirconia have been developed. Currently, toughened zirconia can be reliably produced by milling, and this has allowed the fabrication of implant prostheses that are biocompatible, esthetic, and durable.19 In addition, for PMMA provisional or prototype prostheses, multiple units can be manufactured at low costs (see Fig 5-5). The extra provisional or prototype prosthesis can be quite useful when one is being used to fabricate the definitive prosthesis (see chapters 8 and 10, sections discussing fabrication of monolithic zirconia prostheses).

Fig 5-5 (a and b) Provisional full-arch prosthesis milled of PMMA. Pucks are available in other materials such as cobalt-chromium, titanium, and zirconia.

Fig 5-6 Fully sintered monolithic zirconia prosthesis.

History and Technologic Background

Role of Moore’s law on development of intraoral scanners and digital dentistry

Since the initial description of dental laser holography in the 1970s20 and the first commercial intraoral scanner (IOS) in the 1980s,21,22 many optical imaging technologies have been developed for dentistry. This competition has resulted in numerous affordable scanners that are constantly improving in accuracy, speed, ease of use, and compatibility with multiple design softwares, mills, and printers. Furthermore, IOSs are adding features beyond surface mapping, such as full-color capturing, shade matching, and caries detection. In fact, the current generation of IOSs are vastly better than the previous generation from only 5 years ago in most measurable performance criteria that matter to the clinician. Along with the emergence of powerful CAD software, advances in milling machines and 3D printers, availability of advanced materials, and global adoption of the internet, IOSs have played a key role in the evolution of digital dentistry. In many ways, these major trends have benefited either directly or indirectly from the drastic decrease in the cost for computational power over this time period. In the 1980s, one dollar would purchase enough computational power to perform ten million standard operations per second. Today, the same inflation-adjusted dollar would purchase ten million times more computing power. Over this period, this so-called “price-performance Moore’s law” has resulted in a tenfold increase in computational power per dollar every 4 years. The fact that today’s smartphones and tablets are faster than the fastest workstations in the 1980s has fundamentally changed the IOS engineer’s toolbox. Along with high- performance video cards built for the gaming industry, the new generation of IOSs are able to incorporate technologies involving multiwavelength, structured light sources, moving mirrors, and innovative temporal-spatial patterns to reconstruct accurate 3D models in real time. These require increasingly sophisticated, computationally demanding, mathematical reconstruction algorithms. The reliance on raw computational power by IOSs will only increase, and many systems will require high-end gaming computers to capture, render, and display the 3D images properly as the systems continue to improve over the next 5 years.

Computed tomography

One of the early advancements in digital technology, and perhaps the most important for implant dentistry, was the ability to visualize radiographic images in 3D. In the past, periapical or panoramic radiographs were considered the standard by which we based much of our diagnostic information. The limitation of 2D analyses led to much variation in assessing anatomical landmarks and the placement of implants. Computed tomography (CT) used in medical imaging introduced the dental field to 3D analyses, thereby significantly enhancing our diagnostic abilities and allowing better visualization of the potential implant sites prior to implant placement. The negative aspects of this technology were the cost of the CT scan and the radiation dose delivered to the patient. Subsequently, dental CBCT has been developed specifically for the dental field, which is based on producing divergent x-ray beams that form a cone. The CBCT unit is smaller in size than the CT, making their use ideal for the dental office. Over the last few years, CBCT has become very popular due to the recent advances in low-dose CBCT, the availability of compact CBCT units, and the availability of user-friendly software. As CBCT scanning technology has improved, it has allowed the clinician to differentiate between hard and soft tissue structures to a much greater degree (see Fig 5-7).23 Because a CBCT image clearly outlines the vital anatomical features such as the inferior alveolar nerve, the number, size, angulation, and depth of the implant can be planned virtually. Further, the individual sites for implant placement can be evaluated for adequate bone, and some software programs can evaluate soft tissue volume as well as whether the sites require augmentation prior to or during implant surgery (Figs 5-7 and 5-8).

Fig 5-7 (a and b) This CBCT evaluation allows visualization of the overlying soft tissues and indicates that the gingival tissues are relatively thin. The soft tissue contours and thickness are visible due to the combining of the DICOM files (showing hard tissue) and STL files (showing soft tissue). Accordingly, extra precautions should be taken when this tooth is removed in preparation for implant placement (Reprinted from Moy et al23 with permission.)

Fig 5-8 Virtual planning for immediate implant positioning. (a and b) In the esthetic zone, angulation and position are critical to achieving appropriate esthetic outcomes that will sustain the bone and soft tissues over the long term. Note that the implant is positioned such that the abutment screw channel exits in the cingulum area. (c to f) For posterior quadrants, visualizing vital structures, such as the inferior alveolar nerve and lingual concavity of the mandible, is mandatory. Lateral views are available to determine buccal extent and ensure there is sufficient thickness of bone circumscribing the implants with the chosen positions. Implant positions and angulations can be verified in both 2D and 3D. Note that these implants have been positioned consistent with the application of occlusal forces along their long axis with respect to the curve of Spee and curve of Wilson.

Although the CBCT scan is less accurate than the CT scan, the advantages of the CBCT scan over the CT scan are the radiation exposure is significantly less and the scans can be performed in the dental office. Common sources of error include improper positioning of the patient, not obtaining the appropriate anatomical fields/scan volume, movement by the patient during the scan, or scatter due to significant amounts of dental restorations, especially metal-based ones (Fig 5-9).23,24

Fig 5-9 (a) Horizontal slice of a CBCT demonstrating scatter from metallic dental restorations. (b) Despite autosegmentation, details of the tooth restoration surfaces are not outlined clearly. This will cause any guide fabricated off these to fit poorly. (Reprinted from Moy et al23 with permission.).

It is crucial to properly undergo segmentation of these images. Although most current softwares may automatically perform this step (fully or partially), poor segmentation of these images can still occur. When the segmentation is not carefully performed, it may lead to errors that are manifested during the operatory phase, such as ill-fitting implant surgical guides ultimately leading to poor implant placements or disuse of the guide intraoperatively. The clinician should therefore be familiar with reviewing the CBCT information and the interpretation of possible distortions and artifacts in the images.

Optical scanning technologies

Over a dozen scanning technologies are commercially available for IOSs. Regardless of the core scanning mechanism, all scanners project light onto a target, record the image, analyze the data, and define the 3D coordinate of each point within the scan target zone. By keeping track of the camera movement via integrated accelerometers, actual target topology can be compared against camera motion to generate a digital 3D mesh that can be rendered, displayed, and converted into common 3D file formats. A detailed engineering review of each scanning technology is beyond the scope of this chapter, but this section provides brief summaries of select scanning technologies to illustrate the relationship between scanning mechanisms and their impact on clinical applications. Other systems are described in other outstanding reviews.25

Several scanners rely on a confocal laser that records the x, y, and z coordinates by passing a light source through a pinhole aperture and bending the dispersed light with an optical lens onto the target (eg, Chairside Economical Restoration of Esthetic Ceramics [CEREC]).26,27 Due to light dispersion through the aperture, only a small area on the target will be in sharp focus, and all other neighboring points are out of focus. By collecting the coordinates of the sharp, in-focus points and discarding all out-of-focus coordinates, the neighboring points are connected to form triangles, and adjoining triangles are connected to produce a mesh (triangulation) to represent the surface of the object. This is why most scanned files appear hollow when they are flipped upside down. The earlier versions of confocal laser intraoral scanners utilized infrared light (700–1,000 nm), which has been replaced with blue light (eg, CEREC BlueCam) because the shorter wavelength (450–485 nm) reduces distortion and increases accuracy. A major disadvantage of the basic confocal laser approach is that accurate triangulation requires uniform surface in terms of light absorption, reflection, opacity, and moisture content. Because intraoral materials such as enamel, root dentin, soft tissues, polymers, ceramics, and metals have very different optical properties, it was critical to coat all surfaces to be scanned with a thin layer of powder to confer uniform optical behavior of all surfaces.

Compared to confocal imaging, a relatively recent imaging technique called active wavefront sampling (AWS) was developed at the Massachusetts Institute of Technology.28 Commercially known as 3D-in-Motion, AWS is used in IOSs such as the Lava Chairside Oral Scanner (3M) and the True Definition Scanner (3M), where an optical wavefront of reflected images from scan targets (eg, teeth or scan body) travel through multiple rotating apertures and a series of optical lenses, toward image sensors that capture the images. The rotating apertures and lens system create image disparity, and the amount of blurring depends on the distance between target and camera. If the target distance matches the focal length of the lens, a sharp image is captured with minimum blurring. For all other target surfaces, their exact distance can be calculated from the amount of blurring. By moving the camera over the teeth, the x-y-z coordinates are used to reconstruct the data into surface mesh very rapidly. Although confocal laser scanning and AWS are adequate for clinical use, the requirement for titania powder coating is a significant disadvantage. Besides adding clinical time for spraying and removal, controlling a uniform thickness of spray powder presents a new source of error.

One powder-free imaging technique is parallel confocal scanning (iTero, Align Technology), which directs a white light source through a spinning color wheel to generate an array of focused beams in three different color wavelengths (450–485 nm for blue, 520–560 nm for green, and 635–700 nm for red). The light intensity of the reflected pattern in each color is used to calculate the distance without the need for powder.29 Furthermore, by combining the images captured at specific wavelengths, color information is captured at each point of the surface mesh and rendered as a full-color scan. By adding a fourth light source in the near-infrared (NIR) spectrum (0.7–1.1 µm) and an NIR detector, it can also detect interproximal caries lesions. While the color wheel increases the size and weight of the scan head, this approach is already smaller and less expensive than alternatives such as adding multiple light sources or moving the wheel farther away from the camera. The slightly larger head is potentially a concern when mouth openings are limited or when the camera needs to be rotated in the posterior areas to capture deep preparation margins that have restricted line of sight.

Another variant of confocal scanning operates by oscillating the optical subsystem to modulate the focal plane (TRIOS, 3Shape). By imaging target points over time, the target appears in and out of focus as the focal plane changes internally. The amount of blur and the focal plane location is used to calculate target distance very rapidly in order to reconstruct 3D surface mesh without the need for powder. By adding color beams and NIR, the system can add fully colored renderings and interproximal caries detection.

Another powder-free scanning technology is based on optical coherence tomography (OCT) used in many medical imaging applications. Analogous to ultrasound imaging, OCT conducts high-resolution, cross-sectional imaging by quantifying the intensity and delay time of the reflected light due to optical interference.30 In its most basic form, time domain OCT (TD-OCT) uses an interferometer to split a low- coherence light source into reference and sample beams. The reference beam is reflected by a mirror, and this reflected beam travels backward along the same path within the interferometer as the initial reference beam. Simultaneously, the sample beam is reflected by the target surface. The two reflected beams generate an interference pattern that depends on the delay time and intensity of the reflected sample beam as well as the distance of the reference mirror. As micromotors move the mirror back and forth, the topology-depth-dependent sample reflection can be determined accurately to locate the surface points by analyzing the interference patterns. Because the transit time of the translating mirror limits scan speed, IOSs such as E4D Technologies deploy a more advanced strategy called swept source OCT (SS-OCT) that sweeps a narrow spectral line across the spectral range of a broadband light source.31 To achieve this, SS-OCT replaces the translating mirror with vibrating mirrors at 20,000 Hz, upgrades light sources to high-speed tunable broadband lasers, and replaces monochromatic sensors with spectrometric detectors. The collection of target-backscattered light from the entire spectral range is treated as modulations in the source spectrum, and the target distance is calculated accordingly using proprietary mathematical algorithms.32 Besides increasing scan speed by approximately 100-fold over TD-OCT, SS-OCT also captures at higher imaging resolution and signal-to-noise ratio. The reliance on spatial positioning means that clinically, a rubber insert is added to the camera head to maintain near-constant distance between the camera and the target. However, more engineering optimization may be necessary as SS-OCT was reportedly less accurate than other scanning technologies for full-arch scanning.33 Full-arch scanning is an important clinical issue, as discussed later.

Regardless of scanning technology, most of the current commercially available IOSs can produce reasonably accurate single-tooth restorations in terms of general accuracy as defined by international standards.34 They are adequate for most short-span prostheses (ie, fewer than 4 to 5 units) such as fixed partial dentures and surgical guides for implants and endodontics. Currently, full-arch scanning is limited to fully dentate applications such as orthodontic aligners and bracket trays, occlusal guards, snore appliances, and full-mouth reconstruction comprised of single units and short edentulous segments. No IOS has been shown to be adequate for accurate, simultaneous capture of implant coordinates and soft tissue contours when long edentulous spans are present. One study found that although digital impressions may offer less variability (higher precision), conventional impressions yielded significantly greater accuracy for in vivo full-arch impressions.35 A recent study using laboratory gypsum models instead of intraoral scanning confirmed that even the latest generation of IOSs are less accurate when scanning a fully edentulous gypsum model with six polyetheretherketone (PEEK) scan bodies, relative to scanning a partially edentulous gypsum model with three PEEK scan bodies spanning four teeth. The error in trueness (actual spatial coordinates) for full-arch scanning was found to be as high as 170% that of quadrant scanning, and the error in precision (reproducibility) for full-arch scanning was found to be up to 386% that of quadrant scanning.36 While some scanners performed better than others, all suffered significant performance degradation when full-arch scanning is performed.

It should be emphasized that most scanning accuracy studies are based on stone models that present uniform opacity, optical reflectance and absorption, absence of saliva and blood, and lack of patient head movements, and which are performed by experienced operators under controlled conditions. Each of these clinical factors can increase errors in local triangulation and registration that accumulate as stitching errors when the IOS travels across the arch. For short partially edentulous spans, the stitching errors accumulate over only a short distance, resulting in manageable net error that does not affect clinical fit. For long edentulous spans (eg, six scan bodies in edentulous arch), the errors accumulate over the length of the arch, and the error propagates to unacceptably large discrepancies in both implant position and angulation. The current recommended workflow for full-arch reconstruction is to make conventional impressions with splinted impression copings and then scan the gypsum model in a laboratory scanner. Despite the limitations of impression materials and gypsum models, passive fit of the definitive prosthesis is more easily achieved with this hybrid digital/analog approach than by direct intraoral scanning. However, given the rapid pace of technologic development, it is anticipated that full-arch intraoral scanning will be a reality in the near future.

In summary, despite the significant engineering differences in core scanning technology, commercial scanners have not resulted in meaningful differences in terms of accuracy (trueness and precision), because none of the IOSs are adequate for accureate capture of long span and edentulous ridges, and all are somewhat adequate for most other clinical indications. In fact, the differences in scanning technology have more practical impact on user experience, such as speed, camera head size, ease of use, need for powder dusting, scan pattern/strategy, autoclave compatibility of the scan heads, and total cost of ownership.

Clinical application of optical scanning

The early application of scanning technology in implant dentistry involved laboratory scanning that was purely used for producing custom implant abutments and frameworks. Later, laboratory scanning was combined with digital software to facilitate the planning and customization of the abutments and frameworks. Today, laboratory scanning is a routine procedure used in dentistry to allow for fabrication of dental and implant restorations within commercial dental laboratories or by sending requests for fabrication to a centralized milling center. Recently, there has been significant refinement in digital dentistry, and many systems are available in the market for chairside digital impressions (Fig 5-10) and the manufacture of prostheses for teeth and subsequently for implant prostheses.15,37

Fig 5-10 (a and b) Digital scans of corresponding scan bodies for three molar implants. (c to e) Various views of the scan with the soft tissue contours, the designed custom abutment, and the implant positions.

Although the conventional impression has been the standard of practice for many decades, it is associated with material preparation, ongoing cost, technical time, potential patient discomfort, and a requirement for high clinical skill.38 Regardless of the material and technique, any conventional impression is associated with an inevitable degree of error, which is attributed to the number of steps required and materials manipulation.39 For example, all impression materials are prone to dimensional distortion through their setting reactions. As the impression is removed from the patient’s mouth, unavoidable deformation will occur with the removal of the impression from the undercut areas. Likewise, pouring the impression will further contribute to the distortion during the setting of the stone material. Contrary to conventional impressions, digital impressions have the advantage of omitting the need for impression materials, trays, and cast pouring, which will reduce the impact of material limitations.40–46 Further, digital impressions may potentially reduce clinic time, enhance patient comfort, and allow for visualization of the adequacy of the impression immediately.47–50 With routine use, digital impressions will minimize material wastage and related material costs. As the scanned model will remain virtual, physical models are not needed in many instances, which will reduce the requirement for a storage area.48–50 In addition, the virtual model has the advantage of ease of transfer and reuse. Further, the generated virtual model can be magnified, which will facilitate the prosthesis design.51 Nevertheless, scanning technologies continue to improve and become more accurate. Current scanners are capable of single-unit scans or limited multiple-unit scans, and as technologies improve, accurate full-arch scans should be possible.

For diagnostic purposes, the image obtained from a digital impression can be imported to specialized software for digital analysis and wax-up. The digital impression image can also be merged with the CBCT data with sufficient common points (ie, three or more). Again, the ability of superimposition greatly varies with the softwares, and the “best fit” mode may average out the differences. With progressive advancement in IOSs and greater computing power, these have become less expensive, smaller, and more ergonomic, and thereby faster and easier to use. Recent reviews have reported the capability of digital impressions to produce restorations of comparable accuracy to conventional methods.52,53 However, the digital impressions require initial investment in scanning devices, and they rely on the clinician’s skills to ensure adequate scanning.

New manufacturing techniques

The use of scanning tools and digital software would be limited without manufacturing techniques that translate the digital information into actual objects. Once the prosthesis design is established by CAD software, it is transferred to a CAM unit, which can be subtractive or additive. The traditionally subtractive CAM systems aim to produce a restoration with accurate fit and morphology as planned by the software. Subtractive methods have been more commonly used for implant restorations and are based on milling the restoration from an industrial highly dense blank that can be metal, ceramic, or acrylic resin. As a result, milled restorations have been more durable, more consistent, and less likely to suffer from manufacturing deficiencies compared to conventionally produced restorations. Thus, subtractive manufacturing can be reliably implemented for the fabrication of definitive restorations and components such as abutments and frameworks. However, intricate designs with large and multiple undercontoured surfaces may pose a problem for subtractive manufacturing, such as when milling metal frameworks for fixed hybrid prostheses (see chapter 8, section entitled “CAD/CAM metal frameworks”). The tool path needed for even multiple axes (industry standard of five axes) may be limited. While subtractive machines are commonly available in commercial laboratories and centralized milling centers, they are associated with excessive material wastage. In addition, the milling parameters have to be closely monitored, and the milling apparatus and tools should be well maintained to ensure consistent outcomes.13–15

An alternative production method is additive manufacturing, where the object is produced gradually by building it in layers. This can be achieved by 3D printing, such as stereolithography (STL), drop-on-demand printing, fused deposition modeling, and selective laser melting54 (SLM; Fig 5-11). Additive manufacturing appears to be more economical, because it does not involve material wastage like subtractive manufacturing.

Fig 5-11 A removable partial denture framework designed digitally and fabricated with SLM. (Courtesy of Dr J. Jayanetti.)

For resin printing, the wide variety of printers—from the smaller desktop ones to some larger ones—result in vast differences in accuracy and resolution. Nevertheless, this technology is unique in producing more complex geometries and large objects that cannot be milled due to limitations in tooling paths and the dimension of the starting block/pucks. Thus, resin printing is more commonly used for producing surgical guides and dental casts within the implant digital workflow rather than subtractive milling. However, milling is still the go-to manufacturing technique for definitive restorations due to limitations in materials available for 3D printings, and milling still produces the highest resolution of all 3D printing technologies used in dentistry today.

One type of printed material used in definitive implant restorations is metal. However, current SLM techniques used by commercial laboratories are restricted to a resolution of 20 microns, which poses a severe constraint on surface finish, minimum feature size, and precision fit against implant internal connections. Presently, acceptable fit and finish can be achieved when this technology is used to fabricate removable partial denture frameworks (see Fig 5-11). However, the post-processing required to produce smooth surfaces and the inherent lack of precision fit at the micron scale does not permit this technology to be used for implant frameworks and abutments. New SLM technologies that print at micron-scale resolution using nanopowders are available, but this can require significantly longer times to print frameworks used in implant dentistry. Future SLM modifications involving multiplex, laser, and electron beams will be able to achieve high resolution at a more practical speed.

One of the limitations of both types of manufacturing (milling or printing) is the choice of material, and there is also the issue of having undesired waste. The uses for time-tested and predictable gold alloys are very limited in these processes. For example, in situations in which a restoration would have previously been made with a UCLA abutment out of a cast gold alloy with porcelain directly stacked on it, the planned restoration may now be a full monolithic zirconia crown on a titanium-base abutment. While it may appear cost effective, the longevity and effect of these change in materials and techniques is still undetermined.

Digital Workflow

The traditional implant treatment protocol involves planning implant placement according to the most ideal prosthodontic position via diagnostic casts and radiographs followed by laboratory-made surgical guides. After osseointegration, an impression of the implant fixture is made and used to produce a master cast on which the definitive prosthesis is fabricated by the dental technician. This protocol is still preferred by many clinicians and has the advantage of being well outlined and familiar to the team. However, its drawback is the number of visits, its heavy reliance on the expertise of operators, and the possibility of losing control between the different steps.

Digital technologies have modified the implant treatment protocol by replacing some or even all of the steps of the traditional protocol.7,9,55 Currently, there are multiple digital workflows, some of which still rely on dental laboratories, while others bypass the need for them. Following the comprehensive prosthodontic evaluation, a CBCT scan of the patient is obtained, and digital impressions of both arches are made and virtually articulated. After the integration of the CBCT scan with the virtual arches, a digital wax-up is carried out, and the implants are selected and virtually placed in the ideal position. This can be followed by designing and manufacturing of the implant surgical guide. In addition, the definitive prosthesis can be virtually designed, and the most appropriate implant abutment design and angulation can be selected. Some newly emerged digital protocols allow for production of an immediate implant provisional prosthesis prior to implant placement56,57 (Fig 5-12). This step can be completed if the implant placement is fully guided and the restoration is produced using CAD/CAM technologies. The experience of the entire team will determine the success and efficiency for the treatment being provided, including the surgical and prosthodontic skills of the team members, as well as their familiarity with the digital technologies required to follow this protocol. Because dental laboratories perform many of the digital workflow tasks, it is imperative that the laboratory technician is sufficiently trained to perform the laboratory steps related to the digital technology necessary to support the digital workflow. Any breakdown in the workflow may result in a negative result.

Fig 5-12 An example of a digital workflow resulting in the design and fabrication of an immediate load provisional prosthesis. (a) A series of digital mockups of the steps required to perform an alveolectomy, place the implants, and deliver the immediate load prosthesis. (b) The foundation template, surgical guides, and immediate load prosthesis.(c) Foundation template secured to the mandible with bone screws, which also serves as a bone reduction guide. (d) Surgical drill guide. (e) Immediate load prosthesis being oriented in position prior to (f and g) being secured to the implants. (h) Prosthesis in position (see chapter 8 for details).

The authors recommend that clinicians establish a digital workflow based on the their experience and training, with the understanding that transitioning from digital to traditional protocols and vice versa can be necessary in particular situations. While the digital workflow adds flexibility to implant treatment, each clinical situation should be evaluated on its own merits. If it is determined that the case is simple, straightforward treatment, then the digital workflow may be modified or eliminated altogether, and the necessary steps for completion of implant treatment may be performed using a traditional workflow. In general, the digital workflows can be divided into three streams: (1) laboratory, (2) chairside, and (3) combined laboratory-chairside.

Laboratory stream

In this stream, the clinician opts to make conventional impressions and diagnostic planning and work-up. The digital interaction occurs at the laboratory level, where the casts are scanned and the prosthesis and the relevant components are designed and produced by CAD/CAM (Fig 5-13). Subsequently, the prosthesis can be further modified and veneered by the dental technician. Once the cast has been created, scan flags are attached to the implant analogs and scanned by a laboratory scanner. The prosthetic design that was previously established during the work-up phase is merged against the virtual working cast with the virtual implant analogs by the CAD software. This stream is advantageous because it maintains the familiarity of the traditional treatment at the clinic yet also benefits from the features of laboratory CAD/CAM such as precision, quality control, and increased range of materials. However, it will still require a similar number of visits as the traditional protocol.

Fig 5-13 A typical workflow using a laboratory stream. (a to c) Conventional impressions were made and articulated. CBCT scan and the data from the scanned casts were merged, and the implant position, length, and diameter were determined. (d and e) The custom abutment was designed and milled. (f and g) The implant crown was designed and milled out of a ceramic material. (h and i) The implant crown was cemented to the abutment outside the mouth and retained with the abutment screw.

Chairside stream

The clinician in this stream can complete all clinical and technical steps at the dental office. This requires the use of chairside scanning and a CAD/CAM unit that is compatible with implant treatment. The protocol involves steps such as digital diagnostic impression taking and implant planning, guide fabrication, digital implant impression, and prosthesis fabrication. In this stream, multiple steps of the restorative workflow are easily combined in one clinical visit, which markedly reduces treatment duration and patient inconvenience. For example, in one visit, scan flags can be attached directly to the implant and scanned by the intraoral scanner. On the generated virtual image, the implant prosthesis is designed and subsequently produced by the chairside CAD/CAM unit. However, the clinician should be very familiar with the setup to ensure proper control of the whole treatment. Despite the advantages of this stream, it has several limitations, such as restriction to single and short-span implant prostheses and loss of artistic customization of the implant restoration by the technician. In addition, due to limitations of the chairside milling unit, the implant prosthesis can only be produced from ceramic, acrylic, or composite resin on a metal insert.

Combined stream (chairside-laboratory stream)

This stream is based on digital completion of the clinical steps at the dental office and fabrication of the prosthesis by a commercial dental laboratory. The clinician records the dental arch by digital impression and transfers the virtual image to a planning software. The clinician also controls the design of all workpieces such as surgical guides, components, and prostheses. Once confirmed by the clinician, the designed object is transferred to the commercial laboratory or a centralized production center, where the guides and the implant prostheses are fabricated. This stream combines the advantages of the previous two streams; however, because the quality of the prosthesis depends solely on the virtual image, the clinician should be ready to manage accuracy errors at the clinic in the form of discrepancy of proximal and occlusal contacts. One of the major advantages of this stream is the involvement of the dental technician in fabricating the prosthesis, which allows more detailed esthetic customization. To enhance the outcome of this protocol, it is recommended to generate a dental cast via 3D printing on which the prosthesis can be fitted and customized in the laboratory.8

The digital workflow depends on very fluid and continually developing technologies. As a result, the successful application of digital workflows can be ensured by continuing educational participation, review of the dental literature, and collaboration among colleagues undertaken at every opportunity. While digital technology is state of the art, it is still founded on basic prosthodontic principles and as such is merely a set of tools to aid in our overall goals for patient treatment using dental implants. At this juncture, it is impossible to determine what the future of digital technologies will entail with respect to implant dentistry. Certainly, the advances made with digital technologies in all aspects of dentistry have had a significant impact, and evidence suggests that this scenario will continue. Implant dentistry will continue to evolve, and digital technologies will have a substantial role in both planning and delivery of implant modalities for our patients.

Digital impressions

A virtual dental arch is necessary for the digital workflow. Many clinicians who choose to incorporate digital technology with fabrication of a prosthesis record the impression in the customary fashion to generate a master cast that can then be scanned with a laboratory scanner. From this point, the clinician and the laboratory technician can choose the digital workflow for the specific prosthesis fabrication (see Fig 5-13). To date, this has been the most accurate, convenient, and cost-effective process, as the practitioner does not need to invest in the scanner or its maintenance.

As the acquisition cost decreases, the more contemporary method to produce a virtual dental arch is via digital impression. The concept of digital impressions by intraoral scanners has evolved over the past several years, and like many aspects of dentistry, has seen many advancements and improvements. Nevertheless, when digital impression methods were initially introduced, it was a seldom-used procedure relative to the overall various situations that require an impression to record data for dental treatment. Many reasons exist as to the limited use, with cost being the major factor. The initial investment in this technology is significant compared to conventional impression techniques. Other factors that have limited the use of this technology in the past include accuracy of digital impressions, time to record the necessary data, access to various parts of the mouth, limited numbers of dental laboratories that can receive the digital data, techniques required to generate a working cast, and experience and knowledge of the practitioner. Recently, there has been a progressive move to incorporate digital impressions in routine prosthodontic treatment as IOSs became more versatile, more accurate, and quicker (even for recording the whole arch), with easier digital file storage.6,58,59 Compared to conventional impressions, digital impressions have the advantage of requiring no tray or impression material usage, which may be more comfortable and convenient to patients.60 From the clinician’s perspective, it may be an economical option after the initial investment. However, with ease of storage, the need to maintain a large database may contribute to the expense. In addition, digital impressions allow for immediate viewing and magnification of the virtual image, which can also be revisited in case of errors within the clinical session.60 Still, digital impressions of implants require removal of the healing abutment and accurate fitting of flags or scan bodies onto the implant platform.

The current literature indicates that digital impressions are suitable for diagnostic purposes where the image is used for planning such as measurements, treatment planning, and diagnostic wax-ups.48–50,61 For definitive prosthesis fabrication, the accuracy of digital implant impressions generated intraorally has greatly improved, and some literature has indicated comparable outcomes to conventional techniques.62–67 However, due to the numerous factors that can influence the accuracy of digital impressions, it appears to be too early to make a rigid recommendation about digital impressions being a suitable substitute to conventional impressions, especially when making full-arch impressions.60 The key influencing factor on the accuracy of the digital impressions is the span of scanning. Consistently, studies have indicated that as the span of scanning increases, the accuracy of the generated image is reduced.68–72 However, digital impressions generally produce an acceptable quadrant image, while whole-arch scanning is more prone to error compared to conventional impression making and laboratory scanning of the cast.73,74

The inaccuracies of digital impressions have been attributed to the steps of the scanning procedure. Because digital impressions are based on light emission on the scanned object, excessive light reflection from metal surfaces and saliva creates excessive image noise that influences the sharpness of the 3D image.38,39,75 In addition, areas that can obstruct light emission, such as proximal surfaces, should be scanned carefully, because shadowing will lead to loss of the entire shadowed area.68,76–78 Digital impressions require multiple overlapping images of the dental arch, which will eventually be stitched into one 3D image. However, each stitching process introduces an inevitable degree of error.69,76 Therefore, partial-arch scanning (confined) where stitching is kept minimal has been found to be consistently more accurate than whole-arch scanning where extensive stitching is implemented.69,71,76,79,80 Specifically, the more terminal sites of the arch suffered from the greatest error. On the contrary, laboratory scanning of a conventional cast captures the whole arch dimension and does not require numerous image stitching, which may explain the greater accuracy of laboratory scanning for whole-arch recording.72–74,76,80Additional sources of error with the digital impression relate to its vulnerability to patient factors, such as patient and/or operator movement, access in the mouth, and soft tissue stability.68,81

Currently, for the partially edentulous situation, some laboratory studies have indicated that digital impressions of single implants or a few adjacent implants are comparable to conventional impressions,62,63,65 while other studies indicated the superiority of conventional impressions.82,83 For full-arch implant impressions, digital impressions appear to be prone to errors.70,71,84 On the other hand, some recent laboratory studies have shown greater accuracy for digital impressions than conventional impressions.64,66,67 However, because these studies are laboratory studies, they may not truly reflect the challenges of intraoral scanning of implants, and clinically there are indications that digital impressions may suffer from greater errors85; therefore, a form of accuracy verification should be considered. In conventional impressions, it is recommended to have a verification jig/index to confirm the accuracy of the final master cast. In the digital workflow, this step is not available, and the use of an analog prototype is needed to verify passive fit prior to the fabrication of a larger prosthesis.

If intraoral digital impressions are to be incorporated into the digital workflow on a wide-scale basis, it is imperative that clinicians abide by the necessary techniques to ensure the accuracy of transferring the data. As digital technology continues to improve, it is conceivable that digital impressions will become a reliable method for recording and transferring the data to the laboratory, thereby enhancing the digital workflow.

3D planning and digital workup

The traditional prosthodontic workup has been accomplished with conventional measures such as mounting diagnostic casts on an articulator, the wax-up, and the teeth setup on trial denture bases. The early application of digital implant dentistry to design the restoration was based on scanning the wax-up.86 As per the traditional workup, the diagnostic casts are mounted on a semiadjustable articulator in centric relation. This is followed by a diagnostic wax-up to determine the prosthetic design. The casts are then scanned both with and without the diagnostic wax-up and are virtually articulated. These data sets are then merged with the CBCT data in a treatment planning software (Fig 5-14).

Fig 5-14 (a) Analog wax-up on study cast. (b and c) Analog wax-up scanned and superimposed on the CBCT data in a 3D planning software. (d) Verification of final implant positions and distance to the inferior alveolar nerve.

More recently, the fully digitized wax-up has become a reliable option for implant treatment. Virtual arches can be generated by scanning the physical casts or after digital impression. Digital wax-ups involve the addition of virtual teeth to establish the ideal implant position. The implant site is visualized in 2D and 3D views, and the implant placement can then be virtually planned based on the prosthetic design. Once accomplished, a determination is made whether to place the implant using fully guided, semiguided, or freehand surgery. The use of guided surgery is strongly recommended to further enhance the patient outcome. In addition, the digital wax-up can be used to virtually design the prosthetic implant components and definitive restorations, where the full design of the abutment, framework, and restoration is determined digitally via the software. Currently, several software programs are available to facilitate the implant planning. Some of them are closed systems related to specific implant manufacturers, while others are open programs and allow for planning of the implants from different manufacturers.

Complete digital determination of the prosthesis has been found to be advantageous because it is totally reversible, which simplifies the determination of the restoration contour. The use of the automated features of the software reduces the planning time and the dependence on technical skills for producing wax-ups and tooth setups.87–89 In addition, the software is commonly linked to a “library” of digital teeth that can be used for the digital wax-up.89–92 Digital molds are based on anatomical and esthetic teeth, which may explain why several studies have found the digital protocol produces very esthetic and anatomical teeth with good natural details that are at least as good as what the dental technician can produce using a traditional wax-up.90 Digital modeling of the restoration also ensures completely symmetric anatomy, as the software can reliably implement mirroring of the contralateral tooth or restoration (Fig 5-15).88,93

The type of abutment to be used can be determined at the time of digital treatment planning. The optimized visualization of the prosthetic components has increased the reliability of prosthesis design and selection. For example, premachined transmucosal abutments—including predetermined angle corrections—that best support the prosthesis can be reliably selected (see Fig 5-15e). In addition, the software ensures ideal prosthesis thickness is implemented so the proposed prosthesis exhibits ideal mechanical properties.

Despite all of these advantages, the digital protocol still requires refinement of the establishment of occlusal contacts, which currently appears to be inferior to the conventional protocol. In complex full-arch restorations, a clinical remount is absolutely necessary (see Figs 5-15g and 5-15h). This has been attributed to the accumulated accuracy errors of the scanned image and virtual articulation.94–97 Nevertheless, for implant planning and diagnostic wax-up, minor occlusal discrepancies may not have major consequences. For definitive prostheses, physical casts can still be used by the technicians when they are completing the veneering around the restorations to ensure good occlusal and proximal contacts. Alternatively, if the clinician is following a completely digital protocol, the physical casts can be produced by 3D printing, which allows the dental technician to stain and glaze the restoration and accurately refine the occlusal and proximal contacts. In some instances, routine digital workflow does not allow actual try-in of the prosthesis before processing, which can lead to patient dissatisfaction.89 This can be overcome by generating a trial prosthesis (prototype) that can be modified by the clinician to meet the patient’s demands. Thus, while the software tools will facilitate the treatment, the clinician should be aware of the limitations and know that these technologies do not replace sound prosthodontic principles and skills.

Fig 5-15 Digital planning enables presurgical selection of abutments and permits fabrication of an immediate load conversion prosthesis. (a) “Stacked” surgical guides on a printed bone model. (b) The immediate load prosthesis is keyed to the foundation template. (c) The foundation template is secured with bone screws and also serves as a bone reduction guide. (d) The osteotomy sites are prepared, and the implants are inserted. The drills are designed with shanks that precisely engage the drill sleeves (bushings). (e) Abutments have been secured to the implants. The precision achieved with digital workup and fully guided surgery permits selection of the angled abutments prior to surgery. (f) The immediate load prosthesis keyed to the foundation template and ready to be secured to the abutment cylinders. (g) Remount cast of the final conversion interim prosthesis. (h) Clinical remount to ensure proper occlusal contacts in centric relation position. (i) Prosthesis fixated demonstrating desired occlusal contacts.

Computer-planned and guided implant surgery

From its inception, implant dentistry was driven primarily by the surgical discipline. Before surgical guides, freehand surgery was the primary method by which implants were placed, and this method was largely dependent on the surgeon’s experience and knowledge of the prosthodontic principles related to implant surgery. This led to implants being placed into bone but not necessarily in positions that were optimal for the prosthetic design.98 Eventually, the importance of having a prosthetic plan prior to implant placement gained acceptance. Today, it is generally regarded that implants should be placed according to the prosthetic design.99

As a consequence, surgical guides to control implant positioning have proven to be useful devices when performing implant surgery by relating the implant position to the specific prosthodontic plan of treatment. Traditionally, surgical guides were produced by the laboratory according to the diagnostic wax-up.100 As several aspects of digital technology continue to evolve with respect to implant dentistry, one of the more remarkable advances is the ability to plan implant surgeries from both the prosthetic and surgical perspectives, allowing the implants to be strictly placed via accurate surgical guides. The final prosthesis can be virtually designed according to the intraoral features and available bone observed from the CBCT image, making it possible to plan for the most ideal implant to achieve the planned prosthesis.

The design process begins by merging the STL files obtained from the diagnostic casts, diagnostic wax-up/setup, or existing prostheses with the Digital Imaging and Communications in Medicine (DICOM) data produced from the CBCT scan into a computer software program. The merging process is very reliable, because it utilizes the teeth as common landmarks between the STL files and the 3D image. Eventually, the relationship between the intraoral tissues and the underlying alveolar bone can be reliably viewed. For edentulous patients, a dual-scan technique is implemented. An acceptable denture or denture setup with the correct fit and tooth position is used as radiographic template. It can be modified by placing six to eight fiducial radiopaque markers (eg, gutta-percha or DentalMark products [Suremark]) on both the buccal and lingual denture base areas in a staggered fashion (Fig 5-16). A CBCT scan or surface scan of the radiographic template (denture or denture setup) is then obtained separately, followed by a CBCT scan of the patient with the radiographic template in place. Care should be taken to ensure that the fiducial markers remain in the same position as initially scanned. These two scans are then merged together to outline the clear relationship between the alveolar bone and the planned prosthetic design.101

Fig 5-16 Guided implant surgery planning. (a) Denture with acceptable tooth positions with the fiducial radiopaque markers. (b and c) CBCT scan images superimposed with denture scan using dual-scan protocol such that implant position planning can be initiated. (d) Guide in place fixated with anchor pins and implants placed.

Once the images are visualized in 2D sections and 3D, the implants are virtually placed according to the prosthodontic requirements of the intended prosthesis and the anatomical limitations of the patient. If anatomical limitations exist that prohibit ideal implant placement, then a determination must be made as to the necessity for altering implant position or deciding on augmentation procedures prior to implant placement. In addition, the effect of any alteration in the implant position on prosthesis design can easily be visualized. Once the implant length, diameter, depth, and angulation are determined, the surgical guide is designed to reflect these parameters. Some softwares have the ability to add the prosthetic abutment design at this point. This is particularly useful in planning for angulated prefabricated abutments for multiple units with a full-arch prosthesis. The guide design should allow for soft tissue manipulations without interfering with the positioning of the guide. Once the guide design is verified, it is produced by 3D printing or milling. Metal sleeves that are calibrated to a specific implant system’s guided drills and kits are attached for either fully guided or semiguided surgery. The software can then generate the detailed procedure protocol to be followed closely intraoperatively (Fig 5-17).

Fig 5-17 An example of the guided implant surgery. (a) Details of the planned implants. (b) Surgical protocol for the drill sequence and steps to be followed intraoperatively.

Depending on the seating of the surgical guides, three basic designs are available: (1) tooth-borne, (2) bone-borne, or (3) soft tissue–borne.102 In some cases, a combination of these designs can be considered. When treating a partially edentulous patient, the surgical guide is typically tooth borne (Fig 5-18); however, a combination of tooth- and tissue-borne or tooth- and bone-borne can be considered for large edentulous segments. The friction between the teeth and the guides will stabilize them during surgery. Visual access windows can be incorporated within the guide to ensure proper seating on the teeth.

Fig 5-18 A tooth-borne surgical guide designed for fully guided surgery. (a) Virtually planned implant positions and surgical guide designed. (b) Use of a drill key (arrow) that seats into the drill sleeves (bushings). These drill keys conform to the implant drill dimensions. (c) Implant placement through the surgical guide. (Reprinted from Moy et al23 with permission.)

For the edentulous patient, the guides can rest on the mucosa (see Fig 5-16d) or directly on bone (see Figs 5-12 and 5-15). For stability, these guides can be fixed by lateral/anchor pins/screws to the bone. The level of fit of the guide is thought to influence the accuracy of implant placement in relation to implant planning. The tooth-borne guides are generally more accurate,103 as they are fabricated on an STL of the teeth (see Fig 5-18). The soft tissue–borne guides are based on STL images of the patient’s ridge. However, the compressibility of the tissues may cause some deviation from the planned implant site. The bone-borne guides are purely based on CBCT DICOM data, which are not as accurate as STL images of the intraoral tissues that are produced by a digital impression or a conventional impression followed by a laboratory scanner. This may explain the inferior accuracy reported for the bone-borne guides. However, bone-borne guides have the advantage of surgical visibility during drilling and implant placement. Normally, bone-borne guides are used for patients in need for adjunctive bone reduction during implant placement.102 However, these guides require a larger reflection of the flap to ensure complete seating on bone.

Surgical guides may be used for fully guided or semiguided surgery or both (Fig 5-19). Fully guided implant surgery controls implant surgery by allowing for the preparation of the osteotomies and placement of the implants through the guide. The fully guided surgical guide also accounts for the angulation and depth of the implants. As a result, the fully guided protocol is the most predictable protocol for implant placement. In certain situations, the surgery may be accomplished using a flapless approach (see Fig 1-16)104; however, great care must be used in patient selection to avoid postsurgical complications and to ensure that the implants are properly positioned within the bone. Fully guided surgery has increased in use and popularity, particularly with the immediate loading scenarios employed by many clinicians.

Fig 5-19 A tooth-borne surgical guide designed for both fully guided (black arrows) and semiguided (white arrows) implant surgery. (a) Surgical guide designed. (b) Manufactured surgical guide with the metal sleeve inserts. This is verified for proper fit and stability. (Courtesy of Dr A. Pozzi.)

Some partially edentulous cases require the use of semiguided surgical drill guides, primarily because the mesiodistal space available is insufficient to house the drill sleeves used in fully guided implant surgery. Semiguided surgical drill guides permit the initial preparation of the osteotomy sites with twist drills and control the direction and angulation of the initial preparations. However, the final preparations and the depth of implant placement is completed freehand and dependent on the surgical operator’s judgment. As a result, it is slightly less accurate than the fully guided protocol.105

The diameters of the fully guided drill sleeves (bushings) vary according to the implant manufacturer and are able to accommodate the drills and the implants being placed (see Figs 5-18 and 5-19). The metal sleeves for the semiguided surgical guides are smaller in diameter and allow for only a few drill sizes in the initial preparation of the osteotomies, while the completion of the osteotomies and placement of the implants are performed freehand.

Surgical guides for the fully edentulous patient may be one piece, two pieces, or more depending on the surgical procedure and the necessity of adjunctive therapy. Multiple-piece surgical guides are comprised of a series of stackable templates and when used together can be employed for bone reduction, osteotomy preparation, and placement of the implants and orientation of the conversion (provisional) prosthesis when an immediate loading protocol is employed (see Figs 5-15b and 5-15f). The foundation (base) portion of the guide is typically used as a bone reduction guide in addition to supporting the surgical guide used for the guided implant surgery protocol. The bone screws used to secure the template are interspersed between implant sites. Flaps should be designed to ensure adequate exposure of the bone and placement of the foundation template. Use of a positioning jig enhances proper positioning of the foundation template prior to placement of the bone fixation screws (see Figs 8-69d to 8-69f). The surgical guide with the metal drill sleeves is then attached to the foundation template in preparation for the osteotomies and placement of the implants (see Fig 8-70).

Navigation-guided implant placement

The concept of navigation-guided implant placement has recently been introduced, and several practitioners have been testing its application (Fig 5-20). During the CBCT scan, the patient wears a custom jig with radiopaque markers. Treatment is digitally planned using specifically tailored software. At the time of the procedure, once the unit is calibrated to the patient tracker that is rigidly fitted to the patient’s dentition, the unit scanner is able to detect the patient in 3D and is superimposed onto the CBCT taken prior to surgery. Similar markers on the handpieces allow the unit to compute the virtual space where the implant drills are located and see the surrounding bone and vital structures. The surgeon views the monitor in order to prepare the osteotomy sites and place the implants in the planned positions. Deviation from the planned implant position sounds off an alarm to alert the surgical team. The patient’s head movement and position do not necessarily affect this process. While promising, this procedure is dependent on proper scanning and calibration methods to the tracking units as well as rigid fixation of the patient tracking device.

Fig 5-20 (a) Triple reflective marker spheres are anchored to the handpiece. This allows the system to triangulate its position. This image shows the calibration jig also bearing triple spheres. This allows the software to locate the tip of the osteotomy bur as it relates to the handpiece. (b) The osteotomy site is being created. In this patient, zygomatic implants are planned.

There are available haptic training simulators that provide a close-to-real feel of the procedures and drilling. A less experienced clinician would be able to practice the procedure as many times as they prefer prior to the actual procedure. This can be particularly helpful for a beginning clinician.

Robotic surgery

Another recent development is the introduction of robotic surgery for implant placement. With this method, the team determines the desired implant location with a fully computerized automation system, and the dental implants are placed in the planned positions. While accuracy has not been fully validated by systematic clinical trials, along with the influx of artificial intelligence, the future of automated implant treatment planning and placement appears promising.

Design and fabrication of abutments, frameworks, and prostheses

In terms of design and fabrication of dental prostheses, digital technologies have changed the methods for restoring implants. Traditionally, implant prostheses were fabricated by casting via the lost wax technique, where the abutments, frameworks, or copings are built in wax and cast in metal. This was followed by veneering these structures with ceramic or acrylic resin. This option is still a viable treatment method, and manufacturing companies provide relevant components in the form of UCLA castable abutments and plastic burnout sleeves that can facilitate the fabrication process. However, this protocol has some manufacturing-related limitations because it is labor intensive and requires considerable human handling and skills. As the restoration will be cast and subsequently veneered, it has to be heated several times, which may influence the connection surface quality and the precision of component fit.18 Casting was found to cause rotational misfit of abutments and framework misfit. This is even more prominent for base metal alloys. This is further accentuated with the anatomical contouring of implant restorations, which use more metal.

On the contrary, digital technologies in the form of CAD/CAM overcome several of the traditional casting problems and provide the clinicians with more flexibility and options to treat implant patients. It has been established that CAD/CAM processing for implant dentistry has the advantages of (1) producing accurately fitting components, (2) ease of customizing components, (3) manufacturing components from esthetic materials, and (4) allowing simpler implant restoration concepts. In addition, because CAD/CAM processing avoids using noble metals and reduces human processing, it is a cost-effective method of fabrication.14

The manufacturing units work in conjunction with the CAD software. The generated STL files form the software used to control the manufacturing units. Currently, the most standardized method for producing implant-related restorations is via milling through a computer numeric controlled (CNC) machine. More recently, additive manufacturing has become an option; however, it requires further refinements to produce implant prostheses of acceptable quality (see earlier section entitled “New manufacturing techniques”).106 However, additive manufacturing is extremely beneficial for the production of casts, removable partial denture frameworks (Fig 5-21), and surgical guides from digital data.

Fig 5-21 (a) Designed framework. (b) Printed pattern confirmed to fit the master cast.

Milling-facilitated production of components of more contemporary materials

Milled titanium and base metal alloys (such as cobalt- chromium), abutments, and frameworks can be reliably produced with a fit level closer to prefabricated implant components.1 As a result, several implant companies and milling centers provide customized component options. While titanium has been a material of interest due to its biocompatibility and similarity to the implant material, it cannot be predictably veneered with ceramic. As a result, base metal alloys were proposed as an alternative to overcome the ceramic bonding limitations. In addition, after the introduction and advancement of toughened zirconia, implant components can be produced from zirconia, which is currently the most durable esthetic and metal-free option. To date, milling is the only method to predictably produce zirconia restorations (see chapter 8, section entitled “Monolithic Zirconia Prostheses” and chapter 10, section entitled “Procedures for monolithic zirconia fixed prostheses”).

Whenever possible, it is recommended to customize implant components. The use of CAD software allows for abutments to be reliably customized specifically for the prosthetic design and to be manufactured with CAM technology. As opposed to prefabricated components, customizing implant components for individual patients has multiple advantages such as an ideal finish line location, anatomical contouring, and correct material bulk for durability107 (Fig 5-22). Correct finish line location is necessary for cement-retained restorations, because in deep margins it has been found to be difficult or even impossible to eliminate the cement, which will eventually cause biologic complications. Anatomical contouring is advocated to ensure even veneering ceramic layer thickness and acceptable morphology to retain the cemented restoration. In addition, customizing an abutment ensures achieving an ideal gingival contour, emergence profile, resistance form, and retention form.

Fig 5-22 (a and b) Image of the planned custom abutment design prior to manufacturing. Designs can be modified or approved. (c) Milled custom abutments tried in to verify fit, contours, and margin placements. (d) Definitive cement-retained metal-ceramic restorations.

A clear advantage of this feature was found for zirconia- based restorations where the veneering ceramic can be kept to a minimum or eliminated, thereby reducing the likelihood of ceramic chipping (Fig 5-23). More recently, with the advancement of CAD/CAM technologies, monolithic zirconia has been advocated, where the restoration is made from zirconia with minimal or no ceramic veneering. In addition, the software ensures that a minimal acceptable thickness of the component is provided for milling. Digital fabrication is linked to the design software, ensuring accurate reproduction of the planned components. Therefore, digital customization is more reliable, efficient, and convenient than traditional techniques.

Fig 5-23 (a) Trial (prototype) prostheses. The prostheses were inserted and adjusted as needed to refine the occlusion and hygiene access over a period of several weeks. The prostheses were then removed, placed upon the master cast, and (b) scanned. The tissue surfaces were slightly refined (c), and the definitive prostheses were fabricated from monolithic zirconia (d and e).

Because CAD/CAM reduces the level of human intervention and the overall fabrication steps, it has been speculated that CAD/CAM is capable of producing implant components with greater accuracy than conventional techniques. In addition, as the shape of the implant connection and abutments are based on known parameters, reverse engineering modeling and milling the interfaces to high precision is possible.2,108 This was confirmed by laboratory studies on abutments and frameworks, where the studies consistently found that the fit of CAD/CAM-produced components is superior to conventionally fabricated components.18 This was generally found for titanium and base metal alloys; however, the fit of zirconia components appears promising, although it was more prone to errors in the form of rotational freedom or vertical misfit as well as fractures.109–111 To overcome this problem, prefabricated titanium metal inserts have been considered.

Evolving workflow

Due to the integration of the digital manufacturing with all the features of digital technologies mentioned in this chapter, component and prosthesis fabrication is generally simpler and more reliable than conventional fabrication. For example, digitally produced restorations can easily mimic the digitally planned restoration. Because the CNC machine is controlled by a series of commands from the CAM software, the contour of the restoration can be precisely controlled to generate the planned restoration contour. This will simplify producing esthetic and symmetric restorations. Through the office digital workflow, the clinician is able to produce the implant restoration within the clinic in one restorative visit. This involves scanning the metal insert or prefabricated abutment, designing the prosthesis digitally, and milling the prosthesis via a chairside milling unit. The produced restoration can then be attached to the insert or the abutment. On the other hand, with the aid of a digital impression, an STL image of the implant and the arch can be transferred to the dental technician or milling center for fabrication of the prosthesis. The manufacturing center can produce a dental cast by additive technology on which they can fit the prosthesis for further customization of the contour, shade, proximal contacts, and occlusion. More advanced digital protocols allow for the production of a definitive prosthesis prior to implant placement. Given that implants can be precisely inserted by fully guided surgery, the implants can be immediately restored with a digitally processed prosthesis without significant chairside modifications. However, this protocol requires more validation, because bone and soft tissue healing may influence the appearance of the definitive prosthesis.

Summary

Digital technologies are tools that can enhance clinical outcomes when used properly. However, not all implant surgeries require digital treatment planning, and before digital technology existed, traditional prosthodontic workup methods enabled the prosthodontist or restorative dentist to communicate effectively with the implant surgeon and laboratory technician. Certainly, with digital planning and the associated technologies, the collaboration among the implant team is enhanced. However, more time is spent with planning, and there are increased costs to both the patient and the implant team.

Because the accuracy of guided implant placement largely depends on the quality of the CBCT image, the radiographic image should be obtained with minimal errors. If the patient has a significant amount of metal present in the mouth, heavy scattering within the CBCT image may occur (see Fig 5-9); hence, the patient may be required to wear a specific radiographic template during the CBCT scan to minimize artifacts in the segmented model. In addition, properly positioning the patient and ensuring that the patient is stable during the scan are especially important to eliminate the need to guess the desired outcomes.

Ultimately, the clinician is responsible for making an accurate diagnosis and carefully evaluating the needs of the patient and implant team when deciding to use digital treatment planning. The clinician may experience access difficulties while drilling and placing the posterior implants through the guide. This is more prominent for patients with limited mouth opening. In addition, long sleeves may interfere with the irrigation and cooling of the osteotomy drills. Poorly designed implant guides may have thin sections that can break during surgery. While the guided implant surgery is more accurate and reliable than conventional implant placement, it is still associated with errors. Studies have indicated the deviation of a placed implant compared to planned implant placement is within 1 to 2 mm in the horizontal dimension105,112 and 5 to 10 degrees in angle orientation.103,113 As result, it is crucial for the clinician to appreciate that these technologies, while beneficial, do not replace traditional surgical skills and pros- thodontic design fundamentals.

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