With the introduction of intraoral scanners and the widely used application of implant-supported prostheses produced using CAD/CAM - or Computer-Aided Design/Computer-Aided Manufacturing - it is possible to digitize implant positions directly in the patient's mouth. Making intraoral scans of implants, rather than digitizing plaster casts based on conventional impressions, saves a number of steps in the restorative process. With fewer steps, there is potentially also less risk of errors and discrepancies. This module will focus on the applications of intraoral scanning of dental implants.

After completing this ITI Academy Module, you should be able to: define the most frequently used terms associated with intraoral scanning and digital dentistry and list the available techniques and options; list the advantages and disadvantages of intraoral scanning; and describe the indications and applications where intraoral scanning can be used.

There are a number of terms associated with digital dentistry that are important to know and understand. The wand is the part of the scanner that contains the camera that is guided around the mouth by the dentist. Another important term is scanning abutment or scan body. This is an abutment or insert whose shape is recognized by the software analyzing the scan. This allows the software to determine the exact position of the implant. The abutment can be one-piece or two-piece. One piece abutments are often cylindrical in shape whereas two-piece abutments consist of a titanium base and a plastic cap which is to be recognized by the scanner. STL stands for Standard Tessellation Language and is the file format in which an intraoral scanner stores its three-dimensional pictures. There are also other file formats, such as PLY and OBJ, in which certain scanners store their files. These file formats have the ability to contain, in addition to the 3D file itself, additional case-specific information. DICOM is the acronym for Digital Imaging and Communications in Medicine and describes the three-dimensional raw data obtained from a computed tomograph - abbreviated CT - or from a cone beam CT.

There are two different techniques for mode of capture. There is a choice between a wand or system that acquires information continuously like a video and one that requires a stable moment to take a single picture. Since continuous capture scanners tend to be faster and easier to use, most recently introduced scanners use this technique. Within continuous capture there can be differences in the actual data acquisition. Instead of so-called video-in-motion technology, some scanners - such as the TRIOS - record data by capturing separate images continuously. All systems have their own advantages and disadvantages, therefore it cannot be stated that any mode of capture is superior to another for all possible indications.

Some scanners require a contrast powder or dust to perform intraoral scans. Powder adds contrast to shiny objects like enamel, gingiva, gold or porcelain. These powder particles perform as reference markers. Scanners that require powder necessitate an extra step in the process and are therefore less popular nowadays. Most recently introduced scanners are powder-free, nevertheless, in some indications - such as extended edentulous areas - applying a layer of powder might be beneficial.

In contrast, powder-free systems only require the area to be air-dried while the scan is being performed. Some of the wands have a built-in air blower for this purpose. A powder-free system tends to be easier to use and, because it does not require an extra step in the process, these systems can be more comfortable for the patient. A further benefit of certain powder-free systems is that they are able to scan in color. This makes it easier to distinguish between tooth structure and soft tissues in marginal areas. The latest generation of powder-free scanners even have a built-in tooth shade determination tool.

Several types of scanning abutments or scan bodies are available, and the decision on which to select for a particular situation depends on the implant system or CAD/CAM system being used. Implant manufacturers make their own scanning components, but in addition some CAD/CAM companies have created their own scanning abutment designs that are available for several implant brands. Implant brands often offer only one type of scan body. This may limit the clinical indications suitable for scanning. Using a non-original design from a CAD/CAM company might widen the potential clinical indications, but it is advisable to discuss this with the dental laboratory first.

Most scan bodies are one-piece and cylindrical in shape. To indicate the orientation of the implant they have one flat or cutback side. Alternatively, some brands have developed special healing caps that can be recognized by intraoral scanners. There are also scan bodies that are shaped differently or consist of two pieces. The scan bodies displayed here are plastic caps that click on a titanium base abutment. The benefit of these abutments is that a screw hole is not necessary, and under certain circumstances the titanium base may also be used as a final abutment. However, with the click system, there is a risk of component misfit that could lead to inaccurate scans.

With every introduction of a new technique it is key to evaluate whether it performs better, is faster, or is more user-friendly than its predecessors. Recently many studies have sought to compare intraoral scanners and/or conventional impression techniques. When evaluating the performance of an intraoral scanner or impression technique, two terms are important to understand: accuracy (or trueness) and precision (or repeatability). Accuracy defines how close a certain measurement is to the truth. Precision is the amount of consistency amongst several repeated measurements applying the same technique. These diagrams illustrate different combinations of high and low accuracy and precision. Ideally, an impression technique has both high accuracy and high precision. However, every combination of accuracy and precision is possible. Since determination of accuracy requires knowledge of the 'truth' it is challenging to examine it clinically. A patient's mouth cannot be used as a reference because it is not realistically possible to digitize it using highly accurate industrial scanners or coordinate measurement machines with probes. Therefore most accuracy studies are performed in vitro. In contrary, precision can be studied clinically and is often evaluated by repeating scans or impressions several times in the same patient.

Because many different outcome variables are used in accuracy and precision studies, it is difficult to compare results amongst studies. Some authors use distance deviations to demonstrate differences in accuracy or precision. These distances are often presented in micrometers and usually define a distance from a known reference point to another point. For example, the intermolar width of the reference model may be compared to the intermolar width as measured in an intraoral scan of the same model. Other distance deviations could be the displacement of a known object such as the position of one scan body compared to another.

Another widely used method to compare 3-dimensional images (or surface scans) is to superimpose these images with the reference model for a so-called best-fit alignment. Computer software identifies corresponding shapes, and then positions a scan file over the reference model. Because the images are not completely identical there is a mismatch between the two surfaces, which can be quantified as the so-called root mean square (or RMS) value. This number gives an indication of the difference between two surfaces that are supposed to be identical. Often these studies use 'heat maps' with changing colors to indicate where most of the deviation occurs. There are nevertheless many different methods to apply this technique. The best-fit alignment can be performed on the full surface of a scan file or on selected markers such as scan bodies, specific teeth, or reference markers. In addition, the RMS can be measured over the full surface (including, for example, the soft tissues) or only on specific regions of interest such as teeth or scan bodies. Since so many outcome variables and study designs are used, it is very challenging to compare results on the performance of intraoral scanners. Nevertheless, trends can be observed, and it becomes clear that certain scanners are more suitable for specific indications than others. It is advisable to evaluate study results that are specific to the indications for which you want to use an intraoral scanner - before deciding which device to buy.

Terms and Techniques, Key Learning Points: A wand is used to capture the scanning abutment or scan body, which in turn determines the exact implant position. STL or Standard Tessellation Language is the file format in which an intraoral scanner stores its 3D pictures, but other 3D file formats are also used. DICOM or Digital Imaging and Communications in Medicine is the raw data obtained from a computed tomograph (or CT). There are two modes of scanning: Continuous capture and stable image capture. Some systems require powder application to perform scans; others function without. There are several designs of scan bodies available; each type has its advantages and disadvantages. Scientific data is increasing rapidly, and although results are difficult to compare certain scanners seem to perform superiorly to others in specific indications.

The biggest advantage of intraoral scanning and CAD/CAM digital dentistry in general is the fact that everything is stored and processed digitally. In a regular laboratory workflow there are about 6 to 8 steps before a model is ready to be used as a working cast. This carries risk of damage and deformation and is avoided when using intraoral scanning and CAD/CAM. In addition, the environmental load is much lower due to digital storage and transport of the information. In the regular workflow each step involves human work and therefore carries a certain risk of introducing errors. This risk is reduced by using digital implant impressions. With intraoral scans, the information is also ready to be applied immediately. Since the speed of data acquisition has improved with the latest generation of scanners, a well-trained dentist is usually faster when taking a digital rather than a conventional impression. Literature reports up to twice the speed for full-arch digital impressions when compared with conventional techniques.

Other advantages of intraoral scanning and CAD/CAM digital dentistry are as follows: If problems occur with an existing prosthesis, it is easier to reproduce a structure as the dental technician can simply mill a new structure based on the file information. Because of the reduced time and materials needed, prostheses produced in a fully digitized workflow may be cheaper. An important benefit for the patient is that the time until delivery of the final prosthesis can be shortened. In the case of in-office milling, this may even be the same day. The very unpopular impression-taking can now be a thing of the past. A perhaps underestimated advantage of intraoral scanning is that bite registrations are easy to perform and are normally very accurate: A patient without posterior support can often still bite in the intercuspation position. In addition, bite registration materials that may lead to an increased vertical dimension when placed between the occlusal surfaces are no longer needed.

However, there are also disadvantages and limitations to intraoral scanning, as it is, for example, not yet possible to use the technology for all indications. Scans of large multi-implant configurations are still challenging and only possible with certain devices. Equally, scans cannot determine the functional border extensions for removable dental prosthesis flanges in the mobile soft tissue areas. Starting to work with the digital impression technique requires a large financial and time-intensive investment to the clinician. As with all new techniques it takes time to gain experience. Moreover, dental labs have been generally less flexible with intraoral scans than with conventional cast models. This was (and is sometimes still) caused by the lack of validated workflows and software restrictions. However, these things have improved a lot over the last few years, and nowadays virtually anything is possible using CAD/CAM software.

Advantages and Disadvantages, Key Learning Points: The advantages of digital impressions are: The process is fully digital with less risk of errors and discrepancies. The information is immediately available to the clinician and laboratory. It is easy to reproduce a new prosthesis using stored file information. Shorter delivery time and potentially lower manufacturing costs. Bite registrations are easier to perform with scan than with conventional impressions.

There are a lot of different possibilities for using intraoral scanning in implantology. In theory scans can be used for everything other than recording the functional border extensions of removable dental prostheses flanges in the mobile soft tissue areas. These areas cannot be scanned properly since the shape is not stable enough to be stitched together when the wand is moved further. The availability of documented workflows to use intraoral scanning is however very much dependent on the implant system and the intraoral scanner used. Some scanners have an open source which means that any information obtained with the scanner can be exported as clean and unprotected STL files, which can then be used in any CAD/CAM system. Prospective scientific research on digital implant prosthetics is still scarce, but nevertheless more and more data are available to support specific indications and most probably this database will continue to increase rapidly. It is advisable to discuss comprehensive cases with the laboratory or intraoral scanner supplier before beginning treatment.

It is possible to work with models based on digital impressions in an indirect but only partially digital workflow. Based on the intraoral scan a rapid prototype acrylic model is produced by either milling or printing. Special analogs have been designed by some implant manufacturers for insertion directly into this type of rapid prototype model. In this manner, the dentist or dental technician can continue their work as if it were a conventional cast model. As an alternative, a CAD/CAM abutment for the case can first be designed in the digital environment prior to model fabrication. In this way it is already incorporated into the subsequent rapid prototype model. The implant location will show the designed abutment shape as if it is a regular tooth preparation. These abutment shapes can often be removed from the model with a click system, and the dental technician can then work on the crown without the interference of neighboring teeth. The digitally designed CAD/CAM abutment is then supplied to the clinician, milled and ready for use in the patient's mouth.

With some brands a fully digital workflow has become available. With the digital position of the implant recorded via the intraoral scan, a crown and/or abutment can be designed and milled, as illustrated in this clinical case. The dental technician has worked without a model of any sort. This technology is available for most scanners and implants.

With some systems it is possible to fabricate chairside implant crowns and abutments, as shown in this clinical case. In addition to the intraoral scanner a milling station is needed for this purpose. The titanium base can be adjusted to become a scan body with a plastic click-on cap. Either a screw-retained or a cement-retained crown can be made. The technique is promising, but nevertheless not every prosthetic material is commercially available for in-office milling stations.

With the increasing popularity of cone beam CT planning in implantology, the new possibility of matching or superimposing these files with intraoral scans has become available. Once a rendering - or three-dimensional image of DICOM data - is made, it can be superimposed with the STL file from the intraoral scanner. The teeth can be used as reference points for best-fit alignment or matching since they should be clearly distinguishable in both images. When the images are properly matched, an interactive picture is created that contains information about teeth, soft tissue, and bone. A digital diagnostic wax-up or set-up can be made on this virtual patient. If needed, a scan of the opposing jaw can also be imported. In addition to the diagnostic wax-up, ideal implant positioning can be checked and adjusted according to the available bone visible on the CBCT. Once satisfied with the entire set-up, it can be used for patient counselling or to produce a printed or milled drill guide for guided surgery. With these technologies it is easier to achieve prosthodontically driven implant positioning, minimally invasive (or flapless) surgery, and predictable placement of the prosthetics. Nevertheless, not every case is suitable for this kind of matching procedure. In cases with a lot of metal crowns, the resulting artifacts in the CBCT can prevent proper matching with the intraoral scan. However, digital wax-ups can also be prepared without CBCT and can then be used just for the prosthetic design.

Some cases are difficult to scan. As the scan body needs to be scanned from all sides, it is important that the wand can be moved freely around the scan body. This is especially difficult with very distally angulated implants where the scan body is very close to a tooth or other implant. This situation creates a scanning "blind spot." Scanning may be difficult in patients with inelastic cheeks or a small mouth. Other challenging situations are long edentulous areas. In some scanners these may cause problems when stitching the images together. If the case permits, it may be advisable to make a partial- instead of a full arch scan; such scans are easier to make and tend to be more accurate. Shiny objects like gold and porcelain prostheses can also be challenging and it takes more time to scan these surfaces, especially with powder-free systems.

Intraoral scanning can be readily used in straightforward cases with one implant. As shown earlier, this can be done without a model of any sort. However, many dentists and dental technicians prefer a verification model and therefore use 3D printed casts. In the case shown here, a cylindrical scan body with an indicator for implant orientation is used. Based on the 3D position of the implant a CAD/CAM titanium abutment is designed together with its screw-retained monolithic zirconia crown. Since design of crown and abutment are combined and everything is made via CAD/CAM, the cost for a completely individualized crown is still relatively low.

Some of the latest generation of intraoral scanners exhibit such high accuracy that they can be used in straightforward multiple implant cases. In these cases the accuracy of the scanner is especially important since a passive fit must be realized. This treatment option has become especially interesting since the introduction of titanium-base abutments that are specially designed for multi-unit fixed dental prostheses or FDPs. In this clinical case two implants are provided with a screw-retained 3-unit monolithic zirconia FDP luted onto two titanium-base abutments. The scan bodies are original cylinders from the implant brand with a cut back for indexing of the implant orientation. This is, however, theoretically not necessary, because the abutments do not have anti-rotation characteristics. It is important to note that in these cases, caution must be taken to realize a passive fit, and prior scanning experience is recommended.

When longer edentulous spaces have to be covered between two implants, as seen in this clinical case, some scanners run into problems. This is most often due to incorrect software stitching of images of the smooth mucosa; in these areas, easily distinguishable reference markers are absent. By contrast, a significant benefit in a case like this is that the bite registration with the intraoral scan can be very accurate, even though the patient lacks posterior support. These cases require extensive scanning experience to obtain extreme accuracy under difficult scanning conditions. One also has to remember that not every prosthetic material is suitable for large span monolithic FDPs. Additionally, luting the titanium-base abutments into a zirconia FDP in the exactly correct position is difficult, and this task becomes more challenging as the number of implants within the structure increases, since this can lead to passivity problems. In situations with three or more implants, it is suggested to take additional measurements to achieve perfectly passive luting of the titanium-base abutments in a zirconia FDP. Due to these challenges it is not recommended to use intraoral scanners for these indications without extensive experience.

For anterior cases, an emergence profile can be copied with a so-called triple scan technique. This technique overcomes the intraoral deformation due to collapse of the soft tissues after removal of the provisional prosthesis. The technique was first described in Forum Implantologicum in 2015. After creating a satisfying emergence profile using a provisional prosthesis, three scans are taken: A scan of the provisional crown in the patient's mouth. A scan of the provisional crown including its subgingival portion; this is obtained with the crown held on an analog outside the patient's mouth. A scan of the implant position in the patient's mouth with a scan body. All images can be superimposed by the dental lab and information about the submucosal shape of the provisional crown can be used as virtual wax-up for the definitive prosthesis.

Indications and Applications, Key Learning Points: Dependent on the implant system and intraoral scanner used, digital impressions can be part of both direct and indirect, fully and partially digital workflows. Digital impressions will also increasingly be useful for digital wax-up and case planning when matched with and superimposed on CBCT scans. Case selection is important as not all cases and/or sites are easy to scan. Digital impressions can be readily used in straightforward implant cases for single or adjacent separate prostheses. Digital impressions of two or more splinted implants are more challenging because scan accuracy of their interpositional relationship is crucial to passive fit. Challenging cases should only be performed by experienced users and after consultation with a lab or supplier.

Digital Implant Impression, Module Summary: The implementation of intraoral scanning in oral implantology is very promising; however not every indication is possible for every implant brand or scanner used. There are a lot of scanners and related products available but they exhibit different characteristics. The options offered by intraoral scanning in implantology are increasing every day. Multiple implants or larger reconstructions require scanning experience and consultation with lab or supplier to verify the availability. It is advisable to choose a system after consulting your dental laboratory since some labs are less flexible with scans than with plaster models due to restrictions in software and licenses. Think and talk your cases through!