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Digital technologies have transformed modern dentistry on all fronts, from patient communication and diagnosis to treatment options and recordkeeping. The computer-aided design/computer-aided manufacturing (CAD/CAM) market is growing at an exponential rate, and this technology is now commonly used in dental offices across the globe (Figure 1 and Figure 2).1 A recent survey investigating current trends regarding the integration of intraoral scanners (IOSs) into dental practices reported that 53% of respondents said they use an IOS in their practice and 34% of non-users are considering buying an IOS in 2021.2 The use of intraoral scanning is making dentistry more efficient and predictable.
Although CAD/CAM has only recently become mainstream in the dental industry, its history dates back to when Dr. François Duret proposed optical impressions and CAD/CAM for applications in dentistry as early as 1973. In 1984, he demonstrated the first crown produced using a patented electro-optical scanner for taking digital impressions and a simple chairside CAD/CAM system.3 The technology was met with skepticism at the time, but the need for tooth-colored restorative alternatives prevailed. Recognizing the potential of this market, Drs. Werner Mörmann and Marco Brandestini developed a similar system in 1983 at the University of Zurich, releasing the CEREC 1 unit (Sirona Dental Systems GmbH) in the same year. CEREC®, as it is known today, got its name from the term "CEramic REConstruction." In 1985, the first chairside inlay with the CEREC 1 CAD/CAM system was completed.4 The system did not have complete CAD software at the time, as it simply copied the cavity and required the occlusion to be refined in the mouth. Milling was performed by a single disc working on one-and-a-half axes. Indeed, these were humble beginnings compared to the machines available today.
Advantages of Digital Impressions
Incorporating intraoral scanning into a dental practice can provide countless, well-established benefits for both the clinician and patients. When carried out properly, digital impressions have been shown in the literature to be as accurate as, or even more accurate than, conventional impression techniques.5-8 Digital impressions can be executed much faster and easier than traditional impressions.9 They do not provoke a gag reflex and make treatment more comfortable for patients.10,11 Furthermore, digital impressions and design data are stored on a computer and can be cloned, modified, and/or transferred easily-all clear advantages compared with stone models. Lastly, one of the most significant advantages of an intraoral scan is the provision of immediate feedback to the clinician, who is able to examine the scans on the computer screen during the procedure. The scans can be rotated and enlarged, and some systems highlight potentially inadequate areas for the clinician's convenience; for example, the system may point out insufficient tooth reduction during crown preparation. All of this information is readily available immediately after scanning and has been shown to have a positive impact on the quality of preparations.12
Chairside IOSs have always been optical and are engineered to obtain digital impressions directly in a patient's mouth. Intraoral scanners function by projecting structured light onto the surface of the object, which is recorded as individual images or video and then converted by a software into a 3-dimensional (3D) image.13 There are two prevailing technologies used in intraoral scanners to capture digital images: optical triangulation scanning and confocal laser scanning.11,14,15 Different commonly used scanner models and the scanning technology they utilize are listed in Table 1.
The shape of the oral cavity has limited the design of IOSs over the years, and, therefore, the general appearance of scanners across the various brands is somewhat similar. IOSs have experienced multiple evolutions, and currently there are more than 12 different options on the market. IOSs either are connected to a personal desktop/laptop computer or come with a custom-built cart purchased with the scanner. For clinicians, the question becomes which is the most appropriate model for their practice.
Scan speeds of the latest IOSs from mainstream manufacturers seem to be reaching a plateau point, in that all of the leading scanners are now high-speed, and clinicians can readily achieve full-arch scans in less than 1 minute using most any IOS. Although a very evident learning curve is associated with any IOS,16 scanner speed is no longer a significant dividing factor when comparing modern IOSs. The factors differentiating scanners today are integration, workflows, and, most importantly, software.
When using an IOS, the clinician can acquire a digital copy of the patient's dental and orofacial structures and the relationship of the jaws. When it comes to the scanning process itself, it is crucial to follow the recommended scanning protocols, known as scanning strategies established by manufacturers and literature (Figure 3).17,18 Following scanning protocols improves efficiency and minimizes the risk of incorrect stitching of images, which can result in warped scans. Furthermore, it is well-established in the literature that poor scanning technique is the leading cause of reduced accuracy.19
Multiple studies have been conducted comparing the accuracy of conventional impression techniques using impression material versus digital impressions. Recent reports concluded that digital impressions have comparable accuracy or are even superior to analog impressions.20,21 However, it is important to note that not all scanners are equal; many may struggle with maintaining accuracy when scanning more complicated structures such as edentulous arches or when scanning for full-arch prosthetics.22 Literature often lags behind technology. A recent study showed that in a comparison of 10 of the latest-generation scanners, all of them were within 10 microns of each other; thus, accuracy is no longer the principal determining factor when choosing an IOS.23 For everyday, basic uses such as crown-and-bridge dentistry, today's scanners generally are all accurate enough for clinical use.
Selection Criteria
To aid clinicians in determining which IOS might be best suited for their practice, eight selection criteria may be considered: (1) scanner speed, (2) scanner flow and handling, (3) scanner size and weight, (4) IOS price and subscription requirements, (5) software capabilities and diagnostic features, (6) sterilization process (autoclavable scanning tips), (7) wireless or wired, and (8) CAD integration. The descriptions of each criterion provided in the following sections are based mainly on the author's experience using the latest IOSs at his teaching clinics over the past decade.
Scanner Speed
As mentioned earlier, scanning speed is no longer the ultimate criterion when evaluating an intraoral scanner. All of the leading scanners on the market are high-speed scanners that can achieve full-arch scans easily in under 1 minute. Scanning speed is now a crucial consideration only if a clinician is comparing some of the more economical, low-end scanners on the market.
Scanner Flow and Handling
Scanning flow refers to the overall smoothness of the scanning experience. Artificial intelligence (AI) is built into all the leading scanners, enabling them to be quick to find their place again when the scan process is paused and restarted.
Bite scan alignment also tends to be fast across the board, as a bite alignment of two dentate arches can now be readily achieved within 5 to 10 seconds. Anything longer than this typically means there is an issue with either the technique being used or an individual arch scan, such as not enough buccal information being captured.
The AI built into today's intraoral scanners is responsible for removing any artefacts that the scanner may pick up. Some scanners perform this function automatically during the scan process, while others may require post-scan editing. Most scanners perform well in this aspect for dentate patients; however, clinicians should realize that not all scanners can scan edentulous arches completely accurately, as some clearly perform better than others.23 The discrepancy seen among scanners typically revolves around their ability to stitch images together accurately when there is a lack of obvious landmarks. Edentulous arches pose a challenge due to the lack of clear differences from one image to the other. Scanners with larger fields of view are usually better at performing this function. The AI built into the software also plays a key role in this aspect.
IOS Size and Weight
IOS size and weight directly relate to the scanner's ergonomics and its ease of use for long periods of time (Figure 4). Based on product literature, scanners range in weight from 150 grams to more than 500 grams (Figure 5). Typically, those scanners that use confocal laser scanning technology are larger and heavier than those utilizingoptical triangulation scanning technology. Clinicians should check the weight of a scanner before purchasing it and test it out to ensure they would be comfortable using it in the office.
IOSs typically are available in two variations: cart-based or a mobile unit. Cart-based scanners are heavier as they come with their own custom scanner cart, computer, and monitor. Cart-based scanners help facilitate movement within operatories. Mobile units typically are smaller and lighter and are either plug-and-play USB scanners or tablet-based. The plug-and-play scanners require the operator to buy his or her own computer to run the scanner. These types of scanners can be used on any computer, including chairside with a laptop simply on the clinic bench. Alternatively, third-party computer carts can also be used to facilitate easier movement between operatories.
While the weight of the scanner may not be a concern for many clinicians, it should be noted that larger-sized scanners typically have larger scanner heads, which may be challenging to use in smaller mouths or hard-to-reach areas in the oral cavity. Many larger scanners, therefore, utilize a large field of view to counteract the large size of the scanner, thus requiring less movement to capture the same information that a smaller unit could.
IOS Price and Subscription Requirements
Cost is usually the primary barrier for clinicians entering into the implementation of digital dentistry.24-26 The investment cost is a principal concern of dentists worldwide and a main reason why less expensive scanners exist in the marketplace. Based on the author's research, intraoral scanners alone range from approximately US $15,000 to US $50,000. The least expensive scanners on the market are typically only capable of scanning and sending the scanned file with no CAD software or diagnostic tools, while the higher-end scanners, such as those listed in Table 1, have more expanded features and CAD integration.
Subscription costs also need to be considered before the purchase of an intraoral scanner, as there are various options available. The market seems to be shifting toward the elimination of yearly fees; however, many IOS companies still charge annual fees that the buyer can opt out of at the cost of receiving no software updates. The less expensive IOSs on the market tend to attract customers by offering no yearly fees at all regardless of software updates.
To evaluate subscription costs, it should first be noted that some scanners have a subscription cost tied to the scanner itself for its use. Typically several thousand dollars per year, this subscription usually covers the buyer for a range of features, including cloud storage, warranties, and support. Secondly, the CAD software that comes with some scanners also often has subscription costs, which can total up to $10,000 per year. These yearly fees are essential for companies to continue providing updates and improvements, all of which are included in the subscriptions. Regardless, current sentiment is that dental professionals are dissatisfied with paying yearly fees and subscriptions to keep their technology running. This is why the market seems to be moving toward a no-subscription cost model.
Lastly, another ongoing cost is for the scanning heads. These may be either single-use, autoclavable (which most models are), or only cold-sterilized. Typically, autoclavable scanning heads need to be replaced after 20 to 150 autoclave cycles, depending on the scanner or whether they become damaged. The cost of a scanning head can range from $4 to $300; the cheapest scanning heads on the market generally are single-use, while the more expensive types are autoclavable or designed to be used long-term and only cold-sterilized.
Software Capabilities and Diagnostic Features
As alluded to earlier, software is the number one factor that is now differentiating scanners. Some scanners excel in same-day dentistry and are entirely focused on this workflow. Other scanners provide a range of different diagnostic/treatment planning options, such as caries detection, orthodontic simulations, and digital smile design. Others have basic software with little or no applications, and these are now starting to fall behind.
All intraoral scanners follow a simple step-by-step progression with regard to their use. The typical workflow entails filling out the lab sheet and patient details, scanning the preparation, scanning the opposing teeth, and, finally, scanning the bite. Software across the entire industry is generally easy to follow and intuitive.
What is becoming a point of difference between scanners are the features they offer beyond the primary function of taking a digital impression and eliminating impression material. Features such as digital smile design, orthodontic simulation (Figure 6), caries detection, comparison of scans over time, crown fit detection, and model builders (Figure 7) are now available in various scanners. In addition, the tools available to the clinician when editing and modifying scans also vary widely, with some scanners providing few if any editing-type tools and others offering an arsenal.
Sterilization Process (Autoclavable Scanning Tips)
Cross-infection control has always been an extremely important issue in dentistry and is perhaps more critical today than ever. Understanding how intraoral scanners are sterilized between patients is vitally important. As previously mentioned, scanning heads may be either single-use, autoclavable, or only cold-sterilized. Cold sterilization of scanner heads is arguably a less effective form of cross-infection control when compared to autoclaving scanner heads. Because they are used only one time, single-use scanning heads likely provide the optimum cross-infection control; however, the environmental impact of the plastic waste resulting from their usage is another concern. Removable scanning heads that can be autoclaved seem to be the happy medium in this aspect, and the scanner market seems to be shifting to autoclavable scanning heads.
Another consideration is that although laptop configuration scanners are gaining popularity in the market, they generally have their own challenges with regard to sterilization. Cart-based scanners are medical-grade devices, meaning that common cleaning and disinfection materials can be used on them to effectively provide sterilization. Laptop models are not medical-grade devices and require single-use plastic covers. If such covers are not used, this raises a controversial discussion about ideal cross-infection control and laptop scanners.
Wireless or Wired
IOSs are available in either wireless or wired configurations. While most models are wired, the market seems to be shifting slightly toward wireless scanners, which offer some convenient usability advantages (Figure 8). In the author's experience, when using a wireless scanner the whole scanning experience is generally more enjoyable and seamless. There are no issues with wires getting in the way or wire breakages. Battery life and connectivity, however, are issues that must be contended with, yet significant upgrades have been achieved in these two areas.
Presently, the battery in wireless scanners generally seems to last around 20 to 60 minutes, with minimal lagging or connection problems. Wireless scanners come with a power cord and can be plugged into a power source if the battery power runs out. While the batteries in wireless scanners are relatively lightweight, these scanners with batteries attached typically weigh slightly more than wired models, by about 40 to 50 grams.
CAD Integration
CAD integration is a main factor differentiating products in the IOS market. Generally, scanners either: (1) have a CAD software, (2) can be integrated with third-party CAD software, or (3) offer no intrinsic integration at all (files are exported and imported into third-party software manually).
CAD integration is necessary only for users who want to expand their capabilities by fabricating restorations in-house. Scanners that have CAD software have vast CAD ecosystems capable of designing various restorations and appliances, including crowns, onlays/inlays, bridges, surgical guides, implant restorations, dentures, etc. Scanners that offer CAD software are CEREC® (Dentsply Sirona) (Figure 9), TRIOS® (3Shape), and Planmeca Emerald™ (Planmeca). Other scanners do not have their own CAD software and use third-party software. CEREC and Planmeca are the only scanners whose manufacturers provide an end-to-end solution by making milling machines. All other scanners rely on third-party milling machines. Clinicians looking to carry out the entire CAD/CAM workflow in-house will need to invest in a scanner, CAD software, and milling machine. Some companies offer complete packages, while others provide parts of the workflow.
Summary
Digital dentistry is undeniably the future of the profession and is already being utilized throughout the industry. Current intraoral scanning technologies are faster than and as accurate as, or more accurate than, conventional impression techniques and more comfortable for the patient.
For clinicians choosing their first intraoral scanner, the selection process can be daunting. The most crucial factor for clinicians to consider is their primary motive for buying an intraoral scanner. Practicing chairside CAD/CAM dentistry versus scanning and sending cases to a lab represent two very different needs and likely will result in two very different investment choices. Presently, the market is being split into niches: those who want to perform chairside dentistry typically go in one direction, and those who want a low-cost scanner with no CAD features go in another. There are other elements to consider as well, such as the dental practice's primary treatment modality, whether that be clear aligners, which may steer a practice in one direction, or surgical guides and digital dentures, which may lead a practice in a different direction.
The price point of intraoral scanners has dropped significantly in the past 5 to 10 years, while the functionality and enhancements have skyrocketed. The reduction in cost is beneficial for all dental professionals worldwide, enabling adoption of the technology for those concerned about the initial investment expense. Whether to invest in a scanner is hardly a decision anymore. Dental practices that are not adopting digital dentistry are losing ground.
About the Author
Ahmad Al-Hassiny, BDS (Hons)
Director, Institute of Digital Dentistry, Wellington, New Zealand; Private Practice, Wellington, New Zealand
Queries to the author regarding this course may be submitted to authorqueries@aegiscomm.com.
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