It is our intention to summarize the available scanners and present the optimal model for orthodontists. However, recommending a single option for all buyers is impossible. Hence, the specifications of four relatively popular and recent scanners are summarized in Table 2
After trialing iTero element, TRIOS 2 mono, TRIOS 3 color, TRIOS 3 wireless, True Definition, and CEREC Omnicam, we developed a checklist for those choosing an intraoral digital scanner.
Quality of Scan
Comparison of four recent popular digital intraoral scanners View Hi-Res Image
Scan quality comprises many aspects, and accuracy is undoubtedly the first priority.16
According to ISO 5725-1, accuracy is composed of two parts: trueness and precision. Literally, trueness describes how truly the scanner can replicate actual dimensions. Precision refers to the reproducibility or intra-class deviation of a scanner. The concept is clearly explained by a picture of an arrow hitting or missing a bullseye, but hitting the same spot consistently (Figure 1)
Most IOSs demonstrate high precision in vivo, with no significant differences among them.10
More than one study has revealed that iTero and True Definition have higher accuracy than TRIOS and Omnicam15,28,43-45
, but no study has directly compared iTero and True Definition.
The range of scanning also affects scan accuracy.11,46
Needless to say, the full arch scanning procedure in orthodontics may be less accurate than partial or single abutment scanning.14
Furthermore, the different technologies incorporated into IOSs influence the accuracy in different ways. For example, when applying the point-and-stitch method in the anterior teeth region, little structures can be registered, thus causing subsequent propagation of errors.27
Whether to powder is a controversial topic when considering accuracy. Previously, some scanners have been confined by the imaging principle, requiring a unified surface texture to record precisely. Conversely, improper spraying may reduce accuracy. Powder might also be prone to saliva contamination and lose its function easily. Nevertheless, almost all IOSs are now powder-free, with the exception of True Definition, which still suggests its user to apply a thin coating to increase accuracy.
The intraoral environment always presents obstacles and moisture control and defogging are major challenges in daily dental practice. Drying the teeth surface adequately is recommended before a scan procedure begins to reduce errors resulting from light dispersion caused by saliva or other fluids. Two solutions exist for defogging. One is to heat the scanner tip directly, as with Omnicam and TRIOS. The other is to emit airflow from inside the scanner tip, as with iTero. Scanning time
In discussing accuracy, scanning time must also be mentioned because they are highly correlated.28
Kim et al. advised caution as to whether the study condition is in vivo or in vitro.12
According to a systematic review by Goracci et al.16
, the scanning time varies for the same models among different studies because it can be calculated from either turning on the machine or when scanning actually starts.34
Generally, scanning time decreases with increasing experience of the operator.
Operators have a unique learning curve for each machine.35
One study indicated that iTero may have a longer scanning time, rendering it slower than the traditional impression method. However, clinical experience improves this limitation. Conversely, TRIOS is easier for less experienced operators, with a shorter scanning time than conventional methods, but more practice on TRIOS will not further shorten the scanning time.12 Full-color scanning
Full-color scanning is a new feature of the latest scanners, with the exclusion of True Definition. TRIOS also supplies mono-color scanners for those who do not need color scans. Coloring helps to differentiate the border between gum and tooth. Some brands also claim that their color capturing and expression is precise enough for shade selection. Interference of scan accuracy
The material being scanned affects accuracy.47 Metal and other reflective materials can be difficult to capture. Intraorally, this scenario applies to metal crowns, appliances, or orthodontic brackets. The powder technique is a perfect solution to improve scanning accuracy by generating surface homogeneity. Park et al. studied accuracy for brackets in vitro, revealing that lingual brackets are less accurate than buccal brackets. Both TRIOS and iTero performed well under these conditions.48 Another clinical situation that can compromise accuracy is edentulous areas.49 The lack of teeth as apparent anatomical landmarks for registration makes it difficult to acquire digital impressions accurately. Hardware
Overall and tip size
When choosing a new machine, its size must be considered to determine whether it fits the office space and can easily be moved. Regardless of size, all IOSs are available as a basic type with wheel-stands. In addition, TRIOS Pod and Mobile True Definition are particularly light-weight and portable options for those without sufficient room for a large cart. Although previous models have been combined with dental chairs, these proved unpopular with buyers because being fixed into a certain unit despite updating IOSs contravenes the principle of flexibility.
Another size issue is the scanner tip. In early models, tips were too big for patients with a limited mouth opening. Hence, later generations of IOSs feature a scanner tip that is as small as possible. 3M pioneered the downsizing of scanner wands to mimic conventional hand-pieces. Infection control and potential hazards
Just as with other medical devices, infection control for IOSs should never be overlooked in daily practice. The first level of control relates to the tip; certain sleeves for scanner tips can tolerate a disinfection process under high pressure and temperature, whereas others are designed to be disposable. At the machine body, a normal cleansing procedure should be suitable. Any accessories of the machine used in the scan process, such as the keyboard, mouse, and the tracking ball for CEREC Omnicam or TRIOS Pod, may be a source of cross-contamination. Thus, touch screen and hands-off remote control offer advantages in avoiding unnecessary interruption during a scan procedure.
Another concern is the flashing light emanating from the scanner tip in some IOSs; accumulated exposure may represent an ocular hazard to the operator or patient. Data processing and transmission
Real-time 3D model generation after scanning may rely on different imaging principles and internal computing ability. All present IOSs are built with adequate processing power, memory, and storage. TRIOS Pod allows the practitioner to decide how good the computing power is, since it is connected to an external optional laptop.
Data transmission speed typically depends on the network environment, but even for the same full-jaw scan on a single patient, different IOSs generate different file sizes because of various imaging principles. Larger file sizes cause longer transmission times. In particular, the transmission time of 3M Mobile True Definition is double that of the cart type (3M True Definition) because of the efficiency of the processor (3M Mobile True Def Scanner FAQs, Version Oct 2016). Software
Among the aforementioned IOS manufacturers, 3Shape has earned the greatest acclaim for developing user-friendly software. Ortho Analyzer by 3Shape can produce a standardized digital model, perform analysis, and even provide virtual model setups. Through integration with a 3D printer, doctors are capable of making their own customized clear aligners and appliances.50
Other companies also have unique advantages. iTero has strong technological support from Invisalign. CEREC possesses great experience in CAD/CAM and restorative dentistry and offers educational training programs for technicians, assistants, and doctors. Conversely, 3M developed in the opposite direction, with an open system that allows more technical support. Reality
Price and maintenance
The most basic issue is the cost of bringing an IOS into clinical practice. The normal listing prices of IOSs in Taiwan, as of January 2018, are summarized in Table 2
. The prices range from at least NT$1,000,000 to approximately NT$2,500,000. The options available vary widely according to the different packages offered alongside the machine itself, which may include post-scan software solutions, warranties, or annual fees for upgrading the system.
IOSs require maintenance, in terms of both hardware calibration and software upgrades.51
It is worthwhile to question the length of the repair period and the availability of a replacement if a scanner malfunctions. This information typically requires further inquiry with the salesperson when negotiating a purchase because the situation may be varied.
Comparison of four recent popular digital intraoral scanners View Hi-Res Image
In addition to the price of the machine and the service, the potential cost for implementing such a new technology warrants further discussion.39 Digital impression systems have a learning curve, but how long is this training period and how much opportunity loss accumulates during this period? Dentists must familiarize themselves with this new technology, during which time they could otherwise complete dozens of conventional impression procedures. Assistants and collaborating technicians must also take time to become efficient with the new workflow. Whether all doctors in an office are confident and willing to use an IOS is another issue. Lastly, will patients actually achieve greater overall satisfaction with digital impressions?
Despite certain disadvantages, some advantages warrant mentioning. Digital impressions may produce less waste from disposable supplies (e.g., gloves, disinfection wrappings) and reduce the need for stocks of conventional materials. Digital restorative workflow can offer additional check points while milling a restoration, further enhancing efficiency and productivity. The development of software that is more user-friendly and widely compatible will enhance the clinical performance of IOSs.
Critical thinking must be employed when considering the costly investment of IOSs. How long has the manufacturer been engaged in this market? How is the company’s reputation? Can local dealers or agents offer sufficient technical support when necessary? Orthodontists should always discuss with experienced colleagues before making this monumental decision.39