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Optical Scanners: Is There a Right Choice? by Dr. Anthony M. Puntillo, DDS, MSD

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Over the last two decades our society has made a dramatic transition from analog to digital based communications. Healthcare providers, including orthodontic practices, certainly have not been immune to this evolution. Many orthodontists have moved, or are now moving, from paper charts and film-based photographs and radiographs, to processing and storing electronic health records. Included in those records are 3D dental models. Laser scanning techniques that allowed for the creation of full mouth 3D digital dental models have been available to orthodontists since the mid 1990s. However, the early use of these systems still required a dental impression or a poured model to create an electronic digital file. Around 2007, intraoral scanning machines became available that allowed an orthodontist to directly capture 3D data of a patient's dentition and create a digital model without the need for a dental impression. Over the last two years the final piece of the puzzle, 3D printing, has become more readily available and made the impressionless practice a real possibility. I will highlight the benefits of intraoral scanners, discuss the features that should be considered when deciding which of the commercially available machines to purchase and provide a comparison of five of the more commonly available machines: CS3500, iTero, Lythos, Trios Cart & Pod and True Definition (Figs. 1-5).



The primary reasons that most practices are choosing to transition from impressions to intraoral scanning are cost and efficiency. Of the five machines that will be examined in this article, most report that an accurate scan of the upper and lower dental arches and the occlusal relationship between those arches, can routinely be completed by a trained assistant in under 10 minutes. A similar amount of time would be common for an impression procedure of both arches. However, impressions also involve a material expense and lab time to pour and process the dental models. The material expense associated with impressions can often be significant, particularly if several attempts are required to obtain an accurate impression and the material used is polyvinyl siloxane (PVS). Conversely, there is little to no material expense or lab time necessary for processing a digital model created from an intraoral scan. A virtual model can be diagnostically viewed on a computer screen almost instantaneously without the need to create a hard copy. Consequently, the majority of the expenses associated with intraoral scanning involve the fixed cost of purchase and maintenance of a machine. In addition to those costs, it should be noted that for the times when a hard copy is necessary there is an expense associated with 3D printing of a digital (.STL) file. Three-dimensional printing costs can vary depending upon the type of printer and whether the printing is completed in-house or by a third-party lab provider. Overall, however, digital files created from intraoral scans are substantially more convenient to utilize, transfer and store than plaster models. A file created from an intraoral scan can be printed an unlimited number of times with no loss in accuracy and can be stored indefinitely for little to no cost in-house or in the cloud. The purchase and maintenance costs associated with each of the five previously mentioned scanning machines will be examined in more detail at a later point in this discussion.

Intraoral scanning may not only reduce costs and improve efficiency for orthodontic practices, it may also provide orthodontic patients with a significantly improved experience. Orthodontic patients have been asking for years for an alternative to impressions. Intraoral scans eliminate the mess, gagging and general unpleasantness that can be associated with an impression procedure. In addition to being more comfortable for patients, scanning also gives an office a high-tech appearance allowing patients the ability to view a digital 3D model of their teeth almost instantly. Given the significant efficiencies and patient advantages associated with intraoral scanning, it should not be a question of whether or not to invest in a machine, but rather, which one. There are several models of intraoral scanners presently being marketed to orthodontists. In evaluating each model you should examine accuracy, expense and ease of use. For any intraoral scanner to be of real value it must first be able to produce a dental model at least as accurate as the traditional impression technique. The impression and plaster pour technique involves several steps that allow for the incorporation of discrepancies into the final product. Distortion, material instability and operator error all pose challenges to final model accuracy. A review of the literature turns up some recent studies that have looked at the question of scan accuracy.1,2,3 These studies generally found the accuracy of those scanners examined to be acceptable for diagnosis, treatment planning and manufacturing of tooth-supported appliances. However, not all machines have been subject to published scientific investigations and it can be difficult to distinguish one manufacturer's accuracy claims from another's. The practical question to consider is whether the scans from a machine will generate a model accurate enough for your intended final purpose. The answer to this question may reside with some of the large commercial labs. Dental labs, such as Align Technology and Glidewell, process thousands of electronic files from the most notable machines and have collected a significant volume of data. Align reports that an analysis of more than 400,000 cases found a seven-fold decrease in aligner fit issues on cases submitted through their iTero scanner. Some may argue that this data is skewed, as Align is the manufacturer of the iTero scanner and all of the data reported is from their own machine. Glidewell, on the other hand is an independent lab and reports that based on an analysis of the manufacture of more than 100,000 BruxZir crowns, there was a 55 percent reduction in crown returns for fit issues on cases that were digitally submitted using a variety of intraoral scanning machines. It is important to note, however, that some machines are accurate over only short spans such as a single crown or bridge. For a scanner to be of value to an orthodontist it must be able to create an accurate representation over an entire arch. At the time of this publication, the five machines discussed are the ones that appear most suited for orthodontic use. However, I would recommend you evaluate your intended usage and consult with your lab provider.

After accuracy, the factor that often gets the most attention when discussing intraoral scanners is the expense of the machines. An accurate analysis of the true cost of any piece of equipment must go beyond the simple purchase price. Items that add to the overall cost of a scanning machine include support and warranty expenses, model storage fees, transmission fees and supply costs. Items that can lower the overall cost include rebates or discounts on associated products. In today's fast changing world of technology we should not realistically expect to get more than five years of good use from machines such as these. Consequently, I surveyed the providers of five of the most common machines currently on the market and complied a five-year balanced cost analysis for each of those machines. All of the reviewed manufacturers offer the first year of warranty as part of the purchase price and will extend the warranty for at least an additional two years at an additional cost. Three of the manufactures (Align, 3Shape and 3M) offered the ability to extend the warranty for the full five years of this analysis. The CS 3500 and the Lythos machine both demonstrate lower five-year costs, but stop warranty coverage after the third year. The analysis also shows that with only three years of warranty and limited software for model analysis, the CS 3500 has the lowest five-year cost. The True Definition scanner from 3M offers the lowest initial purchase point. However, there is a substantial monthly subscription fee associated with the True Definition machine, and if a user chooses to do diagnostic analysis on the scanned models there is also an upgraded model fee. The software and ability to perform a thorough diagnostic analysis on all scanned models is included with both the iTero and TRIOS subscriptions. Consequently, even though the initial purchase price of the iTero machine is more than double that of the 3M machine and the purchase price for the TRIOS machines is nearly triple, the total five-year cost for the 3M machine (if all initial models were upgraded for diagnostic analysis) would be significantly more than the five-year cost for the iTero scanner and in the same range of the TRIOS machines. The TRIOS machines from 3Shape (cart or pod) have the highest initial purchase price and also include a significant cost for updating their robust software package over the five-year period, producing an overall cost of ownership at the upper end of this group. All manufacturers offer different opportunities to limit the actual costs of their machines. These can include minimizing the diagnostic analysis performed on the scanned models (Lythos and True Definition), reducing coverage or opting out of the extended warranties, or earning rebates on the use of related products (Lythos). This cost analysis was an attempt to make a balanced comparison of the cost of each the machines. Prices, services and features discussed here can be subject to change. Every office will need to determine how they intend to use the machine and decide which costs will apply to their particular circumstances. The final factor to consider when deciding which machine to invest in is the ease of use. Some of the things to be considered in this category include: powder or powderless, scan type, scan time, file type generated by the scan, unit and wand size, and acceptance of the scans by third-party providers. A comparison of the previously discussed machines (Table I) demonstrates that the 3M machine is the only one of the five that requires the teeth be coated with a light powder to obtain the most accurate scans, but also has the smallest wand size. In terms of scan type or file type created, there seems to be little distinguishable difference between machines. The CS 3500 reports a longer scan time than the other units. However, it should be noted the average scan times were provided by the manufactures and not independently tested. The CS 3500 also offers the ability to directly integrate with some practice management systems, which could provide some time savings. The TRIOS machine reports the shortest scan times with the reported times for most units falling into the five to ten minute range. The CS 3500 and TRIOS pod are the most portable units as they offer a USB connection to any computer with the proper specifications. One final and important item to consider is a machines ability to generate scans for acceptance with third-party tooth alignment systems. Currently, doctors using the Invisalign system can choose between the iTero and the True Definition scanners. The iTero and TRIOS machines have been approved for use with the SureSmile system and the iTero, TRIOS and True Definition scanners have all been approved for use with the Incognito system.

In conclusion, there should be little question that intraoral scanners offer orthodontic practices significant benefits over the traditional impression and plaster pour technique. Consequently, the traditional impression systems within orthodontic practices are being disrupted. Just as orthodontists have transitioned from film-based radiography to digital, a transition from plaster models to scanned 3D images is now occurring. The question is which of the currently available machines is the right one for you and your practice? Hopefully this review has provided some insights that will be helpful in reaching that decision.



References
  1. Naidu, D. and Freer, T.J.: Validity, reliability, and reproducibility of the iOC intraoral scanner: A comparison of tooth widths and Bolton ratios, American Journal of Orthodontics and Dentofacial Orthopedics, Vol. 144, Issue 2, August 2013
  2. Flugge, T.V., et. al.: Precision of intraoral digital dental impressions with iTero and extraoral digitization with the iTero and a model scanner, American Journal of Orthodontics and Dentofacial Orthopedics, Vol. 144 Issue 3, September 2013.
  3. Alkyalcin, S., et. al.: Diagnostic accuracy of impression-free digital models, American Journal of Orthodontics and Dentofacial Orthopedics, Vol. 144, Issue 6, December 2013.
Dr. Anthony M. Puntillo earned his bachelor of science from the University of Notre Dame and then went on to the Indiana University School of Dentistry where he completed his masters of science in dentistry and his orthodontic residency. Dr. Puntillo is a member of many professional associations, including the AAO where he sits on the committee for information technology. Outside of the office, he spends time with his wife, Mary Carol, and their three children.

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