Desktop Scanners 2015

Plainly and simply, desktop scanners are used to render a digitized image of a patient’s dentition. Today’s scanners each have a light source that projects light onto the object being scanned and cameras to record information from the light source on the object. Data is collected from different viewpoints, which ultimately are stitched together to form a “digital” model of the object.

Step by step, the scanning software directs the scanning workflow. While the sequence of scans may vary among devices, most provide 4 scans for a case with a poured model: Individual overview scans of the prepared and opposing arches, a highly detailed scan of the prepared tooth, and a bite relationship scan. The scanning or CAD software uses the bite-relationship scan to align the prepared and opposing arches, placing them in proper centric occlusion.

The price of placing a scanner into a dental laboratory varies from $11,000 to $40,000, and may involve additional costs as in software maintenance or licensing fees. The structure of these fees can be confusing. Laboratory scanners are usually free of additional operating costs after purchase. However, CAD software, usually supplied with scanners, can have maintenance or licensing fees that are applicable a year after the initial purchase. The benefit of maintenance fees is that users are able to upgrade their CAD software with the latest version, taking advantage of enhancements and feature upgrades. In some cases, if the customer does not pay the licensing fees, the manufacturer can disable the CAD software and scanner. Fees may be charged monthly or annually and can range from $1000 to $3000 per year per software license. Before buying, make sure you understand the maintenance or licensing fee structure of the scanner being purchased and whether the associated fees are mandatory.

Laboratory scanners are used predominately to scan models. Laboratory owners examining their productivity and operating costs may realize that using scanning impressions makes sense. It takes time to pour, trim, and articulate a model. Recent studies show that scanning an impression is quicker compared to fabricating and then scanning the model. This equates to greater productivity in the laboratory. Most scanners available today support impression scanning, and some even include dedicated impression scanning fixtures.

Scanning times are often questioned. Typically, model scans take approximately 4 to 8 minutes per case, including the time to combine all the scan data into a final STL or proprietary file. Impression scans usually take 9 to 11 minutes per case. For impressions, additional scans are usually necessary to pick up critical data in the undercut or the incisal/occlusal areas in impressions.

Laboratory scanners are often referred to as “box scanners” because they are generally box shaped, rather than in the form of a wand like their chairside counterparts. Closed-frame scanners are enclosed with a door that is opened to place the object being scanned inside the scanner. It’s almost a requirement with laser-line scanners due to the way data is collected. Early dental laboratory structured-light scanners were usually closed frame, but now open-frame construction is the norm.

Creating a challenge for dental technicians is the fact that fully adjustable articulators do not fit inside closed-frame scanners. Instead of performing overview scans on each arch and a bite relationship scan like they would on small articulators, technicians are forced to scan a single arch with either a bite-registration or diagnostic model. Then they need to repeat the process for the other arch, effectively doubling the scan time and losing the ability to use virtual articulator functions in the CAD software.

Open-frame scanners have a much larger opening to the scanning space, often removing two of the walls and door that would be found on a closed-frame scanner. Some newer models are so completely open (Figure 1) that the name “box scanner” isn’t quite appropriate. With the larger opening, operators can scan bite relationships of cases mounted on larger articulators. Having the right mounting plates and enough clearance, they can perform bite-relationship scans with models mounted on fully adjustable articulators (Figure 2).

Now as third- and fourth-generation 3D scanners enter the market, manufacturers are adding features that often simplify and expedite scanning.

One of the most intriguing new features is the ability of several scanners to reduce the number of scans necessary for each case. One implementation of this feature combines the arch and die scans into a single scan (Figure 3). Then a second scan of the articulated upper and lower arches is completed. A four-scan process is reduced to two scans.

Another implementation of the concept scans both arches side by side (Figure 4). Before lacement in the scanner, a special jig is used to make sure the model bases are parallel on the scanning plates. After scanning, software automatically places both arches in occlusion because the plane of the articulated models is already known. This particular scanner has 4 cameras. Two cameras are in the typical position to provide overview scan detail. Two additional cameras are closer together with a reduced scan angle, which allows both of them to capture margin and axial wall data on the prepared teeth without requiring an additional prep scan step. This implementation can be a significant time saver because one scanning step is required instead of 4. Time will tell if the cameras are close enough together to obtain the margin and wall information for every case.

Laser-line scanners have traditionally projected and used a single line that traces from one side of the object to the other (Figure 5). The speed at which the line travels has a significant impact on overall scanning speed as dental arches can range from 40 mm to 60 mm in length and width. Every time the part is rotated to a different view, the laser has to sweep across the entire object. This is one of the reasons that full-arch cases usually take significantly longer to scan than quadrant cases.

A recent innovation in laser scanners uses multiple laser lines to scan the object. Each laser line sweeps simultaneously, each covering a much shorter distance (Figure 6). Rather than using a single laser line to sweep 50 mm across the arch, multiple lines may each sweep 5 mm, scanning the arch, effectively 10 times faster than what was possible before. Of course, the time necessary to interpret and calculate a point cloud or mesh data set doesn’t necessarily improve, but the data collection time is significantly reduced.

Automatic Impression Flip and Stitch

Scanning triple tray impressions takes more time than models. First, additional scans from different views are necessary to see inside the undercut areas in impressions. Second, the impression must be manually flipped to scan the opposite side. Third, a registration scan must be performed. Finally, a registration or alignment of the upper- and lower-arch impression scans must be done. The registration of upper and lower arches can be a challenge because scanners are usually capturing the smooth external surfaces of the triple tray. Finding landmarks to align arches can be difficult and time consuming.

Several scanners are on the market or coming to the market and can automatically flip the impression and stitch the arches together. This increases the complexity of the scanner, with additional motors and/or axes of rotation (Figure 7), but it significantly simplifies and expedites the scanning process for the user.

For a number of years now, reviewing abutment designs or digital impression margins in the cloud has been possible. It shouldn’t be a surprise. Accounting software can be run in the cloud. Taxes can be calculated and filed and records stored in the cloud. Why can’t dental restoration cases be stored or even designed in the cloud?

In the cloud is just another way of saying being stored online, somewhere secure, on the Internet. The value to online storage is that if the laboratory design computer hard drive fails, as a result of a flood or a fire, for example, years of scans and designs are not lost. Most laboratories do not have an adequate data-backup plan in place. The use of cloud storage minimizes that concern, at least for case scans and designs.

One of these cloud-based systems allows registered users to design from any computer with Internet access without requiring a dongle to be plugged into the computer. This creates some intriguing options for technicians who want to design cases from home or for laboratory owners looking for afterhours design assistance.

The cost of these cloud-based storage programs varies but is around $200 per month, usually including all software updates in addition to the cloud-based file storage.

Scanner manufacturers are paying close attention to how their products are being used. They see the productivity challenges facing laboratory owners and are adding features to simplify and expedite workflows. Look for some of these fully automated scanners to make their way to the dental office, allowing dentists to send their cases digitally to the laboratory without having to change the way they take impressions. Just as the dental industry continues to evolve with new materials and machines to process those materials, scanners are changing as well, shifting in such a way as to make life easier for dental laboratories trying to survive in a highly dynamic digital world.

Chris Brown, BSEE, is the Manager of Aclivi Consulting in Pinckney, Michigan.

Inside Dental Technology // June 2015