Dental Scanner Technology and Software Update

The laser scanner projects a line onto the model and sweeps it from one side of the object to the other (Figure 1). As the line moves, cameras record the contours illuminated by the laser, stitching it together in a point cloud data set. A structured light scanner projects a white or blue light with various striped-line patterns across the model being scanned (Figure 2). Cameras record how the lines deform over the entire model to form a point cloud data set. With both types of scanners, the model is rotated or tilted to another position and another data set is gathered. Special software interprets the collected data to create a 3D representation of the scanned object.

Touch-probe scanners place a small-diameter probe and stylus in direct contact with the model or object being scanned (Figure 3). The probe travels around the model, mapping every contour that it can detect. Resolution of the scan is determined by the probe diameter and the vertical steps that the stylus is moved. Smaller-diameter probes are capable of sensing finer details but may require significantly more time to scan an object.

Regarding precision, all the technologies above are suitable for routine crown-and-bridge applications. In general, structured-light scanners and touch-probe scanners are often preferred for large-span bridges, large screw-retained frameworks, or bars due to slightly better accuracy across the arch.

Most optical/projected-light dental laboratory scanners have two cameras, each with approximately 1-megapixel resolution. Scanners using cameras with up to 5-megapixel resolution are being introduced by some manufacturers. Additional camera resolution improves scanning detail and accuracy, which can be beneficial for large, complex cross-arch cases. At least one scanner available has four cameras. The additional cameras provide quicker scanning speeds and improved accuracy, which may be valuable in high-volume laboratories or those designing bars or large frameworks.

Another interesting feature in new scanners is texture scanning. A scanner not only captures the 3D data but also overlays a still image or photograph of the model onto the scan data. This may be useful if a margin line was marked on a die (Figure 4) or a finish line marked for a removable framework. The feature can be expanded to include the capture lines and colors such as pink tissue on a model for an abutment case. Figure 5 is an example of a color scan from a digital impression system that may provide additional margin information detail plus stain and shade patterns of adjacent teeth.

Blue-light-source scanners are the latest rage. Blue lasers have appeared in laser-line scanners and seem to be less susceptible to the speckling effect, which should improve scanning detail. For structured-light scanners, blue-light sources tend to be less susceptible to background light sources during scanning. This is particularly beneficial when the scanners are of the open-frame type rather than a closed box.

Scanning of traditional impressions is becoming more common. Most laboratory scanners today have impression scanning capabilities. In fact, several manufacturers have developed or are creating dedicated scanners designed specifically to be at a dental clinic. This allows the dental office to enter a prescription and initiate a completely automated scan of the impression, sending it directly to the laboratory for completion of the case.

Dental CAD software continues to evolve. Seven years ago, laboratories were mostly designing substructures with their CAD software. Most laboratory CAD programs at that time were closed-architecture and had limited, if any, communication between equipment platforms. Today, the CAD software available to laboratories is far more open architecture than closed and has expanded far beyond simple substructures.

Software companies typically provide multiple tooth libraries for technicians. Technicians can also scan and create their own tooth libraries, further individualizing their restorations. Most of today’s CAD software also supports mirroring of contralateral teeth during crown design or the ability to morph a crown design to the scan of a pre-operative study or diagnostic model. Restorations can be designed as copings, full-contour, or just about anywhere in between. Cutbacks from full-contour restorations are possible for everything from a uniform thickness, to lingual bands, to facial cutbacks that allow for layered porcelain. Bridges can include just about any combination of full-contour restorations, cutbacks, and traditional framework designs.

Not all restorative materials are created equal. For example, the minimum recommended thicknesses for a zirconia coping, a cast-metal crown, or pressed ceramic differ. Today’s CAD software supports custom settings for various parameters that may be determined by the respective restorative material or manufacturing method. Milled zirconia copings will often have a bulked-up margin area as a hedge against possible chipping during milling. Milled or printed wax for pressing ceramics doesn’t need a bulked-up margin. Being able to make an appropriate material selection in CAD software can mean the difference between a material failure and success, or between a finishing technician taking 30 seconds or 30 minutes on a unit. Most programs are supplied with default values for common restorative materials and also enable the technician to define new materials in the software as they are released.

Virtual articulator modules continue to improve as more fully adjustable articulators and articulator settings are being added to CAD programs. Often, it is the virtual articulator module that is used to manually or automatically correct the bite relationship. The software determining the position of maximum intercuspation can accomplish auto correction. This can significantly improve crown designs because errors can occur during manual articulation or the scan of the articulated models. Scans of bite registrations or even of triple-tray impressions generally leave the digital bite relationship slightly open, so it is a useful tool to have. However, depending on the data available, the software proposal isn’t always right, which is why having a skilled technician available is still necessary to make essential corrections to software proposals.

Every CAD program today has a module for designing custom implant abutments, bars, and screw-retained restorations or frameworks. They are typically add-on modules available for additional fee. Models or arches are generally scanned with a scan locator or scan flag positioned in the implant or implant analog. The design software is able to determine implant position, depth, and angulation by position of the scan locator. Abutment libraries are available from resellers and milling centers based on the platforms and interfaces they are capable of supplying. Some libraries are for implant abutments that are manufactured by the implant manufacturer’s milling center. Others are for factory-compatible abutments made by third-party manufacturers.

Another feature recently introduced in CAD programs to assist in case design is the ability to import a picture of the patient’s actual or proposed smile over the scanned prepped model.

In the last few years, several chairside digital impression systems have incorporated case-processing portals. They are generally used for margin marking or virtual model-building processes and to generate data files that can be imported into dental CAD software. For a few years, laboratories have had virtual inboxes to share restorative designs between the laboratory and a milling center. However, nothing existed to transfer digital impression files directly from the dentist’s impression scanner to the laboratory’s design stations. Now dentists have the ability to send cases directly to their laboratories’ CAD stations for nearly immediate processing. This feature will be particularly useful for laboratory technicians working directly in the dentist’s clinic as opposed to the traditional separate dental laboratory business model.

While pouring and trimming models from impressions is still easy, most new digital impression systems have no model solution. Laboratories are, therefore, required to either fabricate model-less restorations or a build a working model from the scan data using a CAD software model-building module. Such a module guides technicians through adding and creating a model base, adding an articulator interface, and producing working dies. Given the fact a laboratory has no control over the amount of data collected by the dentist’s digital impression scan, significant data modification and manipulation may be required to create the necessary model elements for producing either printed or milled models. The model builder module (Figure 6) is also useful for laboratories that scan impressions and want to print models instead of pouring and trimming them.

Advancements in milling and printing solutions are leading to new possibilities for digital fabrication of removable prosthetics. Special scanner and software packages are now being marketed for laboratories to outsource full-denture fabrication. Most traditional dental CAD software programs available today have modules available for partial framework design, with many being second-generation software releases, which have greatly improved their usefulness and effectiveness.

Software salespeople seldom mention annual software maintenance fees, which are charged through your software reseller to help fund future development. It can range from $1000 per design station license to $3000, depending on the features or modules active in the software. The annual fee allows users to update to the latest release of the program. Some software manufacturers require annual payment of this fee, while others make it optional but restrict software updates to within a specified timeframe. When considering CAD software, ask and understand the available software maintenance options and how it may impact your operations and finances.

Today, more choices are available than ever before, with an intimidating array of technology and software tools. Which equipment and software should a laboratory invest in? No single correct answer can address that question. Every laboratory is unique. For substructures and simple full-contour crowns, buyers may not see a tremendous difference in the available scanning technology and software. Laboratories performing high-volume workloads of screw-retained restorations or bars definitely have different needs and concerns. Also understand that not every feature or function that manufacturer offers is necessary. Ask questions about systems you are considering, and be satisfied with the answers before proceeding. Make sure that the reseller is a company with which you can maintain an ongoing relationship for training and support for your investment.

The march of technology will continue with new models, features, and capabilities always under development. You can choose to wait for these changes or opt to take advantage of what’s available today. In the end, these new developments may or may not be useful for your laboratory business model.

Chris Brown, BSEE, is a Senior Applications Engineer with Axsys Dental Solutions of Wixom, MI.