Knowing Your 3D Laboratory Scanner

Dental laboratories should consider the number of applications that the scanner supports in correlation with the laboratory's needs before investing in any specific scanner. Some of these applications include long-span bridges, custom abutments, implant bars, multiple implants, removable partial dentures (RPDs), and complete dentures. Another factor that needs consideration is each system's adaptability to upgrades, because non-upgradable or simple-application scanners that support only basic functions restrict laboratory production and represent a poor investment in the long term. For example, some scanners have the ability to automatically scan individual dies, while some only scan models. (Night guards and orthodontic appliances do not need die scanning, while implant planning and manufacturing require more detailed scanning). Some of the most important qualities are the accuracy of the scan, its speed, and the user-friendliness of the software.

Most dental laboratory scanners on the market today utilize noncontact 3D scanning with some type of laser (light). Accuracy is based on the number of cameras that the scanner has and their resolution. Many of today's best scanners have four cameras with 5-megapixel resolution. The advancement of scanner software allows for a more precise and faster reading and analysis of collected data. High-resolution cameras allow for "texture scanning," which takes 2-dimensional images of a stone model surface and accurately superimposes them on the 3D model, improving the image with surface details that allow technicians to draw guidance marking in the digital design, also known as marking margins.

The concept behind scanners' structured light technology—the light is projected in a pattern, usually a grid or linear—is triangulation. The light is projected in different patterns and it becomes distorted when it meets the surface of the object to be scanned. The scanner's cameras record the distortion from multiple angles, the software calculates (using triangulation) the distance to specific points on the object, and the recorded coordinates are used to virtually rebuild the object in detail.

Most scanners use blue light lasers because the LED light source has a longer shelf life. Also, the laser has both a cooler operating temperature and a higher resistance to other light sources that can be in the room; additionally, its equipment is more compact.

The data points and triangulation are at the core of reproducing a scanned object, such as: Point cloud (left, 164,475 points) is used to generate the triangle-based surface (middle, 55,380 triangles); smart triangle coping and margin line fit.

Although it is important to collect as much data as possible to have an accurate reproduction of the model/impression, sometimes more data points that are auxiliary to the main features of the object can slow the speed of the scanning. The software uses "smart algorithms" to eliminate or reduce the number of triangles that are unnecessary without affecting the quality of the scan itself. Smart algorithms learn from data and have the ability to select the relevant data to complete the 3D image. However, the scanner's software can detect and adapt the scanning strategies to go faster on flat surfaces or slower on curved areas, and likewise adjust the rate of data capture where the surface presents more features.

On the market today, the majority of dental laboratory scanners use a 5-axis concept, which greatly improves the accuracy of the 3D model (Figure 3)

Furthermore, advances in software development allow the scanner to "read" the surface of the object even if the stone model has a shiny surface. Some less developed scanners still require the use of scanning die stone or some type of anti-light reflection agent applied to the stone model, which slightly modifies the data points and somewhat compromises the accuracy (Figure 3).

The dental laboratory scanner is usually sold in a bundle with CAD/CAM software; therefore, it is critical to select the scanner with software that is compatible with all other elements of the CAD/CAM system, such as 3D printing, milling, or any other workflow production software and equipment. It is recommended to choose an open-system scanner, which can export data in neutral formats, such as:

• STL files, depicting a raw, unstructured triangulated surface;

• Polygon File Format (PLY), acting as a storage for the 3D data from scanners; or

• American Standard Code for Information Interexchange (ASCII), which is an encryption
program for secure communication.

Some important ancillary features that certain scanners offer can improve data collection and the reproduction of the exact replication of the patient's mouth and centric occlusion relation.

Some scanners allow the user to combine scans, making it possible to:

• create pre-op models, which are a guide for designing the final restoration;

• scan both arches via 3D mounting;

• record the bite registration necessary for digital mounting;

• utilize scans of the gingiva and scan bodies, which show the implant system and position; and/or

• scan individual dies.

Some scanners allow retakes; if some portions of the scan have voids, the scan can be retaken, with the technician needing only to change the model position on the scan table.

Others offer automatic alignment of the maxillary and mandibular jaws, which is important in mounting. They also have an option to manually align the arches if necessary.

Another important factor when selecting a scanner is the training and technical/customer support that the scanner manufacturer should provide, which usually is included in the licensing or maintenance fee.

Overall, when selecting a 3D dental laboratory scanner, it is important to keep in mind the scope or the use of the scanner (needing more detailed scans or just basic), the function of the scanner in conjunction with all other components of the CAD/CAM system, and the training and technical support that the 3D scanner manufacturer offers.

Laura Andreescu, MBA, CDT, is an Assistant Professor of Restorative Dentistry at New York City College of Technology, CUNY, in New York, New York.