Efficient Accuracy for Implants

Inside Dental Technology (IDT): What is photogrammetry?

Blake Roney: Photogrammetry is the science of obtaining 3D measurements and information about physical objects using 2D photographs. It involves analyzing and interpreting 2D images acquired from multiple angles to create 3D models or maps of the photographed objects that incorporate accurate measurements.

In photogrammetry, photographs are acquired from various angles with specialized cameras, and then the images are processed using software to create a 3D model or map of the photographed objects. The process involves determining the positions and orientations of the cameras, calculating the spatial relationships between the images, and extracting 3D information from the images to create a detailed and accurate representation of the subject.

IDT: How is photogrammetry used in dentistry?

Roney: In dentistry, photogrammetry is used to capture data about implant placement for full-arch prostheses. Special scan bodies are placed on top of the implant abutments (Figure 1), and an extraoral scanner is used to record very precise data about the location and angulation of the abutments. Because the traditional methods of capturing implant data for full-arch restorations were either inaccurate or labor and time intensive, the use of dental photogrammetry systems (eg, ICam4D, Imetric; MicronMapper, ClaroNav; PIC system, PIC dental) can be seen as the missing piece in providing predictable and efficient fully digital full-arch restorations.

IDT: Why can't clinicians just use their intraoral scanners?

Roney: With photogrammetry, clinicians still use their intraoral scanners. Photogrammetry scanners are actually useless by themselves. Currently, photogrammetry scanners only capture data about where implants are located and their relationships to each other, so an intraoral scanner is still needed to capture the surface of the tissue and the bite relationship between the two arches.

  IDT:   Why can't they use intraoral scanners to capture the implant data as well?

Roney: Intraoral scanners and traditional scan bodies work great for cases involving single-unit implant restorations and small bridges, but due to the nature of these scanners being intraoral, they are only capturing small sections of data at a time and then "stitching" each of these small scans together. In contrast, photogrammetry scanners are extraoral, so they can capture all of the scan bodies at one time. This allows them to not only measure where one implant is located in 3D space but also more accurately record the relationships between multiple implants (Figure 2).

IDT: How is this better than traditional analog methods?

Roney: Going fully digital with photogrammetry allows you to reduce the "time to teeth" for patients. No longer will you need to schedule an entire appointment just to make a verification jig for a stone model. So, although paying $35,000 to $45,000 for these scanners up front sounds like a lot, the downstream savings on materials and time add up fast.

IDT: Exactly how accurate are dental photogrammetry systems?

Roney: People always ask for the accuracy of the scanners to be described using a single value, such as "accurate down to 15 μm," but like most things in life, the truth is much more complicated. The Co-CEO of ClaroNav, Doron Dekel, does a great job of addressing this in his most recent white paper on the MicronMapper, in which he explains that there is currently no standard and verifiable process to obtain such a value. In my opinion, anyone should be wary of vendors selling 3D scanning equipment who provide an accuracy measurement as a single value without explaining their methods. Many factors, including the number of implants involved, the circumstances of the test, and the methodology used to calculate the results down to a single value, should be considered. However, the first question that we should be asking is what clinically significant amount of error is still acceptable for a passive fit? A review of the currently available literature suggests that a root mean square error of 50 μm to 100 μm with less than 1° of deviation will be passive in most clinical cases, and current studies have shown that, in most cases, all of the available photogrammetry systems fall within this acceptable range.

IDT: Can designers use the data in their current software applications?

Roney: Absolutely. Most designers can incorporate this data into the software that they're already using. All of the available photogrammetry systems have a library or workflow for using their data in common dental CAD software applications, such as exocad and 3Shape. Those software applications do not natively know how to design an implant bridge using scan bodies from a photogrammetry system, but when the user imports a library, that library tells the CAD software how to relate the implant data to the photogrammetry data and what shape to cut out in the bridge so it seats on the multi-unit abutments correctly. The same is true for Ti bases and model analogs.

IDT: Why is attaining a completely passive fit so important?

Roney: A passive fit ensures that forces generated during chewing and biting are evenly distributed across the implants. This helps prevent excessive stress on the implants and reduces the risk of implant failure or bone loss. An implant-supported bridge with a passive fit minimizes the potential for micro-movements or excessive forces on the implants. Over time, these movements or forces can lead to implant loosening, bone resorption, and, ultimately, implant failure. Achieving a passive fit on an implant-supported bridge is essential for optimizing the long-term success for all of the mechanical, functional, and esthetic demands of the patient, and photogrammetry can help achieve that.

Blake Roney 
Digital Solutions Manager
S.I.N. Dental USA
Instagram:
@CADCAMBLAKE