Where Digital Doesn’t Make a Good Enough Impression

Scanner technology has come a long way over the past 10 years and continues to make extraordinary leaps in functionality, but are there still some areas of dentistry where a traditional impression is better than a digital one? Unfortunately, as of now, the answer is still yes.

Intraoral scanners are a popular technology for dental practices and labs that have embraced a fully digital workflow. Scanners take digital impressions, which are faster to complete than traditional impressions and are more comfortable for the patient. Some experts say that improvements to scanner systems and digital impression techniques might soon replace conventional impressions.¹

Part of this sweeping prediction is that digital impressions have many advantages over traditional impressions. A 2021 ACE Panel report suggests that of the 369 panel members, 53% use an intraoral scanner. Of those respondents, 70% said it improved their clinical efficiency. Nearly half of the respondents (40%) said the intraoral scanner provides better outcomes than conventional impressions. Also, 90% said they use the scanner the most for single tooth–supported crowns.² However, clinicians use digital impressions in many other restorative situations including inlays, onlays, fixed partials, crowns, aligners, occlusal devices, and surgical guides.³

Research also shows that using digital impressions instead of conventional ones positively impacts implant dentistry. A 2016 Clinical Oral Implants Research study suggests that dentists and dental students found that intraoral scanning for making impressions was relevant and more straightforward than making conventional impressions for implant therapy.⁴ Both groups also considered an intraoral scanner more effective, although more students thought that than practicing dentists. Moreover, 76% of the students preferred intraoral scanning. By contrast, 48% of dentists preferred conventional, whereas only 26% liked intraoral scanning better than traditional impressions. (The remaining 26% of dentists thought either method was acceptable.) Investigators concluded that for single-implant sites, the scanner with its quadrant method scan was more time efficient than a conventional full-arch impression technique.⁴

Where are Conventional Impressions Better?

With that said, there are still some areas where a conventional impression is a better choice. A 2016 Finnish study published in the Journal of Prosthodontics suggests that the traditional impression technique is better than digital for full-arch impressions.⁵

Moreover, a September 2020 article published in Decisions in Dentistry discussed digital dentures and concluded that a conventional impression was still best for the workflow. The biggest challenges with digital impressions that the authors cited include the following⁶:

• The technology’s high cost
• The learning curve’s perceived difficulty
• The ongoing costs associated with subscription fees for the equipment and software

However, there were also the physical challenges of using an intraoral scanner on edentulous patients, namely the tricky nature of accurately capturing the mouth’s complicated anatomy and soft tissue position. Specifically, the investigators indicate that capturing the mucosa in 1 pass is essential because it moves, and going back to recapture missing information results in errors in the digital impression.⁶

A lot has changed with scanning technology since then, but the full-arch scan can still be problematic. In a 2022 article on the American Dental Association’s website, Jacob G. Park, DDS, a clinical professor in the Department of Comprehensive Dentistry at the University of Texas Health at San Antonio, suggests that digital impressions might not be as accurate as a traditional impression for complete-arch digital scans for tooth- and implant-supported prostheses and removable partial and complete dentures.³

Scott Dickinson, DMD, general dentist and owner of multiple private practices with 6 offices, including one in Gulf Breeze, Florida, says that part of the problem with scanning for dentures is that intraoral scanners need hard tissue stops, which enable the software to orient in the mouth. When performing a complete denture, this is incredibly challenging, he says. Although he thinks the scanner manufacturers are getting close, the digital impression cannot get all the anatomy that enables fully removable prosthetics to fit without many adjustments. However, he is seeing promising results when scanning for many partial dentures.

“You still have the same problem if you get a long Kennedy Class I or II. They have a difficult time when you get long stretches of edentulous areas. You have to learn some field tricks to get the scanner to work,” Dr Dickinson says. “But I still use polysulfide when it comes to a fully removable. The digital impression just isn’t there yet.”

Another area where Dr Dickinson has difficulties using an intraoral scanner are in roundhouse situations. For example, if he is crowning teeth 3 to 14, he still wouldn’t scan because even though the intraoral scanners capture the prep beautifully, they can’t grab a proper bite for a crown or bridge case that significant. Dr Dickinson says the computer gets lost.

“Then when you get it back from your lab, you have to grind,” Dr Dickinson says. “What ends up happening is you have to adjust the occlusion so much that you have to kind of remake it. So, for a really big crown and bridge case, whether that’s all on 4 or a multiunit implant or cosmetic work, I still go back to a conventional impression.”

Sometimes Conditions Are the Problem

John Flucke, DDS, technology editor for Dental Products Report, agrees that sometimes a digital impression isn’t as good as a traditional impression, but that these instances are becoming rarer as scanner technology improves. These days, what makes a digital impression challenging to take is the same thing that makes a conventional impression difficult to capture. For example, he explains that if the margin is deeply subgingival, then the dental impression quality will suffer, whether the impression is digital or traditional.

Another situation that could compromise the digital impression is when clinicians use the scanner to capture a digital impression of patients with unhealthy periodontal situations. It is challenging to capture an image when blood, saliva, and other contaminants are in the area. However, those impressions would be difficult with traditional materials as well, he says.

“Digital impressions always work better when the margins are obvious,” Dr Flucke says. “My preparations have a finish of a shoulder or a heavy chamfer, but there might be a situation where a doctor might need to do a feather-edge margin, and that would be harder for a system to pick up. It is not a deal breaker, but I could see where it might be hard for a scanner to pick up.”

Jason Goodchild, DMD, vice president of clinical affairs for Premier Dental Products Company in Plymouth Meeting, Pennsylvania, agrees that the challenges are multifactorial. For example, sometimes the problem with capturing the scan is access, but he says the sensors are getting smaller to address the intraoral scanner’s role in that situation. With that said, the sensor size cannot address how wide the patient can open their mouth or the state of their soft tissue.

Dr Goodchild says the preparation of the tooth, specifically hemostasis and tissue retraction, will often dictate whether the area is scannable. If you cannot achieve appropriate tissue retraction, the scanner can’t work. Intraoral scanners are optical devices; they cannot see through tissue and blood. Moreover, Dr Goodchild explains that clinical situations exist where a digital impression won’t work. “If the margin is subgingival or if you need to put a bevel or a knife-edge margin on a bevel on a tooth, that’s not going to scan very well,” Dr Goodchild says.

Then there is the situation where a dentist’s lab is not digital. For example, Dr Flucke’s small denture lab in the Kansas City metropolitan area in Missouri cannot accept digital impressions. In those cases, Dr Flucke will print the models and send them to that lab, which he finds frustrating.

“It’s sort of like having to ride a horse to send a fax, if you get what I mean,” Dr Flucke says. “Also, this is a bit technical, but I do sleep apnea cases, and there is one very large lab here in [Kansas City] that will take my models via digital, but sleep appliances require a very special bite registration that shows how the arches are oriented when the mouth is open. So that lab requires me to send them a bite registration in the impression material.

“I quit working with them when I told them there was a way to do that digitally, and they told me [there wasn’t]” Dr Flucke continues. “I found that obnoxiously funny because I was working with a lab that could do the whole process digitally.”

Everybody Wants it to Be Good Enough

Dr Goodchild says that since the first commercially available scanners in the mid-1980s, the technology has been improving, from the technology to the software and everything else. So, there are areas where digital scanners aren’t going to work clinically, but it isn’t because the technology is not improving all the time. “It’s like a new iPhone; they’re introducing the next big thing every year or 2 years,” Dr Goodchild says.

Moreover, clinicians want to integrate digital into the daily workflow across the clinical day. Incorporating all the puzzle pieces—from the patient record to occlusal relationships to the treatment plan and digital scan—and making that visually accessible in the operatory is a standard many dentists look forward to achieving. However, Dr Goodchild says the technology cannot support this workflow yet. “There [are] still probably a ton of times when you do [a] simple crown and bridge [where] you just can’t use a scanner,” Dr Goodchild says. “That’s something we are getting better at, but we’re not there yet.”

Dr Goodchild thinks some digital workflow manufacturers think traditional impressions have a life span that will run out as technology improves. However, he doesn’t envision a future where traditional impressions have no place in a dental practice. Dental professionals will always need a work-around because one way to do things does not work for all situations. “The ratio of scanning to traditional impressions is going to continue to move toward the digital side, but I still think there will be a need for those silicone-based impression materials and everything else,” Dr Goodchild says.

Dr Dickinson is optimistic about the future of intraoral scanning technology and digital impressions for full-arch or large-span restorative cases. He is confident the scanner companies will fix the problem because the market for this area in dentistry is enormous. As a result, Dr Dickinson estimates that dentists will see improvements in this area in the next couple of years.

"I think they’re going to get there. I would stake a claim that in 5 years from now, it will be super rare to use impression material,” Dr Dickinson says. “You will always keep it in the office because you don’t want to get caught without it when you need it, but you are going to throw it away and reorder it every year because you won’t use it all before it expires.”

By contrast, Dr Flucke says he already rarely takes traditional impressions. “Sometimes, if we are really busy and someone needs bleaching trays. Other than that, though, it’s pretty uncommon,” Dr Flucke says.

Having both iTero and Trios intraoral scanners in his offices, Dr Dickinson says the future of taking impressions is digital. Moreover, he thinks general dentists without scanning capabilities should invest in one for the office. Having the hardware is essential because he sees that the upgrade will be in the software. “I don’t like to be the first guy on the block to buy the new technology, because I want to see [whether] it works. This really works,” Dr Dickinson says. “If you are a general dentist and are not nearing retirement, this equipment should be in your office.”

References

1. Schmidt A, Schlenz MA, Liu H, Kämpe HS, Wöstmann B. The influence of hard- and software improvement of intraoral scanners on the implant transfer accuracy from 2012 to 2021: an in vitro study. Appl Sci. 2021;11(15):7166. doi:10.3390/app11157166
   
   
2. Versaci MB. ACE Panel report finds about half of dentists use intraoral scanners. American Dental Association. September 21, 2021. Accessed March 28, 2023. https://www.ada.org/publications/ada-news/2021/september/ace-panel-report-finds-about-half-of-dentists-use-intraoral-scanners
3. Versaci MB. Digital dentistry: what to know about a few popular technologies. American Dental Association. June 10, 2022. Accessed March 28, 2023. https://www.ada.org/publications/ada-news/2022/june/digital-dentistry-what-to-know-about-a-few-popular-technologies
4. Joda T, Lenherr P, Dedem P, Kovaltschuk I, Bragger U, Zitzmann NU. Time efficiency, difficulty, and operator’s preference comparing digital and conventional implant impressions: a randomized controlled trial. Clin Oral Implants Res. 2017;28(10):1318-1323. doi:10.1111/clr.12982
5. Ahlholm P, Sipilä K, Vallittu P, Jakonen M, Kotiranta U. Digital versus conventional impressions in fixed prosthodontics: a review. J Prosthodont. 2018;27(1):35-41. doi:10.1111/jopr.12527
6. Punj A, Fisselier F. Digital dentistry for complete dentures: a review of digital dentistry versus conventional approaches to complete dentures. Decisions in Dentistry. September 2020. Accessed March 31, 2023. https://www.researchgate.net/publication/344179328_DIGITAL_DENTISTRY_FOR_COMPLETE_DENTURES_A_REVIEW_OF_DIGITAL_DENTISTRY_VERSUS_CONVENTIONAL_APPROACHES_TO_COMPLETE_DENTURES