Intraoral Scanner vs Traditional Impressions: Accuracy and Comfort

Every custom-made restoration, whether a crown, a veneer or a night guard, starts with an accurate copy of your teeth. For decades that copy was taken with a tray of soft impression material. Today the same record can be captured digitally with an intraoral scanner, a small optical device that builds a 3D model of your teeth on screen. This article explains how scanning works, how it compares with traditional impressions on comfort, time and accuracy, where its limits are, and what happens to the scan afterwards.

Why impressions are needed

An impression is a copy of your teeth, gums and bite that can be worked on outside your mouth. Crowns, bridges, veneers, inlays and onlays, implant crowns and night guards are all designed and made from it. The more accurate the impression, the more predictable the fit, the margins and the bite of the final restoration.

Impressions are not only for making things. They are also used as records in treatment planning, for example to document your starting point before a smile design, so that later steps can be compared against it.

How an intraoral scanner works

An intraoral scanner is a handheld wand with a small camera in its tip. As the dentist moves it slowly over your teeth, it captures a rapid series of images, and software stitches them together into a three-dimensional model. Usually the upper and lower jaws are scanned separately, then a short scan with your teeth together records how they meet. Because the model appears on screen in real time, any missing areas can be spotted and rescanned straight away. The scanner is an optical device that uses visible light; it does not use X-rays.

What it feels like and how long it takes

Only the tip of the wand is in your mouth. Cleveland Clinic's patient information notes that because a small wand replaces a tray of putty, digital scanning is usually easier for people who gag, and it leaves no residue behind. You do need to keep your mouth open for a while, and short breaks are possible if you need them.

How long it takes depends on how much of the mouth is being scanned and on the conditions inside it. A 2021 systematic review by Siqueira and colleagues found that both quadrant and full-arch scans were faster than conventional impressions.

Conventional vs digital impressions

Comfort and the gag reflex

With a conventional impression, a tray filled with material is pressed over the teeth and held until it sets. Upper impressions in particular can trigger gagging as the material moves towards the palate. Scanning avoids that waiting period altogether. Across the 17 clinical studies in the Siqueira review, patients generally preferred intraoral scanning.

Time

The same review found scanning faster than conventional impressions. When the entire workflow is digital, the time savings can grow. In a randomised trial described in a 2017 systematic review by Joda and colleagues, a complete digital workflow for implant crowns was more than twice as fast as a mixed analogue and digital workflow (about 75 minutes versus 157). The authors also noted that randomised trials were few and that firm recommendations were premature.

Accuracy: what the evidence shows

For most patients, accuracy is the key question. A 2022 rapid umbrella review by Afrashtehfar and colleagues found that most of the 11 reviews it examined rated scanner accuracy as comparable to conventional impressions. Clinical equivalence was shown for short-span fixed work of fewer than 4 units, such as single crowns and short bridges. The Siqueira review likewise found similar prosthetic outcomes with both workflows, and Cleveland Clinic describes the accuracy of digital impressions as comparable to, or better than, putty impressions.

Limits: large bridges and removable dentures

Scanning does not replace conventional impressions in every case. The same umbrella review notes that conventional impressions are still recommended for extensive fixed restorations and for removable dentures. Bleeding, saliva or preparation margins that sit below the gum line can also make scanning harder. The right method depends on the treatment and on the conditions in your mouth.

After the scan: 3D design, milling and printing

The scan is imported into computer-aided design (CAD) software, where the restoration is designed in 3D around the shape of the tooth, the neighbouring teeth and your bite. Thickness, contact points and the fit against the opposing teeth can be checked on screen and adjusted before anything is made. It can then be made in one of two main ways:

• Milling (CAD/CAM): the design is carved from a block of ceramic or composite by a computer-controlled milling unit.
• 3D printing: models, mock-up guides, temporary restorations and night guards can be printed layer by layer.

According to Cleveland Clinic, in some cases a tooth can be scanned, the crown designed on screen and milled from a ceramic block in the practice, so that it is fitted in the same visit. The same source stresses that not every patient or tooth is suitable. In other cases the digital file is sent electronically to a dental laboratory. The digital dentistry page gives an overview of the full workflow.

Where it is used

Intraoral scanning can be used in many treatments, including:

• Single crowns and short bridges (crowns and bridges)
• Porcelain veneers
• Ceramic inlays and onlays (inlays and onlays)
• Implant crowns (dental implants)
• Records and mock-up preparation in digital smile design
• Night guards and some other protective appliances

Whether a digital impression suits your treatment is decided at the examination, based on the extent of the restoration and the conditions in your mouth.

Digital records: follow-up and sharing with your home dentist

Unlike physical models, scan files do not wear or break, and they can be stored. That makes it easier to compare later scans with earlier ones, for example when monitoring wear or changes in gum level over time.

For patients who travel for treatment, digital records have a practical advantage: they can be shared with your dentist at home, who can then take over routine follow-up. When records are exchanged, it helps to know how teeth are numbered. Most countries use the two-digit FDI system, while dentists in the United States usually number teeth from 1 to 32, so the tooth a US dentist calls #3 (the upper right first molar) is 16 in FDI notation. The tooth chart shows how the FDI numbers map to each tooth. Because scan files are health data, they should be shared through a secure channel and in line with data-protection rules.