Can a digital dental scan replace a putty impression, and when is an impression still used?

What a digital scan is, and what it is not

A digital scan, sometimes called a digital impression, is a three-dimensional picture of the surfaces of your teeth and gums. A small wand with a camera and a light source is moved around the mouth, and software stitches many overlapping images into a single model that can be viewed on a screen, sent to a laboratory electronically, or used to design and mill a restoration in the office.

It is not an X-ray. X-rays use ionizing radiation to see through teeth and bone, which is how they show decay between teeth, the roots and the bone around them. A scanner records only what its camera can see: the outside of the teeth, the gum line and the way the upper and lower teeth meet. The two records answer different questions, which is why a check-up may include both. How often you need X-rays is a separate decision, covered in Do you need dental X-rays at every check-up?.

A conventional impression, sometimes called a putty impression, works the other way around. A tray filled with soft material is seated over the teeth, held still while it sets, then removed. The material carries a negative of your teeth, which is poured in dental stone to make the physical model a laboratory works from.

What you usually notice in the chair

With a scan, the wand rests against or just above the teeth and the record builds on the screen as it is taken; if an area is missed, the dentist rescans only that area. With a tray impression, the material has to set in the mouth for a few minutes, and some people find the tray uncomfortable or hard to tolerate. In studies that asked, many patients said they preferred scanning, but not everyone does, and neither method is the right one for every mouth.

What the research says

Researchers have compared the two methods mostly by measuring how precisely a restoration made from each one fits, or how closely the digital model matches the real teeth. The findings depend heavily on what is being made.

Single crowns, onlays and veneers

For a crown on one tooth, a systematic review and meta-analysis reports that crowns made from digital scans fit about as well as crowns made from conventional impressions, with no significant overall difference in the fit at the margin, and some results favoring the digital workflow for how closely the crown fits the inside of the prepared tooth. This is the situation where the evidence for scanning is most consistent. Partial-coverage restorations such as onlays, and veneers on front teeth, are made from the same kind of single-tooth record, and the same considerations usually apply.

Aligners and retainers

Clear aligners and many retainers are manufactured from a three-dimensional model of the whole arch, and that model can come from a scan or from an impression. Aligners are planned on the overall shape of the arch rather than on the fine edge of a prepared tooth, and either record can provide that model. What the consultation covers is described in A clear aligner consultation: what your dentist needs to assess.

Bridges and full-arch records

The picture is less settled when the record has to be accurate across a whole arch, as it is for a long bridge, a full set of veneers or a complete-arch restoration. A scanner builds the arch by stitching many small images together, and small errors can accumulate from one side of the mouth to the other. A recent systematic review and meta-analysis of full-arch scans found contradictory results between studies and wide variation in how accuracy was measured, and noted that conventional impressions are still often treated as the reference for this kind of work. A dentist may reasonably choose a tray impression, a scan, or both.

Implant restorations

Implants add a step: the scanner records a small marker attached to the implant, called a scan body, rather than a tooth, and the implant's position has to be transferred precisely. A systematic review and meta-analysis found that digital impressions performed comparably for a single implant, while for several missing teeth in the same arch (a partially edentulous situation) conventional impressions were more accurate in a number of laboratory studies. Reports on full-arch implant cases are mixed. If an implant crown or bridge is part of your plan, the record to be used is a fair question for the consultation; see Dental implants in Santa Barbara: what should a complete consultation include?.

A note on how these studies were done

Most published comparisons are laboratory (in vitro) studies on models rather than on patients, where saliva, movement, bleeding and a limited mouth opening do not interfere. Reviewers regularly call for more clinical trials. That does not undermine the single-crown findings, which are the most consistent, but it is a reason to read any claim that one method is always more accurate with caution.

What changes the choice for your tooth

• Type of restoration. A single crown, onlay or veneer is the clearest case for a scan. A long-span bridge, full-arch work or multiple implants is where reviews report mixed results and where a conventional impression may still be chosen.
• Where the margin sits. A scanner can only record what it can see. If the edge of the preparation sits well below the gum line, the dentist may need to move the gum aside temporarily, or may prefer a conventional impression, since margins below the gum line are a recognized limitation of scanning.
• Gum health and bleeding. Blood and saliva obscure the camera's view of a fine margin. Inflamed gums may mean treating the gums first, or choosing whichever record copes best on the day.
• How the restoration will be made. A restoration milled in the office needs a digital file, so the scan is part of that workflow. A laboratory may accept the digital file and print its own model, or may ask for a physical impression in some cases.
• Comfort and gag reflex. A strong gag reflex, a small mouth opening or difficulty keeping still may favor one method over the other; tell the dentist before the record is taken.
• The dentist's protocol. Dentists also choose the method they can check reliably for a given case. A scan can be reviewed on screen before you leave the chair, and a tray impression can be inspected for voids and retaken if needed.

How the scan fits into a check-up and a same-day crown here

Loul Dental Studio lists a digital scan, digital and 3D X-rays and a bite assessment among its check-up and cleaning components, and lists same-day porcelain crowns, inlays and onlays with in-house milling under biomimetic dentistry. In a same-day crown workflow, a digital scan of the prepared tooth is the record from which the restoration is designed and milled in the office; the sequence is described in A same-day crown appointment: what happens from scan to fit. This page describes those services only as listed. Which record is used for your particular tooth is decided at the examination, and a conventional impression remains an option whenever it is the better tool for the case.

Questions worth asking

Keep your questions short and specific:

1. Which record will you use for my restoration, a scan, an impression or both, and why for this tooth?
2. Is the margin above or below my gum line, and does that affect the choice?
3. Will the restoration be milled here or made by a laboratory?
4. If I have a strong gag reflex, what are my options?
5. Will my scan be kept on file so it can be compared with a later one?

The next step

A scan is a record, not a treatment. Whether it can replace an impression depends on what is being made and on the conditions in your mouth on the day. Bring your questions to a check-up or consultation, and if you have an existing crown, bridge or implant plan from another office, bring that too. You can request an appointment online; a request is not a confirmed appointment, and the team will follow up to arrange a time.