Digital Scan vs Dental Impressions for Orthodontics UK

What are traditional dental impressions?

A dental impression is a physical mould of your teeth taken by pressing a tray loaded with impression material against your teeth and holding it while the material sets. The most common material used for orthodontic impressions is alginate — a seaweed-derived powder mixed with water to create a paste that sets within one to two minutes. Once set, the tray is removed and the impression is sent to a laboratory where plaster is poured in to create a physical model. Polyvinyl siloxane (PVS) is a higher-accuracy material sometimes used for retainer fabrication or detailed planning work.

Why are impressions taken in orthodontics?

Impressions or digital equivalents are taken at multiple stages of orthodontic treatment. Before treatment begins, study models of both arches are required for diagnosis and treatment planning — the clinician uses these to measure tooth sizes, arch widths, and plan tooth movements. During treatment, impressions may be taken to fabricate removable appliances or retainers. At the end of treatment, final models record the finished result. Clear aligner systems require highly accurate upper and lower arch records to manufacture each set of trays — this is the application where impression quality has the greatest impact on treatment accuracy.

How do intraoral scanners work?

An intraoral scanner uses a handheld wand with a camera at the tip, passed systematically over the surfaces of your teeth. The camera captures thousands of images per second which are stitched together by software to create a real-time three-dimensional model on a screen. The process typically takes five to ten minutes for both arches. The most widely used scanners in UK orthodontic practices include the iTero Element series, 3Shape Trios, and the Medit i700. Each system captures full-colour three-dimensional models that can be immediately inspected, zoomed, and measured on screen.

What are the advantages of digital intraoral scanning?

The most immediate benefit for patients is the elimination of the gag reflex trigger associated with traditional impressions. The impression tray and putty-like material are the most common causes of discomfort and anxiety during orthodontic records. A digital scan involves only a slim wand held near but not pressing against the back of the throat. Digital scans provide immediate feedback — the clinician can review the model on screen during the appointment and rescan any area that has been poorly captured. Digital files can be sent electronically to the aligner laboratory within seconds and stored indefinitely with no physical deterioration.

When are traditional impressions still used?

Not all orthodontic practices have invested in digital scanners, as the equipment cost is significant — a high-quality intraoral scanner costs between £15,000 and £35,000. NHS practices and high-volume practices operating on narrower margins may still use alginate impressions routinely. Some highly customised laboratory appliances may still require traditional impressions depending on the laboratory's workflow. For retainer fabrication outside of the aligner ecosystem, some practices still use alginate impressions which are sent to local laboratories — this is often faster and lower cost for simple removable retainer cases.

How do digital scans and alginate impressions compare for accuracy?

For clear aligner manufacture, digital scanning is consistently more accurate than alginate impressions. Alginate is dimensionally unstable — it begins to shrink within minutes of being removed from the mouth, and if not immediately poured with plaster, the impression distorts. Shipping impressions to distant laboratories introduces further risk. Studies comparing iTero and 3Shape Trios against alginate find that digital scans produce aligner-to-tooth fit that is more precise, with fewer tracking issues early in treatment. For fixed appliance bonding and fixed retainer fabrication, the accuracy difference is less clinically significant and traditional impressions remain widely used.

What do patients experience during an intraoral scan?

You will be seated in the dental chair as normal. The clinician or dental nurse will pass a slim scanning wand over your teeth, starting typically at the back molars on one side and working systematically around each arch. The wand does not press on your teeth — it is held a few millimetres away while capturing images. You will see a three-dimensional model of your teeth building in real time on the screen in front of you. The scan of both arches takes approximately five to ten minutes. There is no unpleasant taste, no material to bite into, and no waiting for material to set.

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This guide is for general information only. It is not a diagnosis, treatment plan, or substitute for advice from a registered dentist or orthodontist.