Study Models vs Digital Scans: How Orthodontists Record Your Teeth

What study models and diagnostic records are for

Before treatment planning, orthodontists need an accurate three-dimensional record of your teeth and bite. These records serve multiple functions: they allow the orthodontist to measure tooth sizes, overjet, overbite, arch widths, and crowding; they form the baseline against which treatment progress and outcome can be compared; they are used to communicate with dental laboratories for appliance fabrication; and they are part of the clinical record that must be retained for medico-legal purposes. Records taken at the start of treatment are also used to demonstrate treatment outcomes and, where needed, provide evidence in clinical audits or complaints. Most orthodontists take records at the start and end of treatment; some also take mid-treatment records.

Traditional plaster and alginate impressions

The traditional method involves filling a dental tray with alginate impression material — a seaweed-derived powder mixed with water to a paste — and pressing it over the teeth for approximately 90 seconds while it sets. The impression is then poured with dental plaster (stone) to produce a three-dimensional replica of the teeth called a study model. These models are trimmed, articulated (paired upper and lower), and stored physically. The technique has been used for over a century and, when well executed, produces highly accurate models. However, alginate is sensitive to technique — poor mixing, a gagging patient, bubbles, or distortion during removal can reduce accuracy. Models can be damaged, lost, or deteriorate over time, and physical storage requires significant space.

Modern intraoral scanning — iTero, 3Shape Trios, and Cerec

Intraoral scanners capture the surface of the teeth and soft tissues using a wand-shaped device that is moved around the mouth, capturing thousands of images per second to build a real-time three-dimensional digital model on screen. The most widely used systems in UK orthodontic practices are iTero (Align Technology), 3Shape Trios, and Dentsply Sirona Cerec Primescan. The scan takes 5 to 15 minutes depending on the operator's experience and the patient's co-operation. Results are visible on screen in real time, and the clinician can check for any gaps in the scan and rescan specific areas immediately. Digital files are stored in the cloud or on practice servers and can be accessed instantly, shared with laboratories electronically, and used for digital treatment planning.

Accuracy comparison — digital vs plaster models

Multiple studies comparing intraoral scanning to conventional alginate impressions and plaster models have found that modern intraoral scanners achieve accuracy within 0.5mm for tooth dimensions and arch measurements — equivalent to or better than alginate impressions when performed correctly. The iTero and 3Shape Trios systems have the strongest published evidence bases. Accuracy can be reduced in patients with very deep periodontal pockets (where subgingival margins are relevant) or where there is heavy salivary flow, but for the purposes of orthodontic study model records, digital scanning is now considered the gold standard by most professional bodies. The British Orthodontic Society acknowledges digital scanning as an appropriate and accurate method for orthodontic records.

Storage differences — physical vs cloud

Plaster models must be physically stored for the duration of the clinical records retention period — a minimum of 11 years for adult patients, and until age 25 for patients who were under 16 at the start of treatment, or 11 years after the final entry, whichever is longer. A full course of orthodontic treatment produces two to four sets of models plus retainer models, occupying considerable physical space. Practices must have systems to label, store, and retrieve models reliably. Digital records have no physical bulk, can be backed up redundantly, and can be retrieved instantly by any authorised clinician. The primary risk with digital storage is data loss from server failure or cybersecurity incidents — reputable cloud-based systems mitigate this with redundant backups and encryption.

Use in aligner fabrication

Digital scans have largely replaced alginate impressions as the input for clear aligner fabrication. Align Technology's Invisalign system requires an iTero scan or digital file; sending a physical impression is no longer standard practice. Other aligner systems similarly accept digital files. Digital scans allow direct integration with planning software — the clinician or technician can design the treatment plan virtually, generate staging, and export files for aligner production without the time delay of posting physical impressions to a laboratory. This has shortened the turnaround time from records to receiving aligners and has reduced errors caused by impression distortion or postal damage.

Patient experience

For most patients, intraoral scanning is significantly more comfortable than alginate impressions. There is no material in the mouth, no taste, no risk of gagging from impression material flowing to the back of the throat, and no wait while the material sets. Patients who have a pronounced gag reflex, or who are anxious about having material in their mouth, typically find digital scanning far easier. Children often engage with the process more positively because they can watch the 3D model building on screen in real time. The wand must still be moved methodically around all surfaces of the teeth, so scanner tip contact with the mouth is unavoidable, but the overall experience is generally better than traditional impressions.

When impressions are still used

Despite the widespread adoption of intraoral scanning, alginate impressions and plaster models are still used in some situations. Practices that have not yet invested in scanner technology continue to use traditional methods. Some laboratory procedures — such as certain types of functional appliances or retainers produced by specific laboratories — may still require physical models or polyvinyl siloxane (PVS) impressions rather than digital files. Patients with very restricted mouth opening, unco-operative young children, or significant oral anatomy challenges may sometimes be better managed with impressions. However, in most UK orthodontic practices with modern equipment, digital scanning is now the default.

What happens to your records — UK GDPR and data retention

Your orthodontic records — including study models or digital scans, radiographs, and photographs — are part of your clinical record and are subject to UK GDPR and NHS/private practice retention policies. Digital records should be encrypted, access-controlled, and stored on systems compliant with UK GDPR. You have the right to request access to your records (a Subject Access Request) and to receive copies of your digital records in a usable format. Physical plaster models can be difficult to copy, but digital files can be shared readily. If you change practice mid-treatment, your new orthodontist may request transfer of records; you can facilitate this by requesting your records from the original practice. On completion of the retention period, records should be securely destroyed.

Useful related pages

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