Scan accuracy is discussed constantly in digital dentistry, but the term is often used loosely. For clear aligners, which depend on an accurate full-arch model, understanding what accuracy means and what degrades it in the chair helps reduce fit problems.
Two components of accuracy
International standards on measurement, such as ISO 5725, describe accuracy in terms of two components:
| Term | Meaning | In practice |
|---|---|---|
| Trueness | How close a measurement is to the true value | Does the scan match the real shape of the arch? |
| Precision | How close repeated measurements are to each other | Do repeated scans of the same arch agree? |
A scanner can be precise but not true — consistently producing the same small distortion — so both matter.
Why full-arch accuracy is the challenge
Scanners build a model by stitching together many overlapping images. Small errors can accumulate over the length of the arch, so distortion tends to be greater across a full arch than over a few teeth. Aligners cover the whole arch, which makes full-arch accuracy particularly relevant to fit.
Chairside factors that introduce error
- Saliva and moisture on tooth surfaces
- Movement of the cheeks, tongue and lips into the scan field
- Highly reflective or translucent surfaces, such as metal and some ceramics
- Inconsistent scanning paths or skipping areas and returning later
- Scanning too fast or at an inconsistent distance
- Missing data in interproximal areas and on distal surfaces of last molars
Capturing reliable scans
- Follow the scanning path recommended for your scanner and use it every time.
- Dry the teeth and use retraction to control soft tissue.
- Capture the distal surfaces of terminal molars and the gingival margins completely.
- Check the model for holes and stitching errors before the patient leaves.
- Record the bite in maximum intercuspation and verify it on both sides.
- Keep scanner software updated and calibrate according to the manufacturer's schedule.
How accuracy shows up in aligner fit
Scan errors can appear as trays that seat well on some teeth but not others, particularly on terminal molars. If a first tray doesn't seat, compare the scan to the teeth before assuming a tracking problem. A rescan is sometimes the fastest fix.
Infinity Aligner accepts scans from all major intraoral scanners. Our team reviews incoming scans and will contact you if an area needs to be rescanned.
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