Digital scanning replaced conventional impressions in many practices within a relatively short period. The reasons are mostly about where errors entered the old process.
The conventional chain had several transfer steps
A traditional impression captures the teeth in a setting material, which is then poured in stone to produce a physical model that the restoration is made on.
Each step introduces its own dimensional change, as materials shrink or expand slightly while setting and the model must be separated from the impression without damage.
Errors at any stage carry forward, and their combined effect is what determines how well the finished restoration fits.
Scanning captures geometry directly
An intraoral scanner projects a pattern of light onto the teeth and records how that pattern deforms across the surface, calculating depth from the distortion.
The handpiece captures many frames per second as it is moved across the arch, and software stitches overlapping frames into one continuous surface.
The output is a mesh of points defining the shape, which can be transmitted, stored and manufactured from without any physical intermediate. Nothing shrinks or sets, so the transfer errors of the older chain do not arise.
Stitching introduces a different kind of error
Because the model is assembled from overlapping fragments, small alignment errors accumulate as the scan extends along the arch.
Over a short span this is negligible, but across a full arch the accumulated deviation becomes relevant for work spanning many teeth.
Scan strategy therefore matters, and this is one area where conventional impressions retained an advantage longer than for single units.
Practical differences during the appointment
There is no tray of setting material, which removes a common trigger for gagging and shortens the time the mouth must stay open.
The scan can be reviewed immediately and a deficient area rescanned in seconds, whereas a defective impression must be retaken entirely.
Moisture, blood and soft tissue still obscure margins, so preparation and isolation remain as important as they were before. A camera can only record a surface it can see.
What the digital model enables afterwards
The same data supports designing restorations, planning tooth movement, manufacturing aligners and guiding implant placement without further records.
Stored scans can be superimposed over time to measure changes in wear or gum position that would be difficult to judge by eye.
None of this substitutes for clinical examination, since a surface model records shape and nothing about what lies beneath it.