A full-contour crown is designed and milled as one solid piece from one file, which suits most posterior cases. A split-file design produces two files for the same tooth: a coping that is milled first and a full-contour overlay that guides porcelain layering. It is standard for veneer and layered anterior cases.
"Split file" is one of those terms that gets used constantly in case instructions but rarely explained plainly. If you've ever gotten a case back and weren't sure why it came as two separate files instead of one, this is why.
What a full-contour design is
A full-contour crown is designed and milled as a single solid piece — monolithic zirconia is the most common example. One file, one piece, straight to the mill. Simple, fast, and the right call for most posterior cases where esthetics matter less than strength and turnaround.
What a split-file design is
A split-file design produces two separate files for the same tooth: a coping — the underlying framework or substructure — and a full-contour overlay shaped to guide where porcelain will be layered on top of it by hand or digitally. The coping gets milled first; the layering happens afterward, using the overlay as a shape reference.
This is standard for veneer and layered crown cases, particularly anterior esthetic work, where the natural translucency you get from layered porcelain over a substructure beats what a monolithic block can achieve on its own.
Why it's two files instead of one
The coping and the overlay serve different purposes and often go to different places — the coping to the mill, the overlay as a reference for whoever is doing the porcelain layering, whether that's a ceramist in-house or the same lab handling both steps. Keeping them as separate files makes that handoff clean instead of trying to extract layering guidance from a single monolithic design.
If a case comes back split when you expected full-contour (or vice versa), it's worth checking the original case instructions before assuming something went wrong — material and case-type selection usually drives which one a designer produces.
Which one should you ask for?
Full-contour for posterior cases and anywhere strength and speed matter more than esthetics. Split-file for anterior cases where a layered, natural-looking result is the priority. If you're not sure which a specific case calls for, that's exactly the kind of detail worth putting in your case instructions template so it doesn't have to be guessed at on a per-case basis.