What a scan file actually is
An intraoral scan is stored as a mesh: a surface made of many small triangles that together describe the shape of the teeth and soft tissue. Every common export format stores that mesh. What differs is what else it can carry, mainly color, and how it is packaged.
The three common open formats
| Format | What it holds | Color | Typical use |
|---|---|---|---|
| STL | Triangle geometry only | No | The universal format. Accepted by virtually every dental CAD and 3D printing workflow. |
| PLY | Triangle geometry plus extra properties, usually a color value per point | Yes, stored in the file | Color scans from many intraoral scanners. Widely accepted by current CAD software. |
| OBJ | Geometry plus texture coordinates | Yes, through separate texture files | Color scans where the color is an image wrapped onto the mesh. |
STL
STL describes the surface as a list of triangles and nothing more. It has no color, no texture and no record of units; dental software assumes millimeters. STL comes in two variants. Binary STL is compact and is what scanners normally export. ASCII (text) STL describes the same triangles in readable text and is several times larger. If a lab asks for STL, binary is what they expect.
Because it is so simple, STL is the safest choice when you are unsure what the receiving software supports.
PLY
PLY stores the same kind of mesh but can attach extra values to each point, and scanners use this to store color. A color PLY shows the lab the gingiva, the tooth, the retraction cord and any blood or debris the way you saw it on screen. That is often what makes a subgingival margin readable.
OBJ
OBJ can also carry color, but differently: the color is an image file (often JPG or PNG) mapped onto the mesh, with a small companion material file (.mtl) that links the two. If you send only the .obj file, the lab gets geometry without color. Always send the whole set together, ideally in one zip.
Open versus proprietary formats
Each scanner platform also has its own native format, such as 3Shape's DCM or Medit's own mesh format. Native files can hold more than a generic export: scan history, the bite alignment, color and case details. They open easily in that vendor's own software and its connected labs, and may open with limitations, or not at all, elsewhere.
When you send a case through your scanner's cloud to a connected lab, the platform handles this for you: the lab receives what its system can read, often native data plus exported files. Format choice mostly matters when you export manually. In that case:
- Ask the lab which format they prefer before the first case, and keep a note of it.
- When in doubt, send STL (for compatibility) and PLY (for color) together.
- Do not assume a native file will open at a lab that does not work with your scanner brand.
File sizes
Size depends on how detailed the mesh is, not on the format alone. A binary STL takes a fixed amount of space per triangle, so a dense full-arch scan is larger than a quadrant scan. As a rough guide:
- A full-arch binary STL is usually in the tens of megabytes. A quadrant scan is smaller.
- A color PLY of the same scan is larger than the STL, because color is stored with each point.
- An OBJ set adds the size of the texture images.
- A complete case (both arches, bite, pre-op and implant scans) can exceed 100 MB before compression. If you upload files to a HERi2go order manually, the limit is 300 MB for all scan files on the order; files other than PDFs are zipped automatically.
Email attachment limits are often too small for a full case, which is one more reason to send through your scanner's cloud or a lab portal instead of email.
Do not reduce file size by lowering resolution, simplifying or decimating the mesh. Zip the files instead. Mesh files compress reasonably well, and the lab gets the full detail.
What labs need, by case type
| Case type | Files the lab needs | Format notes |
|---|---|---|
| Single crown, inlay/onlay, veneer | Prep arch, opposing arch, bite registration. Pre-op scan if the original anatomy should be copied. | STL works. Color (PLY or native) helps the lab read margins. |
| Bridge | Same as a crown, with every abutment and the pontic area captured clearly, including the soft tissue under the pontic. | Same as a crown. Make sure all abutment margins are complete. |
| Implant restoration | Scan with the scan body seated, the same arch without the scan body (soft tissue), opposing arch, bite. Plus implant system, platform and scan body type in the Rx. | The scan body scan must keep its position relative to the other scans. Export from the same case so the alignment is preserved. |
| Printed models | Both arches and the bite, with enough of the vestibule and palate or floor of the mouth captured for a stable model base. | STL is standard for printing. Holes in the model area need extra repair work. |
Export tips
- Export each scan as its own file: upper, lower, scan body, pre-op. Do not merge arches into one file.
- Keep the original alignment. Export all files from the same case in one export so the upper and lower arches stay in their bite position. Arches exported separately at different times may lose that relationship.
- Name files clearly, for example upper_prep, lower_opposing, upper_scanbody. Generic names make it easy to mix up arches.
- Use full resolution. Turn off any "reduce", "simplify" or "optimize for sharing" option unless the lab asks for it.
- Include the prescription as a PDF or in the lab's order form. Files carry shape, not instructions.
- Zip everything into one package per patient, with the patient or case identifier in the zip name.
Common file problems and how to fix them
Holes in the scan
Gaps usually appear at interproximal areas, deep margins, and the distal of the last molar. Small holes away from the restoration can be filled in software. A hole at the margin cannot be safely filled, because the lab would be guessing the exact edge of the restoration. Check the margin area on screen and rescan that spot before the patient leaves.
Missing or wrong bite registration
Without a bite, the arches are not related to each other and the lab cannot set occlusion. A bite taken while the patient was not fully closed leads to a crown that is high or out of contact. Check that the bite step was completed and that the arches meet the way the patient actually closes.
Wrong arch or swapped files
An upper scan labeled as lower, or a prep scan sent as the opposing arch, is a common manual-export mistake. Clear file names and a quick look at the case before sending prevent it.
Scan body sent alone
For implants, a scan with the scan body in place does not show the soft tissue around the implant. If only that file arrives, the lab cannot design the emergence profile and will ask for the soft tissue scan.
Low resolution
A mesh that has been simplified for sharing can look fine at a glance but blur the margin line. If the lab reports a soft or faceted margin, re-export at full resolution before considering a rescan.
Plaster model and conversion scans
When a physical impression or plaster model is scanned instead of the mouth, some systems process or convert the data in the background before the final mesh is ready. If the case is sent or exported before that finishes, the lab can receive an incomplete file, or a placeholder instead of the actual model. Wait until the case shows as fully processed in your software, then confirm the file opens and shows the model before sending.
Color sent without the texture
An OBJ without its texture image and .mtl file shows up gray. Send the whole set, or use PLY instead.
Summary
- STL holds shape only and works everywhere. PLY and OBJ add color, which helps the lab read margins and soft tissue.
- Native formats carry the most information but may only open in that vendor's ecosystem.
- Sending through your scanner's cloud avoids most format and size issues. For the steps, see How to Send Intraoral Scans to a Dental Lab.
- When exporting manually: separate files per scan, original alignment, full resolution, clear names, one zip, prescription included.
- Before sending, check margins for holes, confirm the bite, and make sure implant cases include both the scan body scan and the soft tissue scan.