Intraoral Scan Files: STL, PLY and OBJ Exports for Dental Labs

Most problems between clinics and dental labs come down to the wrong export format, an incomplete scan or a file sent the wrong way, and all three are easy to avoid.

Updated 20 October 2026 · 7 min read

Intraoral scan files are the starting point of almost every digital restoration, aligner and printed model. An intraoral scanner captures thousands of overlapping images and stitches them into a 3D surface, which is then exported as STL, PLY or OBJ, or kept in a proprietary format inside the manufacturer's ecosystem. Choosing the right export, checking the scan before sending it and transferring it safely saves remakes and phone calls. This guide covers what each format contains, what labs actually need, and how to deal with the most common problems.

What file formats do intraoral scanners export?

The three open mesh formats you will meet are STL, PLY and OBJ. All three describe a surface made of triangles; they differ in what else they can carry.

STL is the lowest common denominator: every dental CAD package, model-builder and slicer reads it. It has no reliable colour and no units field, so the receiving software assumes millimetres, which is the convention in dental work. PLY can store a colour value for every vertex, which is how most scanners deliver the natural-colour view of teeth and soft tissue. OBJ stores colour as a separate texture image referenced by an MTL file, so an OBJ export is often three files that must stay together.

Open vs closed scanner systems

A closed workflow keeps the scan in the manufacturer's own format and sends it through the manufacturer's portal to a connected lab or milling centre. Scan data often includes extra information such as preparation margins, bite registration and order details that open formats do not carry. 3Shape's DCM format is a common example. Closed workflows are convenient when the clinic and the lab use the same platform.

An open workflow exports standard STL, PLY or OBJ files that any lab can import. Today most scanners offer open export, although on some platforms it is an option you have to enable, may require a particular software version or licence, or is done from the cloud portal rather than the scanner itself. If a lab asks for "open STL", they mean a plain, unencrypted STL that their own CAD software can read.

Which format does the lab need?

Ask the lab, but the usual answers are:

• Crowns, bridges, inlays, implant work: STL of the preparation arch, opposing arch and bite registration, all exported in the same coordinate system so they load already aligned.
• Printed study or working models: STL of each arch. The lab will base and hollow the model in its own software.
• Aligners and retainers: STL of upper and lower arches plus bite.
• Shade or soft-tissue reference, smile design, patient presentations: PLY or OBJ with colour.
• Dentures: STL plus any additional scans the lab requests, such as the existing denture.

A useful habit is to send the STL set for production and a PLY of the preparation arch for colour reference. A lab can always convert PLY to STL, but it cannot recover colour that was never exported.

Mesh resolution and typical file sizes

Scanners produce meshes with variable density: finer triangles on preparation margins and occlusal detail, coarser ones on smooth palate and gingiva. A full-arch scan commonly contains a few hundred thousand triangles, and quadrant scans far fewer.

File size follows directly from triangle count. A binary STL uses 50 bytes per triangle plus an 84-byte header, so:

ASCII STL of the same mesh is roughly four to five times larger and has no advantage for dental use; always export binary if the option exists. PLY stores each vertex once and references it from faces, so a binary PLY of the same mesh is usually smaller than the STL even with colour included. OBJ size depends mostly on the texture image.

Do not decimate a scan to make it smaller before sending it for restorative work. Reducing triangle count smooths precisely the regions that matter, such as margins and contact areas. If a file is too large for email, use a file transfer service rather than reducing detail. Decimation with the STL file size reducer is appropriate for presentation copies, patient-facing viewers or non-critical study models.

How to check an intraoral scan before sending it

Open the exported file in an independent viewer, not just the scanner software, so you see exactly what the lab will receive. The STL viewer and PLY viewer both run in the browser and need no installation. Then check:

1. Margins are fully captured. Rotate around every preparation. The finish line should be continuous with no gaps, blurred areas or soft tissue covering it. Retraction and moisture control matter more here than any software setting.
2. No holes in critical areas. Small holes in palate or distal gingiva are usually acceptable; holes on preparations, contacts, occlusal surfaces of opposing teeth or implant scan bodies are not.
3. Adjacent teeth and contacts are scanned. Labs need neighbouring teeth to design contacts and emergence profile.
4. Bite registration is present and correct. Upper and lower should load in occlusion. If they open apart or intersect heavily, the bite scan needs redoing.
5. No stitching artefacts. Look for doubled surfaces, steps, or floating fragments from tongue, cheek or cotton rolls.
6. Correct arch and orientation. Upper labelled as upper, files named clearly.

Scanner software often fills holes automatically when it finalises the scan. Filled areas look smooth and featureless; that is fine on the palate but misleading on a margin, so check the raw scan if the software allows it.

Converting PLY to STL

If you only have a colour PLY and the lab or printer software needs STL, conversion is straightforward: the triangles are identical, and only the colour information is dropped. Use the PLY to STL converter, then confirm the triangle count and dimensions match the original.

Points to watch:

• Some scanners export PLY point clouds (vertices only, no faces). A point cloud cannot be converted directly to a printable STL; it must first be meshed.
• Units do not change in conversion. Dental scans are in millimetres; if a converted arch appears 25.4 times too small or 1,000 times too large, the issue was in the original export settings.
• Converting does not repair the mesh. If you plan to print the model, check that it is closed or let your model-builder software base and close it.

Sending scan files securely

Intraoral scans are patient health data. Under GDPR in Europe and HIPAA in the United States, they need the same care as radiographs and records.

• Use the scanner's lab portal or a transfer service that encrypts files in transit and at rest, ideally with a data processing agreement in place with the provider.
• Do not put patient names in file names. Use a case number or lab ticket reference; keep the link to the patient in your practice management system.
• Avoid sending scans as plain email attachments. Besides privacy concerns, many mail servers reject attachments above 20–25 MB.
• Zip related files together (upper, lower, bite, any colour PLY) so nothing gets separated, and include a short prescription with tooth numbers, material and shade.
• Set link expiry on shared download links and remove files once the lab confirms receipt.

Common issues and how to fix them

If a model will be printed, an open scan surface needs to become a closed solid first. Simple holes can be closed with the STL repair tool; for a deeper look at mesh errors see the guide to fixing non-manifold STL files.

FAQ

Is STL or PLY better for intraoral scans?

STL is best for production because every dental CAD and printing program reads it. PLY is better when colour matters, such as shade reference or patient communication. Many clinics send both.

Why is my intraoral scan STL not printable?

A raw scan is an open surface with an edge where the scan stops, so it has no inside or outside. It needs a base added and the surface closed, usually in dental model-builder software, before a slicer can print it.

Does converting PLY to STL reduce accuracy?

No. The triangles are copied unchanged; only the colour is dropped. Accuracy is only lost if the mesh is decimated or smoothed.

How big is a typical full-arch scan file?

A binary STL of a full arch is often in the range of 10–30 MB, depending on the scanner and resolution. ASCII STL of the same scan is several times larger.