How to Create Oral Retainer from STL Tooth Scan

[Anonymous]

I would like to 3D print an oral retainer based on a scan of my lower arch.  I have attached both a screen shot of my STL scan and photo of the desired final result.  [The forum did not allow me to attach the actual STL file; invalid extension]

While I am quite familiar with parametric modeling, I have hit a roadblock doing anything useful with a triangulated STL scan of my lower teeth.  Conceptually, I'd simply like to "offset" the scan of the surface of my teeth to create a 1.5mm-thick body.  I would then clean that up to create the retainer that looks similar to the attached photo.

I have tried enough to understand that I cannot simply "offset" a mesh.  In fact, I have yet to be able to anything useful with my STL in Fusion 360 other than add it to my file.  I have poked around in Sculpt and Patch for hours, but haven't found what I need yet.

- STL is triangulated with about 300K verticies

- Tried to use Instant Mesh to convert to quad but it apparently doesn't accept STL(?).  If I had been successful, I would have tried for under 10K vertices, but I could not import the STL to that application

- I am not interested in just printing my arch and vacuum sealing a retainer

- Yes, I will use dental resin for the final product

- Yes, this is being done under strict supervision of my dentist.  He knows dentistry but not this type of technology

I appreciate you helping me understand what needs to be done to make my tooth scan useful and any ideas you might have on how I could essentially achieve the effect of 1.5mm offset to create the pictured retainer.

Thanks so much!

[TMC.Engineering]

attach stl by changing the extension to .zip  the you can attach. anyone downloading can then change it back.  Or you can put it in a zip file.

I would try using sculpt and the pull command.  then thicken and trim as needed

look at this

https://www.youtube.com/watch?v=1xMF0BbSoj0

[Anonymous]

As suggested, I have added the STL to this message but re-labeled as ZIP.  Anyone wanting to check it out can change extension back to STL.

[Anonymous]

I reduced the mesh using fusion but it may not be the best tool for that job. Meshlab and Meshmixer are available with a much more powerful toolset.

There are two commands under the Patch>Sketch Menu under the Mesh Flyout. You use Create a mesh section and then Fit Curves to section. That will give you a curve profile that you can loft between. Be careful that you don't try to fit the curve too tight to the profile or Fusion will think the curve doubles back on itself. I change the default 0.0004 to 0.010 for a smoother fit.

Since you want to make a retainer, I would take the time to rotate the planes that the curves get drawn on to match the sweep of the teeth. (Think like segments of an orange.) 

I would also choose a profile at the center of and between each tooth. That is probably still a bit coarse so you may have to add more sections. It is going to be tedious.

I wear a night guard like what you are making and I can tell you that it doesn't have to fit every cranny perfectly. If it fits too tightly, you just can't get it off. My dentist has these made regularly and we have found that if it is made in two layers, it works much better. The inner layer is made from a flexible material that can give a little and the outer piece is a much more rigid resin.

Good luck.

[Anonymous]

Thank you TMC and SpookyDad.  I have not successfully completed either solution at this point, but I feel like there is good progress toward something workable.  The Pull command appears to be more difficult on complex target shapes and only as good as the density of the Form you wrap around it as well (auto curvature on a loft doesn't appear to offer enough control points).  I've also learned that it is more ideal to Thicken in Model after converting the mesh to a surface in Sculpt.  I'm currently stuck trying to manually repair mesh errors before the conversion (auto repair not fixing all of them).

I'm also pursuing the Mesh Section / Fit Curves method as well to see which turns out more effective.  I can't help but think the sectioning process could become automated in the future based on a path and intervals.  For the moment, it is rather tedious.

I also appreciate all the extra tips on the night guard strategy.  Thank you!

I'm out of time for the moment but will return back here as soon as possible and ultimately report back the final methodology.  Any additional ideas in the meantime are certainly appreciated.

[jeff_strater]

The other approach, which is similar to the Pull command, but offers a bit more control is to use the "Object snap" option in the Create Face and Edit Form commands.  It is a bit painstaking, but you can create a TSpline body which fits to the mesh.

Here is a screencast of creating a very small part of the retainer:

Another choice in your arsenal.

Jeff

[TMC.Engineering]

Ok, here is what I have done.  There probably is a better way.  the fusion file is attached.

My Steps

1. I used mesh mixer Edit / Make Solid command using a 1mm offset to get the outer surface mesh
2. Brought both meshes into Fusion 360.
3. made a cutting plane and cut both meshes (Modify / Plane Cut) no fill
4. Modify / Merged the meshes
5. Modify / Plane cut   a little higher but with Fill on.
6. Export mesh as .obj
7. Import into Instant meshes
8. Re-topology to quads (see pic) export .obj
9. Import mesh back into fusion 
10. change to sculpt mode and Utilities / Convert mesh to t-spline
11. Utilities / Repair (use automatic)  then Utilities / Make Uniform 
12. Utilities / Convert to convert T-spline to B-rep body
13. sketched a spline and used as a splitting plane for B-rep body 

[Anonymous]

Timm,

This sounds wonderful.  I very much look forward to being able to look at what you've done this weekend.  Along with other new option posed as well.  I am incredibly thankful and will report back here.

Chris

[Anonymous]

Timm,

I got a chance to step through the first part of your solution.  Makes wonderful sense and really feels like the right track.  Thank you.  Due to time, I need to pause after Step #5 this evening, which brings me to perhaps a very basic question: The first 5 steps produce a body that I could conceivably print at this point and it might/might not fit.  Could you help me understand the advantages gained in proceeding through steps 6-13, which I'll be doing tomorrow... and not just stopping at Step 5?

I am not questioning the need, only wishing to understand what is fundamentally happening as I go.  All of my previous Fusion work has been restricted to the Modeling mode with precise measurements, so TS and meshes are new territory for my general understanding (have read everything I can in Fusion documentation).  My probably over-simplified guess is that conversion to T-Spline after Step 5 will afford a greater level of customization and control to make small adjustments to the final design as fine tuning is needed.  Is at least that part correct?

Thank you again for the very thoughtful input.  It's very much helping me get on-track to being able to replicate my retainer.

Chris

[Anonymous]

After...

Sculpt > Insert Mesh

Convert (Mesh to T-Spline with New Body Option Selected) - Creates a T-Spline in bodies and presents some conversion errors.  Used this to identify and manually repair some overlapping faces.

Check Conversion - Repeated until all errors I can see are fixed.  Still reports some conversion errors but I cannot find any more red highlights when clicking on the error window.

Utilities > Repair Body

Utilities > Make Uniform

At this point, I wish to preserve the T-Spline body upon returning to the Model workspace, but every time I Finish Form or change to Model Workspace, the T-Spline Body becomes a B-Rep.  While I do wish to have a B-Rep one step later, I am very much interested in maintaining a T-Spline body, so I can return in the future to easily make organic fit adjustments.

In the F3D file Timm provided above, he appears to have successfully exited Sculpt while maintaining a T-Spline Body that can be returned to in the future.

My confusion comes with the Convert command.  I am only attempting at this point to successfully convert a quad mesh to a T-Spline.  I am not sure why it continues all the way through to B-Rep when exiting Sculpt workspace?

Also open to alternate flows.  I simply want to access T-Splines easily and frequently as I make organic fit adjustments to this retainer in the future.  I assumed I would be able to do that and then create a new B-Rep body before going out to print each time.  My file attached.

Thanks!

Chris

[TMC.Engineering]

I used the repair body command to fix the tspline.  If you turn off the timeline the t spline will stay available.  you just won't parameters,  but for this it is not a big deal

[jeff_strater]

@Anonymous,

A bit of clarification on the workflow here.  In a parametric model, when you exit the Sculpt workspace, the TSpline is converted to a BRep, as you've seen.  The rationale here is that a TSpline body by itself is not of much value to any downstream workflows (drawings, CAM, SIM, etc).

However, even though this conversion happens, your TSpline body is still there, and still editable.  If you edit the Form feature in your timeline, you can make changes to the TSpline, and when you exit, it will again get converted to a BRep.  Since you say " I do wish to have a B-Rep one step later", I suspect that this is really what you want after all.  You can, indeed, go back and make changes later, and everything will update correctly.

Jeff

[Anonymous]

Thank you both.  That clarification helps.  When in the Modeling workspace, I had been looking for Edit Form by right-clicking on the body in the Browser.  It's not listed in that context menu, however launching Edit from the Form icon on the timeline is exactly what I needed to be pointed to.  

I'm now to a point that I can start testing prints.  I'd like to offer a few key lessons to other readers who may be entering a similar task with not much knowledge of adapting meshes for use in Fusion.

- Autodesk ReMake is a good tool for converting triangle meshes to quads.  My OBJ did not work in well in Instant Meshes, but clearly it worked for Timm

- I seemed to have caused trouble for myself by failing to Reverse Normal when merging the two mesh bodies in Fusion 360 prior to OBJ export.  My bottom surface was erroneously inside-out.  A Reverse Normal of that face before leaving Fusion 360 seemed to solve a range unknown errors in ReMake.

- I burned several hours trying to get a Quad Mesh to import into Fusion 360.  I thought Instant Meshes and ReMake were failing to export Quads properly.  In reality, the problem was a preference setting in Fusion 360.  By default, Fusion 360 is set to convert all meshes to triangles upon import.  To solve this, go to Preferences > General > Mesh and uncheck the box.  I'm sure there is a good reason for this default, but I would really prefer to either it not be checked by default or to offer a message on all quad mesh imports "Quad mesh converted to triangles on import.  To change this behavior, change Fusion preferences."

- The complexity of my original scanned image caused a bevy of problems.  It needed to be simplified and smoothed.  I found Meshmixer to be the easiest place to do this (Triple-click to Select whole object > Deform > Smooth).  Then, I decimated in ReMake just before exporting a Quad OBJ.  In my case, I decimated to under 10K faces, and then selected the lowest number of quad faces on export (10k)

- Auto repair did not quite solve my problems, I had to use Box mode to delete problem faces and Create Faces to repair per a few tutorial videos out there (one located in ReMake learning section about round-tripping to Fusion 360)

Everyone's help has been invaluable.  Hopefully, the above lessons help fill in some gaps.  I am going to leave this thread open until I successfully print a retainer that fits, so I can continue to chart whatever challenges may still lie ahead.

Thanks,

Chris

[Anonymous]

Fusion seems to keep getting hung up on the same command.  I have B-Rep surface that keeps locking up on the command Patch > Create > Thicken.  I have tried different options in the command all with same results.

The intent is to create a solid from this body that is 1.5mm thick in one direction outward.

I believe this surface to be far simpler and sound than my previous attempts at a retainer, as I started from scratch by vastly simplifying and smoothing the tooth scan in Meshmixer before using Remake to export a Quad OBJ with 10K faces (minimum selectable option in Remake).  I have experienced no errors converting the quad mesh to T-Spline and no errors exiting Form for the T-Spline to become a surface.  In the Box control mode, I can find no overlapping control faces.  I cannot figure out why Fusion locks up during the Thicken command.

F3D file attached.  Working on iMac i7 3.4 Ghz 20GB RAM running OS 10.11.6 on OWC Mercury Pro 6G SSD.  All functions in Fusion 360 work on the range of immediately to within 2 seconds.  I have already chosen "Limit effects to optimize performance" and reduced the size of my application window.

Thank you.

[Anonymous]

hello! 

I am student from University of Singapore

I will like to use your tooth scan for potential publication

I am wondering if it is possible? 

Can you send me the stl file of your tooth scans too ( my email yihsuan@u.nus.edu)

Thank you very much, feel free to contact me

Yi Hsuan