How do intra-oral scanners work?

[Steve4Physics]

TL;DR Summary

How do intra-oral scanners work?

Hi. Needing a crown to cover a damaged molar, I’ve just returned from the first appointment with my dentist.

The dentist used an intra-oral scanner to scan my teeth. This involved putting a ‘wand’ (about the size of a large electric toothbrush) against the insides and outsides of my teeth, working around my mouth; this took several minutes. This was new to me. Initially I had no idea what was going on apart from being told that she was going to ‘do a scan’.

I was then shown (on a computer screen) the ‘3D’ reconstructed image of all my teeth. The image could be rotated and viewed from any position – even from the inside of my mouth. I was gobsmacked (UK terminology).

With some internet research, I’ve found out that such scanners take many images per second and software ‘stitches’ them together to produce the 3D reconstruction. But other than that, online technical information seems practically non-existent.

I find it hard to understand that it can be done using only images and software. Some questions that spring to mind are:
- does the wand contain motion/position sensors?
- is some clever optical/software technique being used, such as taking many images of the same region in and out of focus, to allow surface shape to be determined?

Any insights/links into how this technology works would be very welcome.

 

[berkeman]

Yes, very impressive technology. They must have motion/attitude sensors in the wand, but beyond that I don't know a lot about them. A Google search returns a lot of useful hits:

https://www.google.com/search?client=firefox-b-1-d&q=dental+3d+scanner&bshm=foot/1#ip=1

Also impressive is that more dental offices now have 3-D printers or CNC machines in-house to make crowns on-site for same day service.

 

[BillTre]

TL;DR Summary: How do intra-oral scanners work?

With some internet research, I’ve found out that such scanners take many images per second and software ‘stitches’ them together to produce the 3D reconstruction. But other than that, online technical information seems practically non-existent.

There are similar larger scale things used together with CAD systems to generate digital copies of various objects. There are on-line videos about these.
What I have seen is rapidly laser scanning a lot of points generates surfaces. This is just like CAD programs several years ago. The dental version is miniaturized.

My dentist has the same technology in his large office group. They also have a little milling machine to make crowns out of little ceramic blocks.
First they scan the surface of the tooth.
Then they remove the parts of the tooth to be removed.
Then they scan the remaining surface and determine the difference between the old an new surfaces.
Then they mill the ceramic chunk in to the digitally determined shape (new crown in about 5-10 minutes).
Glue it in in one trip to dentist.

I asked the dentist about this process (maybe 5 years ago). He said the process was around for a while before he got one (he said about 0.5 million $), but he did not think they had a high enough resolution to be useful before he got his. The resolution he wanted was 5 microns.

This also allows him to completely cut out of his process: making casts, sending casts out to a fab lab, getting crown made and sent back, making another appointment. There's a lot of saving on operating costs in there.

 

[Steve4Physics]

A Google search returns a lot of useful hits:

https://www.google.com/search?client=firefox-b-1-d&q=dental+3d+scanner&bshm=foot/1#ip=1

Thanks. But I wasn't being lazy! I'd already Googled. The various hits invariably provide top-level descriptions but (almost) no 'under-the-hood' technical details.

 

[Steve4Physics]

There are similar larger scale things used together with CAD systems to generate digital copies of various objects. There are on-line videos about these.
What I have seen is rapidly laser scanning a lot of points generates surfaces. This is just like CAD programs several years ago. The dental version is miniaturized.

Thanks. I can understand how a typical CAD system works: the camera and the object are in fixed or accurately controllable positions.

But for the intra-oral scan, the the camera ('wand') is handheld and moving around; and the object (teeth) are moving a bit due to patient-movement. It's how the movement is handled that I can't understand.

 

[berkeman]

I'd already Googled. The various hits invariably provide top-level descriptions but (almost) no 'under-the-hood' technical details.

Okay, a better link about the technologies involved:

https://www.dentalproductsreport.co...imaging-principles-used-by-intraoral-scanners

Found with a better Google search for how do intraoral scanners work?

 

[BillTre]

But for the intra-oral scan, the the camera ('wand') is handheld and moving around; and the object (teeth) are moving a bit due to patient-movement. It's how the movement is handled that I can't understand.

Yeah, that's certainly interesting.

The CAD scanners I saw demonstrated 5 or 10 years ago were handheld with two of three scanning parts about a foot apart. The guys doing the scanning even waved the device a round a bit, perhaps to cover more hidden surfaces. The scanning was very fast and the attached computer built and updated a surface pretty rapidly.

Maybe the device had inertial sensors, or could track the movement of the existing surface in repeated scans through time. ???
Whatever techniques were used, they worked.
Miniaturization does not surprise me.
Also the probe will be a lot closer to its target which will increase accuracy.

 

[Steve4Physics]

Okay, a better link about the technologies involved:

https://www.dentalproductsreport.co...imaging-principles-used-by-intraoral-scanners

Found with a better Google search for how do intraoral scanners work?

Thankyou @berkeman. I should have been more persistent with Google. (And thanks for the edit.)

I will now go and read about Confocal Laser Scanning and Active Wavefront Sampling.

 

[DaveC426913]

I was introduced to similar technology when staging my house for sale. They plopped what appeared to be a SmartPhone on a tripod in each room and let it scan.
The software stitches the whole thing together into an interactive 3D model that you can fly through that works right in your browser.

https://sites.google.com/view/63thirdsttoronto/home?pli=1

 

[Steve4Physics]

I was introduced to similar technology when staging my house for sale. They plopped what appeared to be a SmartPhone on a tripod in each room and let it scan.
The software stitches the whole thing together into an interactive 3D model that you can fly through that works right in your browser.

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