Auto gap filling automatically adds a bar between two teeth when there is a gap of more than 3mm between them.
This is useful when you have an extraction space or missing tooth.
The added bar gives the aligner more structural rigidity and makes the aligner easier to trim.
You can see the kind of ridge or bar that is added between the teeth in the image below.
To enable to feature, go to the settings menu by clicking on the gear icon in the lower left side of the screen.
Once inside the settings menu, scroll down to the bottom of the page until you see the "use auto gap-filling checkbox.
Make sure that check mark is placed there, and then export your case.
The ridge/bar will automatically be added to any gap of more than 3mm.