This design was heavily inspired by https://www.thingiverse.com/thing:1032924
I think my design makes it easier to insert the toothpaste, as you can push it in from the side and adapts better to different tube sizes. Furthermore one can push the key to release the toothpaste.
I don't recommend PLA as it deforms under constant pressure and the front part might bend upward over time. PETG seems to work fine.
You can find the design here: