I played through the demo and managed to beat every level but the last one on the Standard difficulty. I know that high difficulty tends to be a trend with your games (at least for me), so I don't really know if dialing it down would make much sense. One thing I didn't care for was how fast the last enemy or two would spawn out projectiles. I learned that you could slow down the tooth with the paste but it did feel really difficult to do so. I got into the strategy of chipping away partial amounts of plaque on each of the last teeth so that it would take me as long to get them clean.
I also felt that more feedback when an enemy was spawning a jellyfish in that one level would have been nice. I did eventually notice the animation but sometimes I felt like I'd be in the thick of the teeth only to get hit by a surprise projectile.
Overall though, this was fun! I liked the chill nature of cleaning the teeth and then the tense action in between. And the early levels to introduce the player to the mechanics and the eventual combat gameplay was really well done! Great work with this and looking forward to trying it again on release!