To Break open the molars you'll need a tier 2 Insect hammer which requires 4 Stinkbug Part, 4 Berry Leather, 1 Boiling Gland. Youll learn the recipe by either analyzing any of those parts or reaching brain power lvl 6.
I used this map/guide from the Grounded wiki to find the Milk Molars
(this second link is broken atm(7/2), may be updated when the full release comes out, so im leaving the link for the moment)
Screenshot of map(sorry its not the best)
Map(by RetroBits):
https://imgur.com/jMBn0bbMap(by RetroBits):
https://static.wikia.nocookie.net/grounded9429/images/4/4e/M...USE THIS
Wiki Page:
https://grounded.fandom.com/wiki/Milk_Molars