That’s quite interesting! When my mouth is closed, at least half of my tongue is always naturally touching the roof of my mouth. Despite my oral hygiene not being the best (I brush my teeth every day, but rarely floss), I’ve never had a cavity (I did have to get my wisdom teeth removed though). I notice it’s much easier for my mouth to produce saliva when my tongue is touching the roof of my mouth, which definitely helps (quoting the linked article: “saliva buffers the teeth against acid attack and bathes them in calcium and phosphate to remineralize their surface”).