Answer:
When you woke up, you took off your retainer. Usually, you put it in its case or in a drawer somewhere, but you forgot and placed it on the table beside your bed. Then, after you left your room to go to the bathroom (you brush your teeth and take a shower or something), your dog enters your room and sees your retainer. Then he decides to pick it up from the table using his mouth and eats it.
Explanation:
ldk
