What will happen if you never brush your teeth?
Our mouth is the best place for bacterias, as its a moist place and it's easy to generate. This is the reason why we brush daily and remove all of them.
So if we don't brush for days then there will be tons of germs which are too huge for our immune system to remove and the first thing is a yellow colored plaque will start appearing they are kind of bacteria to start eating your teeth this is why we get cavities.
The next big problem is if you don't brush all these huge numbers of bad bacterias make way to our blood through the gums and can cause severe diseases like pneumonia and other heart diseases. Not brushing your teeth can also serve as reservoirs for many cancer-causing bacteria.