Eating too much peanut butter can sometimes cause cavities in peoples teeth and wear away the tooth enamel.
However if you eat the peanut butter in moderation and always use some milk to wash the peanut butter down or water or something else to help with the peanut butter getting washed away from your teeth when eating the peanut butter then your teeth should be just fine.
I've eaten peanut butter for a long time and I have kept my teeth cleaned with brushing and flossing after eating the peanut butter and my teeth have remained healthy.
So just make sure you brush your teeth and floss or at least brush your teeth after you eat the peanut butter to remove the excess peanut butter from your teeth to prevent cavities.
The peanut butter though contains protein which can also help strengthen your teeth and bones as well.
Peanut butter is very healthy when eaten in moderation and as long as you take care of your teeth properly by brushing the teeth properly and regularly then your teeth should be just fine.