I can see the lemon juice being a little hard on the teeth, but still doing no damage, I believe in all cases it is the ill teeth, not the fruits as being the problem, otherwise this would bother all people.
I drink the juice of 40 cases of oranges per year in 3 months, my body goes alkaline and after this 3 months I consume about 1 quart of raw apple cider vinegar to balance out being too alkaline.
Oranges are extremely alkalizing, not an acid causing food.