My 3 month old son recently started biting on toys and our fingers. Is this a sign that he has started teething and needs the pressure on his gums to sooth the pain from teething, or can this also be a part of the process of discovering items in the world using his mouth?
According to this article from healthychildren.org (an American Academy of Pediatricians site):
Around 3 months of age, babies will begin exploring the world with their mouth and have increased saliva and start to put their hands in their mouth. Many parents question whether or not this means that their baby is teething, but a first tooth usually appears around 6 months old.
3 months would be early for a first tooth (though certainly not unheard of). If the baby is experiencing pain in the gums, you'll see a slightly different response:
Usually teething doesn't cause children too much discomfort, however, many parents can tell when their baby is teething. Babies may show signs of discomfort in the area where the tooth is coming in, the gums around the tooth may be swollen and tender, and the baby may drool a lot more than usual.
The saliva increase you're probably seeing now is nothing compared to that when they're drooling from teething - you'll know the difference when you see it.