This is from the La Leche League website:
What Should I Do If My Baby Bites Me?
Note: Please know that we are aware that babies come in two equally wonderful genders. For clarity, we are referring to your baby as "he" because mother is most certainly "she."
A bite from your baby can be truly painful, and worse, it keeps you tense in the fear that it will happen again. It's hard to relax and enjoy breastfeeding when your baby has bitten you. Babies who bite are seldom asking to be weaned. There are many reasons for a baby's biting, but the most common one is teething. Sometimes babies bite before their first teeth come in, but usually it's after the front teeth are in and the others are working their way down those hot, sore gums. Other reasons could be a cold or an ear infection (it's hard for your baby to swallow while breastfeeding if his nose is blocked), stress, or even a way of getting mother's undivided attention.
Here are some ideas to help reduce and eliminate biting. Remember: this may take persistence on your part. Your baby may not stop biting immediately but "this too shall pass."
When your baby is latched on correctly and nursing actively, getting milk from your breast and swallowing, it's physically impossible to bite. This is because your baby needs to stop sucking in order to bite. When latched on properly and nursing, your nipple is far back in your baby's mouth. In order to bite your baby has to adjust his tongue and allow your nipple to slide forward towards his teeth. So, as a first "hint" of when your baby is about to bite, try and watch for a moment--usually after the initial hunger has been satisfied--when your nipple slips forward in your baby's mouth. Often the tension in your baby's jaw will change just before this happens.
As soon as you notice this change, slip your finger into the corner of your baby's mouth, between his teeth, and let the nipple come out all the while keeping your finger in your baby's mouth to protect your nipple. Pulling your baby straight off is a very natural and almost automatic response, but it may cause soreness on your nipple.
Baby's position is important, and that means helping your baby stay in a close breastfeeding position, so that he doesn't or can't pull off very easily. If your baby has to strain to latch on, then he will come off and chew the nipple easily. Therefore, another response to biting that some mothers have found useful is to pull baby in closer to the breast, at least momentarily. If your baby begins to position himself away from your nipple, be alert for a possible bite.
When the cause of the problem is a cold, a more upright position can help your baby to breathe easier. Check with your baby's health care provider for suggestions to relieve stuffiness. Your baby may breastfeed better if you offer the breast while walking.
Sometimes older babies with teeth leave a "ring" of teethmarks after breastfeeding. Generally this is not painful and is caused by the teeth resting on the breast during breastfeeding. However, your baby may be clenching or sliding to the end of the nipple. If this is uncomfortable, use some of the same techniques listed in this FAQ to encourage your baby to gently latch on and breastfeed.
Maybe your baby is too young to understand exactly what you say, but your tone and attitude do convey meaning. It's worth trying to tell your baby, even repeatedly, that biting hurts and that he cannot bite you. Some alternatives mothers have used include:
Offer a teething ring and say, "Mommy is not for biting. You can bite this."
Use positive reinforcement. Praise your baby when he breastfeeds without biting. A hug or an extra cuddle will convey an important message.
Allow your baby to choose when to breastfeed. If baby is distracted and pulling off frequently, either try breastfeeding in a darkened room or begin a new activity with baby.
As you help your baby to learn good breastfeeding manners, attend a La Leche League Group meeting in your area for additional information and support. To find a Leader of a local Group, check out the section of our Web site about Finding a Local LLL Group.