It is unnecessary to stop breast-feeding when babies’  teeth erupt (some babies are born with teeth, after all). Babies will not routinely bite as part of the breast-feeding action. However, when teething, gum soreness may alter the way they feed, which may cause sore nipples and occasional, accidental, biting episodes.
If a baby bites the nipple during a feed, the mother’s reaction will often startle him and he may soon learn that this is not acceptable if he wishes to continue feeding. By the time that babies are teething, mothers will often have learnt to recognise signs that indicate the end of a breast-feed (which is when the baby may be less focused, and may bite). Mothers should not force a feed and should be aware of behaviour that leads to biting. If a baby falls asleep whilst feeding, he should be taken off the breast (the mother should gently insert one of her clean little fingers into the side of his mouth). If biting persists, the mother should stop feeding and offer a teething object instead.

From: Journal of Family Health Care Bulletin. Directory of Breast-Feeding Advice. December 2009. Published with JFHC 2009; 19(6). http://www.jfhc.co.uk/images/stories/breastfeeding.pdf