Mine did this until I got Fraqgaria Vesca tablets ( strawberry tablets from Potters). http://mall.cairnrescue.com/mdse/sho...php?itemno=G52
Dogs do this to clean the teeth of plague and tarter of the dominant dog in the pack.
So- clean off the plague and the behavior stops. Not only do we have clean teeth of the dogs, but also that licking of others teeth has stopped as well.