Biting

by Shirley
(Lincolnshire, UK )

Our Coton is very even tempered, you can take anything away from him at any time with no aggression but since about a year ago he will not let us open his mouth either to put a tablet in or try to take something out. He bit me quite badly last year when I was trying to remove an unknown object that he had found on a walk and luckily we wore leather gloves when trying to give him a tablet because he bit our fingers again then. He had had bad health, a serious operation on his spine and more allergies than I could list here, and he has in consequence been spoilt. However, he is a trained and normally obedient dog so I don't know what to do about this biting. Can you please help?