broken tooth as a result of a small stone in a salad from Sainsburys

as a result of biting a small stone which was in pre washed salad from sainsburys i broke  a tooth which was supporting a three tooth bridge in the front of my mouth. i had to have  the nerve removed from the tooth and a temproary crown was fitted for two weeks until the new crown was made and fitted...sainsburys contacted me and offered me Â?350 pounds for good will.. I don't think this is enough considering i have paid the dentist Â?202 pounds for the work he carried out so far. i was in awful pain for about 10 days after the initial dental work. i don't know what to do. can somebody please advise me, i don't really want to go the solicitor route to deal with this.