Incident with dentist

this is a weird question you say in your message it was an accident. If it were deliberate I think maybe you could have a case, but dentist work in the mouth damage to tongue and gums are a small but possible risk.
In Belgium I don't think there is a compensation culture like other places. If you are really worried go and see an Oral surgeon.
Find another dentist if you were unhappy that is the best policy.
Also speak to your doctor to se if there are any topical products se can gargle to ease the pain