Dentist left part of tooth behind, is this classed as negligence? what should i do?

Talk to the dentist: Not sure why a root tip was left behind, or what problems you may be having. But your surgeon may be able to shed some light.

To my knowledge: 'negligence' in law, is the failure to do something that a reasonable dentist of ordinary prudence would do in a certain situation or the doing of something that such a person would not do. Since we have no way of knowing what was done or not done and why, we cannot make a judgement over the internet. Discuss this with your own dentist (and get a 2nd opinion from an oral surgeon) if you wish.