given your experience, and the difference in the care you received between the two surgeries, i would say you definitely have grounds for a complaint. i would write to the dentist concerned via the manager of the surgery and provide as much evidence as possible and ask them to investigate the care the dentist provided. in this day and age, there really is very little reason for somebody to have so much pain when being treated....and i would say that part of assessing whether a tooth is worth saving/infection levels/possible outcomes IS having an xray. it can differentiate between replacing a filling, having root canal treatment/needing an extraction. in addition, check out what body regulates dentists and explore their website/ring them up for help and contact your local nhs health trust too. both will be able to advise you on your next actions - whether you want an apology or the cost of the private treatment refunded.