While you can go to an oral surgeon without a referral, it can be beneficial to speak to your dentist first. Your dentist is much better placed to advise you if you do require specialised care or not. Numerous dentists with a special interest in Implant placement have also gone through vigorous theoretical and hands-on training programs to ensure high standards of treatment for your treatment requirements. If they feel the need to refer you they may also have a specific person to refer you to that specialises in what you need done.
Visiting your dentist and getting a referral also means continuity of care. Your dentist can brief the surgeon beforehand and perform an in-depth a patient handover. Then, once the procedure is complete, the surgeon can debrief your dentist and hand your care over to them. This ensures complete continuity, which can help to ensure a better long-term outcome.
If you think you need to speak to a surgeon about a problem you have, speak to your dentist first. They will ensure you get the right treatment, from the best professional for your needs.