What causes mild/painful swelling @ dental injection? tooth is ok, injection pain was immediate and went down neck on tuesday. pain now local w yellow spots/swelling. no throbbing, no major bruising, just raised and very tender.

This could be an: infection from your description. Call your dentist and ask for an immediate evaluation and examination.

Blood vessel?: Sometimes a dental injection nicks an underlying blood vessel which causes local bleeding and swelling often with bruising. This almost always resolves on it's own but if symptoms persist more than 10 days, go back in for an evaluation.

Trauma: Trauma at the injection site may be the culprit. Inflammation would cause your symptoms, which should abate in a day or two.

Dental injection: This sounds like infection and less likely a reaction. Be checked and treated with antibiotics to swallow and to swish in your mouth. All the best for a speedy recovery.