Are you having a bone scan because you already have bone mets? Sorry I don't know your history. Are you on any bisphosphonates?
I have had things show up on bone scans that have been false positives and related to chemo. It is possible that the scan is showing inflammation in the area that has been infected. I ask about the bisphosphonates as there is a risk of getting osteonecrosis of the jaw.
I had lots of mouth issues on my last treatment and used salt water gargles and diffuse when they were very sore. I did end up in hospital with neutropenia and throat issues due to my ulcers which could not be reached with gargles and the like.
If you are concerned page your dr and ask them questions.
I hope that it is all ok and your mouth feels better soon.
Amanda xx