I'be had a lot of dental problems over the past 10 years and could no longer afford to see dentists.
Some things I've learned
1. Use 2% hydrogen proxide in your mouth.
2. Use Iodine drops - approved for human use - start with a weak solution, 1 drop in water and slowly increase the dose. If you are allergic to shellfish or Iodine don't do this.
With both of these massage your cheeks over the sore areas.
3. Use a Water Pik. You can put a disinfectant mouthwash in the water.
4. Find a different dentist to look at the abcesses.
5. Take increased B vitamins.
I would often get canker sores and that is what your sores may be. This is a common problem with people who are intolerant of gluten in wheat, barley and rye. Since I went on a strict gluten free diet I have not had any canker sores. Ask or demand that your Dr. order the tests for Celiac Disease. You may have to go on a gluten challange diet before taking the tests.