I may be repeating advice you read or hear elsewhere - but I just had an ACST in May, and was extremely nervous about getting sores in my mouth and throughout my digestive system: Stay hydrated throughout each day - and night!-with twelve cups of water/non acidic fluids. Don't eat foods with acid in them even if they're normally healthy: pineapple, lemon, etc.. Avoid chewing gum , if you use it, that has acid in it( always look at ingredients). Do a saltwater after each time you've eaten something. Get toothpaste without extrachemicals in it( whiteners etc) and don't use normal mouthwashes. Keep your foods non sugary as much as possible, and soothing. Get a super soft toothbrush and don't floss for several weeks, but especially not during the stem cell process: treat your mouth gently. And get non-allergenic baby wipes and Desitin cream for your bottom, for whenever you've used the toilet, for a couple of weeks. Treat yourself as you would a baby, in that regard!: Stay clean and dry, other than soothing cream.
Best of luck. Oh and No apple juice, or cranberry juice, etc. They are superacidic.-( I don't know why hospitals serve stuff that stirs up problems, so often!- at least, my NY hospital did). Study antiinflammatory diet lists online, as a guide. Worked for me, anyway.