Does b complex deficiency (b12, riboflavin) actually lead to origination of repeated mouth ulcers? has multivitamin supplements shown to speed up healing or decrease/eliminate recurrence in medical practice? any special role of vitamin c for healing?

Vitamins: Vitamins act as catalysts, bridging one physiologic states. They enhance your bodies normal functions. If you have a well balanced diet you don't need to take extra. Small amounts of extra, like a daily vitamin tab, may be helpful if your diet is insufficient, but will do no harm. Overdosing with anything can create imbalance. You're better off eating a well balanced diet than taking pills.