"A pair of identical twins was brought into Tufts dental clinic while I was there. One twin had perfect teeth without a single cavity. The other had rampant decay all over his mouth. Being from the same family, they both ate the same things at each meal (mom was adamant that she gave them almost no sweets) and being identical twins, they were genetically identical, so neither one should have been any more susceptible to cavities than the other. No one could pry out of the twins any differences in their eating habits. Finally, one of my older professors cornered the two of them and after much prodding finally discovered that the cavity prone one liked to suck on bread balls. "Bread balls?? What are bread balls?" "Well you take the soft middle out of a slice of bread, ball it up real tight and suck on it!" Bread is not sweet. How could that cause cavities? Actually, bread is made of starch which normally does not cause decay, but when kept in the mouth for a long time, an enzyme in the saliva called amylase begins to break down the starches into their constituent parts, and those parts are simply sugar. Try it sometime. If you keep a piece of bread in your mouth for a while it begins to taste sweet."
Taken from this site:
http://www.doctorspiller.com/Decay.htm To which I would add that bread also forms a paste that can stick to your teeth, especially between your teeth, where once your saliva breaks it down into sugar--it forms a perfect growing medium for bacteria whose excretions contain the acids that eat-away at your teeth.
And to make matters worse, many store-bought breads have sugar (Yuk) added to them (corn syrup. Yuk).