When the floss becomes frayed or soiled, a turn of each middle finger brings out a fresh section of floss. After flossing, rinse vigorously with water. If you don't like manipulating floss, try one of the commercial floss holders. They have limited flexibility, however, and you must use them with care to avoid injuring the gum. You may have trouble working with the floss between certain teeth, or the floss may consistently break or tear in certain areas.
Several causes are possible, including calculus buildup, or improperly installed fillings.
Please let us know if this problem occurs. Flossing between bridges requires additional instruction and the use of floss threaders. None of these are as good as floss in tight areas between teeth.