To minimize the chance that strong participant-related effects could distort the outcome of the study, no more than two restorations of each type of material (four total restorations) per participant were allowed. Our initial target was for the distribution of restorations to include approximately one-half anterior teeth and one-half posterior teeth. A minimum of 25 participants at baseline, 20 participants at 6 months, and 15 participants at 18 months is required for evaluation (ADA Guidelines, 2001).