Because the study is designed as an equivalence trial, the power calculation is based not on expected differences between adhesive systems, but rather on differences in performance of the systems across time (baseline versus evaluation times). For an estimated 30 percent difference in clinically unacceptable scores between baseline and 3 years, the sample size used will adequately power the study at 85 percent. At baseline, data on subjects' age, sex and occlusion, lesion characteristics and operator may be compared between the two restorative systems using two-sample t tests (continuous variables) and χ2 (categorical variables), to determine if the two groups are equivalent. The lesion characteristics to be evaluated are internal angle, percentage of enamel margin, sclerosis scale value, and lesion size (height, width and depth) and volume. Modified USPHS direct evaluation criteria scores of restorations placed with OptiBond XTR or OptiBond FL will be compared at each evaluation time for statistically significant differences using the Fisher exact test (P = 0.05). Lesions/restorations will be used as the unit of analysis (cases). Although restorations placed in the same participant are not totally independent cases, the assignment of restorations to participants was randomized. Therefore, subject and lesion characteristics are not expected to affect outcomes. However, to test for the influence of such characteristics on the performance of the restorative systems, logistic regression can be used to control for factors such as operator; subject's age, sex and occlusion; and lesion's location, size and score on the sclerosis scale. Finally, we will run a survival analysis and derive a Kaplan-Meier survival estimate curve on the clinically unacceptable (Charlie) scores for any of the USPHS criteria at the different follow-up times. A log rank test for equality of survivor function will be used to compare the survival estimates of the two restorative systems. We will use Stata 10 data analysis and statistical software (StataCorp, College Station, Texas) for all statistical analyses.