M Beerens

EFFECTS OF MI PASTE PLUS ® : A 3-MONTHS FOLLOW-UP 4 63 Power analysis To assess the influence of CPP-ACPF on the reduction of WSL, a power analysis was conducted using G*-power 3.1.0 to determine the number of required patients (Faul et al. , 2007). Based on a previous observational study at the Orthodontic Department at ACTA (van der Veen et al. , 2007), a statistically significant, but clinically irrelevant, natural reduction in fluorescence loss, of 0.9 ± 0.9%, during a period of 24-weeks was found. A clinically relevant change in fluorescence loss was considered to be an average reduction of 2%, implying an effect size of 0.55. The sample size was calculated for a more conservative effect size of 0.35. For an effect size of 0.35 to be measured between the two groups, a group size of 27 was needed. To compensate for subject withdrawal, we aimed to include 30 subjects in each group. Subjects who dropped out before T2 were replaced to meet the required minimum group size of n = 27. Data analysis The chi-square test and the Students t-test (two-tailed) were used to determine statistically significant differences between both groups at baseline (i.e. T0 for plaque and T1 for WSL) (PASW statistics 17.0; SPSS Inc., Chicago, IL, USA). The fluorescence loss, lesion area, and corresponding integrated fluorescence loss were scored for each lesion at three time-points. The follow-up QLF images were compared with those at baseline (T1). The average fluorescence loss over all WSL, total lesion area, and corresponding IFL were calculated for each subject and then normalized to 20 surfaces by correcting for the number of missing elements and filled surfaces. Lesion progression or regression for the whole group of subjects was determined by repeated measures ANOVA, followed by Bonferroni post-hoc testing. The plaque ecology, described by the total numbers of colony forming units (CFUs) and the proportions of aciduric bacteria, S mutans, and Lactobacillus spp., was assessed at baseline (T0), and the results were compared with those obtained at the follow-up time-points using repeated-measures ANOVA, followed by a Bonferroni post-hoc test. The level of significance for all tests was set at 5%. The intraclass correlation coefficients (ICCs) were calculated to determine intraexaminer and interexaminer agreement for the training set of QLF images.