Table 3.

Changes observed in the mean surface hardness scores in the individual study centers

	Cologne			Leipzig			Geneva
	Test group	Control group	Intergroup comparisona	Test group	Control group	Intergroup comparisona	Test group	Control group	Intergroup comparisona
Observation time
T0	3.5 ± 0.51	3.5 ± 0.51	P = 0.8987	3.5 ± 0.50	3.5 ± 0.59	P = 0.8486	3.1 ± 0.75	3.2 ± 0.89	P = 0.7695
T1	2.8 ± 0.56	3.7 ± 0.60	P = 0.0764	3.3 ± 0.58	3.2 ± 0.69	P = 0.4447	2.8 ± 0.80	3.1 ± 1.02	P = 0.3211
T2	2.0 ± 0.57	2.7 ± 0.67	P < 0.0001	3.0 ± 0.57	2.7 ± 0.65	P = 0.2226	2.5 ± 0.91	3.0 ± 1.08	P = 0.1610
Intragroup comparisona
T0 versus T1	P < 0.0001	P = 0.0089		P = 0.3693	P = 0.1484		P = 0.4212	P = 0.9921
T0 versus T2	P < 0.0001	P < 0.0001		P = 0.0134	P = 0.0010		P = 0.0654	P = 0.6816
T1 versus T2	P < 0.0001	P = 0.0161		P = 0.1031	P = 0.0492		P = 0.2886	P = 0.6889

Test Group, High-fluoride toothpaste (5000 ppm F); Control Group, Regular-fluoride toothpaste (1350 ppm F); T₀, Baseline; T₁, 3 months; T₂, 6 months.

^aPost hoc Bonferroni–Dunn correction for multiple comparisons, adjusted P-value for significance P = 0.0167.