Groups A and C exhibited a significantly lower plaque index scores ( parameter-estimate [ 95 % confidence interval ] = -1.20 [ -1.76 to -0.63 ] for group A , and -1.12 [ -1.69 to -0.56 ] for group C ) and gingival index scores ( -0.13 [ -0.21 to -0.04 ] , and -0.19 [ -0.28 to -0.10 ] ) , respectively , compared with group D ( P < 0.001 for all ) , whereas no significant difference was found between groups B and D , or between groups A and C ( P > 0.05 ) .