Two-way repeated measures MANOVA application: interaction of chewing gums and chewing time on salivary function

Abstract

The two-way repeated measures Multivariate Analysis of Variance (MANOVA) quantifies responses at different times on the same subjects and must meet certain requirements to be performed. The objective was to apply repeated measures MANOVA to determine time-varying changes, with fixed effects, in Streptococcus viridans group (SV) colony-forming unit count per ml (CFU/ml) and salivary flow (SF). A randomized, parallel, double-blind clinical trial was conducted in 36 students aged 18 to 25 years. Four groups were formed according to different chewing gums and assessed at baseline and at 30 min. The decision was significant with a consideration of 5% (p<0.05). There was no significant interaction between the factors (SV and FS) with the chewing gum group, however, it evidenced significant interaction of SV and FS between basal time and after 30 min. The two-way repeated measures MANOVA identified that the factor chewing time of chewing gum for 30 minutes produced a considerable reduction of oral microorganisms by 67% and an increase in FS by 50%.