Background: The aim of this single-use, four-treatment, four-period (visit), cross-over, mono-centered, examiner-blind, cross-over randomized controlled trial (RCT) was to evaluate the efficacy in dental plaque removal of a U-shaped automatic electric toothbrush (U) compared to a conventional powered toothbrush (P), a habitual toothbrushing procedure (H), and no brushing (N). Methods: Eligible participants were volunteer students. Primary outcome measure was the reduction in full-mouth plaque score (FMPS) after brushing. The secondary outcome variable was a visual analogic scale (VAS) on subjective clean mouth sensation. Mixed models were performed for difference in FMPS and VAS. Results: Twenty-two participants were randomized to the treatments in the four periods of the study. The differences between treatments in FMPS reduction after brushing were statistically significant (p < 0.0001). The differences were statistically significant between the U and P groups (difference −48; 95% CI from −54 to −41) favoring the P group, and between the U and H groups (difference −45; 95% CI from −52 to −39) favoring the H group. On the contrary, the difference between the U and N groups was not significant (difference 5; 95% CI from −2 to 12) favoring the U group. The differences between treatments in clean mouth VAS was statistically significant (p < 0.0001) favoring the P and H groups. Conclusions: The U-shaped automatic electric toothbrush tested in this study proved to be not effective in removing dental plaque.