Purpose: Flossing is a well-known component of daily recommended oral care regimens, but patients often find it challenging to perform effectively on a regular basis. The purpose of this 12-week supervised clinical trial was to investigate the effects of twice daily rinsing with a mouthrinse containing a fixed combination of four essential oils (4EO) and supervised daily dental flossing regimens as compared to a negative control 5% hydroalcohol rinse (NC) on the prevention and reduction of plaque, gingivitis, and gingival bleeding. Methods: Volunteer participants who met the inclusion criteria were randomized into the following groups for the 12-week trial: 1) NC; 2) mouthrinse containing 4EO; 3) professional flossing performed by a dental hygienist (FBH); 4) supervised self-flossing (FUS). All participants received a professional dental prophylaxis prior to beginning the trial. On weekday mornings, all participants brushed on site. After brushing, the rinse groups used their products under supervision, and the floss groups had their teeth flossed by a dental hygienist or self-flossed under supervision. Participants performed their assigned regimen in the evenings and the twice-daily weekend use at home. Each individual assessment of oral hard and soft tissue, plaque, gingivitis, and gingival bleeding at weeks 4 and 12, probing depth and bleeding on probing at week 12 was made by the same calibrated examiner. Results: Of 156 randomized participants, 149 completed the trial. Use of the 4EO mouthrinse statistically significantly reduced plaque, gingivitis, and gingival bleeding on probing after 12 weeks as compared to the NC rinse. Both flossing interventions statistically significantly reduced interproximal gingivitis and gingival bleeding at 12 weeks compared to the NC rinse; neither flossing intervention significantly reduced interproximal plaque after 12 weeks compared to the NC rinse. Conclusions: Rinsing with a 4EO mouthrinse statistically significantly impro