Final answer:
Regular tooth brushing using fluoride toothpaste and dental floss are the most effective means to reduce plaque and gingivitis, with mouthwash as a supplementary option due to potential side effects like discoloration.
Step-by-step explanation:
The most effective antimicrobial therapy to reduce plaque and gingivitis is a combination of good oral hygiene practices, which includes regular tooth brushing with fluoride toothpaste and the use of dental floss. Fluoride toothpaste not only contains fluoride to strengthen tooth enamel and fight against acidity from oral bacteria but also is often formulated with antibacterial agents like triclosan or zinc chloride, which prevent gingivitis. While chlorohexidine mouthwash has been known for its effectiveness in controlling plaque and gingivitis, it has side effects such as tooth discoloration, potentially affecting patient compliance. Therefore, consistent use of toothpaste and floss, along with professional dental cleanings, are highly effective measures for maintaining oral health.