Learning Objectives: 

• Compare the antimicrobial activity of commercially available antigingivitis mouthwashes with different active ingredients against Porphyromonas gingivalis and Fusobacterium nucleatum.  
• Describe how turbidity-based growth inhibition and zone-of-inhibition testing evaluate different aspects of mouthwash antimicrobial performance and how product formulation and pH may influence these results.  
• Evaluate the pH of different mouthwash formulations and examine how mouthwash exposure may affect enamel surface hardness and the potential for enamel demineralization.

Gingivitis is a common inflammatory condition associated with dental plaque accumulation and changes in the oral microbial community. Porphyromonas gingivalis and Fusobacterium nucleatum are anaerobic periodontal-associated bacteria that contribute to the development and progression of periodontal disease. Although antimicrobial mouthwashes are frequently recommended as adjuncts to mechanical plaque control, commercially available products contain substantially different active ingredients and mechanisms of action. The purpose of this study was to compare the in vitro antimicrobial activity of seven commercially available antigingivitis mouthwashes against P. gingivalis ATCC 33277 and F. nucleatum ATCC 25586.  Seven commercially available mouthwashes representing different antimicrobial formulations were evaluated. Antimicrobial activity was evaluated using bacterial growth turbidity and zone of inhibition assays. For bacterial growth turbidity testing, each bacterial strain was exposed to the respective mouthwash formulation, and changes in turbidity were used to assess bacterial growth inhibition relative to appropriate controls. For zone-of-inhibition testing, 6-mm diameter cellulose filter paper disks were saturated with each mouthwash and placed on inoculated blood agar. Following anaerobic incubation, zones of inhibition surrounding each disk were measured to compare antimicrobial activity among the mouthwash formulations. Product pH was additionally measured to characterize differences in formulation acidity or alkalinity and provide context for the observed antimicrobial activity as well as the effect on enamel hardness over time.  This study will provide a comparative assessment of commercially available antigingivitis mouthwashes containing different active ingredients and antimicrobial mechanisms against two periodontal-associated bacterial species.