The correct answer is Cetylpyridinium chloride.

- In the context of mouthwash active ingredients, disrupting dental biofilm—which consists of complex bacterial communities adhering to teeth surfaces—is crucial to maintaining oral health and preventing dental caries and periodontal disease.

- Cetylpyridinium chloride (CPC) is a quaternary ammonium compound known for its antimicrobial properties, particularly effective against the bacteria embedded within dental biofilms. It works by disrupting the bacterial cell membranes, thereby reducing plaque formation and biofilm integrity.

- Chlorhexidine gluconate is also a potent antimicrobial agent often considered the gold standard due to its broad-spectrum activity and substantivity; however, it primarily acts by killing bacteria rather than specifically targeting biofilm disruption mechanisms.

- Essential oils have antimicrobial effects but are generally less effective at biofilm disruption compared to CPC and chlorhexidine.

- Sodium fluoride primarily acts as a remineralizing agent to strengthen enamel and prevent caries rather than having significant antimicrobial or biofilm-disrupting effects.

Thus, among the given options, Cetylpyridinium chloride is primarily recognized for its role in disrupting dental biofilm, making it the best answer.

Reference: Ten Cate's Oral Histology, 9th Edition, Chapter 12, Page 234