Which of the following is NOT a component of an irrigation solution used in root canal therapy?

Formocresol is not typically used as a component of irrigation solutions in root canal therapy. Instead, it is more commonly known for its use in pulp capping and as a medicament in primary teeth. The primary purpose of an irrigation solution during root canal treatment is to facilitate the cleaning and disinfection of the root canal system.

Sodium hypochlorite is widely used for this purpose due to its effective antibacterial properties and ability to dissolve organic tissue. Hydrogen peroxide can also be included in some irrigation protocols for its antimicrobial effects. Parachlorophenol (PCP) has been historically used in endodontics but is less common today. However, it does not serve as a primary irrigation solution.

Thus, while formocresol is a valuable compound in certain dental applications, it is not utilized in the irrigation phase of root canal therapy, making it the correct answer to identify as not being a component of the irrigation solution.