Which of the following agents is NOT useful for treating apical infections?

The agent that is not useful for treating apical infections is ethyl alcohol. While it has some antiseptic properties and can be used for disinfection, it is not effective against the specific bacteria commonly found in apical infections, which are often anaerobic and require a more targeted approach to treatment.

Chlorhexidine is a strong antimicrobial agent that is widely used in dental practices. It is effective against a broad range of bacteria including those responsible for apical infections, making it a valuable treatment option. H2O2, or hydrogen peroxide, is also sometimes used in dental practices as it has antimicrobial effects and can assist in mechanical cleaning and reducing infection load. EDTA, primarily known for its role in chelating calcium and helping with root canal disinfection, has a role in disrupting the biofilm associated with apical infections.

In contrast, ethyl alcohol lacks the necessary efficacy against the specific pathogens involved in apical infections, making it a less ideal choice for this particular purpose.