American Board of Orthodontics (ABO) Practice Exam 2025 - Free Orthodontics Practice Questions and Study Guide

The phosphate buffer system is the most active in resting saliva, playing a critical role in maintaining the pH balance within the oral cavity. Saliva is a complex fluid that aids in digestion, helps prevent tooth decay, and supports overall oral health. One of its essential functions is to neutralize acids produced by bacteria in the mouth, and phosphate ions are particularly effective at this task.

Phosphate, present in saliva in varying states (dihydrogen phosphate, hydrogen phosphate, and phosphate), can effectively accept hydrogen ions when acidity increases and can release them when the pH is too basic, thus maintaining a relatively stable pH level. This buffering capacity is vital because it not only protects the enamel from acid erosion but also ensures a suitable environment for oral flora.

While bicarbonate is also a significant buffer in saliva—especially when stimulated by eating or drinking—its activity is more pronounced during these times rather than at rest. Other buffers, such as carbonate and chloride, do not contribute as significantly to the buffering capacity in resting saliva compared to phosphate, making phosphate the predominant salivary buffer during this state.