The most prominent feature of acute apical periodontitis is:

The most prominent feature of acute apical periodontitis is tenderness of the tooth to pressure. This condition arises from inflammation of the tissues surrounding the root of a tooth, which is typically due to an infection or necrosis of the dental pulp. The inflammation leads to increased sensitivity, especially when the affected tooth is subjected to biting forces or pressure, resulting in a characteristic discomfort that patients often report.

Tenderness to pressure is notable because it directly relates to how the inflammation affects the periapical tissues. Patients may experience significant pain when biting or tapping on the tooth, which is a clear indication of the inflammatory response in the area.

While other signs such as extra oral swelling or intermittent pain can occur, they are not as definitive or prominent as the tenderness experienced during pressure application. Pulp vitality, on the other hand, refers to whether the tooth's nerve is still alive, which may not necessarily relate directly to the acute symptoms of periodontitis. Therefore, the hallmark symptom that helps to identify acute apical periodontitis is the tenderness of the tooth to pressure.