What is the histopathology associated with plaque accumulation after 21 days?

Histopathology associated with plaque accumulation after 21 days typically reveals an infiltrate of plasma cells and early bone involvement. This stage of periodontal disease progression indicates a shift from the initial inflammatory response characterized by neutrophils and lymphocytes to a more chronic inflammatory response involving plasma cells, which are indicative of an immune response to persistent bacterial infection.

The presence of plasma cells signifies that the immune system has been activated and is attempting to produce antibodies against the pathogens present in the biofilm of the plaque. Additionally, the mention of early bone involvement suggests that the inflammatory response has progressed enough to begin affecting the surrounding alveolar bone, which can lead to periodontal tissue destruction if left unaddressed.

In contrast, other types of infiltrates mentioned do not align with the expected histopathological findings after this period. A primary infiltrate of lymphocytes would suggest an earlier phase of inflammation, typically seen in the first week after plaque accumulation, while an infiltrate of neutrophils primarily indicates the body's initial response to bacterial invasion.