Temporal histological and immunohistochemical characterization of experimental dental pulp inflammation in rats

To establish a temporal histological and immunohistochemical profile in a rat model of pulpitis by assessing cytokine immunoreactivity at the root canal orifice over time.

This experimental animal study included 28 male Wistar rats allocated to seven groups based on the time elapsed after pulp exposure: D0, D1, D2, D3, D4, D5, D6 (0-6 days). Pulp inflammation was induced in maxillary first molars, and hemimaxillae were processed for histological and immunohistochemical analyses. Cytokines (IL-17, TGF-β, IL-6, IL-1β, IL-10 and TNF-α) were evaluated using the immunoperoxidase technique, and immunoreactivity was semi-quantitatively scored. Inflammatory infiltrate was assessed histologically. Data were analyzed using Kruskal-Wallis and post hoc tests (α = 0.05).

Histological analysis demonstrated a progressive increase in inflammation and tissue damage over time, ranging from absence or mild inflammatory changes in D0-D1 to complete necrosis at D6 (p < 0.05). Immunohistochemical analysis revealed detectable immunoreactivity for TGF-β and IL-17 at the earliest time points (D0-D1), while no significant temporal differences were observed among cytokines from D0 to D2 (p > 0.05). From D3 onwards, all cytokines exhibited a significant increase in immunoreactivity compared to D0 (p < 0.05), with sustained elevated expression through D6.

Pulp inflammation was associated with time-dependent histological alterations and cytokine immunoreactivity at the root canal orifice. Early TGF-β and IL-17 expression was observed at initial time points, while a progressive increase in cytokine immunoreactivity from D3 onwards marked the development of an established inflammatory response and subsequent tissue damage.