The specific objectives were to: (1) establish an AP model in the rat and verify the progression of AP by pulp histology and serum cytokine detection; (2) evaluate the behavior of nociceptive response by head-withdrawal reflex thresholds (HWTs) measurement and open-field test; (3) explore the expression and signaling of TLR4 in the pulp and TGs in the AP models; and (4) observe the rescue effect of eritoran, an antagonist of TLR4, on the nociceptive response. Here, TLR4 is linked to alkaline phosphatase measurement.