Abstract:

Objective To establish a rat hyperalgesia model of acute pulpitis induced by lipopoly-saccharide (LPS) administration to the maxillary molars. In addition, to analyze and evaluate the acute pain and LPS-induced pulpitis, and to investigate the change of pain threshold in rats with acute pulpitis. Methods Forty-five adult male Sprague-Dawley (SD) rats were equally divided into LPS group, normal saline (NS) group, and blank control (SHAM) group, with 15 rats in each group. Under isoflurance anesthesia, the rats in the LPS group had their right upper molar teeth drilled and LPS was sealed temporarily with Caviton, while those in the NS group had their right upper molar teeth drilled and normal saline was sealed temporarily with Caviton. Rats in the SHAM group, serving as blank control group,were only anesthetized with isoflurane. Pain behavioral indexes, including spontaneous pain behavior scores, 50% paw withdrawal threshold (PWT), head withdrawal thresholds (HWT), paw withdrawal latency (PWL), and head withdrawal latency (HWL) were measured before and 2 h, 24 h, 48 h, and 72 h after surgery. After rats were anesthetized and sacrificed, the pathological status of pulp tissues was confirmed with hematoxylin-eosin staining and pathological examination and serum IL-1β and TNF-α were determined by ELISA. Results Concerning spontaneous pain behavior, the facial grooming time in the LPS group was significantly higher than that in the NS group postoperatively (P＜0.05), and increased gradually with time, although there was no significant difference in activity time. The HWT in the LPS group was significantly lower than that in the NS group at 2 h, 24 h, and 48 h postoperatively (P＜0.05). Additionally, 50% PWT in the LPS and NS groups were significantly lower than those in the SHAM group (P＜0.05). The LPS group had a significantly lower HWL than the NA group at 2 h and 48 h postoperatively (P＜0.05). Likewise, the PWL was significantly lower in the LPS group than the NS group (P＜0.05) at 72 h postoperatively. The IL-1β and TNF-α levels in the rats’ serum were significantly higher in the LPS group than in the NS group (P＜0.01 or P＜0.05). Moreover, the IL-1β and TNF-α levels in all groups began increasing 2 h after the model establishment, reaching a peak at 48 h. The pathological results of the LPS group showed a gradual expansion in the neutrophil infiltration area from the point of perforation to the crown pulp and upper root pulp, in 24-72 h after modeling. The rats in the NS group exhibited milder degree of inflammation than those in the LPS group. Conclusion Based on the observations regarding rat behavior, pathological changes of dental pulp, and detection of inflammatory factors in serum, the LPS induced acute pulpitis model causes pathological pain and pain threshold alterations in rats.

Key words: Acute pulpitis, Hyperalgesia, Lipopolysaccharide, Pain behavior, Sprague-Dawley rats