Chronological Analysis of Rat Apical Periodontitis by Micro-CT and Histology

Objectives: To investigate chronological change in induced rat apical periodontitis with in-vivo micro computed tomography (CT) and histological observation.

Methods: The mandibular first molars of six-week-old pathogen-free Sprague-Dawley rats were used to induce apical periodontitis. Cavity was prepared to expose pulp chamber by ¼ round bur. The exposed pulp chamber was coronally either opened (OC) or sealed (SC) and each group was allocated by split-mouth design in a single arch to minimize host-related effects. For OC group, a sterile cotton pellet was only placed in the pulp cavity, while adhesive resin cement (U-200, 3M) was filled over the cotton pellet for SC group. Each group was divided to have 4 sub-groups according to observation period from 1 week to 4 week (n=6). In vivo micro-CT was taken every week to observe the occurrence and change in size for apical lesion from baseline to 4 weeks following pulp exposure. Histo-pathologic change was evaluated through H&E staining at 1-, 2,-3, and 4-week after pulp exposure.

Results: SC showed PDL widening around the apical area at 1 week and did not show significant changes in shape and size afterwards, while OC showed apical lesions with definite border and its continuous expansion throughout the period in micro CT observation. Histologically, OC showed that partial pulp necrosis and fibrosis, liquefaction necrosis, bone remodeling around periapical lesion and active osteoclasts gathering, and abscess formation at 1, 2, 3 and, 4 weeks, respectively. In SC, upper part of pulp chamber showed partial necrosis and lower part did fibrosis. Root canal and periapical area of SC did not show expression of inflammation, and histological change was not seen throughout the period.

Conclusions: Based on in-vivo micro-CT and histologic observation, periapical lesion formation and expansion was reproducibly confirmed in coronally pulp-opened rat model.