Structural characteristics of periodontal ligaments in the pig model with experimental periodontitis

To investigate how the structure of Sharpey's fibers in the periodontal ligaments (PDL) were affected by experimental periodontitis in a young pig model, 7 were periodically inoculated with four types of bacteria and a ligature around the last maxillary molar for 8 weeks to induce periodontitis (PG), and 10 served as controls (CG). The harvested molar blocks were sectioned coronally and stained with either hematoxylin & eosin (H&E) or Sirius Red (SR). The H&E-stained images were first reviewed. Then, images of each adjacent SR-stained sections were captured at the region close to the apex of mesial roots under polarizing light microscopy. Sharpey's fiber numbers in each bundle, total bundle numbers, connection of the bundle to the cementum and alveoli, as well as bundle angulations to the molar long axis were quantified in the defined area 500μm apical to the root apex. Compared to CG, PG showed the following features: 15.13% less total bundle number; 17.8% less bundle size; significantly less connected fiber bundles; 9.2% more interrupted fiber bundles; and 3.85% more oriented toward the cervical in the bundle angulation. These results suggest that experimental periodontitis alters the PDL structure, leading to more interruptions of Sharpey's fiber attachments to the cementum.