Unbalanced cartilage calcification during development contributes to the formation of irregular articular surfaces as revealed by micro-CT images

Introduction: The histological features of irregular mandibular condylar surfaces revealed on CT images remain unknown.Aim: In order to seek clarification, the aim of the study was to describe the histological features of irregular mandibular condylar surfaces detected on micro-CT images.Materials and methods: Due to different modelling requirements, thirty rats were exposed to five experimental occlusal disturbance models at 6-or 8-weeks of age. Another six age-matched rats were used as controls. After 10 or 12 weeks of modelling, the mandibular condyles were sampled for micro-CT scanning and histology, immunohistochemistry and immunofluorescence assessment. The condyles with irregular surface signs were chosen for analysis.Results: Based on the micro-CT images, 10 out of the 30 condyles were diagnosed as having irregular articular surfaces which typically appeared as lacunae on histological sections. The lacunae were filled with degraded cartilage, a fibrous mass, or calcified islets. Type II collagen-, type X collagen-and osterix-positive cells were observed at the side walls of the lacunae. Cleaved caspase-3-positive cells, CD90-positive cells and fibronectin-positive areas were observed inside the lacunae. However, in the subchondral bone at the lower margin of the lacunae, TRAP-positive cells were seldom observed. Conclusions: Irregular mandibular condylar surfaces revealed by micro-CT images during development appeared to be a result of unbalanced cartilage calcification.