[Changes in ultrastructure and bone morphogenetic protein expression in reconstructed mandibular condylar cartilage under continuous mandibular advancement in adult rats].

Objective: This study investigated the reconstructed mandibular condylar cartilage and the ultrastructural variations in mandibular condylar cartilage in adult rats as a result of mandibular advancement.

Methods: Thirty 9-week-old male Sprague-Dawley rats were randomly divided into experimental and control groups. Rats in the experimental group were subjected to mandibular advancement. Rats were sacrificed on days 3, 7, 14, 21, 30. Sections were cut from condyles, and bone morphogenetic protein-2 (BMP-2) expression in condylar cartilage was examined through immunohistochemical analysis. Condylar cartilage samples were harvested, and ultrastructural changes in these samples were observed under Micro-CT and transmission electron microscope.

Results: Compared with the control group, the experimental group obviously displayed cartilage hyperplasia in the middle and rear of the condyle. Moreover, the number of BMP-2-positive cells in condylar cartilage and the gray value gradually increased in the experimental group on day 7 of the intervention. Ultrastructural changes, such as karyopyknosis, reduced microfilaments around the nucleus, reduction in size or even disappearance of lipid droplets, swelling of endoplasmic reticulum compartments, broadened and increased extracellular matrix, were observed in the condylar hypertrophic chondrocytes. Micro-CT revealed that the trabecula and the newly formed bone gradually thickened.

Conclusions: Hypertrophic remodeling of the condylar cartilage and high BMP-2 expression are observed in adult rats as a result of continuous mandibular advancement.