Temporomandibular Joint Inflammation and Mandibular Development in Growing Rats

Objectives: The inflammation caused by juvenile idiopathic arthritis often affects the temporomandibular joint (TMJ) and can have an impact on development of the mandibular condyle. This study evaluated the correlation between TMJ inflammation with or without a prodrug of dexamethasone (P-DEX) and several measurements of condylar development.
Methods: Joint inflammation was induced by injecting 2 doses of complete Freund’s adjuvant (CFA) at one month intervals into the right TMJs of 24 growing Spraque-Dawley male rats (left side controls). With the second CFA injection, three equal groups received: 1) intra-articular 5mg P-DEX, 2) tail vein 15mg P-DEX, or 3) CFA alone. Four rats received no treatments. Animals were euthanized 28 days later, and the skulls underwent radiographic measurement of the ramus height (CsGoInf) and micro-computed CT analysis of condylar width (CW), bone volume (BV), and bone density (BD). The TMJs then underwent histological preparation, and the area of inflammatory infiltrate and inflammatory cell/connective tissue percentages (grid intersection point counting) were performed in the retrodiscal tissue. Three measurements were taken of the fibrous, prechondroblastic, chondroblastic, and hypertrophic layers of the condylar head at 300μm intervals from the condylar midpoint. Correlations (Pearson’s) between inflammation data and condylar measurements (CsGoInf, CW, BV, and BD) were measured.
Results: Area of inflammatory infiltrate and percent lymphocytes were negatively correlated to CsGoInf (r=-0.31,-0.40 respectively; p<0.01), while percent non-inflamed retrodiscal connective tissue was positively correlated with CsGoInf (r=0.36, p=0.004). Level of inflammation did not affect CW, BD, or BV. Significantly thicker condylar fibrous layers were found in TMJs treated with CFA compared to controls (p<0.01), and fibrous layer thickness was negatively correlated to all ramus and condylar measurements (r=-0.28 to -0.51, p<0.05).
Conclusions: The amount of TMJ inflammation has a proportional negative impact on ramus height growth.