Summary Objective Altered loading is an important etiological factor for temporomandibular joint (TMJ) disorders. Studies examining altered loading of the TMJ have been done in rats but the response of the TMJ to altered loading in mice is largely unknown. Therefore, due to the potential usefulness of genetically engineered mice, the goal of this study was to develop a mouse TMJ altered functional loading model. Methods One hundred and thirty four, 21-day-old CD-1 female mice were divided into two groups: (1) normal loading (hard pellet diet) for 2–6 weeks and (2) altered functional loading (incisor trimming every other day and soft dough diet) for 2–6 weeks. The mandibular condylar cartilage was evaluated by histology, the subchondral bone was evaluated by microcomputed tomography (micro-CT) analysis and gene expression was evaluated by real time polymerase chain reaction (PCR) analysis. Results Altered functional loading for 2–6 weeks caused significant reduction in the thickness of the condylar cartilage whereas, only at 4 weeks was there a significant decrease in the bone volume fraction and trabecular thickness of the subchondral bone. Gene expression analysis showed that altered functional loading for 4 weeks caused a significant reduction in the expression of SRY-box containing gene 9 (Sox9), Collagen type X (Col X), Indian hedgehog (lhh), Collagen type II (Col II) and Vascular endothelial growth factor (Vegf) and altered loading for 6 weeks caused a significant decrease in the expression of Sox9, Col II, Vegf and Receptor activator of NF-κB ligand (Rankl) compared to the normal loading group. Conclusion Altered functional TMJ loading in mice for 2–6 weeks leads to a loss of the condylar cartilage and a transient loss in the density of the mandibular condylar subchondral bone.

Objective-Little is known about the natural progression of the disease process of temporomandibular joint (TMJ) osteoarthritis (OA), which affects approximately 1 % of the US population. The goal of this study was to examine the early microarchitectural and molecular changes in the condylar cartilage and subchondral bone in biglycan/fibromodulin (Bgn/Fmod) doubledeficient mice, which develop TMJ-OA at 6 months.Methods-TMJs from 3 month old (n=44) and 9 month old (n=52) wild-type (WT n=46) and Bgn/ Fmod (n=50) double-deficient mice were evaluated. Micro-CT analysis of the subchondral bone (n=24), transmission electron microscopy for condylar cartilage fibril diameters (n=26), and real time PCR analysis for gene expression for bone and cartilage maturation markers (n=45) was performed.Results-A statistically significant increase in collagen fibril diameter of the condylar cartilage and a decrease in expression of Parathyroid related protein in the mandibular condylar head were observed in the 3 month Bgn/Fmod double-deficient mice compared to WT controls. The 9 month Bgn/Fmod double-deficient mouse demonstrated an increase in bone volume and total volume in subchondral bone, and an increase in the expression of Collagen Type X and Aggrecan in the mandibular condylar head compared to the WT controls.Conclusion-We found that changes in the microarchitecture of the condylar cartilage preceded changes in the subchondral bone during OA in the TMJ in Bgn/Fmod double-deficient mice.