While this group included subjects with autoimmune diseases, such as Sjögren’s syndrome and rheumatoid arthritis, and skeletal diseases, such as osteoporosis and multiple OA, their increased TNF-α level might have reflected a degree of inflammation that could have been a predisposing factor to DJD-TMJ, as with other age-related diseases [42]. This evidence concerns the gene TNF and rheumatoid arthritis.