TMD is well accepted as a multi-factorial disease. In order to clarify the nature of TMD, I would like to first review previous studies in terms of the association of various factors with the onset of TMD. Based upon these findings, it is shown that mechanical loading, if excessive, is an important and significant cause of TMD. Furthermore, the problem-oriented therapeutic system has been established. In this system, the examination and differential diagnosis are essential for appropriate treatment. Finally, I would like to discuss the availability of a certain treatment modality integrated with orthodontic approach for the correction of TMDs with different intra-articular pathologies.