“The Ball on the Hill”: A new perspective on TMJ functional anatomy

1 | INTRODUC TION Much has been written about the anatomy of the temporomandibular joint (TMJ) as well as its associated extraarticular tissues. There is general agreement on the static anatomic features of these structures, as described in a variety of textbooks and scientific papers. However, there is some debate regarding functional anatomy concepts, because these require interpretations and assumptions about how the various structures work during mandibular functions. A prime example is the question of where the mandibular condyle is (or should be) located relative to the skull, when the mouth is fully closed. This debate has implications for clinical practice in orthodontics as well as in several aspects of general dentistry, because it obviously intersects also with the important topic of occlusion. In this paper, a new perspective is offered on these topics by analyzing a set of wellestablished static and dynamic anatomic facts. Hopefully, this new perspective on condylar position will prove to be helpful to dentists as they deal with the clinical challenges they face every day. So, let us begin by asking: What kind of a joint is the temporomandibular joint (TMJ)? Is it similar to the shoulder, which is essentially a ball articulating on a flat plate? NO. Is it similar to the knee, which is essentially two balls articulating on two platforms that can bear a lot of weight? NO. Some people seem to think that the TMJ is similar to the hip, which is a ball articulating in a socket. The consequence of this belief is that we see a lot of language describing the TMJ as follows: