The masticatory system is a very complex and interrelated system of muscles, bones, ligaments, teeth, and nerves. It is difficult, but necessary, to simplify the description of this system to understand the basic concepts that influence the function and health of all its components.
The mandible, a bone attached to the skull by ligaments, is suspended by a muscular sling. When the levator muscles (i.e., masseter, medial and temporal pterygoid) are activated, their contraction raises the jaw until contact is made and a force is applied to the skull in three areas: the two temporomandibular joints and the teeth. Since these muscles are capable of generating intense forces, the chances of injury to these three locations are high. Thus, these areas must be carefully examined to determine the optimal orthopedic relationship that will avoid, minimize, or eliminate potential disturbances or trauma.
Lateral translational movement of the mandible is a mass displacement of the mandible to one side that occurs during lateral movements, also called Bennett movements.
In this lateral displacement of the jaw, the canine guide originates, which is a guide for occlusion where in lateral movement the canines are the only teeth that touch. This laterality guide is considered ideal.
During a lateral displacement of the mandible, the orbiting condyle (that is, the one that performs the function) moves up and down, back to front and from outside to inside in the mandibular fossa, around axes located in the opposite condyle ( that is, condyle of rotation). If the temporomandibular ligament of the condyle of rotation is very tight and the medial wall is close to the orbiting condyle, a pure arc movement will take place around the axis of rotation at the condyle of rotation. When this situation occurs, no lateral translation of the mandible is generated.
Most of the time there is a certain laxity of the ligament and the medial wall of the mandibular fossa maintains a medial position with respect to an arc drawn around the axis of the rotational condyle. When this occurs, the orbiting condyle moves from the outside in towards the medial wall and produces a lateral translational movement of the mandible.
The lateral translation movement has three attributes: quantity, time of appearance and direction.
- The amount and the moment of appearance are caused by the degree of medial separation of the medial wall of the mandibular fossa with respect to an arc traced around the axis located in the rotational condyle. The degree of lateral movement of the rotational condyle that the ligament allows also influences. The more medial the position of the wall to the medial pole of the orbital condyle, the greater the amount of lateral translational motion, and the looser the ligament attached to the rotational condyle, the greater the lateral translational motion.
- The direction of the lateral translational movement depends fundamentally on the direction that the rotational condyle follows during mass displacement.
