Physiology: movement possibilities of the lower jaw - Anatomy and physiology of the head, neck and chewing system
Physiology: movement possibilities of the lower jaw
The movements of the lower jaw with respect to the upper jaw are caused by contraction of muscle (group) and and by gravity. The jaw head or process condylaris can make two movements in the joint: a rotation and a shift. By combining these two movements, there are many movement options due to the special construction of the temporomandibular joint. An overview of this is given below.
- Forward-backward movements. The mandible can move forwards and backwards (afterwards). We call the forward movement a proal movement or protraction. The movement backwards is called retraction. With the forward-backward movements, almost only a shift occurs in the jaw joint.
- Up and down movements. The lower jaw can be moved down and up. We call this opening and closing of the mouth detraction and elevation respectively. When the mouth is opened, a rotation first occurs in the joint, followed by a shift. If we close the mouth again, first a shift of the jaw head will take place in the joint and then a rotation.
- Sideways movements. The lateral movements of the lower jaw have already been discussed during the construction of the jaw joint. As the chin tip moves to the right, the right jaw head rotates, but it stays in place in the bowl in the skull. The left jaw head, on the other hand, is moved forward. So a shift takes place on the right.
- Combination of movements. Especially during chewing, not only one of the previously mentioned movements occurs: all movement possibilities of the jaw joint are used interchangeably and simultaneously. We call the combination of movements circumduction. Rotations and shifts of the jaw heads occur (see table below).
Overview of the different movement possibilities of the lower jaw with the muscles that make these movements possible.
|Forward||M. Pterygoideus lateralis (double sided)|
|Forward||M. Pterygoideus medialis (Double sided)|
|Down||Mouth floor muscles|
|Upwards||M. Pterygoideus medialis|
|Sideways||M. Pterygoideus lateralis (Single-sided)|
|Sideways||M. Pterygoideus medialis (Single sided)|