What typically causes an unfavorable horizontal mandible fracture displacement?

An unfavorable horizontal mandible fracture displacement is most commonly caused by the action of the masseter muscle. This muscle plays a significant role in chewing and generates powerful forces during contraction. When a horizontal fracture occurs, the contractions of the masseter can lead to unfavorable displacement of the fracture fragments.

In the context of a horizontal fracture, the masseter pulls the distal fragment of the mandible superiorly and posteriorly, resulting in misalignment and displacement away from the ideal anatomical position. This can complicate treatment and healing, as achieving proper occlusion may become challenging.

While the temporalis, medial pterygoid, and platysma muscles can influence mandibular movement, they do not exert the same relevant pulling force on the mandible that the masseter does in cases of horizontal fractures. Therefore, it is the masseter muscle's strong contraction during mastication that typically causes this specific type of displacement, making it the primary muscle responsible in this scenario.