What defines a functional cause of crossbite?

A functional cause of crossbite primarily refers to the influence of muscle activity and dental relationships in determining occlusion. In cases where there is a muscularly determined posture, the position of the jaw and teeth can be altered, leading to a crossbite. This is often due to the way the muscles—such as the tongue and those that control jaw movement—dynamically position the jaw during function, affecting dental occlusion.

While altered eruption paths and crowding of teeth may contribute to the presence of a crossbite, they are typically classified as structural or anatomical factors rather than functional. Structural factors relate to the physical arrangement and available space for teeth, whereas functional factors involve how muscle forces interact with these structures during jaw movements and at rest.

Therefore, the definition of a functional cause is best captured by the notion that muscular dynamics play an essential role in determining dental alignment and occlusal relationships, which is emphasized in the option that highlights muscularly determined posture.