In patients with Class II Division I, what often causes mentalis muscle hyperactivity?

In patients with Class II Division I malocclusion, the positioning of the teeth and the relationship between the upper and lower dental arches can lead to specific muscle activities, including hyperactivity of the mentalis muscle. This malocclusion is characterized by protruded maxillary incisors and retruded mandibular incisors, which can alter the patient's lip posture and cause the mentalis muscle to become overactive as a compensatory response to the dental and skeletal relationships.

The mentalis muscle plays a crucial role in lip movement and chin expression. In Class II Division I, the altered position and function of the teeth often necessitate increased activity of the mentalis to maintain lip closure or to assist with facial aesthetics. This hyperactivity may lead to problems such as mentalis strain or a distinct chin appearance due to the muscle's tension and contraction patterns.

Other options provided may contribute to muscle function or facial appearance, but they do not directly cause hyperactivity of the mentalis muscle in the specific context of Class II Division I malocclusion.