Which muscle is primarily affected by overextension on the mandibular anterior buccal flange?

The muscle primarily affected by overextension on the mandibular anterior buccal flange is the orbicularis oris. This muscle encircles the mouth and plays a crucial role in controlling the movements of the lips. When the mandibular anterior buccal flange of a dental prosthesis or appliance extends excessively, it can place undue stress on the orbicularis oris, potentially leading to irritation, discomfort, or functional problems such as difficulty in lip closure and speech.

In this context, the masseter and temporalis, while they are important muscles involved in mastication, do not play a direct role in the function and movement of the lips or the buccal regions in the same way that the orbicularis oris does. The buccinator muscle also contributes to the overall function of the cheeks and helps keep food positioned during chewing, but it is not as directly impacted by the anterior flange's overextension as the orbicularis oris. The orbicularis oris is more closely aligned with the effects of the anterior flange since it is responsible for lip motion and maintaining the integrity of the oral cavity.