Final answer:
The labial vestibule flange on the mandible is limited inferiorly by the mylohyoid muscle, which forms the floor of the oral cavity.
Step-by-step explanation:
The labial vestibule flange on the mandible is limited inferiorly by the mylohyoid muscle. This muscle forms the floor of the oral cavity and attaches to the mylohyoid lines on both sides of the mandible. The mylohyoid line is a bony ridge that extends along the inner aspect of the mandibular body. The mylohyoid muscle's function is critical for actions such as swallowing and speaking, and it acts as a boundary for the placement of dentures.