In the following illustration, structure "b" is the

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At the midline of the lower lip, a fold of connective tissue known as the mandibular labial frenum can be found. A mandibular frenal attachment that extends too close to the gingiva may contribute to gingival recession. A corresponding structure, the maxillary labial frenum, is present at the midline of the upper lip. Both structures, as well as additional less well-defined frena, serve to attach the lips to the arch and contain only connective tissue. Structure "a" is the maxillary labial frenum. Structure "c" is the mucogingival junction. Structure "d" is the mucobuccal fold.

In the Following Illustration, Structure "B" Is the