DermDx: Brown Macule on Lip Dermatology Advisor In the process of removing a Labial Melanotic Macule. A Labial Melanotic Macule is a well defined, oval, brown to black, flat patch on the central third of the lower lip, as seen Oral pathology: Noting a pigmented macule that often presents a diagnostic dilemma Registered Dental Hygienists ORAL MELANOTIC MACULE (OMM) (Also called focal melanosis labial melanotic macule) A benign, localized, flat pigmented lesion of the oral mucosa Caused by a focal increase in melanin production