Melanin: the biophysiology of oral melanocytes and physiological oral pigmentation

Abstract

The presence of melanocytes in the oral epithelium is a well-established fact, but their physiological functions are not well defined. Melanin provides protection from environmental stressors such as ultraviolet radiation and reactive oxygen species; and melanocytes function as stress-sensors having the capacity both to react to and to produce a variety of microenvironmental cytokines and growth factors, modulating immune, inflammatory and antibacterial responses. Melanocytes also act as neuroendocrine cells producing local neurotransmitters including acetylcholine, catecholamines and opioids, and hormones of the melanocortin system such as proopiomelanocortin, adrenocorticotropic hormone and α-melanocyte stimulating hormone, that participate in intracellular and in intercellular signalling pathways, thus contributing to tissue homeostasis.There is a wide range of normal variation in melanin pigmentation of the oral mucosa. In general, darker skinned persons more frequently have oral melanin pigmentation than light-skinned persons. Variations in oral physiological pigmentation are genetically determined unless associated with some underlying disease.In this article, we discuss some aspects of the biophysiology of oral melanocytes, of the functions of melanin, and of physiological oral pigmentation.

Figure 1

Multiple, light brown maculae with well-defined borders on the gingiva.

Figure 2

Physiological oral pigmentation on the gingiva presenting as bilateral, symmetrical, dark brown discolouration of the labial gingiva, including the marginal and papillary gingiva but not transgressing the mucogingival junction.

Figure 3

Diffuse, light brown physiological oral pigmentation on the hard palate.

Figure 4

Uniform dark brown-black pigmentation of the lower lip and labial mucosa.

Figure 5

Physiological oral pigmentation in a black male: a well demarcated brown band on the attached gingiva, not transgressing the mucogingival junction and not affecting the marginal/interdental papillary gingiva. (The foreign body at the upper left is a post-biopsy suture).

Figure 6

Light brown pigmentation of the alveolar mucosa not transgressing the mucogingival junction.