Mucosal melanotic macule - 口腔黑斑 https://en.wikipedia.org/wiki/Oral_pigmentation#Melanotic_macule
口腔黑斑 (Mucosal melanotic macule) 可见于口腔黏膜、唇、腭和牙龈。口腔黑斑 (Mucosal melanotic macule) 是口腔中常见的良性色素病变,由上皮层和固有层色素沉着增加所致。临床表现通常为界限清楚的棕色、黑色、蓝色或灰色斑块,病变直径一般小于10 毫米,但在少数情况下可更大。该病为良性。

诊断和治疗
若形状和颜色均匀,通常为良性。

更多信息 ― 简体中文
References Black and Brown: Non-neoplastic Pigmentation of the Oral Mucosa 30671761 
NIH
Addison’s Disease (Hypoadrenocorticism),Peutz–Jeghers Syndrome,Laugier–Hunziker Syndrome (Idiopathic Lenticular Mucocutaneous Pigmentation),Drug-Related Discolorations,Melanotic Macule,Melanoacanthoma,Smoker’s Melanosis,Amalgam Tattoo/Foreign Body Tattoo,Black Hairy Tongue