International Journal of Molecular Sciences Review Acute and Chronic Pain from Facial Skin and Oral Mucosa: Unique Neurobiology and Challenging Treatment Man-Kyo Chung 1,* , Sheng Wang 1, Se-Lim Oh 2 and Yu Shin Kim 3,* 1 Center to Advance Chronic Pain Research, Department of Neural and Pain Sciences, School of Dentistry, Program in Neuroscience, University of Maryland at Baltimore, Baltimore, MD 21201, USA;
[email protected] 2 Department of Advanced Oral Sciences & Therapeutics, School of Dentistry, University of Maryland at Baltimore, Baltimore, MD 21201, USA;
[email protected] 3 Health Science Center at San Antonio, Programs in Integrated Biomedical Sciences, Department of Oral & Maxillofacial Surgery, School of Dentistry, Translational Sciences, Biomedical Engineering and Radiological Sciences, University of Texas, San Antonio, TX 78229, USA * Correspondence:
[email protected] (M.-K.C.);
[email protected] (Y.S.K.) Abstract: The oral cavity is a portal into the digestive system, which exhibits unique sensory proper- ties. Like facial skin, the oral mucosa needs to be exquisitely sensitive and selective, in order to detect harmful toxins versus edible food. Chemosensation and somatosensation by multiple receptors, including transient receptor potential channels, are well-developed to meet these needs. In contrast to facial skin, however, the oral mucosa rarely exhibits itch responses. Like the gut, the oral cavity performs mechanical and chemical digestion. Therefore, the oral mucosa needs to be insensitive, to some degree, in order to endure noxious irritation. Persistent pain from the oral mucosa is often due to ulcers, involving both tissue injury and infection. Trigeminal nerve injury and trigeminal neuralgia produce intractable pain in the orofacial skin and the oral mucosa, through mechanisms Citation: Chung, M.-K.; Wang, S.; distinct from those seen in the spinal area, which is particularly difficult to predict or treat.