**4.3 Mechanism of action of stem cells in defects and diseases of craniofacial region**

The key role of stem cell therapy in oral mucosal lesions is primarily aimed at neoangiogenesis, tissue regeneration, increased cellularity, modulation of collagen gene expression and immunomodulation, thus making it a versatile promising treatment modality.

Stem cells are divided into embryonic and adult types. Among these the embryonic stem cells are derived by invitro fertilization, elective abortion, somatic cell nuclear transfer and cloning. The adult stem cells can be obtained from three sources such as [2] bone marrow (subdivided into hematopoetic and mesenchymal), [3] oro facial region (decidous teeth, tooth follicle, buccal mucosa, alveolar bone, periodontal ligament, dental pulp, periosteum) [4] other body tissues (skin, adipose tissue).

At present the stem cell research is focused on treatment of oral mucosal lesions such as oral mucositis, oral ulcers, pemphigus vulgaris, oral lichen planus, submucous fibrosis, oral carcinomas etc. In oral submucous fibrosis it is believed to act in removal of pathologically altered collagen and stimulation of healthy collagen through collagen gene expression and immunomodulation (b) Promoting neoangiogenesis. (c) promoting antioxidant action [7].
