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What is A patient shows gingival swelling in lower premolar region. Biopsy was taken and histopathological examination showed endothelium-lined vascular spaces and the extreme proliferation of fibroblasts and budding endothelial cells. What could this lesion be: and explain in detail?
Clinically, pyogenic granuloma is a raised lesion on either a sessile or a pedunculated base. Its surface may have a smooth, lobulated, or, occasionally, warty appearance that is erythematous and often ulcerated. Depending on the age of the lesion, the texture varies from soft to firm and is suggestive of an ulcerated fibroma. 
Because of the pronounced vascularity of these lesions, they often bleed easily when probed.
Histologically, the pyogenic granuloma presents as a remarkable proliferation of plump fibroblasts and endothelial cells with the formation of prominent numbers of  thin-walled, endothelium-lined vascular channels. A polymorphous inflammatory cell infiltrate is present, and the overlying surface epithelium is often ulcerated. Treatment consists of surgical excision, with care being taken to completely remove any local irritant that may still be present that would predispose to recurrence of the lesion.
Reference: McDONALD AND AVERY’S DENTISTRY for the CHILD and ADOLESCENT, 10th ed page no 604,605