The oral mucosa is the first element of the periodontium, which appears at the first vertebrates, cartilaginous (sturions) and osseous (teleosteen) fishes, in the s hape o f a c amp o f “ scales” î n d iverse s tages o f evolution, which cover the walls of the oral cavity. At the fossil reptiles, the proper periodontium is differentiated from the oral mucosa, which differentiates into enamel and from the subjacent mesodermic mesenchim, from which the dental root differentiates; the collagen fibers from the mesenchim where the cement and the alveolar osseous tissue differentiates, which remain set-in into these mineralized tissues; and at the middle remain the fibroblasts (oxytalan) which multiplies through direct division. The clinical forms of periodontitis are very numerous, adding to the anatomo-clinical, etiologic and eventually topographic diagnosis, as it is recommended in atropology. -“Periodontitis lewis” is established on the tumefaction and the red color of the gingival mucosa; the bottom o f t he g ingival s ack h as 2 m m i n d epth, u p t o 3 mm. In the form of “periodontitis gravis” the bottom of the gingival sack has reached between 3-4 mm and lamina propria has been perforated. “Periodontitis complicata” has 2 phases: at one, the bottom of the sack has 4-6 mm, at the other, the most dangerous, the bottom of the sack exceeds 6 mm in depth.