PERIODONTIUM (Greek peri around, near + odus, odontos tooth; synonym: periodontal sheaf, pericementum) — the connective tissue sheaf holding a fang in a tooth socket of a jaw.
The item develops along with a fang shortly before its eruption, i.e. in postembryonal the period. P.'s development happens at the expense of mezenkhimny cells of a periblast of the tooth sack surrounding a dental germ (see. Teeth ). The created P. consists of bunches of the collagenic fibers tense between cement of a fang and bone walls of a tooth socket. Bunches of collagenic fibers P. have various arrangement. At edges of a tooth socket they have generally horizontal direction. Are interwoven by Nek-rye from these fibers into a gingiva, and others bend around a neck of tooth and form a so-called circular sheaf. Interdental fibers also concern to the same group, to-rye pass over top of an interalveolar partition and connect the next teeth. In side sites of a periodontal crack bunches of collagenic fibers have generally slanting direction, and in the field of a top of a fang are located radially. In intervals between bunches of collagenic fibers there are layers of friable connecting fabric with separate elastic fibrils in which there pass vessels and nerves. Among bunches of collagenic fibers P. so-called oksitalanovy fibers are found, to-rye on chemical structure are intermediate as if between collagenic and elastic fibers.
A cervical part of a periodontal crack is a zone of accumulation of cells (fibroblasts, plasmatic and mast cells, osteoblasts, osteoclasts). On other extent of a periodontal crack of a cell are grouped closer to a bone of a tooth socket and to cement of a root. Also small islands of epithelial cells (so-called islands of Malasse), to-rye as consider meet, represent the remains of the epithelial tooth body which is formed at development of tooth and development of an epithelial vystilka of tooth granulomas and okolokornevy cysts can be a source (kistogranuly).
At a histochemical research in P. a large number of acid glikozaminoglikan and high activity of oxidation-reduction enzymes in cellular elements is found.
Veins P. form quite dense network. They anastomose with vessels of a gingiva and marrowy spaces. Larger vessels are located in deepenings of a wall of a tooth socket. In P. vascular balls, and also an arteriovenous anastomosis are described.
The item contains many free kustikovidny nerve terminations, to-rye, apparently, are mechanioreceptors and register tightness of bunches of collagenic fibers P. during the act of chewing. With age fibers P. are exposed to partial destruction, especially in a cervical part, the quantity of young cellular elements decreases.
The item has high regenerator ability. It allows to implant at P.'s injuries or a complete dislocation of tooth and a rupture of fibers P. tooth in a tooth socket (see. Replantation ). Among patol, P.'s processes meet inflammatory, including formation of okolokornevy tooth granulomas of a brush (see. Periodontitis ), and also periodontosis (see).
Bibliography: Gavrilov E. I. Biology of a parodont and pulp of tooth, M., 1969; Gemonov V. V. and Kozlovi-ts of e r T. V. Fibrous structures of a periodontium, Stomatology, t. 53, No. 2, page 9 * 1974; Of e of m about N about in V. V., and l of l of e r JI. And. and Kozlovitsert. V. K to a question of oksitalanovy fibers of a periodontium, in book: Changes in fabrics of a periodontium before and after protezir., under the editorship of Sh. V. Bo-kanov and A. I. Voloshin, page 57, M., 1972; F and l and I am L. I. Gistologiya and embryology of an oral cavity and teeth, M., 1963; Schumacher G. - H. u. Schmidt H. Anatomie und Biochemie der Zahne, B., 1972; Structural and chemical organization of teeth, ed. by A. E. W. Miles, y. 1, N. Y. — L., 1967.
B. B. Gemonov.