. Cunningham's Text-book of anatomy. Anatomy. 1122 THE DIGESTIVE SYSTEM. Structure of the Teeth. Crown Tooth cavity Neck As mentioned above, the teeth are composed of three special tissues, substantia adaman- tina or adamant ( enamel), substantia eburnea or ivory ( dentine), and sub- stantia ossea ( crusta petrosa or cement), in addition to the pulp which occupies the tooth cavity. The chief mass of the tooth is formed of substantia eburnea, which surrounds the tooth cavity and extends from crown to root; outside this is a covering of substantia adamantina on the crown, and a layer
. Cunningham's Text-book of anatomy. Anatomy. 1122 THE DIGESTIVE SYSTEM. Structure of the Teeth. Crown Tooth cavity Neck As mentioned above, the teeth are composed of three special tissues, substantia adaman- tina or adamant ( enamel), substantia eburnea or ivory ( dentine), and sub- stantia ossea ( crusta petrosa or cement), in addition to the pulp which occupies the tooth cavity. The chief mass of the tooth is formed of substantia eburnea, which surrounds the tooth cavity and extends from crown to root; outside this is a covering of substantia adamantina on the crown, and a layer of substantia ossea on the root. The substantia adamantina is the dense, white, glistening layer which forms a cap, thickest over the tubercles, for the portion of each tooth projecting above the gum (Fig. 888). At the neck it ceases gradu- ally, being here slightly overlapped by the sub- stantia ossea. It is composed chiefly of phosphate and carbon- ate of lime (phosphate of calcium 89-82 per cent, carbonate of calcium 4*37 per cent, magnesium phosphate T34 per cent, a trace of calcium fluoride, other salts -88 per cent), and has generally been considered to contain about 3 6 per cent of organic substance ; but this Tomes has recently shown to be inaccurate : " That which has heretofore been set down as organic matter is simply water combined with the lime salts. The substantia adamantina is to be regarded as an inorganic substance composed of lime salts, which have been deposited in particular patterns and formed under the influence of organic tissues, which have themselves disappeared during its forma- ; The adamantine substance consists of calci- fied microscopic prisms, prismata adamantina, radiating from the surface of the ivory, on which their inner ends lie, to the surface of the crown, on which they terminate by free ends. These prisms are hexagonal in shape, solid, and of considerable length, for most of them reach from the ivory to the surface of the
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