The American text-book of operative dentistry / In contributions of eminent authorities. Ed. by Edward C. Kirk.

  • Edward Cameron Kirk
Date:
1900
Catalogue details

Licence: Public Domain Mark

Credit: The American text-book of operative dentistry / In contributions of eminent authorities. Ed. by Edward C. Kirk. Source: Wellcome Collection.

Provider: This material has been provided by the Augustus C. Long Health Sciences Library at Columbia University and Columbia University Libraries/Information Services, through the Medical Heritage Library. The original may be consulted at the the Augustus C. Long Health Sciences Library at Columbia University and Columbia University.

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    fused together. Thus iu uinu the incisors arc formed oi' a sin<2;le cone, the truncated apex of which is compressed to form the wide cutting- edge (Fig. 1, (f). The canine or cuspid is a single cone, the apex of which is com- pressed into a trihech'al point, or pointed pyramid (b). The bicuspids are composed of two coiu^s fused together, the forms of the cones being (piitc distinct the entire k'ugth of the tooth, as iu the upper bicuspids (c). The typal upper molar is formed by the addition of the third cone to the l)icuspid form, as ])lainly noticed in the three roots and the primitive three cusps ((/). The usual ([uadrieuspid form is made by the addition of a cingule. The lower molar consists of four cones, which may be plainly distinguished by an analysis of its elements {e). Each cone in the structure of a tooth is surmounted by a cusp or tubercle. Extra cusps above the number of primary cones are but cingules or undeveloped cusps. In the genesis of tooth forms, therefore, the complex teeth, as the bicuspids and molars, are formed by the repetition and addition of cones and their accompanying cusps, both laterally and longitudinally of the jaw. 4. The Dental Arch.—The teeth of man are arranged around the margins of the upper and lower jaws in close contact, and have no Fig. 2. Square. Rounded Square. Rounded. Rounded V. The main types of the dental arch. interspaces between them. The basal arch is a graceful parabolic curve, with some variations which lead from the round arch to the incomplete parallelogram or even to a w^ell-defined V shape. These variations may be classified as follows: First: The square arch (Fig. 2, a). This is found usually in persons of strong osseous organization, of Scotch or Irish descent—i. e. of Gaelic extraction—and is probably derived in the first instance from a dolichocephalic people. The squareness is more or less dependent upon the prominence of the large canines, which stand out very markedly at the angles of the square. The incisors present a flat front and project slightly, with little or no curve of the incisive line. The bicuspids and molars fall backw\ard from the canines with no per- ceptible curve. The two sides are quite parallel, but sometimes there may be a slight divergence toward the cheek at the rear. This is the low form of arch which appears in the apes and some low races.