The American text-book of operative dentistry / in contributions by eminent authorities.
- Edward Cameron Kirk
- Date:
- [1905]
Licence: Public Domain Mark
Credit: The American text-book of operative dentistry / in contributions by eminent authorities. 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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![The mot is lontx, Hattciicd, and tajx-rin^ {<t, h, c). It is shorter tlian that of the upper canine. It is grooved on the mesial and distal sides,— so much so as to tend toward bifurcation. This, indeed, sometimes hap- pens in man, thereby ri'calling the Ibriu usual to the ])riniates and some other lower animals. The root canal is of tlie same general form as the root, often pre- senting the spindle shape on section. It is somewhat difficult to enter on account of its flattened shape and narrowed channel. Fig. 17. b c The upper bicuspids. ment of a root to support it. The Bicuspids. 12. The Upper Bicuspids.—The upper l)icus])id is formed by duplica- :ion of the primitive cone and cnsp in a transverse direction (Fig. 17, a), \'iewed from the standpoint of com- j)arative dental anatomy, the external cone is the (•(intiic cone—and to this is added the internal nr hictispirJ cone, the tooth being a double canine. The bi- cuspids are the first of the complex- teeth. Tile internal cusp is formed by the raising of the inner primitive cusp of the canine and the devclop- The distinctive feature of the architec- ture, therefore, is its formation from two cones, and this makes it a weak tooth as regards its mechanical structure and resistance to mas- tication, for the binding of the bases of the cones and cusps depends upon the connecting power of the two marginal ridges (h, b), and when these are destroyed the cones readily part and split off. The bicuspids in man are homologous with the ])remolars of the quadrumana and other lower mammals. They succeed and displace the molars or grinders of the deciduous set. They are placed next after the canines in both jaws, and midway between the cutting and grinding teeth. Their function is the crushing of food preparatory to mastication. The upper first bicuspid approximates the canine on the distal side. The buccal face (c) is of spear-head shape, similar to that of the canine. This is more apparent in some lower mammals than in man, in whom it is much reduced and rounded, so as to give usually the apjiear- ance of a long, rounded oval. Tiie buccal cusp (c) rises sharply and prominently from the lower centre of the face, from which a strong ridge (fJ) leads up to the cervical border. The mesial and distal lobes (e, e) are rarely conspicuous, and the furrows between them and the central ridge lead but half way up the crown. The lobes sometimes have prominent points at the morsal margins which in lower mammals become pro-](https://iiif.wellcomecollection.org/image/b21216617_0038.jp2/full/800%2C/0/default.jpg)
