Principles and practice of operative dentistry / by John Sayre Marshall.

  • Marshall, John Sayre, 1846-1922.
Date:
1901
Catalogue details

Licence: Public Domain Mark

Credit: Principles and practice of operative dentistry / by John Sayre Marshall. 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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    below; molars, three above, three below, equals sixteen on either side of the median line, or thirty-two in all. The ten anterior permanent teeth of each jaw are sometimes called the teeth of replacement, or succedaneous teeth, from the fact that they replace the deciduous teeth. The permanent incisors and cuspids take the x)lace of the temporary teeth of the same name, while the bicuspids assume the positions occupied by the temporary molars. The permanent molars appear one by one behind the position occupied by the second deciduous molars. DESCRIPTIVE ANATOMY OF THE TEETH. The teeth are specialized organs of mastication implanted within the alveolar processes of the superior and inferior maxillse in man and in many animals. The teeth are composed of five tissues (Fig. 4) : a vitreous-like substance which completely covers the crown—the enamel (1); a bone-like substance which envelops the root—the cementum (2) ; and a hard substance, less dense than enamel but harder than bone, which forms the interior or body of the organ—the dentin (3) ; while a small mass of soft tissue occu- pies a central cavity (4) within the crown and the root—the pulj); and a fibrous membrane covers the cementum of the root—the pericementum. In a normally developed individual of the genus homo the teeth are arranged in the form of two parabolic or elliptical curves, the su^oerior arch describing a trifle larger curve than the inferior, so that the teeth of the former slightly overreach their antagonists in the latter. The buccal cusps of the ux^iDer bicuspids and molars close over the buccal cusps of the lower teeth; this brings the buccal cusps of the lower teeth within the sulci of the upper, and the palatal cusj)S of the upper teeth within the sulci of the lower. The incisors, cuspids, and bicuspids of the lower jaw are smaller than the corresponding teeth in the upper, the greatest differ- ence being in the size of the incisors. The superior incisors and cuspids are slightly longer than the inferior and overlaj) them, while the cuspids and molars not only overreach their opposites in the inferior maxilla, but so interlock at their occlusal surfaces that each tooth, except the third sux^erior molars, occludes or antagonizes with two of its fellows in the opposite jaw, when the teeth are brought into their normal occlusion. (Fig. 5.) This arrangement permits the whole of the occlusal surfaces of these teeth to be brought into contact by the various movements of the jaws in mastication, thus rendering the function of triturating the food and pre- paring it for digestion most effective. A normal incisor tooth presents certain characteristics which are com- mon to all the dental organs of man ; it will therefore serve the purpose of illustrating the anatomical divisions of the teeth, which are as follows : the crown, the cervix, the root, the pidp-chaml>er, the pulp-canal, the morsal-'<^ or cutting edge, the apex, and the apical foramen. A more minute description relative to the cusps, surfaces, angles, margins, grooves, fissures, etc., will be reserved for the special anatomy of the individual teeth. * The term morsal is used, following the suggestion of Dr. Thompson, in the-place of incisive or cutting edge and occlusal surface.