A DESCRIPTION OF THE MOLAR TEETH AND INVESTING TISSUES OF NORMAL GUINEA PIGS

¹ Division of Dental Research, Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada

A description of the gross and microscopic structure of guinea pig molars and their supporting tissues has been presented, together with an account of the normal physiologic changes which occur with age and function. The report is based on a study of sections of the teeth and jaws of 16 normal guinea pigs, and of dried skulls of animals from 3 days to one year old. The points of divergence between this and previous descriptions, and of information in addition to that previously reported, are listed below.

As the molar teeth erupt, carrying with them reduced ameloblasts and stratum intermedium cells, the latter proliferate just before they reach the basal cells of the oral epithelium and assume the microscopic appearance of cells of the intermediate and basal layers of a stratified squamous epithelium. As eruption proceeds, these cells blend with the deeper layers of the oral epithelium.

The nature of the attachment of fibers of the periodontal membrane to the cartilage portion of the tooth has been described.

Secondary cementum forms over, and at each side of the cement pearls, in order to attach additional fibers.

The heavy collagen bundles, which form the interdental fibers of the periodontal membrane, are produced in the area immediately occlusal to the crest of the interdental septum, are carried occlusally with the teeth to which they are attached, and disappear just below the oral epithelium.

The pattern of deposition and resorption of the bony walls of the alveoli has been described. This pattern is the result of two main factors which dictate the direction and amount of movement of the molar teeth through the jaws: first, all of the molars increase both in length and diameter as the animal ages; second, the teeth are curved along their long axes, and the curvature decreases from the first to the fourth molar. The direction of the occlusal force on the teeth causes them to tip in their sockets, and the amount and rotation are related to the tooth curvature.