Gustav W. Rapp

Composition and Mechanical Properties of Gutta-Percha Endodontic Points

Gutta-percha endodontic filling points were found to contain approximately 20% gutta-percha (matrix), 66% zinc oxide (filler), 11% heavy metal sulfates (radiopacifier), and 3% waxes and/or resins (plasticizer). The mechanical properties were indicative of a partially crystalline viscoelastic polymerfc material. They were found to obey Hookes law and displayed a prominent upper and lower yield point when stressed beyond the proportional limit. The essential differences in mechanical properties of individual brands were found to be a function of the gutta-percha and zinc oxide concentration.

Composition and physical properties of gutta-percha endodontic filling materials

Gutta-percha has been the predominant root canal filling material for over a century. It has been used in various filling techniques and its effect on biologic tissues has been studied; however, knowledge of its chemical and mechanical properties has grown little since its introduction into dentistry. In this investigation, the mechanical properties of five brands of gutta-percha endodontic filling materials were determined, and their chemical compositions were compared. Significant correlations were found to exist between some of these parameters.

Effect of Age on Water Content in Human Teeth

a significant increase of collagen with respect to the mucopolysaccharides.2 A general statement has been made that the ratio of mucopolysaccharides to collagen decreases with age.3 Most the bulk of the human tooth is dentin. It is a well-known fact that with aging there is a continuous apposition of dentin on the pulpal surface of the tooth, which adds to the quantity of dentin. Ground sections of root dentin in old teeth show a transparency when examined microscopically. Moreover, such dentin resists the permeation of dyes. Such transparent dentin is composed of marrow-calcified tubules-sclerotic dentin.4 7 Sclerosis of dentinal tubules occurs after the odontoblastic process degenerates or dies. Odontoblasts become fewer in number as the surface area of the pulp chamber

An enzymic theory of local anesthesia

4 NESTHESLA may be defined as a physiologicall;y reversible condition a produced by some agent or technique, in which there is an absence of sensations. A sensation may be said to be an interpretation of a stimulus arising somewhere in or outside of the body. It is clear that in order for us to interpret the effect of the stimulus it must reach the brai:n. The pathways over which the stimuli are transmitted to the brain are, of course, the nerves. The stimuli are received at their starting points by definite ch.aracteristic structures, the sensory receptors, In the light of the foregoing, anesthesia results when either the receptors, the nerves, or the brain are not functioning. If the nerves are prevented from carrying the impulses, we have regional, or local, or truncal anesthesia. If the brain is rendered physiologically nonfunctional, the condition is general anesthesia, while when the receptors are not capable of receiving the stimuli, we have topical or surface anesthesia. This discussion will concern itself only with the first type mentioned : nerve block or local anesthesia.