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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 polymeric material. They were found to obey Hooke's 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.

The changes that occur in human teeth with increasing age probably include a loss of water. Intact whole teeth and teeth with enamel and pulp contents removed showed loss of water on dehydration at 105 C. Old teeth showed less water loss than young teeth.One of the most pervasive changes with advancing age in man is the progressive loss of water from the connective tissues. An increased accumulation of collagen and a decrease in mucopolysaccharidesl accompany this water loss. Comparison of the thoracic aorta, myocardium, and skin of the normal fetus with similar organs from man between 4 months and 86 years old showed 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.

Investigations of cationic interactions with proteins have been relatively few as compared with the extensive studies done with organic anions. Recent work, however, has indicated that interactions with cations show some similarities as well as some major differences to interactions with anions.' Quantitative comparisons of binding ability by the equilibrium dialysis method have shown that, among ions of equal size, organic cationic dyes are bound much less than organic anionic dyes by plasma albumin.' On the other hand, Glassman2 has observed that long chain detergents form a stoichiometric complex with plasma albumin, in which the number of detergent molecules corresponds closely to the number of carboxyl groups on the protein.Examples of organic cations of considerable importance in the biological sciences are the group of synthetic agents commonly referred to as local anesthetics. As is well known, local anesthetics are drugs that in sufficient concentration are capable of blocking nerve conduction along both sensory and motor fibers. When carefully controlled concentration is used, it is possible to produce loss of sensation without motor paralysis because sensory fibers are always affected before motor fibers. Most local anesthetics, when used properly, can produce anesthesia in a ceratin definite portion of the body without producing a systemic effect. Some of the anesthetic agents exert not only a local action but also a central one. The synthetic agents, however, have slight effect on the central nervous system, and it was a select group of these agents that was chosen for this study of the interaction of these agents with blood-serum proteins.Various organic compounds are effective local anesthetic agents, and their usefulness in the treatment of patients has been demonstrated. On the other hand, certain limitations to the effectiveness of the drugs have resulted from unfavorable side effects that develop in some patients following increasing concentrations of the drugs. If these side effects, which become quite serious in some patients and result in necessary withdrawal of the drugs, could be eliminated, then the usefulness of the drugs could be greatly extended. The plasma proteins, by interacting with small organic ions and molecules, render them biologically inactive, thus decreasing the concentration of free drug and in turn reducing the toxic effects.3 Also, the interaction between local anesthetics and the plasma proteins would aid in the transport of the compounds from one

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