Effect of soft tissues on radiographic measurements of the head

Influence of dentine on the pulpward release of eugenol or acids from restorative materials

The diffusion gradient which develops across dentine and the clearance into the capillary circulation at the pulpal side of the tissue both reduce the concentration of potential toxins applied to dentine, thus protecting pulpal cells. The data presented on eugenol indicates that when release of a potential toxin from a solid material is hydrolytic the limited wetness of dentine, i.e. the limited availability of water for hydrolysis, contributes to the protective effect of the tissue. The data on strong acids indicates that a third protective mechanism, buffering by hydroxyapatite, can contribute to dentine's protective effect in situations where the potential toxin is strongly acid. There may be other mechanisms by which dentine protects the pulp against chemical toxins from restorative materials. However, the three described: diffusion limitation; limited wetness for hydrolysis; and buffering by dentinal hydroxyapatite, appear to allow the relatively safe use of a wide range of tooth restorative materials.

Effect of eugenol on respiration and division in human pulp, mouse fibroblasts, and liver cells in vitro

Eugenol depressed cell respiration in homogenates of human dental pulp and in mouse fibroblast monolayers. The depression was concentration-dependent, with a threshold at about 10(-4)M and a maximum at 10(-3)M in both preparations. Onset of the depression appeared to be rapid. The effects of variation in both duration and concentration of eugenol exposure on subsequent uptake of 3H-thymidine were examined in mouse fibroblast monolayers and human pulp explants. Fibroblasts survived short-term (up to 12 hr) exposure to 10(-3)M eugenol or less, but died after exposure to 10(-3)M for one day or more. The cells survived exposure to 10(-4)M for ten days, the longest period examined. Human pulp maintained in tissue culture medium showed similar eugenol susceptibility. Analysis of these data, when coupled with those of previous studies on eugenol release from ZOE and diffusion through dentin, gives strong support for the concepts that: the blandness of ZOE when applied to intact dentin is due to eugenol reaching the pulp in sub-toxic concentrations, and the irritant effect of ZOE when applied directly to soft tissue is due to the development of concentrations of eugenol in tissue adjacent to ZOE sufficient to inhibit respiration and thus kill cells.

An analysis of the release and the diffusion through dentin of eugenol from zinc oxide-eugenol mixtures

Tritium-labeled eugenol was released from mixtures of zinc oxide eugenol (ZOE) into aqueous solution at rates which declined exponentially with time, and which were directly proportional to the liquid-powder ratio. The release pattern was consistent with a model of progressive hydrolysis of zinc eugenolate in a limited-thickness ZOE surface layer. Intervening dentin had a profound effect on this pattern of release. In human teeth in vitro containing ZOE as a base or temporary filling, peak eugenol release at the pulpal surface of dentin was of the order of a thousand-fold less than that at the salivary surface. In such teeth, eugenol reached concentrations in excess of 10(-2) M in dentin just beneath ZOE, and 10(-4) M or less adjacent to the pulp space. Both pulpal outflow and dentin concentrations of eugenol remained relatively constant for more than a week, unlike release into aqueous solution. While these data were derived from studies on human teeth in vitro, they give a strong indication of probable events in vivo, and appear to provide a basis for the explanation of the paradox of the therapeutic and toxic actions of ZOE.

Effect of eugenol on constrictor responses in blood vessels of the rabbit ear

Aqueous solutions of eugenol depressed vasoconstrictor responses to exogenous norepinephrine (NE), histamine, and peri-arterial sympathetic nerve stimulation in the isolated central artery of the rabbit ear and in the isolated perfused whole rabbit ear. The depression was dose- and time-dependent, and was slowly reversible. Eugenol appeared to act as an inhibitor of smooth muscle contractility.