The protective effect of zinc on rosin and resin acid toxicity in human polymorphonuclear leukocytes and human gingival fibroblasts in vitro.

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Abstract

Combinations of rosin and zinc are used in dentistry as components of periodontal dressings and cements and as root canal sealers. The composition and properties of rosins differ largely depending on source and refinement processes. Rosin (colophony) is composed of approximately 70% resin acids. In order to study the toxic effects of different natural rosins and purified resin acids and the detoxifying effects of zinc, these compounds were analyzed and tested on human polymorphonuclear leukocytes (PMN cells) and human gingival fibroblasts using the radiochromium release method. The rosins and the pure resin acids showed a strong dose-related cytotoxicity, which was inhibited by increased zinc concentrations. The purified resin acids (isopimaric, levopimaric, and neoabietic acid) were more toxic than the natural rosins. The contents of these resin acids might explain the difference in toxicity of the rosins tested. It is concluded that rosin and zinc are not to be considered inert compounds and that the cytoprotective effects of zinc and its role in dentistry products merit further investigations.

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Factors affecting the long-term results of endodontic treatment.

Ulf Sjögren, Björn Hägglund, Göran Sundqvist … (1990)

The influence of various factors that may affect the outcome of root canal therapy was evaluated in 356 patients 8 to 10 yr after the treatment. The results of treatment were directly dependent on the preoperative status of the pulp and periapical tissues. The rate of success for cases with vital or nonvital pulps but having no periapical radiolucency exceeded 96%, whereas only 86% of the cases with pulp necrosis and periapical radiolucency showed apical healing. The possibility of instrumenting the root canal to its full length and the level of root filling significantly affected the outcome of treatment. Of all of the periapical lesions present on previously root-filled teeth, only 62% healed after retreatment. The predictability from clinical and radiographic signs of the treatment-outcome in individual cases with preoperative periapical lesions cases was found to be low. Thus, factors which were not measured or identified may be critical to the outcome of endodontic treatment.

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Toxic effects of some conifer resin acids and tea tree oil on human epithelial and fibroblast cells.

Thor A. Söderberg, Anders Johansson, Rolf Gref (1996)

The present study was undertaken to assess and compare the in vitro cytotoxic effects of three resin acid analogues: dehydrobietic acid, podocarpic acid, O-methylpodocarpic acid; an essential oil from Australia (tea tree oil); and tapped oleoresin from Thailand, on human epithelial and fibroblast cells, using a quantitative neutral red spectrophotometric assay. All of the investigated compounds except for tea tree oil exhibited a cytotoxic activity which was proportional to their concentrations and time of exposure up to 24 h, i.e. higher concentrations and longer time of exposure caused increased cell death. Dehydroabietic acid and the oleoresin were the most toxic compounds followed by O-methylpodocarpic acid, whereas podocarpic acid and tea tree oil showed a lower level of toxicity. On the basis on these findings it is concluded that an isopropyl group on the aromatic C-ring is of great importance for the cytotoxicity of the tested abietane resin acids, thus indicating that the cytotoxic activity of oleoresins most probably is caused by synergistic or additive effects of resin acids. The results from this work support the view that antibacterial activity parallels cytotoxic activity which suggests a similar mode of action, most probably exerted by membrane-associated reactions.

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Antibacterial activity of gutta-percha cones attributed to the zinc oxide component.

W R Moorer, J Genet (1982)

Growth of several species of bacteria was inhibited by the presence of endodontic gutta-percha cones. Microbiologic analysis, measurement of osmolarity, microscopy, x-ray diffraction analysis, and scanning electron micrography were used to identify the biologically active component that slowly leaches from gutta-percha cones. This component is zinc oxide in the form of small solid particles, from which active, soluble Zn2+ ion is mobilized by hydrolysis. A hypothesis on the "depot" effect of the ZnO particles is formulated, and is used to discuss some earlier reported literature on toxic and antibacterial activity of zinc oxide-containing materials. It is concluded that zinc oxide is not to be considered an inert compound. Its widespread uses in medicine and dentistry seem to reside in its "inert," biocompatible, and astringent properties mainly. The biologically active role of zinc oxide, however, merits further investigation.