Anodische Oberflächen- und Volumenoxidation graphitischer Materialien in neutralen und alkalischen wäßrigen Lösungen / Anodic Surface and Bulk Oxidation of Graphitic Materials in Neutral and Basic Aqueous Solutions

Anodic oxidation of graphitic materials in aqueous electrolytes is a complex process which may yield e.g. higher stage intercalation compounds and lamellar graphite oxides, acidic surface or defect oxides and gaseous or colloidal decomposition products. Kind and concentration of the electrolyte solution are the most important parameters to control this wide-spread distribution of products. Based on electrochemical and microscopic studies on HOPG and carbon fibres, a mechanistic concept of electrolyte effects is proposed:

In dilute aqueous solutions, attack of OH• radicals formed in the primary electrochemical step is the dominant reaction pathway leading to formation of covalent carbon-oxygen bonds. Due to their reactivity, OH• radicals are able to attack basal plane carbon sites and also to create 3-dimensional defect oxides. Dissociation or capture of OH• radicals - which is favoured in basic and in most concentrated neutral solutions, respectively, - results in less active radical species and limits the attack to thermodynamically less stable carbon atoms at edge sites which may be either oxidized or removed. Due to acidification of the diffusion layer of anodes even in neutral aqueous electrolytes, direct current oxidation always yields higher stage acid intercalation compounds and lamellar graphite oxide as by-products. This can be almost prevented by alternating current oxidation.

Antiseptic mouth rinses: an update on comparative effectiveness, risks and recommendations

PURPOSE

Antiseptic mouth rinses are widely recommended and marketed to improve oral health. This article summarizes current studies on the comparative effectiveness of selected antiseptic mouth rinses in controlling plaque and gingivitis, as well as risks associated with daily exposure, including salivary flow rate, oral cancer and wear of composite restorations.

METHODS

Electronic database searches were conducted using Google Scholar and PubMed to identify articles comparing the effectiveness of 4 commercially marketed antiseptic mouth rinses differing in active ingredients (0.12% chlorhexidine gluconate, essential oils (menthol, thymol and eucalyptol) and methyl salicylate, 0.7% cetylpyridinium chloride and 20% aloe vera gel) for controlling plaque and gingivitis. Criteria for inclusion included controlled clinical trials and systematic reviews appearing in English language publications evaluating the comparative effectiveness of the mouth rinses in controlling plaque and gingivitis, as well as risks associated with daily usage.

RESULTS

The majority of studies have shown mouth rinses containing chlorhexidine gluconate or essential oils and methyl salicylate provide clinically significant anti-gingivitis and anti-plaque benefits. Cetylpyridinium chloride has been found to provide only limited clinical benefits compared to inactive control mouth rinse. Inadequate evidence is available to evaluate the clinical effectiveness of aloe vera gel. Chlorhexidine, essential oils and cetylpyridinium have been found to be safe. However, limited data are available on the effects of the mouth rinse on wear patterns of dental restorations. Studies reviewed reported no significant difference in salivary flow rate related to alcohol based mouth rinse.

CONCLUSION

Research supports the effectiveness of antiseptic mouth rinses in reducing plaque and gingivitis as an adjunct to home care. Insufficient evidence is available to support the claim that oral antiseptics can reduce the risk of developing periodontitis or the rate of progression of periodontitis.