Eugenol, oxidation

Zinc oxide beds Zinc oxide eugenol Zinc oxides Zinc-oxygen cell... 

Antioxidants. Widely used antioxidants are eugenol, ionol, and the like. They retard premature oxidation of inks on the press rollers when used at low concentrations. 

In paints, zinc oxide serves as a mildewstat and acid buffer as well as a pigment. The oxide also is a starting material for many zinc chemicals. The oxide supphes zinc in animal feeds and is a fertilizer supplement used in zinc-deficient soils. Its chemical action in cosmetics (qv) and dmgs is varied and complex but, based upon its fungicidal activity, it promotes wound healing. It is also essential in nutrition. Zinc oxide is used to prepare dental cements in combination with eugenol and phosphoric and poly(acrylic acid)s (48) (see Dental materials). 

Zinc Oxide—Eugenol Cements. Zinc oxide—eugenol cements have many uses in dentistry. The admixture of powdered zinc oxide [1314-13-2] and Hquid eugenol [97-33-OJ, fotins a bland, easily mixed paste having exceUent working time but slow-setting characteristics. 

The compositions of zinc oxide—eugenol impression pastes are similar to those of the zinc oxide—eugenol cements (86). Variations in specific characteristics are achieved by the proportions of the ingredients (87). Properties vary in commercial products (88). The modifications of the zinc oxide—eugenol system intended for bite-registration pastes may include agents to increase the body or thixotropic character of the unset mix to improve... 

Zinc oxide—eugenol impression pastes are used primarily as corrective washes over compound impressions, as veneer impressions, as temporary liners or stabilizers in base-plates and dentures, and as bite-registration pastes for recording occlusal relationships in inlay, crown, and bridge techniques. 

This type of cement has been further improved by the substitution of -hexyl van ill ate [84375-71-3] and similar esters of vanillic acid [121 -34-6] and/or syringic acid [530-57 ] for eugenol (93—95). These substituted cements are strong, resistant to dissolution, and, unlike ZOE and EBA cements, do not inhibit the polymerization of resin-base materials. Noneugenol cements based on the acid—base reaction of zinc and similar oxides with carboxyhc acids have been investigated, and several promising types have been developed based on dimer and trimer acids (82). 

Calcium Chelates (Salicylates). Several successhil dental cements which use the formation of a calcium chelate system (96) were developed based on the reaction of calcium hydroxide [1305-62-0] and various phenohc esters of sahcyhc acid [69-72-7]. The calcium sahcylate [824-35-1] system offers certain advantages over the more widely used zinc oxide—eugenol system. These products are completely bland, antibacterial (97), facihtate the formation of reparative dentin, and do not retard the free-radical polymerization reaction of acryhc monomer systems. The principal deficiencies of this type of cement are its relatively high solubihty, relatively low strength, and low modulus. Less soluble and higher strength calcium-based cements based on dimer and trimer acid have been reported (82). 

By methylation with dimethyl sulphate and potash, it yields methyl-eugenol, boiling at 248° to 249° and which on oxidation yields veratric acid, melting at 179° to 180°. 

In the 1870s more effective liquid cement-formers were found ortho-phosphoric acid and eugenol (Wilson, 1978). It was also found that an aluminosilicate glass could replace zinc oxide, a discovery which led to the first translucent cement. Thereafter the subject stagnated until the late 1960s when the polyelectrolyte cements were discovered by Smith (1968) and Wilson Kent (1971). 

The Arrhenius definition is not suitable for AB cements for several reasons. It cannot be applied to zinc oxide eugenol cements, for these are non-aqueous, nor to the metal oxychloride and oxysulphate cements, where the acid component is not a protonic acid. Indeed, the theory is, strictly speaking, not applicable at all to AB cements where the base is not a water-soluble hydroxide but either an insoluble oxide or a silicate. 

This concept covers most situations in the theory of AB cements. Cements based on aqueous solutions of phosphoric acid and poly(acrylic acid), and non-aqueous cements based on eugenol, alike fall within this definition. However, the theory does not, unfortunately, recognize salt formation as a criterion of an acid-base reaction, and the matrices of AB cements are conveniently described as salts. It is also uncertain whether it covers the metal oxide/metal halide or sulphate cements. Bare cations are not recognized as acids in the Bronsted-Lowry theory, but hydrated... 

Unlike other aqueous dental cements, the zinc polycarboxylate retains plastic characteristics even when aged and shows significant stress relaxation after four weeks (Paddon Wilson, 1976). It creeps under static load. Wilson Lewis (1980) found that the 24-hour creep value for one cement, under a load of 4-6 MPa, was 0-7 % in 24 hours, which was more than that of a zinc phosphate cement (0-13 %) and a glass-ionomer cement (0-32%), but far less than that of the zinc oxide eugenol cement (2-2%). 

Zinc oxide eugenol ZOE) cements 9.2.1 Introduction and history... 

Molnar, 1942). Its use specifically to relieve toothache was recorded by Vigo in the sixteenth century and reactions with metal oxides were reported by Bonastre (1827a,b). The earliest zinc oxide chelate cements used creosote (King, 1872) and later this was mixed with oil of cloves (Chisholm, 1873). Then oil of cloves was used by itself (Flagg, 1875) and finally its essential constituent, eugenol (Wessler, 1894). 

Cement formation is the result of an acid-base reaction between zinc oxide and eugenol, leading to the formation of a zinc eugenolate chelate. Water plays a vital role in the reaction. 

Eugenol, 4 allyl-2-methoxy phenol, is capable of forming cements with ZnO, CuO, MgO, CaO, CdO, PbO and HgO (Brauer, White Moshonas, 1958 Nielsen, 1963). Other 2-methoxy phenols are also capable of forming cements with metal oxides, provided the allyl group is not in a 3- or 6-position where it sterically hinders the reaction (Brauer, Argentar Durany, 1964). These include guaiacol, 2-methoxyphenol, and the allyl and propylene 2-methoxy phenols. 

Eugenol is a very weak acid (p = 10-4) and will not react with zinc oxide in the absence of promoters. These reaction promoters include water, acetic acid and zinc acetate. 

The importance of water as an initiator and catalyst for the reaction between zinc oxide and plain eugenol has been demonstrated by a number of studies (Smith, 1958 Crisp, Ambersley Wilson, 1980 Batchelor Wilson, 1969 Prosser Wilson, 1982). In particular, the reaction is accelerated by the humidity of the atmosphere during mixing (Batchelor Wilson, 1969 Crisp, Ambersley Wilson, 1980). 

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