Calcium hydroxide chelate cements

Unfortunately, although EBA cements have been subjected to a considerable amount of development, this work has not been matched by fundamental studies. Thus, the setting reactions, microstructures and molecular structures of these EBA cements are still largely unknown. In addition, the mechanism of adhesion to various substrates has yet to be explained. Such knowledge is a necessary basis for future developments. 

Skinner, Molnar Suarez (1964) studied the cement-forming potential of 28 liquid aromatic carboxylic acids with zinc oxide. Twelve yielded cohesive products of some merit. Of particular interest were cements formed with hydrocinnamic, cyclohexane carboxylic, p-tertiary butyl-benzoic, thiobenzoic and cyclohexane butyric acids. One of these cements is on the market as a non-eugenol cement. It is very weak with a compressive strength of 4 0 MPa, a tensile strength of 11 MPa and a modulus of 177 MPa, and is only suitable as a temporary material (Powers, Farah Craig, 1976). 

Pastes of calcium hydroxide with water have been used as pulp-capping materials for many years and it is the material of choice for this application (Granath, 1982). Its favourable tissue responses have been known for many years (Zander, 1939). It has a healing effect, for it induces the formation of hard tissues of reparative dentine when pulp has been exposed (Eidelman, Finn Koulourides, 1965). This action seems to be associated with its high alkalinity (pH 12-5) and consequent bactericidal and proteinlysing effect (Fisher, 1977). 

9-23 % zinc hydroxide 0-29 % zinc stearate in 7V-ethyl toluene sulphonamide 

The manipulation of calcium hydroxide paste is not easy, however, and Dougherty (1962) introduced the calcium hydroxide salicylate cements. These are based on the reaction between calcium hydroxide and salicylate esters and come in two-paste packs which are easy to mix in the dental surgery. 

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Table 9.7. Composition of a calcium hydroxide chelate cement American Dental Association, 1977)...

More recently, the question of the performance of light-cured resin-based calcinm hydroxide materials has been considered [41], In this study, the brand Biocal was compared with two self-cure calcium hydroxide chelate cements, Dycal and Hidro C. Two criteria were evaluated, namely water sorption and solubility, with pure water being the medinm in both cases. Results are shown in Tables 9.4 and 9.5. 

Physical and chemical properties of Biodentine are shown in Table 9.8. The material can be seen to set rapidly, and to have a reasonable compressive strength and Vicker s Hardness Number at 24h [85,86]. It shows a snbstantial wash out (solubility) in Hank s balanced salt solution (HBSS), which is presumably at least matched in deionized water. However, the pH of deionized water following storage of set Biodentine is only around 9 at 24h, rather than the 11-12.5 of traditional calcium hydroxide chelate cements or supersaturated solution. This may suggest that Biodentine is less bioactive than such materials, and hence less effective at promoting the growth of reparative dentine. 

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). 

Not unexpectedly in view of the related functions of luting and lining materials, most of the materials discussed in Section n.B as luting agents are more or less equally useful as cavity base and liner cements. Cements classified as cavity liners include the calcium hydroxide materials, the zinc phosphates, zinc chelating agents, polycarboxylates, and glass ionomers. 

Another chelate cement, zinc oxide-eugenol has been suggested as a treatment for exposed and inflamed pulp [61]. However, its use has been reported to canse adverse biological responses, including chronic inflammation and eventnal necrosis of the pulp [67,68]. As a result, its use is no longer recommended for direct application to the pnlp. However, its application with a calcinm hydroxide system as the means of retaining the calcium hydroxide remains widely nsed and is recommended. 

As well as chelate cements of this type, there are also curable calcium hydroxide cements available [39]. These materials have superior mechanical properties to the chelate-type calcium hydroxide cements [40] and also better chemical resistance [41], since they are not affected by treatment with phosphoric acid etchants. A typical example is Biocal , which has the composition shown in Table 9.2. 

From these tables, it can be seen that the resin-based calcium hydroxide shows substantially less water sorption and lower solubility than the two chelate-based cements. It has been snggested that high strength and low solubility are the desirable characteristics of a base or liner material in tooth repair because of the need to resist occlusal forces in service, and also to resist degradation and corresponding loss of function [41]. However, the evidence of the mechanism by which these materials act therapeutically does not support this suggestion, at least as far as resistance to degradation is concerned. 

Calcium hydroxide can be used as a supersaturated solution, as chelate cements and as a light-cured resin (in UDMA systems). 

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