Chelate cements

The calcium chelate cements are limited to the use of a cavity liner. They may be placed directly over an exposed tooth pulp to protect the pulp and stimulate the growth of secondary dentin, or used as a therapeutic insulating base under permanent restorations. The high alkalinity and high solubihty of these materials prohibits use in close proximity to soft tissues or in contact with oral fluids. 

The Lewis definition covers all AB cements, including the metal oxide/metal oxysalt systems, because the theory recognizes bare cations as aprotic acids. It is also particularly appropriate to the chelate cements, where it is more natural to regard the product of the reaction as a coordination complex rather than a salt. Its disadvantages are that the definition is really too broad and that despite this it accommodates protonic acids only with difficulty. 

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). 

Active zinc oxide is capable of forming chelate cements with a number of liquid organic chelates. These include the ) -diketones, ketoacids and ketoesters as well as the 2-methoxy phenols (Nielsen, 1963). 

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

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. 

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

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