J, Dent. 1991; 19: 3-l 3 3 Review Calcium hydroxide in restorative dentistry A. Milosevic Department of Clinical Dental Sciences, School of Dentistry, University of Liverpool, UK ABSTRACT This paper reviews the various calcium hydroxide preparations available for use in restorative dentistry and their constituents. The significance of individual constituents in relation to the properties of such materials and their mode of therapeutic action with respect to the dentine pulpal response and antibacterial activity is discussed. Applications of calcium hydroxide in restorative dentistry are also reviewed. KEY WORDS: Calcium hydroxide, Restorative dentistry, Review J. Dent. 1991; 19: 3-l 3 (Received 16 May 1990; reviewed 10 July 1990; accepted 10 September 1990) Correspondence should be addressed to: Mr A. Milosevic, Department of Clinical Dental Sciences, School of Dentistry, University of Liverpool, Pembroke Place, PO Box 147, Liverpool L69 3BX, UK. INTRODUCTION Calcium hydroxide preparations are used extensively in restorative dentistry as a therapeutic cavity liner, as an interim root canal dressing to induce hard tissue formation in various endodontic situations, and as the basis of permanent root canal sealers. This extensive usage, however, is not matched by clear understanding of how calcium hydroxide promotes osteodentine bridge formation nor its putative anti- bacterial activity, although hard tissue repair in pulp capping and in the periapical tissues after calcium hydroxide treatment has been widely reported (Glass and Zander, 1949; Berman and Massler, 1958; Stanley and Lundy, 1972; Schroder, 1973; Tronstad, 1974; Hendry et al., 1982; Holland and de Souza, 1985). The first part of this paper endeavours to review the tissue reactions and therapeutic activity of calcium hydroxide and aims to identify the areas of confusion that still exist. The applications of calcium hydroxide within restorative dentistry have widened with the great range of preparations now available. The second half of this paper discusses these applications. Indeed the long history and wide application are further surprising since this alkaline material is inherently non-biocompatible (Granath, 1982). Currently there is a wide range of commercially available products, but no specification for calcium hydroxide-based cements,. dressings or sealers. Some manufacturers utilize technical data relating to American Dental Association Specification No. 30 for zinc oxide @ 1991 Butterworth-Heinemann Ltd. 0300-5712/91/010003-011 eugenol cements, but most do not specify the chemical constituents in the product literature and some change the constituents or their proportions without notice. TISSUE REACTIONS AND THERAPEUTIC ACTIVITY OF CALCIUM HYDROXIDE Material constituents and effect on solubility The constituents and the proportions of commercially available calcium hydroxide cements vary from product to product. De Freitas (1982) and Prosser et al. (1982) have characterized calcium hydroxide preparations, and Table I is based upon their results. However, like all other dental cements, calcium hydroxide cements set by an acid-base reaction, the phenolic group in the alkyl salicylate ester acting as an acid (Prosser et al., 1979). Once set, therapeutic activity of the set material will depend upon the release of CaZ+ and OH- which can only occur if the cement is water soluble. It is the nature of the plasticizer that imparts this solubility. Currently, most cements set by some of the available Ca(OH), reacting with the salicylate ester chelating agent in the presence of a toluene sulphonamide plasticizer. The latter is hydrophilic and soluble. The set cement contains a matrix of calcium-a&y1 salicylate chelate, and excess unreacted calcium hydroxide. The fragility of the set cement suggests that the chelates are held together by weak secondary attractions rather than a