CALCIUM HYDROXIDE IN CONSERVATIVE DENTISTRY

Editor's Notes

1. It is important to distinguish between two terms “liners” and “suspension liners”. Both terms should not be used synonymously. Liners (previously referred to as low-strength bases or cement liners or subbases) are materials placed in deep portions of the cavity preparations that harden when mixed to form a cement layer (100–500 μm) usually with minimum strength and low rigidity functioning as a barrier to irritating chemicals and providing therapeutic benefit to the pulp. Suspension liners are set by physical means (drying) and upon the evaporation of the volatile solvent form a relatively thin film (20–25 μm) that serves as a protective barrier between dentine and the restorative material and provides some therapeutic effect and provide no mechanical strength, no thermal insulation, and should only be used to line dentine.
2. Dycal® is a self-setting radiopaque calcium hydroxide material containing sulphonamide (plasticizer) butylene glycol disalicylate (setting activator), which was introduced back in 1962 (41). Life® is a self-curing calcium hydroxide–based material containing zinc oxide and a resin phase (methyl salicylate and butyl benzene sulphonamide). The setting reaction in both Dycal and Life leads to the formation of Ca-salicylate chelate through an acid-base reaction (Ca ions replace acidic phenolic protons in the carbonyl groups of the salicylate) thereby generating free water (by the combination of OH- from Ca(OH)2 with H+ from phenolic groups) absorbed into the structure of the setting materials. The presence of a resin phase is likely correlated with the low solubility of these materials, although the solubility values can be enhanced by the free water formation. Dycal and Life showed similar solubility (4.91% and 3.98%) and apparent porosity (9.04% and 7.49%) and water sorption (5.06% and 4.41%) values, all statistically lower than those of the other materials. The increase in free Ca ions together with a basic pH are undoubtedly connected with the appreciable formation of CaP deposits by both Dycal and Life. Moreover, the salicylate and zinc oxide in the composition, acting as Ca-chelating agents, probably facilitate the deposition of calcium phosphate (23): Gandolfi MG, Taddei P, Modena E, Siboni F, Prati C. Biointeractivity-related versus chemi/physisorption-related apatite precursor-forming ability of current root end filling materials. J Biomed Mater Res B Appl Biomater. 2013; 101(7): 1107-1123 Setting reaction: Lime-lite showed a high rate of water sorption (8.9%), but the solubility was very low (1.7%) and ion release scant, despite the manufacturer’s claims. The high water sorption is likely to cause a hygroscopic expansion. Calcium silicate and calcium hydroxide materials for pulp capping: biointeractivity, porosity, solubility and bioactivity of current formulations Maria Giovanna Gandolfi1 , Francesco Siboni1 , Tatiana Botero2 , Maurizio Bossù3 , Francesco Riccitiello4 , Carlo Prati1,5; 2015