H.J. Prosser

Mechanism of adhesion of polyelectrolyte cements to hydroxyapatite

The interaction between polyacrylate ions and hydroxyapatite was examined using extraction techniques and infra-red spectroscopy. These studies have shown that polyacrylate ions become irreversibly attached to the surface of hydroxyapatite by displacing existing phosphate ions. The mechanism is not one of simple ion exchange, since calcium ions are displaced by the phosphate ions.

Glass-ionomer Cements of Improved Flexural Strength

The effect of glass and polyacid composition on cement strength has been investigated with a view to improving the glass-ionomer cements. The flexural strength of glass-ionomer cements was found to be greatly dependent on the glass and polyelectrolyte used to prepare them. Opaque and opal glasses containing crystallites tended to yield cements with high flexural strength. Flexural strength was also found to be increased by increasing the molecular weight of the polyacid. In water-setting systems, cement strength was shown to be critically dependent on the glasslpolyacid ratio.

Development and use of water-hardening glass-ionomer luting cements.

The current glass-ionomer luting cements, supplied as a powder and polyacid liquid, are still deficient in some areas. The two principal deficiencies are early solubility in saliva caused by the slow formation of a strong gel-salt and the clinical problem of judging the correct powder/liquid ratio because of the high viscosity of polyac:id liquids. There is a tendency to reduce the glass powder content to obtain a creamy consistency, which results in a weaker cement that is susceptible to aqueous attack. Loss of cement from the margins of the restoration can result in exposure of dentin and patient complaints of postoperative sensitivity. For this reason some manufacturers recommend the use of an insulating varnish. To overcome these problems recourse was made to a system developed at the Laboratory of the Government Chemist. (LGC) in 1969 by Wilson and Kent’ and tested clinically by McLean. At that time, gelation of the cement-forming liquid hindered the development of a practical system; one solution examined was that offered by water-hardening glass-ionomer cements. In this system the polyacid is freeze-dried and blended with the glass powder. Cement formation is initiated by mixing the blend with water. This development was set aside for dental application at that time in favor of the Aspa IV system (Dentsply International, DeTrey

Characterization of glass-ionomer cements 7. The physical properties of current materials

Abstract The physical properties of a number of glass-ionomer cements have been compared. Water-hardening cements were found to be easier to mix than conventional ones and there are some indications that they are more plastic. Otherwise, the properties of both types of cement are broadly similar. There are differences in electrical properties, which must reflect some differences in setting chemistry, but these differences are only maintained during the first 24 hours after mixing.

An infra-red spectroscopic study of cement formation between metal oxides and aqueous solutions of poly(acrylic acid)

An infra-red spectroscopic study of the formation of cements between metal oxides and aqueous solutions of poly (acrylic acid) is reported. Oxides of divalent metals form cement gels more readily than oxides of trivalent metals. An attempt was made to gain structural information from the observed frequency shifts of the absorption bands of the carboxylate groups in the metal poly(acrylate) gels relative to those recorded for the purely ionic form. The form of cation binding to the polyanion chain is discussed.

The Effect of Composition on the Erosion Properties of Calcium Hydroxide Cements

Calcium hydroxide - alkyl salicylate cements are based on bidentate chelate structures. All of the cements are hydrolytically unstable. The release of calcium, hydroxide, and salicylate ions into aqueous solution depends on the nature of the plasticizer.

Adhesion of carboxylate cements to hydroxyapatite: I. The effect of the structure of aliphatic carboxylates on their uptake by hydroxyapatite

An investigation was made into the effect of the structure and functionality of aliphatic carboxylates on their sorption onto hydroxyapatite with a view to ascertaining factors affecting the adhesion of polyacrylate cements to tooth materials. In general, the amount of carboxylate sorbed was found to increase with the number of groups contained in the molecule. Thus, polyacrylate was found to be much more strongly sorbed than low molecular weight species. Sorption of the low molecular weight species appeared to be related to stereochemical factors rather than to the stability constants of their calcium chelates.

Infrared Spectroscopic Studies on the Development of Crystallinity in Dental Zinc Phosphate Cements

An infrared spectroscopic study has been made of the development of crystallinity (hopeite) in dental zinc phosphate cements. Crystallization in the bulk of a cement is prevented only by the incorporation, in the liquid, of aluminum which forms complexes with phosphoric acid. The development of surface crystallinity is related to the chemical composition of the cement and the speed of the reaction. No acid phosphates are to be found in the matrix which consists solely of neutral orthophosphates.

The Effect of Additives on the Setting Properties of a Glass-Ionomer Cement

Studies of the setting behavior of glass ionomer cements formed from either glass powders and polyacid solutions or from glass-dry polyacid blends mixed with water have been carried out using an oscillating rheometer. Certain acids accelerate the setting rate, but none is as effective as D-tartaric acid. Bases added to the cements slow the setting reactions by partially neutralizing the acid.

Long-term monitoring of microleakage of dental cements by radiochemical diffusion

Radioactive 14C sucrose was found to be an ideal marker for microleakage because it did not penetrate tooth tissue, dental cement, or mounting resin. The main finding is that the adhesive cements--the glass-ionomer and polycarboxylate--are significantly more effective at preventing microleakage than are the traditional phosphate cements--silicate and zinc phosphate. The differences can be as high as two orders of magnitude. The adhesive cements provide almost perfect and reliable seals. By contrast, the nonadhesive cements are erratic sealants with most of the restorations leaking.