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.
Mechanical properties of visible light-cured resins reinforced with hydroxyapatite for dental restoration.
OBJECTIVES
The purpose of this study was to measure and analyze the mechanical properties of several composite materials designed for dental restoration.


METHODS
The materials were composed of a visible light-curing monomer mixture (either Bis-GMA+TEGDMA or Bis-GMA+HEMA) as a matrix and hydroxyapatite (either microscopic or nanoscopic particles) as a reinforcing filler. The surface of the hydroxyapatite particles was modified by using a coupling agent (citric, malic, acrylic or methacrylic acid). Five specimens of 14 different composites were prepared for each mechanical test: flexural strength, Young's modulus and Vickers hardness. Mean values and standard deviations were calculated, and ANOVA and Student Newman Keuls multiple comparison tests were applied (P < 0.05).


RESULTS
The addition of 50-60 wt% of hydroxyapatite particles to the unfilled monomer mixtures led to the increase of both Young's modulus and surface hardness of the material, while the flexural strength decreased. In general, when microscopic instead of nanoscopic hydroxyapatite was used as a reinforcing filler, mechanical properties were favored. The mechanical properties were also improved by adding citric, acrylic or methacrylic acid as a coupling agent.


CONCLUSIONS
An adequate surface modification of the hydroxyapatite particles conferred enhanced mechanical properties to the final dental composite. Microscopic-hydroxyapatite particles are preferred to nanoscopic ones.
Reactions in Glass Ionomer Cements: II. An Infrared Spectroscopic Study
The transmission and attentuated total reflectance spectra of a dental cement formed from an aluminosilicate glass and aqueous polyacrylic acid (ASPA) are reported. Interpretation of spectra show that a siliceous hydrogel is formed together with the polyacrylate salts of calcium and aluminum. In the fully hardened cement a minor proportion of -COOH remains unconverted to — COO- groups for steric reasons.