Journal of Dental Research, Vol 64, 1405-1408, Copyright © 1985 by International & American Associations for Dental Research Online Journals
Adsorption of zirconyl salts and their acids on hydroxyapatite: use of the salts as coupling agents to dental polymer composites
D. N. Misra
Zirconyl methacrylate (I) and zirconyl-2-ethylhexanoate (II) were
synthesized, and their adsorption isotherms from solutions onto synthetic
hydroxyapatite were studied. The isotherms of methacrylic and
2-ethylhexanoic acids were also determined from the same solvents. The
adsorption of I was irreversible from methylene chloride, and that of II
was irreversible from cyclohexane. The adsorption in both cases was
constant from solutions above a certain concentration, and exhaustive below
this threshold concentration. Both compounds rendered the dried apatite
powder extremely hydrophobic; however, the adsorbate was slowly washed off
by excess water. The configuration of the adsorbate molecules, deduced from
the maximum adsorption and other adsorption characteristics of the two
compounds, indicated that: (i) in both cases the adsorbate may be held to
the surface by concerted hydrogen bonding of the carboxylate and zirconyl
oxygen atoms; and (ii) the hydrocarbon moieties in both adsorbates expose
themselves toward the solution, thereby making the dried surface
hydrophobic. The adsorptive behavior of the respective acids was similar to
that of the salts. Polymer, filled with synthetic hydroxyapatite covered
with irreversibly adsorbed I, had a diametral tensile strength about 50%
greater than that of the polymer filled with untreated apatite. The
strength of the composite was not affected by treatment of the apatite with
II or with the acids.
