Crystal Growth of Hydroxyapatite In Vitro and Dental Calculus and Plaque Formation on Human Teeth In Vivo

Abstract

1. ABSTRACT Sodium polyvinylphosphonic acid (SPVPA) was synthesized using vinyl phosphonyl dichloride and azobisisobutyronitrile (AIBN) as a radical initiator. The homopolymer obtained was characterized by molecular weight, purity and impurities by using gel permea-tion chromatography and NMR. The pure polymer was used to assess the influence on crystal growth kinetics of hydroxyapatite (HAP) in vitro. Briefly, the experimental solution supersaturated with respect to hydroxyapatite (HAP) was prepared from stock solutions of CaCl2, K2HPO4, KH2PO4, and NaC1. The crystal growth was initiated by adding pure seeds of HAP at 37 °C. The precipitation kinetics was followed using a pH-stat and measuring calcium phosphate in the solution. The effect of the polymer on the crystal growth kinetics was assessed, and it was found that the polymer inhibited the growth at 10-5 M. The inhibitory effect of the polymer was related to its adsorption onto the growing crystals. The adsorption parameters were derived from an adsorption isotherm-yielding a K value of 1,950 m1/mM and the N value of 0.038 mM/m 2. A topical application of 1% solution of the polymer onto teeth was effective in reducing calculus formation by 18% in rat model system. SPVPA was also very effective in reducing adsorption (>90%) of radio-labelled bacteria, Streptococcus mutans, and Actinomyces viscosus, onto saliva-coated hy-droxyapatite beads and disks. The polymer was also tested in short-term human clinical studies and showed that 1% and 3% solutions significantly (P = 0.05) reduced bacterial plaque film on teeth by 21 to 36%, respectively. Collectively, the data indicated that the Water Soluble Polymers, edited by Amjad Plenum Press, New York, 1998 91