INFLUENCE OF PROCESSING CONDITIONS ON THE RELEASE OF SODIUM-FLUORIDE FROM OLIGOMERIC L-LACTIC ACID MATRICES

Matrices were prepared in the shape of rods with a diameter of 4 mm an d a length of 10 mm. They were composed of oligomers of L-lactic acid (M(w) 2 550-11 730 Daltons) and micronized sodium fluoride particles. Sodium fluoride concentration was kept in the range 5-60%. Matrices we re prepared by melting the mixture of L-lactic acid oligomer and sodiu m fluoride. Two types of products according to the applied cooling rat e were prepared and evaluated for release characteristics in vitro. Si nk conditions of isotonic phosphate buffer solution pH = 7.4 at 37 deg rees C were maintained throughout the experiment. The concentration of dissolved sodium fluoride was determined by ion-selective electrode. It was documented that the release rate of sodium fluoride is strongly dependent on the molecular weight of oligomer. The effects of sodium fluoride concentration and cooling rate of melted mixture were evaluat ed by ANOVA, separately for each oligomer. The effect of sodium fluori de concentration was significant at each oligomer studied, while the i nfluence of cooling rate was significant with higher molecular weight oligomers. Moreover, this effect is ambiguous and dependent on the cap ability of oligomers to form crystalline phases and on the form and ge ometric arrangement of this phase. (C) 1996 Elsevier Science Limited