Methods: The work of adhesion (WOA) and maximum force of detachment (Fmax) were determined using a static bioadhesion model based on tensile testing of formulations applied to hydroxyapatite (HA) and pellicle-coated HA. In addition, because of the in vivo impact of saliva flow on retention of the dosage form, the substantivity of formulations under conditions of dynamic flow was studied using an adapted parallel plate flow model. Retention under dynamic conditions was facilitated by addition of triclosan as an insoluble marker.
Results: Tensile testing showed a clear positive relationship between Carbopol concentration and bioadhesion. Increasing the PEG 400 concentration in formulations containing glycerol, 2% w/w Carbopol and 0.30% triclosan produced a local minimum for both WOA and Fmax at 10% w/w. Values for WOA and Fmax decreased threefold in the presence of a salivary pellicle. Pearson's correlation coefficients of 0.87 and 0.97 were obtained for WOA vs Fmax for HA and pellicle-coated HA respectively. Relative retention performance under dynamic flow conditions was comparable to that observed using tensile testing. An excellent correlation was obtained for retention half-life and the elastic modulus (G') of the formulation.
Conclusion: The bioadhesive parameters WOA and Fmax of NADS exhibit a strong positive correlation with each other and with the G' of the formulation. The presence of a salivary pellicle markedly reduces the bioadhesive interaction between the NADS and the substrate.