Bioadhesion and retention of non-aqueous delivery systems in a dental hard tissue model

Effective delivery of active agents to dental hard tissues is critical to product performance and pertinent to biofilm control, caries, erosion, hypersensitivity and tooth bleaching. The aim of this study was to investigate in vitro the bioadhesion and retention behaviour of non-aqueous delivery systems (NADS) based on glycerol, PEG 400, Carbopol 974P and triclosan.

Tensile testing was employed to calculate the work of adhesion (WOA) and maximum force of detachment (F(max)) for formulations applied to hydroxyapatite (HA) and pellicle-coated HA surfaces (HAP). Formulation substantivity under conditions of dynamic flow was studied by monitoring the release of incorporated triclosan. The release data were fitted to a first-order model to generate a removal half-life (t(1/2)).

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 F(max) at 10% (w/w). Values for WOA and F(max) decreased threefold in the presence of a salivary pellicle. Good correlations were obtained between (i) WOA and F(max) and (ii) WOA and t(1/2) and (iii) the elastic modulus of the formulations and t(1/2).

The presence of a salivary pellicle markedly reduced the bioadhesive interaction between the NADS and the substrate. Increased Carbopol content appeared to be the dominant factor in promoting the WOA, elasticity and retention of NADS to HA surfaces. Such formulations might provide a suitable platform for developing systems suitable for promoting retention to hard surfaces within the oral cavity.