Development of a novel papain gel formulation: Exploring different concentrations for smear-layer deproteinization and enhanced dentin bonding

Background: The self-etch adhesive system modifies but does not completely remove the smear layer, leading to the weakening of the bond strength due to the formation of a hybridized layer. Smear-layer deproteinization with papain enzyme partially removes the smear layer, and increases the bond strength with self-etch adhesive. The aim was to develop a deproteinizing agent with a high papain enzyme concentration to enhance dentin bonding with self-etch adhesives. Methods: Papain enzyme gel formulations (15 and 30 IU/g) were prepared and tested for physical stability, viscosity, pH, homogeneity, and organoleptic properties. Moreover, 64 teeth were used to test the deproteinization efficiency of the formed gel. Fourier transform infrared was used to calculate the ratio of organic to inorganic components of smear-layer after deproteinization with 15 and 30 IU/g papain gel and a 6 IU/g commercial papain gel. Moreover, tensile bond strength was measured after deproteinization and dentin bonding with self-etching adhesive for the same groups. A molecular modeling simulation was also performed to evaluate the protein-protein binding interaction, predict the conformational/orientation patterns, and estimate the binding energies of papain with collagen target protein. Results: Both 15 and 30 IU/g gels exhibited similar viscosity, pH, homogeneity, and organoleptic properties. However, after 60 s, the 15 IU/g gel was solid, while the 30 IU/g gel was half-solid. All tested groups decreased the amide:phosphate ratio and increased tensile bond strength. Binding complexes between papain and three deposited collagen-1 structures formed strong binding energies with high negative values and residue-wise binding patterns. Conclusions: The production of the papain enzyme gel with a concentration of 15 IU/g was successful. In addition, it demonstrated promising results when used as a smear-layer deproteinization agent.