Schematic illustration of the instability of the hybrid layer
. Apatite crystals are removed from dental hard tissues with acid conditioning and should be replaced by resin monomers. Note the incomplete infiltration of the adhesive in the collagen matrix that remains with interfibrillar spaces saturated with water (arrow). In addition, the possibility of discrepancy between the depth of infiltration of the adhesive and that of conditioned dentin leaving collagen exposed without hybridizing. The resin tags partially seal the dentinal tubules and decrease the permeability of the dentin. The resin monomers do not penetrate homogenously into the collagenous network (double arrow) [58
] (with permission).