Hybridization of the dentin with resin by monomer interdiffusion has been i
dentified as the basic bonding mechanism resulting in an intimate interlock
ing of the cured resin with the dentin. Today, growing efforts are made to
simplify and shorten the bonding procedures, e.g. by combining the function
s of primer and adhesive. Ultrastructural investigations using high-resolut
ion optical technology provided exciting insight into the interactions of b
onding systems and dentin. It became clear, that the maintenance or recover
y of microporosities in the dentin is most important for optimal hybridizat
ion. This can be achieved by the moist bonding technique, which is mandator
y in acetone-based systems. The observation that certain bonding systems ar
e able to bond to dentin depleted from the demineralized collagen network r
aised the question of whether the collagen-resin interdiffusion mne really
represents a prerequisite for successful bonding to dentin. The use of stro
ngly acidic primer monomers introduced the concept of "self-etching" primer
s not only to dentin but also to enamel, which eliminates the necessity of
a separate conditioning step. Clinical investigations are necessary to eval
uate the potential of recently developed all-in-one products which combine
the functions of conditioner, primer, and adhesive. With improvements in de
ntin bonding and the development of new resins that exhibit little or no sh
rinkage upon polymerization, even greater applications for adhesive technol
ogy will be found in dentistry.