[Formulation of photocurable bonding liner and adhesion to dentin. Effect of photoinitiator, monomer and photoirradiation].

An investigation was undertaken to evaluate the effect of both photoinitiators (camphor-quinone-amine systems) and the adhesion promoting monomer (4-MET) on photopolymerization of bonding liners and their adhesion to dentin. Photopolymerization of bonding liners was measured with differential scanning calorimetry (DSC). The bonding liner containing 2-(dimethylamino)ethyl methacrylate (DMAEMA) as a reducing agent decreased the rate of polymerization in the presence of 4-MET. On the other hand, the bonding liners containing N-phenylglycine (NPG) and N,N-dimethylaniline derivatives as a reducing agent showed good polymerization in the presence of 4-MET. The results of the tensile bond test suggested that bonding liners containing NPG and 4-(dimethylamino)benzoic acid (DMABA), one of the N,N-dimethylaniline derivatives, with or without 4-MET bonded well to dentin treated with EDTA 3-2. NPG and DMABA are recommended not only as reducing agents but also as aids in the diffusion of monomers into the dentin substrate. The relationship between the strength of the bond to dentin and photoirradiation of the bonding liner and composite resin was studied. Elongation of photoirradiation of both the bonding liner and composite resin was effective in impacting the strength of the bond to dentin. Furthermore, sufficient photoirradiation of the bonding liner prior to any filling of composite resin was especially important to obtain high bond strengths. SEM and TEM observations supported good adhesion being achieved by hybrid formations between photocurable bonding liners and dentin.