IADR Abstract Archives
High-Resolution Modulus Mapping of the Adhesive-Dentin Interface
Objectives: 10-methacryloyloxydecyl dihydrogen phosphate (MDP) has been used with additional co-monomers, such as hydroxyethyl methacrylate (HEMA) and/or 4-methacryloyloxyethyl-trimellitic acid (4-MET), mainly to enhance the chemical bonding properties. However, the use of co-monomers may compromise the rigidity of the adhesive–dentin interface.
Methods: Three non-carious human third molars were used. Four dentin disks were then prepared by making parallel cuts perpendicular to the longitudinal axis. The ground dentin surfaces were treated with MDP-based self-etch adhesives with HEMA and/or 4-MET co-monomers. The flowable composite (MI Flow II A2, GC Co. Ltd, Tokyo, Japan) was then placed on the bonding resin and light-cured. G2-Bond Universal (GC Corp., Tokyo, Japan) is a representative two-step HEMA-free adhesive containing 4-MET in 1 primer, whereas SE BOND 2 (Kuraray Noritake Dental Inc., Tokyo, Japan) is formulated with HEMA in both the primer and bonding portions. The chemical formulations of the adhesives are shown in Table 1. We used high-resolution modulus mapping and typical dynamic indentation test across the adhesive-dentin interface to discern the in situ mechanical properties of each target region at the nanoscale.
Results: HEMA increases the diffusion properties of MDP into dentin structures. However, the rigidity of the adhesive–dentin interface indicated by the storage modulus was markedly lower in G2-H20-15, G2-H20-30 and SE than in G2. Dynamic indentation testing revealed that the bonding layer was more deformable in the presence of HEMA. Moreover, the presence of MDP in the bonding layer might also increase the deformability because the polymerization linearity allows a large degree of viscoelasticity. These factors also diminish the rigidity of the adhesive–dentin interface.
Conclusions: 4-MET is a better co-monomer than HEMA in MDP-based dental adhesives. Modulus mapping and nanoindentation are introduced as new tests for the dentin-adhesive interface to address queries about the effectiveness of dental adhesives.
Methods: Three non-carious human third molars were used. Four dentin disks were then prepared by making parallel cuts perpendicular to the longitudinal axis. The ground dentin surfaces were treated with MDP-based self-etch adhesives with HEMA and/or 4-MET co-monomers. The flowable composite (MI Flow II A2, GC Co. Ltd, Tokyo, Japan) was then placed on the bonding resin and light-cured. G2-Bond Universal (GC Corp., Tokyo, Japan) is a representative two-step HEMA-free adhesive containing 4-MET in 1 primer, whereas SE BOND 2 (Kuraray Noritake Dental Inc., Tokyo, Japan) is formulated with HEMA in both the primer and bonding portions. The chemical formulations of the adhesives are shown in Table 1. We used high-resolution modulus mapping and typical dynamic indentation test across the adhesive-dentin interface to discern the in situ mechanical properties of each target region at the nanoscale.
Results: HEMA increases the diffusion properties of MDP into dentin structures. However, the rigidity of the adhesive–dentin interface indicated by the storage modulus was markedly lower in G2-H20-15, G2-H20-30 and SE than in G2. Dynamic indentation testing revealed that the bonding layer was more deformable in the presence of HEMA. Moreover, the presence of MDP in the bonding layer might also increase the deformability because the polymerization linearity allows a large degree of viscoelasticity. These factors also diminish the rigidity of the adhesive–dentin interface.
Conclusions: 4-MET is a better co-monomer than HEMA in MDP-based dental adhesives. Modulus mapping and nanoindentation are introduced as new tests for the dentin-adhesive interface to address queries about the effectiveness of dental adhesives.