Interaction of MDP-based Adhesive With Dentin Studied by Solid-state NMR

Objectives: 10-Methacryloyloxy-decyl-dihydrogen-phosphate (MDP) is one of the most effective functional monomers and formulated into self-etch adhesive systems. In this system, the remnant of smear layer is supposed to hybridize with resin-monomers. We investigated molecular-level interaction of MDP with dentin components by solid-state ³¹P NMR measurement on cured adhesive.
Methods: We used a MDP-based all-in-one adhesive (Clearfil S3 Bond Plus,S3B, Kuraray Noritake) as reagent, and hydroxyl apatite (HAp) particles (Taihei Chemical Industrial Co. Ltd.), type I collagen powder from bovine achilles tendon (Sigma-Aldrich) and bovine dentin powder as substrates. Mixtures of S3B with each substrate (HAp particle, collagen powder or dentin powder) were reacted for 1 min, 5 min and 60 min, air-dried and light-cured. Pure substrate-free S3B was air-dried and light-cured (control). Cured samples were subjected to ³¹P CP-MAS NMR measurements using ECA II spectrometer (JEOL RESONANCE 700MHz) at 16.5 T.


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Results: When S3B was reacted with HAp particles, the ³¹P HAp and MDP peaks became slightly broader, which indicated a slow reaction between HAp article and MDP. When S3B was reacted with collagen powder, the ³¹P MDP peak showed no remarkable changes, mening that polymerization of MDP in S3B was not impaired by collagen. When S3B was reacted with dentin powder, the ³¹P HAp and MDP peaks showed time-dependent changes. At 5 min and 60 min reaction time, increased intensity of ³¹P HAp peak indicated that MDP bound to HAp and formed MDP-HAp assembly. However, at 1 min, this MDP-HAp binding reaction was limited. The broad ³¹P MDP peak at 60 min implied that MDP-HAp bound assembly influenced MDP polymerization.
Conclusions: The ³¹P CP-MAS NMR results suggested that the binding-reaction of MDP with HAp in dentin was improved with increasing reaction time. Meanwhile, the formation of MDP-HAp bound assembly in hybrid layer may influence polymerization behavior of MDP-based adhesive