Polymerization- and solvent-induced phase separation in hydrophilic-rich dentin adhesive mimic

Abstract

Current dental resin undergoes phase separation into hydrophobic-rich and hydrophilic-rich phases during infiltration of the over-wet demineralized collagen matrix. Such phase separation undermines the integrity and durability of the bond at the composite/tooth interface. This study marks the first time that the polymerization kinetics of model hydrophilic-rich phase of dental adhesive has been determined. Samples were prepared by adding varying water content to neat resins made from 95 and 99wt% hydroxyethylmethacrylate (HEMA) and 5 and 1wt% (2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl1]-propane (BisGMA) prior to light curing. Viscosity of the formulations decreased with increased water content. The photo-polymerization kinetics study was carried out by time-resolved FTIR spectrum collector. All of the samples exhibited two-stage polymerization behavior which has not been reported previously for dental resin formulation. The lowest secondary rate maxima were observed for water content of 10-30%wt. Differential scanning calorimetry (DSC) showed two glass transition temperatures for the hydrophilic-rich phase of dental adhesive. The DSC results indicate that the heterogeneity within the final polymer structure decreased with increased water content. The results suggest a reaction mechanism involving both polymerization-induced phase separation (PIPs) and solvent-induced phase separation (SIPs) for the model hydrophilic-rich phase of dental resin.

Polymerization Behavior of Hydrophilic-Rich Phase of Dentin Adhesive

“…For the hydrophilic-rich phase, we suggested a possible polymerization mechanism involving PIPs and SIPs (Abedin et al 2014). Based on the proposed mechanism, microgels form following auto-acceleration, which are localized regions of a higher degree of conversion and/or cross-linking density.…”

“…A fixed amount of liquid at 30 µL was placed on the horizontal face of the internal reflectance crystal. A transparent plastic cover slip was placed on the sample, and its edges were sealed using tape to prevent D 2 O evaporation during the collection of the data (Abedin et al 2014). In this study, D 2 O was used The rate of polymerization was evaluated from the first derivative of the time against conversion curve.…”

“…The composition of the model hydrophilic-rich phase was determined quantitatively, and the results indicated limited cross-linkable dimethacrylate monomer and photoinitiators in the hydrophilic-rich phase (Ye et al 2012). A separate but complementary investigation showed solvent-and polymerizationinduced phase separation (SIPs and PIPs) in the hydrophilic-rich phase mimics (Abedin et al 2014). The composition of the hydrophilic-rich phase is primarily water and HEMA.…”

Bond Strength and Cytotoxicity of a Universal Adhesive According to the Hybridization Strategies to Dentin

“…Lanza et al (4) identified HEMA in the culture medium in contact with MDPC-23 cells 24 h after the application of ASB and CSB to the occlusal sides of dentin discs. Studies have also demonstrated that HEMA is the main resin monomer capable of diffusing through dentin (23), since this monomer is responsible for promoting resin infiltration in deep demineralized dentin (9). It has been shown that this low-molecular-weight monomer is highly cytotoxic, causing pulp cell death mediated by oxidative stress and inhibiting cell phenotype expression related to healing (23).…”

“…Next to the pulp chamber, the diameter and number of dentinal tubules per area increase, resulting in high permeability (5). This permeable substrate features a large quantity of dentinal fluid, which may interfere with the polymerization of resin materials enhancing the local presence of toxic unreacted free monomers (2,9). Therefore, since chemical composition of dental materials as well as the protocols of application to dentin play a central role in defining their mechanical behavior and compatibility with the pulp-dentin complex (2,5,10), the objective of this study was to evaluate the microtensile bond strength (µTBS) and transdentinal cytotoxicity of a universal adhesive system according to the hybridization strategies to dentin.…”