Polymerization Behavior of Hydrophilic-Rich Phase of Dentin Adhesive

Abstract

The 2-fold objectives of this study were 1) to understand whether model hydrophobic-and hydrophilic-rich phase mimics of dentin adhesive polymerize similarly and 2) to determine which factor, the dimethacrylate component, bisphenol A glycerolate dimethacrylate (BisGMA) or photoinitiator concentration, has greater influence on the polymerization of the hydrophilic-rich phase mimic. Current dentin adhesives are sensitive to moisture, as evidenced by nanoleakage in the hybrid layer and phase separation into hydrophobic-and hydrophilic-rich phases. Phase separation leads to limited availability of the cross-linkable dimethacrylate monomer and hydrophobic photoinitiators within the hydrophilic-rich phase. Model hydrophobic-rich phase was prepared as a single-phase solution by adding maximum wt% deuterium oxide (D 2 O) to HEMA/BisGMA neat resins containing 45 wt% 2-hydroxyethyl methacrylate (HEMA). Mimics of the hydrophilicrich phase were prepared similarly but using HEMA/BisGMA neat resins containing 95, 99, 99.5, and 100 wt% HEMA. The hydrophilic-rich mimics were prepared with standard or reduced photoinitiator content. The photoinitiator systems were camphorquinone (CQ)/ethyl 4-(dimethylamino)benzoate (EDMAB) with or without [3-(3, 4-dimethyl-9-oxo-9H-thioxanthen-2-yloxy)-2-hydroxypropyl]trimethylammonium chloride (QTX). The polymerization kinetics was monitored using a Fourier transform infrared spectrophotometer with a time-resolved collection mode. The hydrophobic-rich phase exhibited a significantly higher polymerization rate compared with the hydrophilic-rich phase. Postpolymerization resulting in the secondary rate maxima was observed for the hydrophilic-rich mimic. The hydrophilic-rich mimics with standard photoinitiator concentration but varying cross-linker (BisGMA) content showed postpolymerization and a substantial degree of conversion. In contrast, the corresponding formulations with reduced photoinitiator concentrations exhibited lower polymerization and inhibition/delay of postpolymerization within 2 h. Under conditions relevant to the wet, oral environment, photoinitiator content plays an important role in the polymerization of the hydrophilic-rich phase mimic. Since the hydrophilic-rich phase is primarily water and monomethacrylate monomer (e.g., HEMA as determined previously), substantial polymerization is important to limit the potential toxic response from HEMA leaching into the surrounding tissues.

Relative photon absorption determination and the influence of photoinitiator system and water content on C=C conversion, water sorption/solubility of experimental self-etch adhesives

“…Combination of these events leads to phase separation, as already described. [22][23][24][25] However, it is important to highlight that phase separation may be even more severe where C=C conversion is higher, such as for these groups formulated with BAPO and TPO, unless the rate of reaction is very fast. Although it was already demonstrated that phosphine-oxide-based initiators might develop faster reaction than CQ, 18 the photopolymerization kinetics was not determined for the materials tested in the current study.…”

Effect of Partition of Photo-Initiator Components and Addition of Iodonium Salt on the Photopolymerization of Phase-Separated Dental Adhesive

“…This resulted in a cloudy mixture since 33 wt% of D 2 O was above the miscibility limit for this formulation [14]. Then, the photo-initiators were replenished based on the quantity of D 2 O added so that the final composition of each photo-initiator reached 0.5 wt%.…”

“…Then a plastic cover slip was placed on it. The edges of the coverslip were sealed using tape to prevent evaporation of D 2 O from the sample; D 2 O evaporation could cause variation in the polymerization kinetics [14, 15]. The D 2 O profile was also monitored to ensure that there was no evaporation of D 2 O and the initial slight changes in the profile could be related to diffusion, either away from or towards the ATR crystal, within the sample [15].…”

“…Detailed characterization studies of this phase have been very limited [14-16]. It was found that the polymerization efficiency of the hydrophilic-rich phase mimic is lower as compared to the hydrophobic-rich phase mimic [14].…”

“…Detailed characterization studies of this phase have been very limited [14-16]. It was found that the polymerization efficiency of the hydrophilic-rich phase mimic is lower as compared to the hydrophobic-rich phase mimic [14]. The polymerization mechanism of the hydrophilic-rich phase involves polymerization-induced and solvent-induced phase separation [15].…”