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

Abstract

The polymerization kinetics of physically separated hydrophobic- and hydrophilic-rich phases of a model dental adhesive have been investigated. The two phases were prepared from neat resin containing 2-hydroxyethyl methacrylate (HEMA) and bisphenol A glycerolate dimethacrylate (BisGMA) in the ratio of 45:55 (wt/wt). Neat resins containing various combinations of popular photo-initiating compounds, e.g., camphoquinone (CQ), ethyl 4-(dimethylamino)benzoate (EDMAB), 2-(dimethylamino)ethyl methacrylate (DMAEMA) and diphenyliodonium hexafluorophosphate (DPIHP) were prepared. To obtain the two phases 33 wt% of deuterium oxide (D2O) was added to the neat resins. This amount of D2O exceeded the miscibility limit for the resins. The concentration of each component of the photo-initiating system in the two phases was quantified by HPLC. When combined with CQ, DMAEMA is less efficient as a co-initiator compared to EDMAB. The addition of DPIHP as the third component into either CQ/EDMAB or CQ/DMAEMA photo-initiating systems leads to comparable performance in both the hydrophobic- and hydrophilic-rich phases. The addition of the iodonium salt significantly improved the photopolymerization of the hydrophilic-rich phase; the hydrophilic-rich phase exhibited extremely poor polymerization when the iodonium salt was not included in the formulation. The partition concentration of EDMAB in the hydrophilic-rich phase was significantly lower than that of DMAEMA or DPIHP. This study indicates the need for a combination of hydrophobic/hydrophilic photosensitizer and addition of iodonium salt to improve polymerization within the hydrophilic-rich phase of the dental adhesive.

Computer-aided molecular design of water compatible visible light photosensitizers for dental adhesive

“…As mentioned earlier with the conventional photosensitizer camphorquinone (CQ), almost no polymerization of the hydrophilic-rich phase was observed, and in the presence of an iodonium salt it could reach 20% to 32% depending on the co-initiator (Abedin et al ., 2016). The proposed candidate molecules have a significantly higher DC which is an improvement over the camphorquinone for the hydrophilic-rich phase.…”

“…In our previous studies, it was observed that DC of the hydrophilic-rich phase mimics was in the range of 63% to 97% given that the photo-initiator concentration was sufficient (Abedin et al ., 2014; Abedin et al ., 2015c). In another study, it was observed that the DC of the hydrophilic-rich phase for physically separated model dental adhesive system was approximately 20% to 32% in presence of a reaction accelerator, iodonium salt (Abedin et al ., 2016). The low DC for this case was most likely due to the lack of either or both photosensitizer/co-initiator or low efficiency of the co-initiator within the hydrophilic-rich phase (Abedin et al ., 2016).…”

“…In another study, it was observed that the DC of the hydrophilic-rich phase for physically separated model dental adhesive system was approximately 20% to 32% in presence of a reaction accelerator, iodonium salt (Abedin et al ., 2016). The low DC for this case was most likely due to the lack of either or both photosensitizer/co-initiator or low efficiency of the co-initiator within the hydrophilic-rich phase (Abedin et al ., 2016). Based on our earlier studies on the mimics, the target value for the DC was chosen to be 80% (Abedin et al ., 2014; Abedin et al ., 2015c).…”

“…and Abedin et al . have discussed this phase separation process (Abedin, 2016; Abedin et al ., 2016; Ye et al ., 2012). The polymerization kinetic study was performed in ATR sampling mode using the time resolved spectrum collector with a resolution of 4 cm -1 .…”

Probing the neutralization behavior of zwitterionic monomer-containing dental adhesive

“…The average of the last 50 values of the time-based spectra is reported as the DC value. The maximum polymerization rate $false(R_P^{\mathit{max}}/false[Mfalse]false)$ was determined using the maximum slope of the linear region of the DC vs. time plots [34, 36]. …”