Effect of initiator on photopolymerization of acidic, aqueous dental model adhesives

Abstract

This study evaluated different initiator systems in self-etching model adhesives, in which camphorquinone (CQ) or [3-(3,4-dimethyl-9-oxo-9H-thioxanthen-2-yloxy)-2-hydroxylpropy] trimethylammonium chloride (QTX) was employed as a photoinitiator (dye). N-phenylglycine (NPG), ethyl 4-dimethylaminobenzoate (4E) or 2-(dimethylamino) ethyl methacrylate (DMAEMA) was used as the coinitiator (CI). The role of diphenyliodonium hexafluorophosphate (DPIHP) in the polymerization process was also studied. The concentrations of dye, CI, and DPIHP in model adhesives were all maintained at 0.022 mmol per gram monomer. The model adhesive contained two monomers: (bis[2-(methacryloyloxy)ethyl] phosphate) (2MP) and 2-hydroxyethyl methacrylate (HEMA) whose mass ratio was 1:1, thus representing an acidic and hydrophilic formulation. The polymerization rate and the degree of conversion (DC) of the model adhesives with 5, 15, or 25% water content were determined using FTIR/ATR with a time-based spectrum analysis. The results indicated that with CQ as the photoinitiator, 4E appeared to be the most efficient CI, whereas the CQ-DMAEMA combination led to very low radical generation efficiency (DC < 5%). DPIHP exhibited little effect on the polymerization process. With QTX as the photoinitiator, however, DPIHP played an essential role. Without DPIHP, all three QTX-CI systems failed to initiate polymerization (DC < 5%). The QTX-DPIHP combination, on the other hand, was found to be a viable initiator system. The above results provide the critical information for the development of self-etching adhesive systems.

Degree of Conversion of Etch-and-Rinse and Self-etch Adhesives Light-cured Using QTH or LED

“…17,28 The polymerization process of adhesive resins is dependent on many factors, such as monomer structure and functionality, 1 viscosity, 1,24 temperature 24 and the presence of solvents. 10,[22][23]27 Thus, the current study did not aim to compare the DC among the bonding agents, but rather the effect of the LCUs for each system. The current results indicate that the impact of QTH and LED lights on the DC of bonding agents was material-dependent.…”

“…9 This wide spectrum embraces the absorption range of most photoinitiators used in adhesive systems. [10][11] However, some factors may compromise the performance of QTH units, such as fluctuation in the line voltage, long-term degradation of the bulb and filter, contamination of the light guide, damage to the fiber-optic bundle and bulb overheating within the unit. [12][13] On the other hand, the use of light-emitting diodes (LEDs) is increasingly popular among clinicians.…”

Influence of Photoinitiator System on Physical-Chemical Properties of Experimental Self-Adhesive Composites

“…It presents an intense yellow coloration and requires a co-initiator molecule to optimize the polymerization reaction, which unfortunately may suffer oxidation with time, leading to higher intrinsic discoloration. Furthermore, in acidic media, CQ shows limited regeneration (6).…”

“…The acidic monomers are capable of chemically interacting with calcium from the tooth substrate, leading to ionic bond (5). However, their low pH may neutralize the tertiary amine by an acid-base reaction, decreasing the composites' polymerization (6). Furthermore, the acidic monomers are more hydrophilic and possibly influenced the increase of water absorption by the polymer.…”

Durable bonds at the adhesive/dentin interface:an impossible mission or simply a moving target?

“…[136][137][138][139][140]This was accomplished by using bulky and/ or branched functional groups that were poor esterase substrates but sufficiently hydrophilic to be water compatible. Water-compatible photoinitiators were developed as a means of promoting monomer/polymer conversion and thus, reducing the susceptibility to esterase hydrolysis by reducing the number of unreacted pendant groups [ 11,112,[141][142][143].…”