Abstract
Camphorquinone is the most conventionally used photoinitiator in Dentistry. Although different alternative photoinitiators have been proposed, no photoinitiator was capable of completely substituting camphorquinone. The combination of photoinitiators has been considered the best alternative.Objectives:To evaluate the effect of combining Norrish type I and II photoinitiators on the cure efficiency of dental resin-based composites.Methodology:Experimental composites were produced containing different photoinitiator systems: Norrish type I-only, mono-alkyl phosphine oxide (TPO); Norrish type II-only, camphorquinone (CQ); or its combination, CQ and TPO, in a 1: 1 molar ratio. UV-vis absorption spectrophotometry was performed to assess the consumption of each photoinitiator after curing (n=3). A multi-wave LED (Bluephase® G2, Ivoclar Vivadent) was pre-characterized and used with a radiant exposure of 24 J/cm2. The degree of conversion was evaluated by Raman spectrometry, and the elution of the monomers by nuclear magnetic resonance analysis (n=3). Data were analyzed using ANOVA and Tukey's test (α=0.05; β=0.2).Results:The combination of CQ and TPO increased the consumption of the photoinitiator system compared to CQ-only (p=0.001), but presented similar consumption compared to TPO-only (p=0.52). There was no significant difference in the degree of conversion between the composites regardless of the photoinitiator system (p=0.81). However, the elution of the monomers was reduced when both photoinitiators were combined. TPO-based material presented the highest elution of monomers.Conclusions:The combination of the photoinitiator systems seems to be beneficial for the cure efficiency of dental resin-based composites.
Highlights
Light cured resin-based materials are composed of monomers that, after exposure to light, form a polymer
The combination of CQ and TPO increased the consumption of the photoinitiator system compared to CQ-only (p=0.001), but presented similar consumption compared to TPO-only (p=0.52)
There was no significant difference in the degree of conversion between the composites regardless of the photoinitiator system (p=0.81)
Summary
Light cured resin-based materials are composed of monomers that, after exposure to light, form a polymer. This process of building a polymer through the combination of monomers is called polymerization. When polymerization is triggered by a physical medium, such as light, this process is called photopolymerization.. Photoactivation promotes the excitation of the photoinitiators. The free radicals, in turn, are responsible for breaking the double bonds of the monomers. That for the chemical stabilization of the molecule, the monomers bind together, forming larger units and the polymers.
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