Influence of Different Concentration and Ratio of a Photoinitiator System on the Properties of Experimental Resin Composites.

Caio Vinícius Signorelli Grohmann,Mário Alexandre Coelho Sinhoreti,Regina Maria Puppin-Rontani,William Cunha Brandt,Eveline Freitas Soares,Saulo Geraldeli,Eduardo José Carvalho Souza-Junior

doi:10.1590/0103-6440201701372

Abstract

The aim in this study was to evaluate the influence of different ratio of camphorquinone/tertiary amine concentration on the flexural strength (FS), elastic modulus (EM), degree of conversion (DC), yellowing (YL), water sorption (WS) and water solubility (WSL) of experimental composites. Thus, acrylate blends were prepared with different camphorquinone (CQ) and amine (DABE) concentrations and ratios by weight: (CQ/DABE%): 0.4/0.4% (C1), 0.4/0.8% (C2), 0.6/0.6% (C3), 0.6/1.2% (C4), 0.8/0.8% (C5), 0.8/1.6% (C6), 1.0/1.0% (C7), 1.0/2.0% (C8), 1.5/1.5% (C9), 1.5/3.0% (C10). For the FS and EM, rectangular specimens (7x2x1 mm, n=10) were photo-activated by single-peak LED for 20 s and tested at Instron (0.5 mm/min). Then, the same specimens were evaluated by FTIR for DC measurement. For YL, disks (5x2 mm, n=10) were prepared, light-cured for 20 s and evaluated in spectrophotometer using the b aspect of the CIEL*a*b* system. For WS and WSL, the volume of the samples was calculated (mm³). For WS and WSL, composites disks (5x0.5 mm, n=5) were prepared. After desiccation, the specimens were stored in distilled water for 7 days and again desiccated, in order to measure the WS and WSL. Data were submitted to one-way ANOVA and Tukey's test (5%). The groups C8, C9 and C10 showed higher DC, EM and YL means, compared to other composites. Therefore, the FS and WS values were similar among all groups. Also, C1, C2 and C3 presented higher WSL in 7 days, compared to other composites. In general, higher concentrations of camphorquinone promoted higher physical-mechanical properties; however, inducing higher yellowing effect for the experimental composites.

Highlights

To achieve satisfactory polymerization of the resin composites, a proper combination of photoinitiator/coinitiator system, which are usually camphorquinone (CQ) and a tertiary amine, respectively [1,2] should be used
The composites Composite 6 (C6), Composite 7 (C7), Composite 8 (C8), Composite 9 (C9) and Composite 10 (C10) showed higher degree of conversion (DC) when compared to the other composites (p=0.00001)
The type and concentration of the photoinitiator system are fundamental parameters that determine the polymerization characteristics of a resin composite [1]

Summary

Introduction

To achieve satisfactory polymerization of the resin composites, a proper combination of photoinitiator/coinitiator system, which are usually camphorquinone (CQ) and a tertiary amine, respectively [1,2] should be used. Light absorption raises CQ to an excited state that interacts with a tertiary amine, forming a triplet exciplex that disintegrates into free radicals. These radicals initiate the polymerization of methacrylates, which success conducts on obtaining a reliable bond and good polymerization [3]. The concentration of CQ and amine, as well as the CQ/amine ratio, play important roles in the polymerization efficiency and in the physical and mechanical properties of resin composite materials [4,5,6]. CQ is inherently yellow and can cause a color mismatch in aged aesthetic resin-based composite restorations. The intense yellow hue of CQ places practical limits on the concentration of photoinitiators that can be used, because of the esthetic properties, but this may not limit the degree of polymerization and depth of cure that can be attained [9]

Methods

Results

Conclusion