Effect of Camphorquinone Concentration in Physical-Mechanical Properties of Experimental Flowable Resin Composites

Abstract

The aim of this study was to evaluate the effect of camphorquinone concentration in physical-mechanical properties of experimental flowable composites in order to find the concentration that results in maximum conversion, balanced mechanical strength, and minimum shrinkage stress. Model composites based on BISGMA/TEGDMA with 70% wt filler loading were prepared containing different concentrations of camphorquinone (CQ) on resin matrix (0.25%, 0.50%, 1%, 1.50%, and 2% by weight). Degree of conversion was determined by FTIR. Surface hardness was assessed before and after 24 h ethanol storage and softening rate was determined. Depth of cure was determined by Knoop hardness evaluation at different depths. Color was assessed by reflectance spectrophotometer, employing the CIE-Lab system. Flexural strength and elastic modulus were determined by a three-point bending test. Shrinkage stress was determined in a Universal Testing Machine in a high compliance system. Data were submitted to ANOVA and Tukey's test (α = 0.05). The increase in CQ concentration caused a significant increase on flexural strength and luminosity of composites. Surface hardness was not affected by the concentration of CQ. Composite containing 0.25% wt CQ showed lower elastic modulus and shrinkage stress when compared to others. Depth of cure was 3 mm for composite containing 1% CQ and 2 mm for the other tested composites. Degree of conversion was inversely correlated with softening rate and directly correlated with elastic modulus and shrinkage stress. In conclusion, CQ concentration affects polymerization characteristics and mechanical strength of composites. The concentration of CQ in flowable composite for optimized polymerization and properties was 1% wt of the resin matrix, which allows adequate balance among degree of conversion, depth of cure, mechanical properties, and color characteristics of these materials.

The Photoinitiators Used in Resin Based Dental Composite—A Review and Future Perspectives

“…When the concentration of CQ is higher than 1 wt%, there was not significant different in surface hardness. Lower than 1 wt% concentrations of CQ reveal higher flexural strength [31].…”

“…CQ/amine photoinitiator system is the most common in commercial dental composites, however it has many disadvantages. Major disadvantage is yellow color of the restoration [2,21,23,31] and the camphorquinone maintains the same color after generation of free radicals [25]. Not only is CQ responsible for color of dental resin, the large amounts of tertiary amine may result in long-term darkening of these materials [22,23].…”

“…The CQ is consider as toxic [21,36], because it can change the metabolism of structural lipids which affects membrane integrity and permeability [2]. There are also reports that CQ have toxic effect on pulp cells and it is connected with the concentration of CQ in dental composite: the higher concentration, the stronger cytotoxic effect [31]. The CQ is less cytotoxic than BAPO, but it has genetic toxicity potential, due to production of ROS/RNS [37].…”

“…Commercially it is used in Tetric EvoCeram Bleach (Ivoclar/Vivadent) and Vit-1-escence (Ultradent Products Inc) [6,18]. It can be a stand-alone photoinitiator system or it can be used synergistically with CQ and it does not require co-initiators to accelerate photopolymerization process [18,31]. The use of Lucirin TPO eliminated the amine group and that increase stability of color upon aging [42] and the color stability is the highest according to resins containing BAPO and CQ/amines [38,42].…”

A Combined Approach for the Aesthetic Management of Stained Enamel Opacities: External Bleaching Followed by Resin Infiltration

“…Yet during light curing, the CQ loses this colour as it infiltrates the lesion. In case of incomplete consumption of CQ, the resin may remain yellowish which may indicate the presence of unconsumed CQ [ 17 , 18 ].…”