Abstract
The use of a free-radical polymerization inhibitor, butylhydroxytoluene (BHT), and a common photo-initiator, camphorquinone (CQ), to reduce polymerization stress in dental composite was investigated in this study. Samples were prepared by mixing Bis-GMA, UDMA, and TEGDMA at a 1:1:1 ratio (wt%), and silanized borosilicate glass fillers at 70 wt% were added to form the composite. Sixteen groups of resin composite were prepared using combinations of four CQ (0.1%, 0.5%, 1.0%, and 1.5%) and four BHT (0.0%, 0.5%, 1.0%, and 1.5%) concentrations. For each group, six properties were tested, including flexural strength (FS), flexural modulus (FM), degree of conversion (DC), contraction stress (CS), stress rate, and gel point (GP). The effects of CQ and BHT combinations on each of these properties were evaluated using two-way analysis of variance (ANOVA) and Fisher's Protected Least Significant Differences test at the 5% significance level. Groups with low CQ and BHT showed moderate values for FS, FM, and CS with a 70% DC. Increasing the BHT concentration caused a decrease in CS and DC with an increase in GP values. Increasing the CQ content led to a steady increase in values for FS and FM. High CQ and BHT combinations showed the most promising values for mechanical properties with low stress values.
Highlights
Polymerization shrinkage is an inherent property in resin composite and occurs when the monomer is converted into a polymer
Composite resin preparation Resin composite material was prepared by mixing bisphenol A glycidyl methacrylate (Bis-GMA), urethane dimethacrylate (UDMA), and tetraethylene glycol dimethacrylate
The highest flexural strength (FS) value was recorded at CQ = 1.5% and BHT = 1.0%, whereas for flexural modulus (FM), the highest reading was obtained at CQ = 1.5% and BHT = 0.5%
Summary
Polymerization shrinkage is an inherent property in resin composite and occurs when the monomer is converted into a polymer. This phenomenon is still considered a drawback of composite resin because it has a major impact on its clinical performance.[1] Many research studies have investigated this issue. Systematic investigation into the interplay of the various components in the initiator system provides a starting point for the understanding of the impact of the initiator system on the polymerization kinetics of the polymer. An example is the work by Pfeifer et al.,[2] where changing the concentration of photo-initiators or co-initiators in the unfilled resins was shown to reduce the polymerization rate while keeping the final degree of conversion. Attempts aimed at reducing polymerization stress were usually complicated by a marked increase in the susceptibility to liquids, such as ethanol,[3] and decreased mechanical properties.[4]
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