Effect of the Degree of Conversion of Composite Resins on Their Color Stability, Hardness, Flexural Strength and Flexural Modulus at Different Storage Time in Artificial Saliva
Journal Title: International Journal of Medical Science and Innovative Research (IJMSIR) - Year 2018, Vol 3, Issue 9
Abstract
Good esthetics and the ability of establishing a bond to enamel and dentin makes composites a common restorative material.1 Composites employing adhesive technologies allow for minimal invasive interventions and sometimes do not require tooth preparation.2 Resin based composites are basically composed of an organic matrix i.e. dimethacrylate monomers – such as bisphenol-A-glycidyldimethacrylate (Bis-GMA), urethane dimethacrylate (UDMA), bisphenol-A-ethoxydimethacrylate (Bis-EMA) or triethyleneglycoldimethacrylate (TEGDMA).3 and inorganic fillers. Inorganic fillers in resin composites have been progressed from macrofills to microfills and from hybrids to microhybrids. Materials such as packable and nanofilled composites also have been introduced to the dentistry.4 Microfilled composites with smaller particle fillers allowed better polish retention which results in enhanced esthetics, but provide less strength. Hybrid composites combines larger particle fillers to improve strength but were less polishable. Particles size of 1-4 µm responsible for optimal wear resistance and adequate mechanical properties of composites.5 The newer generation of nanohybrid composites creates durable restorations which maintain a gloss shine which reduces plaque accumulation and provide maximum esthetics. Nanofilled resin materials consist of nanomeric particles blended with nanoclusters in a conventional resin matrix, having filler particle size ranges from 0.1 to 100 nanometers6. Higher amount of filler content results in reduced polymerization shrinkage and improved mechanical behavior, like diametral tensile strength, flexural strength, flexural modulus, compressive strength and microhardness, which is very critical in areas with high functional stress in oral cavity.7-9 Polymerization stage is the most critical aspects of a composite resin restoration. Complete polymerization may result in a resin having low porosity, more hardness, high polishing and low staining capacity and no detrimental effects on pulp caused by the free monomers10. The polymerization process during setting reaction of composite materials is never complete. The average value of the degree of conversion of the composites is 43-75%.11 The number of double carbon links (C=C) present in the monomers, which are converted into single links (C-C) to form the polymeric chain during the polymerization process, is called degree of conversion (DC).12 Physical properties of composites are dependent on the degree of conversion of the resin matrix.13 A previously published study showed a correlation between the degree of conversion, color stability, hardness, modulus of elasticity and flexural strength of restorative resin material.1, 14 Mechanical properties of composites are influenced by their chemical composition and the environment to which they are exposed.15 It ultimately leads to decrease the mechanical properties of the material and affects the longevity of resin composite restorations. Color stability of light cured composite resin remains a concern after long term intraoral exposure.16 Hence this study was conducted to evaluate and compare the effect of degree of conversion of microhybrid, nanohybrid and nanofilled composite resins on their color stability, hardness, flexural strength and flexural modulus at different storage time in artificial saliva.
Authors and Affiliations
Dr. Roopali Warade
Keywords
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