Abstract
The aim of this study was to determine the degree of conversion (DC) for five orthodontic resins with different viscosities, to examine a probable relationship between the viscosity factor and the degree of conversion of the materials. Five commercially-available light-cured orthodontic bonding resins were used in this study: two medium viscosity resins [transbond XT (TR); opal bond MV (OB)]; two low viscosity resins [vertise flow (VF); opal bond flow (OF)]; and a fluoride-releasing sealant [opal seal (OS)]. The specimens were made and polymerized for 20 s. Fourier Transformed Infrared spectroscopy (FTIR) was used to assess the DC of carbon-carbondouble bonds from all samples. The DC was significantly different among the materials: (TR, 24.6 ± 0.04 %; OB, 39 ± 0.02 %; VF, 44.3 ± 0.01 %; OS, 52.5 ± 0.01 %; OF, 53 ± 0.04 %; p < 0.05) and the lowest viscosity materials had the highest DC values. The resins studied have different DC values, which can be explained by the unique composition of each brand of resin. There is a relationship between the viscosity of a material and its degree of conversion, which is shown in this study by the two low-viscosity orthodontic resins that had a higher DC.
Highlights
A wide variety of orthodontic resins are currently being used clinically for the bonding of orthodontic brackets, orthodontic bands and fixation of lingual appliances
Studies show that components released by dental resin composites, including diluents such as triethylene glycol dimethacrilate (TEGDMA), some additives, plasticizers (dicyclohexyl phthalate; bis (2-ethylhexyl) phthalate), can make collagen and protein found in the oral cavity and throughout the human body less resistant to enzymatic degradation
Based on the mean values of conversion recorded for each material, the materials with a lower viscosity showed a higher degree of polymerization than those with higher viscosity
Summary
A wide variety of orthodontic resins are currently being used clinically for the bonding of orthodontic brackets, orthodontic bands and fixation of lingual appliances. Among the options available on the dental market, resin composite adhesives are a good choice for orthodontic bonding because these materials have good mechanical and aesthetic properties and low failure rates [1]. Orthodontic resin-based adhesives with photo-activation properties are a widely accepted group of composites in the profession because of their advantages such as high early bond strength, better aesthetic performance and controlled working time [2, 3]. Flowable or low viscosity composites have been applied for orthodontic use by many clinicians. Studies show that components released by dental resin composites, including diluents such as triethylene glycol dimethacrilate (TEGDMA), some additives, plasticizers (dicyclohexyl phthalate; bis (2-ethylhexyl) phthalate), can make collagen and protein found in the oral cavity and throughout the human body less resistant to enzymatic degradation. Mechanical and physical properties of new materials need to be studied, to validate their safety when used in the oral environment
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