Abstract
AIM: To evaluate the effect of different radiant exposures on the degree of conversion (DC), Knoop hardness number (KHN), plasticization (P), water sorption (WS), and solubility (S) of different monomer resin-based composites. METHODS: Circular specimens (5 x 2 mm) were manufactured from methacrylate and silorane composite resins, and light-cured at 19.8, 27.8, 39.6, and 55.6 J/cm2, using second-generation LED at 1,390 mW/cm2. After 24 h, DC was obtained using a FT-Raman spectrometer equipped with a Nd:YAG laser, KHN was measured with 50-g load for 15 s, and P was evaluated on the top and bottom surfaces by the percentage of hardness reduction after 24 h immersed in absolute alcohol. WS and S were determined according to ISO 4049. Data were subjected to statistical analysis (α=0.05). RESULTS: Methacrylate material presented higher DC, KHN, P, and WS than silorane (p 0.05). The increased radiant exposures improved only the KHN (p<0.05). In general, top surfaces showed higher DC and KHN than bottom, for both materials (p<0.05). The increase of the radiant exposure did not improve most physical properties of the composites and were monomer-base dependent. CONCLUSIONS: Chemical composition of the composite resins resulted in different physical properties behavior and could affect the clinical longevity of dental restorations, but overall these properties were not influenced by the different radiant exposures evaluated in the study.
Highlights
Since the development of the dental composite resin in the 1960s, numerous improvements in its composition and characteristics were made and with the increased demand by patients for esthetic restorations and simplification of the bonding procedures, light-cured composites have been widely used in the dental practice[1]
The objectives of this study were to evaluate the effect of the radiant exposure on the degree of conversion (DC), Knoop hardness number (KHN), plasticization (P), water sorption (WS) and solubility (S) of methacrylate- and silorane-based composite resins
The methacrylate material presented higher curing degree than silorane (p0.05)
Summary
Since the development of the dental composite resin in the 1960s, numerous improvements in its composition and characteristics were made and with the increased demand by patients for esthetic restorations and simplification of the bonding procedures, light-cured composites have been widely used in the dental practice[1]. Dental composites are classified in nanofilled, microfilled, or micro/nano hybrid composite resins[2]. These materials are composed basically by polymeric matrix based on methacrylate monomers, inorganic filler particles, silane and photo-initiator system[3]. Methacrylate restorative materials exhibit volumetric polymerization shrinkage[5], ranging from 1.9 to 3.5 vol%6, and a significant proportion of unreacted monomer due to incomplete C=C bond conversion[7]. A higher DC increases the shrinkage strain and the resulting polymerization stress may result in cuspal deflection[8], de-bonding at adhesive interface, post-operative sensitivity[9,10], microleakage[9], marginal staining, secondary caries formation, restoration and dental fractures[10], affecting the restoration durability. In the attempt to reduce these problems some techniques were proposed to decrease the shrinkage stress effects, such as different incremental composite placement[10], light-curing protocols and intermediate layer with hybrid glass ionomer or flowable composite[11]
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