MENEZES, Marco Aurélio de and MUENCH, Antonio. Relative number of free radicals and knoop hardness of composites. Rev Odontol Univ São Paulo [ online]. O objetivo deste trabalho foi avaliar a profundidade de polimerização e a dureza Knoop do compósito restaurador P60 fotoativado por diferentes métodos. cimentados com diferentes materiais; (2) a dureza Knoop de cimentos Palavras-chave: Pino de fibra de vidro, Integridade Marginal, Dureza Knoop, Cimento.
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Evaluation of depth of cure and Knoop hardness in a dental composite photo-activated using different methods. The aim of this study was to evaluate the depth of cure and Knoop hardness in the P60 composite resin photo-activated using different methods. A bipartite brass matrix 3 mm in diameter X 11 mm in height was filled with the composite and photo-activation was performed using continuous light, exponential light, intermittent light, plasma arc curing PAC or light-emitting diodes LED.
After opening the matrix, the uncured material was removed with a steel spatula and the polymerized composite was measured using a pachymeter. The specimens were then included in self-curing acrylic resin and worn longitudinally and the hardness was measured on the surface and at depths of 1, 2, 3, 4 and 5 mm. The results showed that the depth of cure was higher with the intermittent light, followed by continuous light, exponential light, PAC and LED methods.
Up to a depth of 2 mm, all methods revealed similar hardness values, but there were differences between them at other depths, at which LED demonstrated the lowest values followed by PAC. The light-activated composite resins, brought into practice in the ‘s, introduced expressive changes that made their satisfactory application in posterior teeth possible.
However, characteristics such as composition, light intensity and exposure time can modify the final properties of the material and, thus, restrict the clinical applications.
Type, size, quantity and refraction index of the fillers into composite exert an influence upon light transmission across the material and, consequently, the light attenuation and the depth of cure may be altered 1,2. With respect to the organic matrix, the nature of the involved monomer molecules and the degree of conversion obtained in composite resin has an important effect upon mechanical properties 3where the higher degrees of cure will improve the final properties of the material.
A higher degree of conversion can be obtained by using a high light intensity 4.
However, this higher intensity may result in greater polymerization shrinkage and greater marginal leakage 5. Thus, new photo-activation techniques have been proposed, such as the programmed use of low and high intensities that have shown to be more effective in decreasing the stress generated by polymerization shrinkage, whilst maintaining a high degree of conversion and satisfactory mechanical properties Since the introduction of this method, other photo-activation methods have been suggested including intermittent light 9,10plasma arc curing PAC 11 and, more recently, a new technology employing light-emitting diodes LED 12, However, these innovative techniques require further investigation before they can be effectively applied in dental practice.
Thus, the aim of this study was to evaluate the depth of cure and Knoop hardness using different photo-activation methods.
This study used the Filtek P60 composite resin 3M, St. Composition and batch are reported in Table 1. The composite was placed in a bipartite brass matrix that presented a central opening of 3 mm in diameter and 11 mm in height. The composite was then covered with a polyester strip and pressed with a glass slab to accommodate the material into the matrix. Five specimens were prepared for each photo-activation method. The total exposure time was 80 s.
The light exposure time was 3 s. After photo-activation, the brass matrix was opened and all uncured material was removed using a steel spatula. The polymerized composite cylinder was measured using a digital pachymeter Digital pachymeter, model CDC, Mitutoyo, Japanwhich was positioned in the center of the specimen, determining the depth of cure.
Finishing and polishing were then performed with sandpaper of decreasing grits of, and Five readings were taken for each region and the arithmetic means were calculated for each region of the specimen. The results of the depth of cure and the Knoop hardness are presented in Tables 2 and 3respectively. The intermittent light method had the highest depth of cure 6.
However, there were statistical differences between these, in which the LED demonstrated the lowest depth of cure. At 3 mm, the LED method presented the lowest value and the continuous light technique demonstrated an intermediate value and was statistically similar to the other methods.
Furthermore, the continuous light method demonstrated no difference from exponential light and PAC methods. At this depth, the continuous light method presented an intermediate value with no statistical difference from the other methods. The development of new technologies for photo-activation of restorative composite resins has caused great interest among researchers However, the real advantages of these techniques are not yet totally known.
Before these methods can be clinically applied, the final properties of the photo-activated composites must be evaluated. Thus, this study evaluated the depth of cure and the Knoop hardness of the P60 composite resin, using different photo-activation methods.
The results of this study showed that the depth of cure is strongly affected by photo-activation methods. The intermittent light demonstrated the highest depth of cure 6.
Dureza Knoop de cimentos de ionômero de vidro indicados para o tratamento restaurador
The intermittent, continuous and exponential light methods supply energy for photo-activation via halogen lamps, and the white light must be filtered to khoop only the blue spectrum of the visible light. To generate blue light, the lamps must be heated to very high temperatures 14resulting in the emission of heat through the curing light tip 15, This heat transmission to the material may be, in part, responsible for the higher depth of cure values achieved using these methods, because the heat may increase the mobility of the monomers, increasing the probability of the occurrence of conversion.
Another factor that may have influenced the depth of cure and caused the difference between the intermittent light and the continuous and exponential methods is the total amount of durez supplied to the composite for the polymerization. According to Sakaguchi and Berge 8maximum light intensity is achieved at 0.
Conversely, the intermittent light method employs 2 s of light exposure followed by 2 s without light, meaning that the maximum light intensity peak is achieved every time that the light is emitted.
Since the polymerization process seems more dependent on the total energy available for photo-activation than the light intensity property 8, 17this method may provide a higher amount of energy to the material, which may explain the higher depth of cure values achieved using the intermittent method.
The PAC method employs a different technology in which the light is produced by two electrodes that are placed very close to each other, emitting light when a high voltage is applied rather than by heating a tungsten filament as a halogen lamp However, the depth of cure value was lower than that obtained by methods that employ halogen lamps. This result may be due to the reduced photo-activation time used in PAC, representing a lower amount of energy 8,17 and a short time period for the light to nkoop deeper regions of the material, since part of the light necessary for polymerization is absorbed and scattered by the already polymerized composite 1, According to Peutzfeldt et al.
This energy is calculated as the product of the output of the curing light unit and the time durdza irradiation and may be termed as energy density. According to these authors, the Apollo 95 E emits less energy in 3 s than do the conventional curing light units. This could explain the lower depth of cure obtained with this method when compared to methods that use the halogen lamp.
The spectral output of gallium nitride blue LED falls conveniently within the absorption dyreza of the camphoroquinone photo-initiator nm presented in most light-activated composite resins, thus no filters are required in LED light curing units 12, However, the LED demonstrated the lowest depth of cure. Increasing the exposure time or the light intensity could minimize this problem. The Knoop hardness test showed that, up to a depth of 2 mm, all photo-activation methods provided similar values.
This result demonstrates that despite the particular characteristics of each method, the light intensity and the exposure time were enough to adequately polymerize this thickness of composite. At a depth cureza 3 mm, the LED demonstrated the lowest hardness value, while the continuous light knolp revealed an intermediate value with no statistical difference from the other methods.
The lower value observed with LED may be due to the low intensity produced by this technique. This fact may explain the lower hardness observed at 3 mm nkoop when LED was used. Despite this scattering and absorbance of light, all other methods supplied higher amounts of energy to the composite and, thus, provided higher hardness values at 3 mm depth.
At a depth of 4 mm, the intermittent and continuous light methods demonstrated the highest hardness values without differences between them.
The continuous light was similar to the exponential light and PAC, whilst the LED presented the lowest hardness, with statistical differences from the other methods. This result may be due to the total amount of energy that reached the material fureza this depth. The total energy is related to exposure time and light intensity generated by each method, i. At a depth of 5 mm, the LED and the PAC methods could not be evaluated dreza they did not achieve a depth of cure of 5 mm.
At this depth, the continuous light method presented an intermediate value and was no different from the intermittent and exponential methods.
However, the intermittent light revealed a higher hardness value than the exponential technique. Again, the probable explication for this occurrence may be the total amount of energy supplied to the camphoroquinone, even at great depth.
Mnoop seems that the intermittent method was able to provide a higher amount of energy at this depth, probably due to intermittence itself, where the maximum intensity is achieved at 0. Whilst all the photo-activation methods provided depth of cure values that fulfilled the requirements of the ISO 19there were differences observed between the methods at depths greater than 2 mm. These differences were probably due to the characteristics of each method such as the light intensity, exposure time and heat generated.
Therefore, in spite of the P60 composite manufacturer’s claims of increments of 2. Factors affecting cure at depths within light-activated resin composites. Am J Dent ;6: Influence of curing tip distance on composite Knoop durezx values. Braz Dent J ; Dyreza effect of cure rate on the mechanical properties of dental resins. Effect of dueza intensity and exposure duration on cure of resin composite. Polymerization contraction and conversion of light curing Bis-GMA-based methacrylate resins.
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Marginal adaptation of a restorative resin polymerized at reduced rate. Scand J Dent Res ; Influence of light intensity on polymerization shrinkage and integrity of restoration-cavity interface. Eur J Oral Knnoop ; Reduced light energy density decreases post-gel contraction while maintaining knoo; of conversion in composites. Effect of the photo-activation method on polymerization shrinkage of restorative composites.
The effect of the photopolymerization method on the quality of composite resin. J Oral Rehabil ; Characterization of resin composites polymerized with plasma arc curing units. Depth of cure and compressive strength of dental composites cured with blue light emitting diodes LEDs.
Hardness evaluation of a dental composite polymerized with experimental LED-based devices. Cordless LED curing unit. Harrington E, Wilson HJ.
Knoop hardness test
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