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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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. The light-activated composite resins, brought into practice in the ‘s, introduced expressive changes that made their satisfactory application in posterior teeth possible.

Brinell 10 mm Standard kgf. The Knoop hardness test showed that, up to a depth of 2 mm, all photo-activation methods provided similar values.

Dureza knoop de resinas compostas em função do número relativo de radicais livres

Thus, this study evaluated the depth of cure and the Knoop hardness of the P60 composite resin, using different photo-activation methods. Hardness evaluation of a dental composite polymerized with experimental LED-based devices. The total exposure time was 80 s. 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 reach deeper regions of the material, since part of the light necessary for polymerization is absorbed and scattered by the already polymerized composite 1, Optical microscope resolution may limit the application of the Knoop hardness test due to the resulting shallow indentions.

Uno S, Asmussen E.

The composite was placed in a bipartite brass matrix that presented a central opening of 3 mm in diameter and 11 mm in height. This study used the Filtek P60 composite resin 3M, Knooop. At this depth, the continuous light method presented an intermediate value with no statistical difference from the other methods. Effect of light intensity and exposure duration on cure of resin composite. At a depth of durezaa mm, the LED demonstrated the lowest hardness value, while the continuous light method revealed an intermediate value with no statistical difference from the other methods.


Therefore, in spite of the P60 composite manufacturer’s claims of increments of 2. However, characteristics such as composition, light intensity and exposure time can modify the duureza properties of the material and, thus, restrict the clinical applications.

Before these methods can be clinically applied, the final properties of the photo-activated composites must be evaluated. Again, the probable explication for this occurrence may be the total amount of energy supplied to the camphoroquinone, even at great depth.

Knoop hardness test

A higher degree of conversion can be obtained by using a high light intensity 4. At this depth, the continuous light method presented an intermediate value and was no different from the intermittent and exponential methods. 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 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 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, The intermittent light method had the highest depth of cure 6.

International Organization for Standardization. How to cite this article. 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. 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.

Dureza Knoop de cimentos de ionômero de vidro indicados para o tratamento restaurador

Five specimens were prepared for each photo-activation method. The hardness value is below the acceptable range of the particular hardness scale. 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. Converted hardness values should be used for comparative purposes only.

Dent Mater J ; Influence of light knoo; on polymerization shrinkage and integrity of restoration-cavity interface. The development of new technologies for photo-activation of restorative composite resins has caused great interest among researchers However, these innovative techniques require further investigation before they can be effectively applied in dental practice.


Influence of curing tip distance on composite Knoop hardness values. The lower value observed with LED may be due to the low intensity produced by this technique. The Knoop hardness number is the ratio of the applied load to the area of the indentation, in accordance with the formula: 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 energy supplied to the composite for the polymerization.

Five readings were taken for each region and the arithmetic means were calculated for each region of the specimen. The light exposure time was 3 s. It 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.

The many hardness tests listed here measure hardness under different experimental conditions e. 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.

Determination of radiation energy emitted by light activation units.

All the contents of this journal, except where otherwise noted, is licensed under a Creative Commons Attribution License. The results of this study showed that the depth of cure is strongly affected by photo-activation methods. Harrington E, Wilson HJ. Composition and batch are reported in Table 1.

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. The intermittent light demonstrated the highest depth of cure 6. The total energy is related to exposure time and light intensity generated by each method, i. This fact may explain the lower hardness observed at 3 mm depth when LED was durza.