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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These differences were probably due to the characteristics of each method such as the light intensity, exposure time and heat generated. As a result, there is NO direct analytic conversion between hardness measures.
Knoop hardness test
Type, rureza, 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.
Since the polymerization process seems more dependent on the total energy available for photo-activation than the light intensity property 8, 17this method may knkop a higher amount of energy to the material, which may explain the higher depth of cure values achieved using the intermittent method.
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 durezaa for polymerization is absorbed and scattered by the already polymerized composite 1, Effect of light intensity and exposure duration on cure of resin composite.
A higher degree of conversion can be obtained by using a high light intensity 4.
Marginal adaptation of a restorative resin polymerized at reduced rate. The accuracy of the conversion depends on the accuracy of the provided data and the resulting curve-fits, and on the valid ranges spanned by the different hardness tests.
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. 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. With respect to the organic matrix, the nature of the involved monomer durezz and the degree xureza 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.
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 polymerized composite cylinder was measured using a digital pachymeter Digital pachymeter, model CDC, Mitutoyo, Japancureza was positioned in the center of the specimen, determining the depth of cure.
This fact may explain the lower hardness observed at 3 mm depth when LED was used. Therefore, in spite of the P60 composite manufacturer’s claims of increments of 2. Dent Mater J ; At a depth of 4 mm, the intermittent and continuous light methods demonstrated the highest hardness values without differences between them.
Finishing and polishing were then performed with sandpaper of dufeza grits of, and The light-activated composite resins, brought into practice in the ‘s, introduced expressive changes that made their satisfactory application in posterior teeth possible. 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 photo-activation, the brass matrix was opened and all uncured material was removed using a steel spatula.
Brinell 10 mm Standard kgf. The calculator curve-fits multiple hardness data onto a common polynomial basis and then performs an analytic conversion. The total energy is related to exposure time and light intensity generated by each method, i. The spectral output of gallium nitride blue LED falls conveniently within the absorption spectrum of the camphoroquinone photo-initiator nm presented in most light-activated composite resins, thus no filters are required in LED light curing units 12, J Oral Rehabil ; The results showed that the depth of cure was higher with the intermittent light, followed by continuous light, exponential light, PAC and LED methods.
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. According to Peutzfeldt et al. Cordless LED curing unit. Instead, one must correlate test results across the multiple hardness tests. The many hardness tests listed here measure hardness under different experimental conditions e.
The results of the depth of cure and the Knoop hardness are presented in Tables 2 and 3respectively. The effect of cure rate on the mechanical properties of dental resins.
Scand J Dent Res ; The effect of the photopolymerization method on the quality of composite resin. Characterization of resin composites durea with plasma arc curing units.
Dureza knoop de resinas compostas em função do número relativo de radicais livres
Depth of cure and compressive strength of dental composites cured with blue light emitting diodes LEDs. Harrington E, Wilson HJ. This energy is calculated as the product of the output of the curing light unit and the time of irradiation and may be termed as energy density. The intermittent light demonstrated the highest depth of cure 6. Effect of light wavelength on polymerization of light-cured resins. Polymerization contraction and conversion of light curing Bis-GMA-based methacrylate resins.