RESUMO
This study evaluated the irradiance of curing units through core and veneered hot-pressed ceramics as well as the transmittance of these materials. Discs of 0.7, 1.4 and 2 mm in thickness of Empress (EMP) and Empress Esthetic (EST), and 0.8 (n=5) and 1.1 mm (n=5) thickness of Empress 2 (E2) were obtained. For E2, two of the 0.8-mm-thick discs were covered with dentin (1.2- and 1.4-mm-thick) and two with dentin + enamel (1.5-mm-thick). The 1.1-mm-thick specimens were submitted to the same veneering procedures. Specimens were evaluated by UV-Vis transmittance analysis and the percentage of transmittance was recorded. Irradiance through each specimen was evaluated with a quartz-tungsten-halogen (QTH), used in continuous or intermittent exposure modes, or a blue light-emitting diode (LED). Data were analyzed by Dunnett's test, ANOVA and Tukey's test at 5% significance level. Exposure through ceramic decreased the irradiance for all ceramics. Irradiance through EST was significantly higher than through EMP. For E2, reduction in irradiance depended on the core and/or veneer thickness. The QTH intermittent mode showed higher irradiance than the continuous mode, and both showed higher irradiance than LED. The ceramic significantly influenced irradiance and transmittance, which were found to decrease with the increase in thickness.
Assuntos
Silicatos de Alumínio/química , Materiais Dentários/química , Porcelana Dentária/química , Silicatos de Alumínio/efeitos da radiação , Cor , Lâmpadas de Polimerização Dentária , Materiais Dentários/efeitos da radiação , Porcelana Dentária/efeitos da radiação , Facetas Dentárias , Vidro/química , Vidro/efeitos da radiação , Temperatura Alta , Humanos , Luz , Compostos de Lítio/química , Compostos de Lítio/efeitos da radiação , Teste de Materiais , Processos Fotoquímicos , Espectrofotometria , Espectrofotometria Ultravioleta , Propriedades de SuperfícieRESUMO
This study evaluated the irradiance of curing units through core and veneered hot-pressed ceramics as well as the transmittance of these materials. Discs of 0.7, 1.4 and 2 mm in thickness of Empress (EMP) and Empress Esthetic (EST), and 0.8 (n=5) and 1.1 mm (n=5) thickness of Empress 2 (E2) were obtained. For E2, two of the 0.8-mm-thick discs were covered with dentin (1.2- and 1.4-mm-thick) and two with dentin + enamel (1.5-mm-thick). The 1.1-mm-thick specimens were submitted to the same veneering procedures. Specimens were evaluated by UV-Vis transmittance analysis and the percentage of transmittance was recorded. Irradiance through each specimen was evaluated with a quartz-tungsten-halogen (QTH), used in continuous or intermittent exposure modes, or a blue light-emitting diode (LED). Data were analyzed by Dunnett's test, ANOVA and Tukey's test at 5 percent significance level. Exposure through ceramic decreased the irradiance for all ceramics. Irradiance through EST was significantly higher than through EMP. For E2, reduction in irradiance depended on the core and/or veneer thickness. The QTH intermittent mode showed higher irradiance than the continuous mode, and both showed higher irradiance than LED. The ceramic significantly influenced irradiance and transmittance, which were found to decrease with the increase in thickness.
Este estudo avaliou a irradiância de unidades de fotoativação através de cerâmicas para subestrutura com e sem cobertura, e a transmitância desses materiais. Discos de 0,7, 1,4 e 2 mm de espessura de Empress (EMP) e Empress Esthetic (EST), e de 0,8 (n=5) e 1,1 mm (n=5) de espessura de Empress 2 (E2) foram obtidos. Para E2, dois discos de 0,8 mm foram cobertos com dentina (1,2 e 1,4 mm de espessura) e dois com dentina + esmalte (1,5 mm de espessura). Os discos de 1,1 mm de espessura foram submetidos aos mesmos procedimentos de cobertura. Os espécimes foram avaliados por análise de transmitância UV-Vis e o percentual de transmitância foi registrado. A irradiância através dos discos foi avaliada com fonte de luz de lâmpada halógena de quartzo-tungstênio (QTH), utilizada nos modos contínuo ou intermitente, e diodo emissor de luz (LED). Os dados foram analisados com testes de Dunnett, ANOVA e Tukey com nível de significância de 5 por cento. A exposição através da cerâmica reduziu a irradiância para todas as cerâmicas. A irradiância através de EST foi maior que EMP. Para E2, a redução dependeu da espessura da subestrutura e/ou cobertura. O modo intermitente para QTH mostrou maior irradiância que o modo contínuo; ambos apresentaram maior irradiância que o LED. A cerâmica influenciou significativamente a irradiância e transmitância, que diminuíram com o aumento da espessura.
Assuntos
Humanos , Silicatos de Alumínio/química , Materiais Dentários/química , Porcelana Dentária/química , Silicatos de Alumínio/efeitos da radiação , Cor , Lâmpadas de Polimerização Dentária , Facetas Dentárias , Materiais Dentários/efeitos da radiação , Porcelana Dentária/efeitos da radiação , Vidro/química , Vidro/efeitos da radiação , Temperatura Alta , Luz , Compostos de Lítio/química , Compostos de Lítio/efeitos da radiação , Teste de Materiais , Processos Fotoquímicos , Espectrofotometria , Espectrofotometria Ultravioleta , Propriedades de SuperfícieRESUMO
The extended track interaction model (ETIM) has been formulated to explain the TL-fluence response for peak 5 to heavy ions using radial dose distributions produced by the ions in LiF and their luminescent centre occupation probability distributions. In this work, an experimental study of the TLD-100 fluence response to carbon and oxygen ions and its interpretation in terms of a Monte Carlo simulation of ETIM applied to peak 5 are presented. Irradiations were performed with 7.34 and 10.3 MeV 12C and 8.34 MeV 16O ions in the fluence interval between 2 x 10(7) and 2 x 10(11) cm(-2). Individual glow curve responses show the expected increase of supralinearity as the peak temperature increases. Data for peak 5 show a weak dependence with energy. These latter results are difficult to understand when one considers the differences in the expected radial occupancies for different ion energies.
Assuntos
Radioisótopos de Carbono/análise , Fluoretos/química , Fluoretos/efeitos da radiação , Compostos de Lítio/química , Compostos de Lítio/efeitos da radiação , Modelos Químicos , Oxigênio/análise , Dosimetria Termoluminescente/instrumentação , Simulação por Computador , Desenho Assistido por Computador , Relação Dose-Resposta à Radiação , Desenho de Equipamento , Análise de Falha de Equipamento , Íons , Transferência Linear de Energia , Magnésio/química , Magnésio/efeitos da radiação , Doses de Radiação , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Dosimetria Termoluminescente/métodos , Titânio/química , Titânio/efeitos da radiaçãoRESUMO
The absorption spectra and glow curves of LiF:Mg,Ti exposed to high doses of 60Co gamma rays as well as the optical density curves and thermoluminescent (TL) response as a function of dose were measured. Absorption peaks around 442 nm (2.8 eV), 307 nm (4.0 eV) and 248 nm (5.0 eV) were observed. The optical density is a linear function of dose up to 2500 Gy and then sublinear for the 5.0 eV band, and for the 4.0 eV band it is sublinear with a filling constant of 2.1 x 10(-4) and 6.2 x 10(-4) Gy(-1). The dose response of the 2.8 eV band is linear from 2500 Gy to 10 kGy with a slope of 1.0 x 10(-5) Gy(-1). Once the absorption spectra were obtained, the glow curves and the TL response were obtained. In the dose range, 290-10,000 Gy, the TL response of peaks 5 and 7 was supralinear-sublinear.
Assuntos
Fluoretos/química , Fluoretos/efeitos da radiação , Raios gama , Luz , Compostos de Lítio/química , Compostos de Lítio/efeitos da radiação , Dosimetria Termoluminescente/instrumentação , Radioisótopos de Cobalto , Relação Dose-Resposta à Radiação , Desenho de Equipamento , Análise de Falha de Equipamento , Temperatura Alta , Magnésio/química , Magnésio/efeitos da radiação , Teste de Materiais , Doses de Radiação , Dosimetria Termoluminescente/métodos , Titânio/química , Titânio/efeitos da radiaçãoRESUMO
The dosimetry of beta radiation is a difficult process especially because of the low penetration of beta particles in matter. The dosemeter utilised for this kind of procedure needs to approximate an ideal point-like detector: it should be as thin as possible, and its area should be small. The thermoluminescence dosemeters (TLDs) meet with these requirement properties. The aim of this work was to study the dosimetric characteristics of different TLDs to verify the possibility of their use for the calibration of 90Sr+90Y plane applicators. The response reproducibility, calibration curves, TL response as a function of the source-detector distance, the transmission factors and the linearity of the sample response were obtained for several types of dosimetric pellets.
Assuntos
Partículas beta , Radioisótopos de Estrôncio/análise , Dosimetria Termoluminescente/instrumentação , Radioisótopos de Ítrio/análise , Fluoreto de Cálcio/efeitos da radiação , Sulfato de Cálcio/efeitos da radiação , Calibragem , Relação Dose-Resposta à Radiação , Disprósio/efeitos da radiação , Fluoretos/efeitos da radiação , Compostos de Lítio/efeitos da radiação , Manganês/efeitos da radiação , Reprodutibilidade dos TestesRESUMO
Strong doubts havc been expressed about the validity of the quasi-equilibrium (QE) assumption used in the derivation of the analytical expressions of thermoluminescence (TL). So far there is no established method available to check if QE actually prevails during the emission of an experimental TL signal. The present study shows that the level of QE changes with a change in the heating rate beta. The change in the level of QE in its turn gets reflected in a change in peak shape when the system turns to a non-QE condition. This property is used as the first ever experimental method to test whether or not the emission of a given glow peak occurs under the QE condition. An essential condition for holding the QE condition is found to be T(R)/taum> or = 10(-3) where T(R) and taum are the glow peak recording duration and the maximum value of the free carrier lifetime, respectively. This relation between T(R) and taum is useful in finding the approximate value of taum. The value of taum being a function of the concentration and cross section of the TL related centres, one may be able to assess these basic parameters from the study of TL glow curves. The theoretical results are discussed in the perspective of LiF (TLD-100).
Assuntos
Dosimetria Termoluminescente/estatística & dados numéricos , Fluoretos/química , Fluoretos/efeitos da radiação , Temperatura Alta , Compostos de Lítio/química , Compostos de Lítio/efeitos da radiação , Modelos Teóricos , RadioquímicaRESUMO
In order to better understand the most important experimental aspects for performing correct measurements of relative thermoluminescent (TL) efficiencies, an investigation has been carried out to quantify the effect of using different experimental procedures in the evaluation of 3 MeV proton-to-gamma relative efficiency (etap,gamma) of LiF:Mg,Ti. Variations in batch, presentation, annealing and reader have been studied. When the same protocol is used to measure proton and gamma TL response, efficiency values obtained range from 0.36 to 0.59 for peak 5 and from 0.44 to 0.79 for the total signal. The use of different annealings and different batches leads to 20% and 10% differences in etap,gamma respectively. Large differences (40%) are found between efficiency values measured with TLD-100 chips and those obtained using TLD-100 microcubes. When 'mixed' procedures are used to measure the proton and the gamma response, differences in etap,gamma may increase even more. The main conclusion of this work is to stress the importance of measuring an entire series of experiments in the same laboratory with a carefully defined protocol and using dosemeters from the same batch to obtain heavy charged particle TL response and gamma TL response with identical annealing and readout procedures.
Assuntos
Dosimetria Termoluminescente/métodos , Fluoretos/química , Fluoretos/efeitos da radiação , Raios gama , Compostos de Lítio/química , Compostos de Lítio/efeitos da radiação , Magnésio/química , Prótons , Radioquímica , Dosimetria Termoluminescente/estatística & dados numéricos , Titânio/químicaRESUMO
The extended track interaction model, ETIM, has recently being proposed to explain the TLD-100 fluence response of peak 5 to heavy ions. This model includes the track structure information through the use of the luminescent centre occupation probability obtained from radial dose distributions produced by the ions as they travel through the dosemeter. In this work an implementation of ETIM using Monte Carlo techniques is presented. The simulation was applied to calculate the response of peak 5 of both sensitised and normal TLD-100 crystals to 2.6 and 6.8 MeV 4He ions. The simulation shows that the TL-fluence response has a strong dependence on ion energy, in disagreement with experimental observations. In spite of this, good agreement between the simulated TL-fluence response calculated for the 6.8 MeV 4He radial distributions and the experimental data for the two energies was achieved.
Assuntos
Dosimetria Termoluminescente/métodos , Fluoretos/química , Fluoretos/efeitos da radiação , Hélio , Compostos de Lítio/química , Compostos de Lítio/efeitos da radiação , Magnésio/química , Modelos Teóricos , Método de Monte Carlo , Radioquímica , Dosimetria Termoluminescente/estatística & dados numéricos , Titânio/químicaRESUMO
Modified track structure theory (MTST) has been successfully applied to evaluate proton-to-gamma and helium-to-gamma relative TL efficiencies in LiF by using Monte Carlo radial dose distributions and the measured dose response function, fdelta(D), of 8.1 keV X rays. In this work, an investigation is performed to study the effect of the choice of fdelta(D) for the reference test radiation field, on the predicted MTST proton-to-gamma and helium-to-gamma efficiency values. Results from two sets of calculations are presented. Set 1 investigates five fdelta(D) functions with different shapes and its influence on the MTST efficiency values while set 2 applies MTST using several fdelta(D) functions selected with fdelta(D)max ranging from 2 to 4. Comparison of the predicted efficiency values with experimental data show that the choice of 8.1 keV X rays gives the best description of the data. Results from set 2 show that predicted efficiencies may vary by as much as 44% for peak 5 and as much as 70% for the total signal among different fdelta(D). This confirms the importance of using the adequate fdelta(D) from a test radiation which simulates as much as possible the energy spectra and irradiated volume produced by the secondary electrons arising from the heavy charged particle radiation under study.
Assuntos
Dosimetria Termoluminescente/métodos , Fluoretos/química , Fluoretos/efeitos da radiação , Compostos de Lítio/química , Compostos de Lítio/efeitos da radiação , Modelos Teóricos , Radioquímica , Dosimetria Termoluminescente/estatística & dados numéricosRESUMO
The thermoluminescence response of LiF:Mg,Ti (TLD-100) to 20 keV electrons from a scanning electron microscope has been measured. Radiochromic dye films previously calibrated were used to determine the fluence incident on TLD-100 chips. The procedure for irradiation and glow curve deconvolution was adhered to the protocols previously determined in our laboratory for gamma rays and heavy charged particles. The response at electron fluences higher than 4 x 10(10) cm(-2) is supralinear, due to the increasingly relevant contribution of the high temperature peaks. The relative contribution of the high temperature peaks to the TL signal is abnormally small, about half that observed in gamma irradiation and four times smaller than what has been measured in low-energy X ray exposure.