Estudo fotoacústico de dentes humanos submetidos à radioterapia / Photoacustic study of human teeth submitted to radiotherapy

Objetivo: Esta pesquisa teve como objetivo a caracterização, pela técnica de Espectroscopia de Absorção Fotoacústica, do efeito da radiação X sobre os tecidos dentais humanos mineralizados, irradiados com doses usada para tratamento de pacientes portadores de câncer de cabeça e pescoço. Materiais e métodos: As radiações foram fornecidas por um acelerador linear em dentes humanos seccionados longitudinalmente, onde a porção central foi investigada em três regiões: esmalte, dentina coronária e dentina cervical, antes e após as irradiações. 20 dentes foram analisados, onde um grupo formado por 10 dentes foi irradiado com dose total de 70 Gy fracionada em doses diárias de 2 Gy, enquanto outro grupo também com 10 dentes foi irradiado com uma dose única de 70 Gy. Resultados: Após a irradiação, foi observada uma redução significativa na difusividade térmica de 47 e 40% no esmalte, 43 e 37% na dentina coronária e 60 e 48% na dentina cervical, para a radiação em dose fracionada e única, respectivamente. Discussão: As medições da difusividade térmica das regiões analisadas, antes de serem irradiadas, mostraram que os valores encontrados estão de acordo com a literatura, enquanto que a forte queda da difusividade mostrou uma degradação da estrutura dentária. Além disso, a aplicação da radiação X gerou danos significativos ao dente que podem propiciar a for-mação e propagação das cáries de radiação. Conclusão: A redução da difusividade térmica observada retarda tanto a dissipação do calor, quanto a velocidade que este atinge as regiões internas do dente, levando a um retardo na sensação da dor, podendo acarretar no uso excessivo de energia durante os procedimentos odontológicos.

Aim: This research aimed to characterize, by the technique of Photoacoustic Absorption Spectroscopy, the effect of X-radiation on mineralized human dental tissues, irra-diated with doses used for the treatment of patients with head and neck cancer. Materials and methods: Radiation was introduced by a linear accelerator in humans teeth longitudinally sectioned, where the central portion was investigated in three regions: enamel, coronary dentin and cervical dentin, before and after irradiation. 20 teeth where analyzed, where a group formed by 10 teeth was irradiated with a total dose of 70 Gy, divided into daily doses of 2 Gy, while another group, also with 10 teeth, was irradiated with a single dose of 70 Gy. Results: After irradiation, a significant reduction in thermal diffusivity of 47 and 40% in enamel, 43 and 37% in coronary dentin and 60 and 48% in cervical dentin was observed for radiation in fractional and single doses, respectively. Discussion: The measures, obtained before the radiation, of thermal diffusivity on the analyzed regions, showed that the values found in this work are in agreement with the literature, while the strong fall in the thermal diffusivity showed that a degradation in the dental structure happened. In addition, the application of X radiation caused significant damage to the tooth that could promote the formation and propagation of radiation caries. Conclusion: The reduction in thermal diffusivity observed slows down both heat dissipation and the speed at which it reaches the internal regions of the tooth, leading to a delay in the sensation of pain, which may result in excessive energy usage during dental procedures.

Evaluation of the coefficient of thermal expansion of human and bovine dentin by thermomechanical analysis

The mismatch of thermal expansion and contraction between restorative materials and tooth may cause stresses at their interface, which may lead to microleakage. The present work compared the coefficient of thermal expansion (CTE) with the thermomechanical behavior of human and bovine teeth and determined if the CTE is a suitable parameter to describe tooth behavior. Fifteen human third molar and 15 bovine incisor tooth slices (6×5×2 mm) were allocated to 3 groups according to the test environment: G1 - room condition, G2 - 100 percent humidity, G3 - desiccated and tested in dry condition. Each specimen was weighed, heated from 20 to 70ºC at 10ºC min−1 and reweighed. The CTE was measured between 20 and 50ºC. Fresh dentin (human -0.49 percent ± 0.27, bovine -0.22 percent ± 0.16) contracted on heating under dry condition. Under wet conditions, only human teeth (-0.05 percent ± 0.04) showed contraction (bovine 0.00 percent ± 0.03) accompanied by a significantly lower (p<0.05) weight loss than in dry specimens (human 0.35 percent ± 0.15, bovine 0.45 percent ± 0.20). The desiccated dentin expanded on heating without obvious weight changes (0.00 percent ± 0.00). The CTE found was, respectively, in dry, wet and dissected conditions in ºC-1: human (-66.03×10-6, -6.82×10-6, 5.52×10-6) and bovine (-33.71×10-6, 5.47×10-6, 4.31×10-6). According to its wet condition, the dentin showed different CTEs. The thermal expansion behavior of human and bovine dentin was similar. A simple evaluation of the thermal expansion behavior of tooth structure by its CTE value may not be appropriate as a meaningful consideration of the effects on the tooth-material interface.

A discrepância entre a expansão e a contração térmica dos materiais restauradores e o dente podem causar estresse na sua interface, podendo levar a uma microinfiltração. O presente trabalho determinou e comparou o coeficiente de expansão térmica (CET) com o comportamento termo mecânico dos dentes humanos e bovinos e determinou se o CET é um parâmetro adequado para descrever o comportamento dental. 15 fatias (6×5×2 mm) de terceiros molares humanos e 15 de incisivos bovinos foram divididos em 3 grupos de acordo com o ambiente testado: G1 - condição ambiente, G2 - 100 por cento de umidade, G3 - dissecado e testado em condição seca. Cada espécime foi pesado, aquecido de 20 a 70C a 10ºC min-1 e pesados novamente. O CET foi mensurado entre 20 e 50ºC. Dentina fresca (humana -0,49 por cento ± 0,27, bovina -0,22 por cento ± 0,16) contrai no aquecimento sobre condição seca. Em condição úmida, somente dente humano (-0,05 por cento ± 0,04) mostrou contração (bovina 0,00 por cento ± 0,03) acompanhado por uma significante (p<0.05) perda de massa que os espécimes secos. A dentina dissecada expande no aquecimento sem mudanças óbvias de peso (0,00 por cento ± 0,00). O CET encontrado foi, respectivamente, em condições seca, úmida e dissecada em ºC-1: humana (-66,03×10-6, -6,82×10-6, 5,52×10-6) e bovina (-33,71×10-6, 5,47×10-6, 4,31×10-6). De acordo com sua condição de umidade, a dentina mostrou diferentes CETs. O comportamento de expansão térmica de dentes humanos e bovinos é similar. Uma simples avaliação do coeficiente de expansão térmica da estrutura dental pelo seu valor de CET pode não ser apropriada para uma consideração significativa dos efeitos na interface dente-material restaurador.

Changes of Hepatic Microcirculation Measured by Thermal Diffusion Probe after Vasopressor Infusion

PURPOSE: Various vasopressor agents are used to raise systemic vascular resistance (SVR) during liver transplantation. After grafted liver was reperfused, postreperfusion syndrome could be treated with various vasopressors. However, epinephrine can decrease the splanchnic perfusion and oxygen saturation and then hepatic blood flow would be jeopardized. Decreased hepatic blood flow might result in centrilobular necrosis which contributes to disruption of liver functions. We tried to know the effect of epinephrine on tissue perfusion of the liver. METHODS: In this study, measurement of hepatic microcirculation (HMC) and hemodynamic changes was performed in eight dogs to investigate the effect of vasopressors on hepatic microcirculation. Animals were divided into four groups in which low-dose epinephrine (0.05mug/Kg/min) and high-dose epinephrine (0.5mug/Kg/min) were randomly infused into the systemic vein and portal vein (1/6 of systemic dose) for ten minutes. Hepatic microcirculation was measured by Thermal Diffusion Probe. RESULTS: At low-dose systemic infusion of epinephrine, mean arterial bloodpressure (MABP), cardiac output (CO), and hepatic microcirculation (HMC) were significantly increased but systemic vascular resistance (SVR) was decreased. On high-dose epinephrine, MABP, CO (P=0.01), and SVR were significantly increased without changes of HMC. Intraportal infusion of low- and high-dose epinephrine increased hepatic vein pressure and SVR, respectively. CONCLUSION: These results would provide clues that systemic low-dose epinephrine infusion is enough to raise HMC and high-dose infusion of epinephrine to raise SVR could be used without jeopardizing HMC.

Continuous Monitoring of Regional Cortical Blood Flow in Aneurysm Surgery

OBJECTIVE: The tolerance and the safety of temporary arterial occlusion in aneurysm surgery are variable among patients because of individual variations of their collateral circulation. We recorded continuous intraoperative regional cortical blood flow(rCoBF) with thermal diffusion flowmetry(TDF) in patients with aneurysmal subarachnoid hemorrhage to determine a safe time limit for temporary occlusion in relation to rCoBF. PATIENTS AND METHODS: From Oct. '97 to Sep. '98, 40 patients with cerebral aneurysm at anterior cerebral artery(ACA) or middle cerebral artery(MCA) were included in this study. The TDF probe was placed over the cortex which was supplied by corresponding arteries. For data analysis, we included only the patients with Hunt-Hess grade I or II on admission. RESULTS: The total occlusion time of the proximal parent artery in 24 patients was on average 21.8 minutes, ranging between 9 minutes and 68 minutes. The lowest rCoBF in relation to temporary occlusion time in patient with excellent outcome was as follows: 0ml/100mg/min for 13 minutes and 6ml/100mg/min(11% of basal rCoBF) for 18 minutes in the middle cerebral artery and bilateral anterior cerebral arteries, respectively. The multiple regression equation regarding safe time for temporary clipping was as follows: safe time = 5.5 + 0.06 X rCoBF intra + 0.25 X rCoBF pre. And reperfusion time for the full recovery of rCoBF was within 4 minute in most cases, except some no-reflow cases. CONCLUSION: In our study with proper brain protection, a safe time limit for temporary occlusion was calculated 18 minutes even at 0ml/100mg/min in the MCA and this technique seems to be very useful to detect a continuous real time change of rCoBF during aneurysm surgery.