Physical and chemical properties of orthodontic brackets after 12 and 24 months: in situ study.

OBJECTIVE: The aim of this article was to assess how intraoral biodegradation influenced the surface characteristics and friction levels of metallic brackets used during 12 and 24 months of orthodontic treatment and also to compare the static friction generated in these brackets with four different methods of the ligation of orthodontic wires. MATERIAL AND METHODS: Seventy premolar brackets as received from the manufacturer and 224 brackets that were used in previous orthodontic treatments were evaluated in this experiment. The surface morphology and the composition of the deposits found in the brackets were evaluated with rugosimetry, scanning electron microscopy, and energy dispersive X-ray spectroscopy. Friction was analyzed by applying tensile tests simulating sliding mechanics with a 0.019x0.025" steel wire. The static friction levels produced by the following ligation methods were evaluated: loosely attached steel ligature around all four bracket wings, steel ligature attached to only two wings, conventional elastomeric ligation around all 4 bracket wings, and non-conventional Slide® elastomeric ligature. RESULTS: The results demonstrated the presence of biodegradation effects such as corrosion pits, plastic deformation, cracks, and material deposits. The main chemical elements found on these deposits were Carbon and Oxygen. The maximum friction produced by each ligation method changed according to the time of intraoral use. The steel ligature loosely attached to all four bracket wings produced the lowest friction levels in the new brackets. The conventional elastic ligatures generated the highest friction levels. The metallic brackets underwent significant degradation during orthodontic treatment, showing an increase in surface roughness and the deposit of chemical elements on the surface. CONCLUSION: The levels of static friction decreased with use. The non-conventional elastic ligatures were the best alternative to reduce friction.

Desenvolvimento de metodologia para fabricação de pastilhas de cobre para utilização em esterilização feminina não cirúrgica com quinacrina / Development of methods for the manufacturing of copper pellets to use inquinacrine female non-surgical sterilization

Objetivo: A esterilização feminina não cirúrgica por meio da aplicação intracervical de pastilhas de quinacrina foi considerada um método contraceptivo definitivo, de baixo custo, seguro e eficaz, e é sabido que a adição do cobre aumenta a eficácia da quinacrina. Com o objetivo de produzir pastilhas de cobre a serem aplicadas juntamente com pastilhas de quinacrina, foi desenvolvido, no Centro de Desenvolvimento daTecnologia Nuclear da Comissão Nacional de Energia Nuclear (CDTN/CNEN), um processo para sua fabricação. Material e métodos: Utilizou-se póde cobre metálico esferoidal e amido de milho e empregaram-se as mesmas técnicas de metalurgia do pó empregada na fabricação de pastilhas combustíveis nucleares. Resultados: Foi possível definir o teor ideal de amido de milho para diminuir o intertravamento entre as partículas metálicas de cobre que propicia uma adequada desagregação das pastilhas quando umidificada, de modo a criar no útero um ambiente rico em cobre antes da dissolução das pastilhas de quinacrina. Conclusões: Foram, então, produzidas 200 pastilhas de cobre com 6% em peso de amido de milho, para viabilizar um projeto de pesquisa da Faculdade de Medicina da Universidade Federal de Minas Gerais sobre esterilização feminina não cirúrgica com quinacrina. São descritas as técnicas, os testes e os resultados do desenvolvimento desta metodologia.

Objectives: Non-surgical female sterilization through the transcervical insertion of quinacrine pellets was considered a definitive, low-cost, safe and effective contraceptive method. The addition of copper increases the efficacy of quinacrine, reducing the risk of pregnancy due to a failure in the obstruction’s procedure of the Fallopian tubes. In order to produce copper pellets to be applied together with the quinacrine pellets, a manufacturing procedure was developed at Centro de Desenvolvimento da Tecnologia Nuclear da Comissão Nacional de Energia Nuclear (CDTN/CNEN). Material and Methods: It was used spheroidal metallic copper and corn starch and the same technics of powder metallurgy employed to the fabrication of nuclear fuel pellets. Results: It was possible to defi ne the ideal corn starch content to decrease the interlock degree between the metallic copperparticles that provide an appropiate desintegration of the pellets when humidfied in order to create in the uterus an environment rich in copper before the quinacrine pellet dissolution. Conclusions: Two hundred copper pellets were produced with 6% by weight of corn starch to make possible a research project of Faculdade de Medicina of Universidade Federal de Minas Gerais about non-surgical female sterilization with quinacrina. The techniques, tests and results of the developed methodology are here presented.

Measurement of thermophysical properties of human dentin: effect of open porosity.

UNLABELLED: In dentistry caries removal can be performed with rotatory instruments or high intensity laser. Both techniques can heat the tooth and harm the pulp. The literature review about the measurement of human dentin thermophysical properties revealed a great variation of the values obtained by several authors, and most of the studies are outdated. Most of these studies have not directly measured the thermal diffusivity of human dentin, and the reported values are calculated values based on measurements of conductivity, density and specific heat. OBJECTIVE: The aim of the present study was to measure human dentin thermal diffusivity, density, open porosity and specific heat, and then to calculate its thermal conductivity and analyze the influence of open porosity in these properties. METHOD: The methods used were: flash laser method for measuring thermal diffusivity, method of penetration and immersion with xylol for density and open porosity and differential scanning calorimetry for measuring specific heat. Calculated results of the thermal conductivity are shown as well. RESULT: Results of diffusivity, density, open porosity, specific heat and thermal conductivity of measurements performed on five samples are presented and compared with results of other authors. The open porosity of the samples varied between 1.11% and 3.08% of the sample volume, corresponding to densities ranging between 2090 and 2400 kg m(-3), thermal diffusivity: 0.199 and 0.265 x 10(-6)m2 s(-1), specific heat: 872.5 and 1181.0 J kg(-1)K(-1), thermal conductivity: 0.363 and 0.666 W m(-1)K(-1). CONCLUSION: It has been found that there exist a strong correlation between the open porosity of human dentin and its thermal conductivity and density. Both human dentin thermal conductivity and density decrease with the increasing of open porosity, with a confidence of at least 98% and 96.6%, respectively.