OBJETIVO: analisar separada e comparativamente cinco marcas comerciais de elásticos sintéticos (Morelli, Ormco, GAC, TP e Unitek) quanto à degradação da força gerada por estes em função do tempo, quando mantidos continuamente estirados em uma distância de 20mm. METODOLOGIA: as leituras das quantidades de força gerada pelos elásticos foram feitas nos intervalos 1/2, 1, 6, 12, 24, 48 horas; 7, 14, 21 e 28 dias. Construiu-se um gráfico de força versus tempo, onde se pôde observar significativa redução na quantidade de força liberada pelos elásticos na primeira hora de ativação. RESULTADOS: verificou-se uma redução na quantidade de força gerada pelos elásticos de 20,31 a 38,47% na primeira hora de testes e de 47,7 a 75,95% em 28 dias de estiramento constante. CONCLUSÕES: concluiu-se que todas as amostras das marcas comerciais estudadas sofreram significativa redução na quantidade de força liberada na primeira hora de ativação e que a média de força gerada em 21 e 28 dias de testes foi semelhante para todas as amostras pesquisadas.

Objective: The purpose of this study was to assess the effects of laser irradiation and self-etching primer on the microleakage of apicoectomized teeth retro filled with mineral trioxide aggregate (MTA). Materials and Methods: A total of 60 bovine teeth were endodontically treated and had the apical 3 mm resected. Root-end cavities were prepared and the specimens were divided into five groups: Group 1 -control group, teeth only retrofiled with MTA; Group 2 -specimens treated with neodymium-doped yttrium aluminum garnet (Nd: YAG) laser on the inner walls of the root-end cavities; Group 3 -specimens treated as Group 2 added with Nd: YAG laser on the surface of the apical resection; Group 4 -teeth treated with self-etching primer on the inner walls of the root-end cavities, and Group 5 -teeth treated as Group 4 and in addition, treated with self-etching primer on the surface of the apical resection. All the specimens were retrofiled with MTA and sealed with varnish. The teeth were immersed in 2% rhodamine B dye for 24 h. After this period, roots were washed, dried and resected. Marginal microleakage at material/root surface interface was evaluated quantitatively through linear measure in mm with the aid of a steromicroscope and calculated by an image program. Results:The mean values obtained were: Group 1 -2.76 ± 0.60; Group 2 -2.30 ± 0.84; Group 3 -2.21 ± 0.85; Group 4 -1.04 ± 0.76, and Group 5 -0.84 ± 0.40. ANOVA showed a significant difference among the groups (P < 0.05) and Tukey's test revealed that Group 1, Group 2 and Group 3 were different from Group 4 and Group 5. Conclusion: It was concluded that groups that used self-etching primer presented significantly lower degrees of marginal microleakage. Teeth treated with Nd: YAG laser presented same results as control group. The area of application did not reduce marginal leakage (for both laser and self-etching primer). Only MTA as a retro filling material was not sufficient to prevent marginal microleakage.