Assessment of the mechanical properties of glass ionomer cements for orthodontic cementation

OBJECTIVE: To evaluate the mechanical properties of three glass ionomers cements (GICs) used for band cementation in Orthodontics. METHODS: Two conventional glass ionomers (Ketac Cem Easy mix/3M-ESPE and Meron/Voco) and one resin modified glass ionomer (Multi-cure Glass ionomer/3M-Unitek) were selected. For the compressive strength and diametral tensile strength tests, 12 specimens were made of each material. For the microhardness test 15 specimens were made of each material and for the shear bond strength tests 45 bovine permanent incisors were used mounted in a self-cure acrylic resin. Then, band segments with a welded bracket were cemented on the buccal surface of the crowns. For the mechanical tests of compressive and diametral tensile strength and shear bond strength a universal testing machine was used with a crosshead speed of 1,0 mm/min and for the Vickers microhardness analysis tests a Microdurometer was used with 200 g of load during 15 seconds. The results were submitted to statistical analysis through ANOVA complemented by Tukey's test at a significance level of 5%. RESULTS: The results shown that the Multi-Cure Glass Ionomer presented higher diametral tensile strength (p < 0.01) and compressive strength greater than conventional GICs (p = 0.08). Moreover, Ketac Cem showed significant less microhardness (p < 0.01). CONCLUSION: The resin-modified glass ionomer cement showed high mechanical properties, compared to the conventional glass ionomer cements, which had few differences between them.

OBJETIVO: avaliar as propriedades mecânicas de três cimentos de ionômero de vidro (CIVs) utilizados para cimentação de anéis ortodônticos. MÉTODOS: foram utilizados dois CIVs convencionais (Ketac Cem Easy mix/3M-ESPE e Meron/Voco) e um CIV modificado por resina (Multi-Cure Glass ionomer/3M-Unitek). Para os testes de resistência à compressão e tração diametral, foram confeccionados 12 corpos de prova de cada material. Para os testes de microdureza, foram confeccionados 15 corpos de prova de cada material; para os testes de resistência de união ao cisalhamento, foram utilizados 45 dentes bovinos incluídos em resina acrílica, sobre os quais foi cimentada uma lâmina de anel ortodôntico com braquete soldado a ela para a realização dos ensaios. Para os testes de compressão, tração diametral e cisalhamento, foi utilizada uma máquina universal de ensaios a uma velocidade de 1mm/min; para os testes de microdureza Vickers, foi utilizado um microdurômetro com 200g de carga durante 15 segundos. Os resultados foram submetidos à análise estatística ANOVA, complementada pelo teste de Tukey ao nível de significância de 5%. RESULTADOS: os resultados demonstraram que o Multi-Cure Glass Ionomer apresentou resistência à tração diametral significativamente maior (p < 0,01) e maior resistência à compressão (p = 0,08) em relação aos CIVs convencionais. Além disso, o Ketac Cem apresentou microdureza significativamente maior que os demais materiais (p < 0,01). CONCLUSÃO: o CIV modificado por resina apresentou propriedades mecânicas superiores às dos CIVs convencionais, que, por sua vez, apresentaram poucas diferenças entre si.

Cytotoxicity of silver solder employed in orthodontics.

OBJECTIVE: To test the null hypothesis that the silver soldering employed in orthodontics is not cytotoxic for fibroblasts. MATERIALS AND METHODS: This in vitro study was performed using a culture of mice fibroblasts (lineage NIH/3T3), divided into four groups (n = 10 each): control, negative control (stainless steel archwire), positive control (amalgam disks), and test group (silver soldering). After cell culture in complete Dulbecco modified eagle medium and achievement of confluence in 80%, the suspension was added to the plates of 24 wells containing the specimens and incubated in an oven at 37 degrees C for 24 hours. The plates were analyzed on an inverted light microscope, photomicrographs were obtained, and the results were recorded as response rates based on modifications of the parameters of Stanford according to the size of the diffusion halo of the toxic substance and quantity of cell lysis. RESULTS: The results revealed a maximum response rate for the silver soldering group, as well as severe inhibition of cell proliferation and growth, more round cells with mostly darkened and granular aspects, suggesting lysis with cell death. A similar response was seen in the positive control group. CONCLUSION: The hypothesis is rejected. The silver soldering used in orthodontics represents a highly cytotoxic material for the cells analyzed.