Effect of different enamel conditionings on the bond strength of glass ionomer cement and ceramic brackets

Aim: To evaluate the effect of different enamel conditionings on the shear bond strength (SBS) and bond failure patterns of a resin modified glass ionomer cement (RMGIC) used to bond ceramic brackets. Methods: 105 human premolars extracted for orthodontic reasons were divided into 7 groups according to the enamel surface treatments: conditioners (35% phosphoric acid and 10% polyacrylic acid), type of adhesive (Transbond(r) and Fuji Ortho LC Capsule(r)), washing time and drying of the surface. Results: A significant p<0.05 was observed among the shear bond strength values obtained with seven different types of enamel preparation prior to bonding. The group that had the tooth surface conditioned with polyacrylic acid and enamel surface slightly dried before bracket placement showed no significant difference (p>0.05) to the group that had brackets bonded with composite resin. The two groups that had enamel prepared with polyacrylic acid and brackets bonded with GIC on a wet surface showed significantly lower shear bond strength than the control group (p<0.05). Conclusions: Moisture contamination decreased SBS, but not enough to preclude the use of RMGIC as an alternative to composite resin (CR) for direct bonding of ceramic brackets.

Comparison of the mechanical properties of two nano-filled composite materials / Comparação das propriedades mecânicas de dois materiais nanocompósitos

OBJETIVO: A finalidade deste estudo foi quantificar e comparar as propriedades mecanicas de dois materiais restauradores nanocompositos disponiveis comercialmente. MATERIAL E METODO: Especimes de dois nanocompositos, Z350TM e GrandioTM, foram polimerizados com luz LED por 30 segundos e submetidos a testes mecanicos. As propriedades testadas incluiram: resistencia flexural, resistencia tensil diametral, resistencia a fratura e microdureza (topo e fundo). RESULTADOS: O Grandio apresentou valores de resistencia flexural media maiores quando comparados com o Z350 (89.1 MPa vs 61.9 MPa). O Grandio demonstrou maior microdureza das superficies de topo de cada composito quando comparada com sua correspondente superficie de fundo. As propriedades de resistencia a fratura e forca tensil diametral nao foram fatores discerniveis neste estudo em particular. CONCLUSAO: Grandio possui maiores valores para propriedade de resistencia flexural e dureza quando comparado com o Z350. Nao houve diferencas entre os dois materiais em relacao a resistencia a fraturas e resistencia a forcas tenseis diametrais.

OBJECTIVE: The purpose of this study was to quantify and compare the mechanical properties of two commercially available nanocomposite restorative materials. MATERIAL AND METHODS: Specimens of two nanocomposites, Z350TM and GrandioTM, were polymerized with a LED light for 20 seconds and subjected to mechanical tests. Properties tested included: flexural strength, diametral tensile strength, fracture toughness and microhardness (top and bottom). RESULTS: Grandio exhibited significantly higher mean flexural strength values when compared to Z350 (89.1 MPa vs 61.9 MPa). Grandio exhibited significantly higher top microhardness values when compared to Z350. Additionally when microhardness for the top surfaces of each composite were compared with their corresponding bottom surfaces, the bottom surfaces demonstrated significantly lower readings. The properties of fracture toughness and diametral tensile strength were non-discerning factors in this particular study. CONCLUSION: Grandio has greater observed values for the properties of flexural strength and hardness when compared with Z350. There was no difference between the two materials with respect to their fracture toughness and diametral tensile strength.