Avalição in vitroda resistência ao cisalhamento de braquetes colados em diferentes sistemas cerâmicos / In vitro short-term evaluation of shear strength of brackets bonded to different porcelain systems

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

Orthodontic treatment in the adult population has lately gained popularity in an attempt to improve esthetic and function. It is, however, a common feature in these patients, that their dentition is restored by resin veneers, porcelain fused to metal and all ceramic crowns. In this context, the orthodontist faces the challenge of bonding brackets to different porcelain based materials, of unknown ability to resist shear forces. Thus, the aim of this investigation was: 1) to test the null hypothesis that shear strength of brackets bonded to feldspathic and AllCeram porcelain surfaces is not affected by different hydrofluoridric etching times and 2) to test the null hypothesis that there is no direct relation between shear strength values and the adhesive remanescent index (ARI). Sixty feldspathic porcelain disc shaped specimens were randomly divided into 3 groups of 20 each, according to hydrofluoridric acid etching time of either 15, 30 seconds and 1 minute (groups 1, 2 and 3, respectively). Another 60 AllCeram specimens of the same shape were subjected to the same division, according to etching time (groups 4, 5, and 6 respectively). Bonding the brackets to the porcelain surfaces included silane coating, an overlying photoactivated resin and a standardized 500g cementation force. Twenty-four hours after cementation, at 37oC in destilled water, specimens were subjected to a shear force in a universal testing machine at a cross-head speed of 0,5mm/min and shear values registered in Kgf and then converted to MPa. Type of failure was lso recorded using ARI by means of a stereoscope at 4x augmentation. The highest shear strength was found for group 1 (21.21 MPa), which was significantly different than groups 2, 3, 4, 5, and 6 (11.01, 10.64, 14.31, 10.59, 10.39 MPa). The lower values found in the remaining groups were not different among each other. Median ARI scores for groups 1, 2, 3, 4, 5, and 6 were 2, 3, 3, 0, 3, and 3, respectively. The first hypothesis must be partially rejected since only feldspathic porcelain group 1 was affected by different hydrofluoric etching times, when compared to groups 2 and 3, while AllCeram groups 4, 5, and 6 were not. On the other hand, the second null hypothesis must be accepted since no direct relation between ARI score and shear strength values could be determined.

ASSUNTO(S)

colagem braquetes hydrofluoric acid brackets porcelana ácido fluorídrico bonding porcelain

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