Tensile Bond Strength of Light-Activated Glass Ionomer for Bonding Metal and Ceramic Brackets

Abstract

Visible light-activated glass ionomer offers several advantages over conventional autopolymerizing adhesives, such as extended control of working time, immediate ligation, fluoride release, and a chemical bond to enamel. This study compared in vitro tensile bond strength of a new light-activated glass ionomer with that of a chemically-cured glass ionomer for bonding ceramic and metal orthodontic brackets. The manufacturer's recommended light-activation time of 30 seconds was evaluated by Knoop hardness testing. Specimens cured for 30 and 60 seconds were evaluated with Knoop hardness testing at various time intervals over a 24-hour period. An evaluation of the data indicated that the manufacturer's recommended cure time was adequate. Human maxillary premolars were divided into six groups of 20. Each group was bonded with either light-activated glass ionomer or a chemically-cured glass ionomer utilizing either metal or ceramic brackets. After bonding, specimens were thermocycled and stored in water at 37°C for 14 days. After the 14-day storage period specimens were tested in the tensile mode of an lnstron testing machine until failure. Ceramic brackets were found to have a significantly greater mean tensile bond strength than metal brackets when light-activated glass ionomer was used as the bonding agent. Mean tensile bond strength of metal brackets bonded with light-activated glass ionomer were significantly greater than metal brackets bonded with a chemically-cured glass ionomer. Ceramic brackets had a negligible bond strength when bonded with a chemically-cured glass ionomer. The light-activated glass ionomer tested in this study appears to have an adequate in vitro mean tensile bond strength to be considered for an orthodontic bonding adhesive.