Bond strength of fiber-reinforced composite bars for orthodontic attachment

Long fiber-reinforced composites (FRC) have been shown to have enhanced mechanical properties that allow their use in orthodontic appliances as bars that join teeth to form either anchorage or active units. This study was designed to determine if the bonding of an orthodontic attachment has sufficient strength to withstand loading during clinical use. The experimental model consisted of a hydroxyapatite stone that simulated enamel, FRC bars, and a bonded metal hook. Three specimen types were compared: (1) a metal hook-pad (the control), (2) a woven FRC with a hook-pad, and (3) a unidirectional FRC with a hook-pad. Loads were applied both parallel and at 90 degrees to the tooth surface. Under no condition was the FRC pad combination weaker than the control pad. Under some loading conditions, the loads before failure were as much as 3 times greater than those for the control. The lowest strength was found with loads at 90 degrees to the tooth surface for all 3 types. Failure normally occurred in the FRC and rarely at the bracket or tooth interface. The excellent bonding of the orthodontic attachment to the FRC and the high strengths of the FRC attachment combination demonstrate the ability to form connecting bars between teeth for either anchorage or active segmental movements. These bars offer advantages in simplicity in treatment by reducing the need for some bands, attachments, or wires.