Translucency, Stain Resistance, and Hardness of Composites Used for Invisalign Attachments

Align Technology, the company behind Invisalign, shipped more than 422,300 clear-aligner prescriptions in 2013; as of 2015, the company supports 44,240 active providers, including both orthodontists and general practitioners. Perhaps the most important advantage of clear aligners, at least from the standpoint of patient acceptance and demand, is their esthetic appearance. To maintain that "invisible" look while achieving difficult movements such as rotation, composite attachments are bonded to the facial surfaces of teeth. Although Invisalign markets a dental restorative composite for making these attachments, some practitioners use orthodontic adhesives due to their convenience and availability. Because orthodontic adhesives are formulated for bonding brackets, however, their esthetic and mechanical properties may not be sufficient for making attachments. An aligner attachment needs to either match the color of the natural tooth or be translucent enough to blend with the underlying tooth. Translucency is preferable because it allows the use of one material for all patients and is more esthetic when working with polychromatic teeth. A second important esthetic consideration is the attachment's resistance to staining. Finally, the wear of composite attachments, as the patient repeatedly removes and replaces the aligners, is crucial because it may affect the retentive force of the aligner and thus lead to less efficient tooth movement.