(http://www.invisalign.com/generalapp/us/en/what/index.jsp, January 20, 2006).
Invisalign can theoretically be used to attempt to treat all malocclusions, but this technology has some confines. It is difficult to use Invisalign in situations that have crowding or spacing of over 5mm, severely tipped or rotated teeth, skeletal anterior-posterior discrepancies of over 2mm, and situations which require the extrusion of teeth (Joffe, 2003). Aside from these limitations, Joffe (2003), found that Invisalign technology is a beneficial treatment option over conventional appliances, providing nearly ideal esthetics, comfort during wear, and simplicity of oral hygiene. However, major drawbacks to Invisalign include that control over root movements are limited, including gross rotation correction, tooth extrusion, and root paralleling. There is also a lack of operator control after treatment has been initiated due the fact that all the aligners for a specific case are made at the beginning of treatment. The operator, therefore, has no ability to alter the appliances mid-treatment without restarting the treatment from the beginning, which increases the cost to the patient (Joffe, 2003). In a 2004 study Djeu, Shelton and Maganzini, compared the treatment outcomes of Invisalign versus full fixed braces. They found many of the same findings as Joffe (2003), indicating that Invisalign was not proficient at extruding teeth, treating large skeletal anterior-posterior discrepancies, or spaces larger than 6mm. It was also shown that Invisalign was not able to attain adequate occlusal contact compared to those found with full fixed braces. This study did nonetheless, find that Invisalign treated cases were able to achieve a similar result to full fixed braces with regard to root angulations. This result was somewhat surprising as Invisalign was thought to be poor at controlling root position, but may have been due to the fact that extraction cases were not studied. A study of extraction cases treated with invisalign revealed that Invisalign is not able to produce correct root inclinations as the spaces were generally closed though crown tipping, rather that bodily movements (Giancotti, 2006)