What is Invisalign and How Does It Move Teeth (Part 2)?

(This is Part 2 of a 2-part Invisalign post. Part 1 of this article discussed the design and manufacturing of Invisalign aligners.)

There are three steps to "delivering" your aligners
After your Invisalign aligners have been designed by your orthodontist and manufactured by Align Technology, the entire set is shipped to your doctor’s office. There is more to achieving a successful result however than merely handing a box full of plastic shells to a patient. If that were not the case, Align would merely ship the aligners directly to the patient and cut out the “middleman.” There are three additional procedures provided by your orthodontist at the delivery appointment that are essential for the success of your treatment.

Attachments are bonded to provide "handles" on the teeth
The first procedures is the bonding of “attachments” onto the surfaces of some teeth to enable movements that without them would be physically impossible. Imagine a generic tooth that is not only smooth and round, but also tapers to a point at the end. By itself, a plastic shell would have no way to hold onto such a tooth to rotate (turn) or extrude it (make it longer). These movements require some mechanism for the aligners to grip the tooth. Tooth-colored bumps or attachments serve this function for Invisalign. Picture the colorful hand holds that are attached to climbing walls so climbers have something to hold onto as they ascend. Similar “hand holds” are bonded to some of the teeth prior to Invisalign treatment using the same tooth-colored composite that a dentist uses for restoring broken or decayed teeth.

Attachments are prescribed by your orthodontist for specific movements
Attachments have different shapes and sizes that are dictated by the desired direction and amount of force that must be generated. If a tooth needs to rotate, the attachment will have a flat surface on which the plastic can push to cause that movement. For a tooth to be made longer, there is a different shaped attachment onto which the aligner can push to accomplish that. While patients may wish they didn’t need to have anything glued to their teeth during treatment, there are just some movements that are impossible without attachments. Although computers algorithms at Align Technology initially propose the size and shape of the bumps, it is up to the prescribing doctor to dictate exactly how fast and which direction a tooth moves. For this reason, some doctors are better than others at straightening teeth with aligners. Remember that Invisalign is just a tool the doctor uses to move teeth. The Invisalign manufacturer does not determine how to move the teeth or what the final result will look like.

Sometimes reshaping the teeth is necessary so they will "fit together"
The second procedure performed at the delivery appointment (or some time along the way) is the reshaping of the teeth so that they will fit correctly at the end of treatment. I use slenderizing or Inter-Proximal Reduction (IPR) in about 75% of my conventional braces patients. The timing and amount are determined along the way. The digital setups created for the manufacturing of the aligners however let me know up front which teeth must be altered and by how much. The most common reasons for IPR include crowding, mismatched tooth sizes, or the creation of dental compensations to help correct skeletal problems (i.e. slenderizing the upper anteriors to reduce excessive “overbite”). Cases can be treated without IPR, but it may be impossible to arrive at the best result without it. As with braces, about 75% of my aligner patients require some enamel reshaping.

As with braces, correcting your bite may require rubber bands
The last step of aligner delivery is the delivery of any adjunct (additional) devices required for treatment. The most common of these are elastics or rubber bands. Although aligners can make teeth straight within their respective arch, the correction of bite problems between the upper and lower sets of teeth require that something be connected between the two. Conditions requiring that elastics be worn include overbites, underbites, and crossbites. Attaching rubber bands to the teeth may required that “buttons” be bonded to the teeth in one or both arches. Although some elastics can be attached directly to the aligners, others create a direction of pull that would unseat them and make them ineffective. High tech alternatives to classic rubber bands have been developed (i.e. the Motion appliance), but the result is the same.

After the attachments, buttons, and IPR are completed, the orthodontist finally delivers the aligners and gives the patient instructions on how to wear and care for them. Look for articles on my blog discussing these and other aligner topics.

NOTE: The author, Dr. Greg Jorgensen, is a board-certified orthodontist who is in the private practice of orthodontics in Rio Rancho, New Mexico (a suburb on the Westside of Albuquerque). He was trained at BYU, Washington University in St. Louis, and the University of Iowa in the United States. Dr. Jorgensen’s 25 years of specialty practice and nearly 10,000 finished cases qualify him an expert in two-phase treatment, extraction and non-extraction therapy, functional orthodontics, clear aligners (Invisalign), and multiple bracket systems (including conventional braces, Damon and other self-ligating brackets, Suresmile, and lingual braces). This blog is for informational purposes only and is designed to help consumers understand currently accepted orthodontic concepts. It is not a venue for debating alternative treatment theories. Dr. Jorgensen is licensed to diagnose and treat patients only in the state of New Mexico. He cannot diagnose cases described in comments nor can he select treatment plans for readers. Please understand that because he has over 40,000 readers each month, IT IS IMPOSSIBLE FOR HIM TO RESPOND TO EVERY QUESTION. Please read all the comments associated with each article as most of the questions he receives each week have been asked and answered previously. The opinions expressed here are protected by copyright laws and can only be used with written permission from the author.