Invisalign

Editor in Chief: Berna Zorkun DMD [mailto:bernazorkun@gmail.com]

Invisalign is a series of clear, removable teeth aligners that both orthodontists and dentists use as an alternative to traditional metal dental braces. As of April 2008, more than 730,000 patients have completed or are currently in treatment.

Invisalign is designed, manufactured, and marketed by Santa Clara, California-based medical-device company Align Technology, Inc. Align says that over 35,790 doctors are trained to provide Invisalign treatment in the U.S., with 48,130 doctors worldwide.

Advantages
The most obvious advantage of the treatment is cosmetic: the aligners are completely transparent, therefore far more difficult to detect than traditional wire and bracket braces. This makes the method particularly popular among adults who want to straighten their teeth without the look of traditional metal braces, which are commonly worn by children and adolescents. In addition, the aligners are marketed as being more comfortable than braces. Due to the removable nature of the device, food can be consumed without the encumbrance of metallic braces.

Clinically, aligners avoid many of the side effects of traditional fixed appliances, for example the effects on the gums and supporting tissues. Fixed appliances are known to cause the roots of teeth to shorten for most patients, and demineralisation or tooth decay occurs in up to 50% of patients because they cannot be removed for eating and cleaning, and because they prevent accurate x-rays from being taken. Patients "graduate" to a new set of aligners in their treatment series approximately every two weeks. The aligners give less force per week and less pain than do fixed appliances (traditional metal braces). Fixed appliances are adjusted approximately every six weeks and apply greater forces.

Aligners should be removed to eat, drink, to clean the teeth, or to have them checked by the clinician. (It is acceptable to wear aligners while drinking water.) Computerized treatment planning is compulsory as part of the Invisalign protocol. As with other forms of orthodontic treatments that incorporate a computerized plan, this allows the prospective patient to review the projected smile design, learn how long the treatment is likely to take, compare different plans, and make a more educated decision about whether or not to use Invisalign.

Invisalign treatments have been claimed to be quicker than traditional orthodontics. A large-scale study of 408 patients with traditional appliances in Indiana took an average of 35.92 months with a maximum of 96 months, while Invisalign takes between 12–18 months. In a much smaller study Invisalign was shown to be faster and achieve straighter teeth than alternatives but relapsed to ultimately get similar results to the traditional appliances examined. The study was considered by the authors, however, to be too small for many conclusions to be statistically significant. Furthermore, this general concept that Invisalign is faster has been challenged by the Invisalign review which points out that there are other brace appliance systems that take half the time, for example by incorporating surgery or temporary implants that insert into the patient's bone, to accelerate the procedure.

Disadvantages
The product also has potential disadvantages: the very fact that the aligners are removable means they are not continually correcting the teeth. Unlike traditional fixed braces, they are largely dependent on a patient's habits and their consistency in wearing the aligners. The success of the Invisalign aligners is based on a patient's commitment to wear the aligners for a minimum of 20–22 hours per day, only removing them when they are eating, drinking, or brushing their teeth.

The system is also somewhat expensive, as conceded by the Align company, and can be more expensive than traditional wire and bracket systems.

The aligners must be removed for eating. They and the teeth should be cleaned before re-inserting afterwards. This can be troublesome for people who are constantly snacking and may mean the patient has to clean their teeth up to six times daily.

Because the aligners are removed for eating, they can become lost. Because the aligners must be removed for eating and re-inserted, problems occur in patients who forget to do these things. Invsialign treatment will not be successful in patients who forget to remove the inserts, who forget to re-insert them, or who lose them.

By their very nature, Invisalign aligner trays are not as proficient as fixed braces at moving teeth in the vertical dimension. Certain teeth are also slightly problematic for Invisalign aligners to rotate. Some lower premolars with their rounded shape can be difficult for the aligners to grasp and apply a rotational force to.

Unlike traditional braces, if a patient grinds or clenches his or her teeth during the day or while sleeping, the aligners can become damaged. In practice, however, this problem is very rare and a new aligner can be ordered. Also, similar to traditional metal braces, aligners may cause a slight lisp at the beginning of treatment. This usually disappears as the patient becomes used to the treatment.

The aligners are constructed of implantable grade polyurethane, and the Align company has acknowledged that, though extremely rare, there may be cases of allergic and toxic sensitivity reactions to Invisalign. Minor symptoms such as sore throat, cough, and nausea have been reported. In more serious cases, the FDA has received reports of systemic swelling or throat pain that has extended to the upper chest and wind passages requiring emergency medical treatment and discontinuation of the Invisalign treatment. While the Invisalign company provides no information except the MSDS (material safety data sheet) directly to patients or orthodontists, working through the patient's orthodontist Invisalign will make the aligners with several different materials to attempt to reduce toxic or allergic sensitivity.

Should the treatment go off track, or patients fail to keep the aligners in for the required length of time, then the next aligner in the series will not fit, and a new set of impressions and aligners will be necessary, adding to the cost.

Scientific studies
In a systematic review of the literature, is published in the Journal of the American Dental Association in 2005, Drs. Manual Lagravere and Carlos Flores-Mir were unable to draw strong conclusions about the effectiveness of the Invisalign system. They pointed to the need for randomized clinical trials. Since this paper, more studies about the clinical effectiveness have been published; for example in the UK, Dr Paul Humber has analyzed 100 back-to-back Invisalign cases. In the USA, Akhlaghi and colleagues compared treatment with the invisalign system with treatment with conventional braces and concluded that "conventional fixed appliances achieved better results in the treatment of Class I mild crowding malocclusions". In a comparison of outcomes between the two approaches, Kuncio et al. reported that the Invisalign group displayed greater relapse saying "the mean alignment of the Invisalign group was superior to the Braces group before and after the retention phase, but these differences were not statistically significant. Therefore, even though the Invisalign cases relapsed more, they appear to have the same, if not better, overall alignment scores." In a larger study Djeu and colleagues had similar findings to Akhlaghi above and concluded that "Invisalign was especially deficient in its ability to correct large anteroposterior discrepancies and occlusal contacts". They felt that "The strengths of Invisalign were its ability to close spaces and correct anterior rotations and marginal ridge heights." They added "Invisalign patients finished 4 months sooner than those with fixed appliances on average."

Pricing
The treatment price is often the same as or more than traditional braces. Treatment price is set by the dentist or orthodontist, although the cost of treatment varies considerably by doctor. Doctor fees are usually determined by complexity and length of treatment. In the U.S., treatments range in price from $3,500 to $7,000, depending on geographic location. For example, in northwest Ohio, the case of a patient with a mild overbite and several teeth that needed to be turned cost $5,580.00 in 2008 (for a 13-month treatment). Braces would have cost $4,500.00 (if the express treatment were available, it would have been $4,300). It is important to remember that costs vary from case to case.

In Europe, the treatment price ranges from €3,000 to €5,700, depending on case complexity and length. Medical insurance is not as common in Europe, and cosmetic treatments are generally not covered by the state-supported universal health-care systems, so the braces are usually paid for entirely by the patients. Financing is frequently available.

Treatment
An orthodontist begins by taking dental impressions, x-rays and photographs of the patient's teeth and sending them to Align Technology. The impressions are put through a CT scan from which a computer creates a three-dimensional model. Technicians then individualize the teeth in the computer model and move them to their final position as prescribed by the orthodontist. Custom software then simulates the movement of the teeth in stages. The orthodontist reviews the simulation online using Align Technology's ClinCheck via a web browser and approves or modifies the treatment. Once approved, a plastic resin aligner is manufactured for each stage of the computer simulation and shipped to the orthodontist.

'Attachments' are sometimes bonded to teeth that need to be "rotated" or moved more than other teeth. Patients can expect as many as thirteen attachments. They are tooth-colored and made of a glass-like substance.

'Reproximation' is a process by which the contacts between teeth are filed down to allow for a better fit. This may also be a part of treatment.

Average treatment time is about one year, again depending on the complexity of the treatment. Simple treatments (minor crowding, minor spacing) may be as short as twenty weeks&mdash;this is known as the "Invisalign Express" program. Although the aligners are removable, they must be worn at least 20 to 22 hours per day to avoid delaying the treatment process. If they are not worn consistently, treatment time will increase.

After the regular aligner or braces treatment is complete, retainers composed of a similar plastic material are usually required to be worn, at least at night.

Like other orthodontic systems, the patient has some flexibility. The final position of the teeth is not completely determined by the last aligner. If the patient wants to change the end position because the actual position is not optimal, new aligners are ordered, which are usually included in the originally quoted cost, called a 'Refinement.'