Invisalign : Invisible Teeth Aligners

Saturday, 11 October 2008 09:07

Invisalign is a series of clear, removable teeth aligners that both orthodontists and dentists use as an alternative to traditional metal dental braces.It is made from a trans-parent, thin (typically less than 1 mm) plastic material formed with CAD-CAM laboratory techniques. These aligners are similar to the splints that cover the clinical crowns and the marginal gingiva . Each aligner is designed to move the teeth a maximum of about 0.25 to 0.3 mm over a 2-week period, and is worn in a specifc sequence. The Invisalign appliance is currently recommended for adults and for adolescents with fully erupted permanent teeth who meet an acceptable standard of compliance. Excellent compliance is mandatory since the appliance has to be worn a minimum of 20 to 22 hours a day and each aligner should be worn 400 hours to be effective.

Indications:

Jofe suggested that the Invisalign appliance is most successful for treating mildly malaligned malocclusions (1 to 5 mm of crowding or spacing), deep overbite problems (e.g., Class II division 2 malocclusions) when the overbite can be reduced by intrusion or advancement of incisors, nonskeletally constricted arches that can be ex-panded with limited tipping of the teeth, and mild relapse after fixed-appliance therapy.

Contraindications:

Conditions that can be diffcult to treat with an Invisalign appliance or are contra-indicated altogether include:
• crowding and spacing over 5 mm
• skeletal anterior-posterior discrepancies of more than 2 mm (as measured by discrepancies in cuspid relationships)
• centric-relation and centric-occlusion discrepancies
• severely rotated teeth (more than 20 degrees)
• open bites (anterior and posterior) that need to be closed
• extrusion of teeth
• severely tipped teeth (more than 45 degrees)
• teeth with short clinical crowns
• arches with multiple missing teeth.

Use of the Invisalign appliance is relatively new for orthodontists and is still being developed. Currently, few clinical studies and case reports have assessed the efectiveness of this technique. Although Align Technology has suggested guidelines for its appropriate use, clinicians have encountered numerous limitations when using the appliance.

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 orthodontic appliance

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 also prevent accurate x-rays from being taken which can be nullified with invisalign

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,however this claim has been challenged bythe 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 very fact that the aligners are removable means they are not continually correcting the teeth. Unlike traditional fixed braces, they are largely dependent on patient compliance and cooperation

More expensive than traditional treatment in most cases

Higher chances of patient losing it

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.

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

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

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. Clients can expect as many as thirteen attachments. They are tooth-colored and made of a glass-like substance.The final position of the teeth is not completely determined by the last aligner. 'Reproximation' is a process by which the contacts between teeth are sanded down to allow for a better fit. This may also be a part of treatment.

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.'

Treatment Time:

The clinician’s treatment time can be lengthened because of the additional time required for documentation during Invisalign case preparation. The treatment plan must include the sequential movements for every tooth from the beginning to the end of treatment.If changes are needed afer treatment starts, signifcant additional time and documentation are required to modify the treatment plan. In addition, the lag time between formulating a treatment plan and inserting the appliance can be up to 2 months. This lag time can cause further delays if the dental changes are signifcant because of the additional time needed for planning and documenting the treatment again, in addition to the extra waiting period required to make new aligners.