Winter 2000 Presentation Summary:

Dr. Boyd presented a report on a project at the University of Pacific testing the clinical capabilities of the Invisalign System of orthodontic tooth movement. The Clinical Investigative Team members involved in the project are Drs. Vicki Vlaskalic, Ross Miller, Jae Ahn and Mohamed Fallah.

The Invisalign system is a computer-supported method of making a series of 20-50 plastic overlay appliances that align the teeth according to a series of 0.25mm adjustments built into the appliances with the help of some remarkable computer technology.

The series of aligners are made at the Align Technology laboratories in Silicon Valley, California, under the specific instructions of the treating orthodontist. The computer graphic representation of the specific tooth movements are assessed by the orthodontist via email transmissions.

What the founders of Invisalign have brought to the party is a highly accurate impression scanning technique, and software to not only represent the patient’s dentition in 3D, but to allow individual tooth movement on the screen. They also have a lot of development money, and have embarked on major advertising directed at both the patient and the orthodontist. This is a cause of uneasiness among many. However, to date, Align Technology is taking the high road, offering the technique only to orthodontic specialists who have received some basic training in the method.

Bob’s talk was a highly anticipated report of observations by researchers at the University of Pacific in San Francisco. They are not confining their treatment with aligners to the recommended limited cases, such as adult minor crowding, non-extraction or lower incisor extraction. Rather they are also treating more complex cases, extraction cases, long face cases, adolescents, periodontally involved, Class II, Class III, and orthognathic surgery. They are not treating impactions or mixed dentition cases.

Dr. Boyd showed clinical photographs and headfilms documenting the progress on many cases. He showed three complex cases that had completed the aligner series.

Some general comments on the finished cases:

• The aligners aligned the teeth!

• Intrusion, de-rotation, arch form changes, space closure, bite opening, root parallelism are all movements clearly possible to make with the aligners.

• Many of the final tooth positions were inadequate – especially rotations, and torques were not fully corrected. Dr. Boyd stated that the clinicians are presently revising the aligner series on these patients to build in over-corrections, and that appears to be successful.

• He advises practitioners to include overcorrection on rotations and torque.

Limitations

• While the diagnosis and treatment planning is still done with full records, the aligners are made from dental images alone. The orthodontist must bring in relevant information from his or her analysis of the head film, CO/CR, mandibular functional movements, skeletal variations, root form and position, alveolar bone quality, gingival tissue health, soft tissue analysis, etc. The orthodontist must still be the captain of the team.

• Extrusion of individual teeth. Bob feels that this may be possible, but it has been a challenge. They have experimented with different divot designs, but so far have no great suggestions. (Divots are bonded lumps of composite on individual teeth that enhance control of the tooth movement). While placement of divots may be essential, they are not successful on teeth with buccal restorations, due to the decreased bond strength.

• Ectopically positioned teeth. An example is the lingually blocked lower premolar. The aligner cannot easily be seated on such a tooth because of the radical undercut. They find that they have to modify the aligner, cutting away the undercut area. They are working with sequencing, first moving the molars distally, and then tipping the premolar into the arch.

• Partially erupted third molars are trouble. They should be removed prior to treatment, if indicated. The appliances can’t really include them, and they will over-erupt, causing an open bite.

• All dental work must be completed prior to aligner treatment. Any changes in dental morphology will adversely affect the fit of the aligners, requiring new impressions and a new computer plan.

• The patient is not expecting divots on the front teeth. Be sure to warn patients if they are necessary.

• They don’t have a good plan yet for concealing the space from a missing tooth.

Good news

• There is obviously less pain with the technique.

• Compliance is better than he expected. No patients are tempted by the offer to switch to fixed appliances.

• So far no cases have experienced root resorption. Bob is not sure why. Finite element studies seem to indicate that the forces on the teeth are distributed over the coronal area of the root, rather than the apex area as with fixed appliances.

• Molars can be distalized, even unilaterally. They have shown this both with headfilms and palatal rugae analysis. This could be a major treatment planning asset. Teeth can be moved in segments, using other parts of the arch as anchorage.

• Open bite is not a contraindication. The appliances seem to control the vertical. In steep angle cases, the facial height has not increased, and in some cases they have seen a decrease.

• Aligners may be the best choice in periodontally managed patients, since hygiene is vastly easier, and the tooth movements are gentle and steady.

• Breakage not a big problem

• Doctor time is less than fixed appliances, although you may have to finish the case with fixed appliances.

• So far there have been no allergic responses

In the four bicuspid extraction cases shown they have uncovered a number of areas of concern.

• If the patient decides to wear the appliances at night only, there is a big risk of tipping into the extraction sites.

• Use of narrow, long-axis divots are necessary to give parallel roots in the extraction sites. If divots are used and the patient is compliant, anchorage holds, and correct root parallelism is possible.

• Posterior open bites typically develop due to the thickness of the aligners between the teeth. Once treatment is completed, this can be easily remedied by cutting off the posterior portion of the aligner to allow the teeth to erupt into full occlusion.

Dr. Boyd cautioned the audience that this is a new method of applying forces to the teeth. At UOP, they are testing the limits of the system. He advises the private practitioner not to exceed the established limitations suggested by Align Technology.

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