Treatment with Invisalign® in specialist practice

Aligner material and attachments

The aligners are currently made in SmartTrack® material, which is claimed to deliver both high elasticity and a relatively constant force. Attachments are a vital part when treating patients with the Invisalign® system. Placement of these attachments helps ensure that the tooth movements occur similarly to those shown in the CC treatment plan, and is an essential step to achieve the patient outcomes that have been promised. There are two types of attachments that could be used during an Invisalign® treatment:

In the author's practice, for reasons of aesthetics, it is attempted to avoid attachments 3−3 in the upper jaw, during the initial set of aligners. After a discussion with the patient, the required attachments are often added during the second set of aligners.

In premolar extraction treatments, standard horizontal 4−5 mm x 1 mm thickness attachments are recommended instead of the optimized attachments, and this modification has proved effective, in the author's practice, to avoid tipping during space closure.

According to the author's clinical experience, to be able to achieve a high quality treatment outcome, almost all Invisalign® treatments require a second set of aligners to reach the treatment goal. In some more challenging treatments, a third set of aligners may even be required. Gu et al evaluated the treatment outcome, the duration and the improvement in two groups of patients in a retrospective study.¹ One group was treated with a conventional fixed appliance and one with Invisalign®. However, Gu et al's claim that Invisalign® treatment takes less time than fixed appliance therapy seems to be inaccurate. In the author's experience, Invisalign® treatment takes just as long as fixed appliance treatments to be able to achieve an excellent result.

Cases

Three Invisalign® cases are going to be presented to give an overview of the treatment possibilities:

Case 1: (Figure 1) Class I (Cl II tendency) crowding. Non-extraction treatment

In this case, after the treatment plan was completed, a pre-scanning IPR was performed. The reason for performing pre-scanning IPR is to avoid ‘round tripping’ when aligning the teeth. In total for this case, 71 aligners were used. The first treatment sequence involved 38 aligners, and the second set (Additional Aligners) involved another 33 aligners. The total treatment time was 17 months and the achieved result was retained by bonded Memotain® retainers 3−3 in both jaws and, in addition, a vacuum-formed retainer in the upper jaw at night.

As previously described, no attachments were used UR3−UL3 in the first set of aligners for aesthetic reasons. During the second set of aligners, an optimized attachment was added to UL2 to achieve derotation and extrusion. On UR2, a standard epsiloid attachment was added.

Post-treatment evaluation

The arches were well aligned, and the sagittal and transversal relations improved on the left side. Since the patient had significant gingival recession before the treatment, efforts were made, during the CC process, to add palatal root torque when expanding the arches, hopefully to avoid further gingival recession.

Case 2: (Figure 2) Class I, large overjet, crowding. Lower incisor extraction treatment

In this case, it was decided to extract one lower incisor due to the severe crowding in the lower front. To be able to correct the 7 mm overjet and to create space in the upper jaw, pre-scanning IPR was performed. In addition, transversal expansion in the molar-premolar area (2 mm at each side) were added to the CC. The first set of aligners included 25 aligners, followed by a set of additional aligners, including 22 aligners. Power ridges were added at UR1 and UL1 at the second set of aligners stage to improve the palatal root torque on the upper incisors. Overcorrected lingual root torque was added cuspid-to-cuspid in the lower jaw to avoid lingual tipping of these teeth during the space closure.

The total treatment time was 12 months and the treatment result was retained by bonded retainers 3−3 in both jaws.

Post-treatment evaluation

The arches were well aligned, and the overjet was normalized. The Class I intercuspation was maintained and, in addition, occlusal contacts were also present in the front, despite extracting in only the lower jaw. This was probably achievable because of the large size of the lower incisors and the slightly diminutive upper lateral incisors.

Case 3: (Figure 3) Class I, open bite, gingival recession at LR1 and extraction of UL7

This case included several clinical challenges. The patient had an open bite forward of the molars, UL7 needed to be extracted due to a vertical fracture, and the patient also had a severe gingival recession on LR1, possibly due to earlier orthodontic treatment.

The treatment plan included intrusion of posterior teeth to correct the open bite. In this case, extrusion of incisors should be avoided as the patient already showed the ideal amount of tooth display of the upper incisors. In order to intrude posterior teeth, the following instruction was added during the CC process: ‘Intrude posterior teeth tooth by tooth to correct the open bite’. With this explicit instruction, the most posterior right and left molars in both jaws are intruded simultaneously as all of the other teeth are used as anchorage. Then, once this intrusion is achieved, the next tooth pair is intruded using the remaining teeth again as anchorage. To be able to control the intrusion, standard rectangular 4 x 1 mm attachments are added on all molars and premolars. Another important consideration is to add palatal crown torque on the molars to avoid buccal flaring of these teeth.

The next challenge was to add lingual root torque on LR1 to torque the root back into the alveolus. A power ridge was added at LR1 to help to achieve the lingual root torque. The last challenge was to close the space created after extracting UL7 effectively. Substantial overcorrection of the tip was added to UL8 to counteract the mesial tipping which would otherwise occur during space closure.

Post-treatment evaluation

All treatment goals were achieved using three sets of aligners and the total treatment time was 20 months. The result was retained with bonded retainers 3−3 in both jaws and a vacuum-formed retainer at night in the upper jaw. Parallel roots at UL6 and UL8 were successfully achieved despite the extraction of UL7. The root of LR1 was torqued into the bone and the amount of gingival recession reduced substantially.

Discussion

Working hard on the CC is vitally important to reach excellent treatment results with Invisalign®. When attempting difficult tooth movements, it is often necessary to add overcorrections to be able to achieve the desired treatment result. In a review by Rossini et al, extrusion and rotation were claimed to be the least predictable movements with Invisalign®.² Consequently, it is often necessary also to slow down the movement velocity during difficult and less predictable movements when treating with Invisalign®. This specific and explicit instruction needs to be given to the CC technicians and a check done on the revised CC to see that instructions have been followed to the letter. In addition, it is often necessary to use attachments when performing unpredictable tooth movements.

Gu et al evaluated the treatment outcome, duration and improvement in two groups of orthodontic patients:¹ one treated with a fixed appliance and one with Invisalign®. They found that Invisalign® is not as effective as a fixed appliance in achieving great improvement and that Invisalign® treatment was faster than fixed appliance treatment. The reason for this difference in quality of the outcome reported could be the shorter treatment time with Invisalign®. In the author's experience, Invisalign® treatments take just as long as fixed appliance treatments to achieve the same standard of outcome. As mentioned previously, to achieve a high quality result almost all Invisalign® treatments require two sets of aligners. Gu et al, in their study only used one set and this could be the main reason for the difference in quality between the fixed appliance and the Invisalign® group results.¹

In fixed appliance treatments, it is frequently necessary to replace brackets and to bend the archwires to get a well finished treatment result. In an Invisalign® case, a second or even a third set of aligners should be considered as the necessary finishing required to achieve a quality result.

Khosvari et al evaluated treatment effects when treating deep and open bites with the Invisalign® appliance.³ In open bites, the median deepening was 1.5 mm and this was mainly due to extrusion of incisors, which was in accordance with their planning in the CC. In the author's practice, planning for less extrusion of incisors and more intrusion of molars and premolars is often performed. By doing a stepwise, tooth by tooth intrusion, this procedure to intrude two pairs of teeth (upper and lower jaw) is possible using the anchorage potential of all the other teeth.

Conclusions

Orthodontic treatment with Invisalign® can be performed to a high standard but, as with all orthodontic techniques, developing expertise requires time and effort.

The most important factor is for the clinician to take full control when planning and working with the case using the ClinCheck software.

In moderate open bite cases, in experienced hands, Invisalign® can be superior to fixed appliance due to the possibility to intrude posterior teeth sequentially, thus enabling good vertical control of the case.