Resolution of a Complex Malocclusion Using a Hybrid Aligner Approach

Diagnosis and Treatment Plan

A 27-year-old female presented with the chief complaint of unsightly front teeth and traumatic biting in the right posterior cheek region (Fig. 1A).

Extraoral analysis found a convex profile, a long lower third of the face, and lip strain from the attempt to achieve lip competence. The patient had a gummy smile with complete incisor exposure, bilateral buccal black corridors, and a slight occlusal cant. She had borderline Class I molar and canine relationships with excessive overbite and overjet. The lower midline was deviated 1mm to the left of the upper midline, and the curve of Spee was accentuated on both sides. Moderate crowding and malalignment were present in both arches. A scissor bite of the upper and lower second molars was observed on the right side (Fig 1B).

The patient did not report any TMJ symptomatology, as confirmed by the clinical and functional exam. All teeth were present on the panoramic radiograph. Cephalometric analysis (Table 1) indicated a moderate biretrusive skeletal Class II (ANB = 5.5°) with a primarily mandibular component (SNB = 73.8°) and a hyperdivergent pattern (FMA = 31.5°). Upper and lower incisor inclinations seemed to be normal.

The main treatment objectives were to maintain the bilateral Class I molar and canine relationships, resolve the malalignment and crowding in both arches, reduce gingival exposure in smiling, center the midlines, and improve lip competence. An additional objective was to correct the scissor bite and resolve the traumatic biting issue in the right cheek region.

Because the patient requested esthetic treatment, conventional fixed labial appliances were not considered. We evaluated the possibility of using lingual appliances, but the marked lingual inclination of the lower right second molar and the close contact between the buccal surface of the lower right second molar and the lingual surface of the upper right second molar would have hindered lingual bracket placement on these teeth. A lingual bracket on the upper right second molar would likely have been sheared off due to premature contact with the opposing arch. An alternative was to bond lingual brackets to all teeth except the upper and lower right second molars, where buccal tubes could be placed using the so-called “crossover technique.”¹⁴ Despite this viable option, the patient preferred an appliance that would be less invasive and more comfortable than a full lingual setup.

We therefore proposed an esthetic approach using clear aligner therapy. We recognized that the unilateral scissor bite would be more difficult to resolve because the posterior section of the aligner is more elastic, and it is therefore less suitable for delivering the orthodontic forces and moments necessary to resolve such a complex problem.

Treatment Progress

The patient was advised to have all four third molars extracted before orthodontic treatment. Digital models were then obtained from a CS 2600^* intraoral scanner, and a digital setup was performed. The first phase of treatment involved a series of 12 individualized F22^** clear aligners per arch (Fig. 2).

In the upper arch, grip points were positioned on the right first molar (8.8° distal rotation), left first molar (11.7° distal rotation), right canine (8.1° mesial rotation), left canine (15.9° mesial rotation), and right lateral incisor (.6mm extrusion). In the lower arch, grip points were placed at the left canine (10.6° mesial rotation), right canine (7.5° distal rotation), right first premolar (16.1° mesial rotation), and right second premolar (18.1° mesial rotation). The patient was instructed to wear each pair of aligners 22 hours per day for 15 days, removing them only for meals and brushing.

The patient was seen monthly to check progress and to perform the interproximal reduction (IPR) needed to facilitate the rotation and extrusion movements and resolve the crowding. The amount of IPR prescribed in the upper arch was .2mm from the mesial contact of the right second premolar to the mesial contact of the right central incisor, and .1mm at the contact points between the left central and lateral incisors and the left canine and first premolar. In the lower arch, .3mm of IPR was prescribed from the mesial contact of the left second premolar to the mesial contact of the right second premolar.

After two months of treatment, the scissor bite had not improved, and the patient complained of difficulty in fitting the aligners over the posterior regions of both arches (Fig. 3).

With the patient’s consent, we decided to cut off the remaining aligner trays on the right side in both arches and to end the first phase of therapy, postponing the correction of the scissor bite to the refinement stage. The patient was instructed to wear each pair of modified aligners for 10 days. This first treatment phase lasted four months and 20 days (Fig. 4). The crowding and malalignment were resolved, gingival exposure in smiling was reduced, and the midlines were partially centered.

A 1.5mm × 8mm orthodontic miniscrew^‡ was manually inserted into the buccal interradicular space between the lower right second premolar and first molar. An .017" × .025" stainless steel sectional wire^† was attached from the screw head to the buccal surface of the lower right first molar to obtain indirect anchorage for buccal uprighting of the lower right second molar. Temporary bite turbos were built with light-cured flowable resin on the occlusal surfaces of the mandibular first molars to facilitate scissor-bite correction.

After the sectional appliances were placed, new intraoral scans were taken and a refinement setup was performed, involving eight trays in each arch. Before the refinement aligners were delivered, a 1.5mm × 8mm palatal miniscrew was inserted in the interradicular space between the upper right first and second molars, and metal buttons were bonded to the palatal surfaces of the upper right second molar and the lower right second molar. An elastic chain was connected directly between the miniscrew and the palatal button on the upper right second molar to exert an intrusive force for the scissor-bite correction (Fig. 6).

A month later, .019" × .025" nickel titanium orthodontic archwires were placed in the upper and lower arches, while the criss-cross elastics continued to be worn. The refinement stage lasted five months and 10 days. The miniscrews were then removed, and removable retainers were delivered.

Treatment Results

After a total 10 months of treatment, the objectives had been achieved (Fig. 8A).

Both the lip competence and the anterior dental display in smiling were improved. The Class I molar and canine relationships were preserved, the anterior crowding and malalignment were corrected, the midlines were fully centered, and satisfactory overjet and overbite were attained. The scissor bite on the right side was resolved (Fig. 8B.

The post-treatment panoramic radiograph showed good root parallelism with no signs of root resorption or bone defects. Cephalometric analysis confirmed retroclination of the upper anterior teeth and slight intrusion and proclination of the lower teeth (Table 1). The skeletal divergence did not worsen, and a proper vertical facial relationship was maintained.

Discussion