8: Aligners in extraction cases
Kenji Ojima, Chisato Dan, Ravindra Nanda
Introduction
The demand for inconspicuous and natural-feeling orthodontic appliances has been rising over time. The introduction of the Invisalign system marked a significant step forward in orthodontics in that it allowed for inconspicuous orthodontic correction using appliances with a natural feel. The original Invisalign system, however, came with serious limitations: the control of root movement was not possible and it was difficult to move large teeth over significant distances.1–10 Recent advances in the quality of materials, the use of attachments, and the introduction of a new force system have expanded the range of applications of the Invisalign system from mild crowding to more difficult extraction cases.11–16
As is the case with all orthodontic procedures, one of the greatest sources of dissatisfaction among adult patients with aligner therapy is the long treatment time. This report describes the treatment of a patient with severe anterior crowding who was treated with Invisalign appliances after the extraction17–20 of her three remaining premolars. Her lower left premolar had already been removed. A photobiomodulation device was used to possibly accelerate tooth movement.
Diagnosis and treatment plan
When this 25-year-old female presented at our clinic, she expressed a desire to correct her maxillary anterior crowding and improve the aesthetic appearance of her smile. While the patient’s facial profile was straight, both lips were slightly recessive with regard to the E-line (Fig. 8.1). An intraoral examination showed a class II molar relationship with a 2-mm overjet, a 3-mm overbite, and coincident midlines. The arch-length discrepancy was 15 mm in the maxilla and 10 mm in the mandible. Infralabioversion was noted for both upper canines and a marked buccal shift of the upper left second molar (Fig. 8.2).
Cephalometric analysis indicated a skeletal class II relationship with a steep mandibular plane angle (Fig. 8.3). The upper central incisors were slightly inclined lingually and the lower central incisors were inclined labially. The lateral gap in the mandibular head confirmed by her panoramic x-ray did not impede mandibular function. There was evidence of slight regression in the periodontal tissue around the upper canines; with no tooth mobility, the maximum pocket depth was 5 mm.
Based on these observations, the patient was diagnosed as a skeletal class II case with infralabioversion of the maxillary canines and a steep mandibular plane angle. The treatment plan called for the retraction of both upper and lower incisors: 17.8 mm of movement was required in the maxilla and 14.8 mm in the mandible. First, the two upper first premolars and lower right second premolar were extracted. Her lower left second premolar had been removed in her early teens. Therefore, to allow for mesial movement, her upper left second molar and upper right third molar were extracted, too. Because the patient expressed concern about the poor aesthetics of fixed orthodontic appliances over a potentially long period of time, the decision was made to implement the Invisalign system in conjunction with photobiomodulation (OrthoPulse) to possibly speed up treatment.21–32
ClinCheck software was used to analyze the location, angle, and need for the recontouring of the canine in relation to the final desired occlusion (Fig. 8.4). Adequate incisor retraction in this class II malocclusion required the 2-mm distal movement of the upper first molars and 2-mm mesial movement of the lower first molars. Even after the extractions, there was insufficient space to move the maxillary anterior teeth by premolar extraction alone. To create more space, the overexpansion of the dental arches was required. Tooth movements were simulated on the ClinCheck software (Fig. 8.5), the amount of expansion required in each arch was estimated, the positions were planned, and the shapes of the required attachments were decided.
Treatment progress
Three third molars were removed (except the upper left third molar) before treatment. After the extraction of the upper premolars and lower left first premolar, aligner treatment was initiated. We used all the maxillary teeth from first molar to first molar as anchorage for the distalization of the second molars. In the mandible, we used all the teeth excluding the canines and second premolars as anchorage for the mesial movement of the canines. Since the root of the lower right canine was angled outward, we moved the tooth simply by tipping; the lower left canine was moved bodily along with its root. The distalization of the upper second molars was completed in 12 weeks and distal movement of the upper first molars was completed 2 weeks later. The closure of the lower extraction space continued during this period with mesial movement of the lower first molars.
After 5 months of treatment, retraction movement of the upper canines was completed, with the incisors of the midline corrected. At this point, we recalculated the retraction space for the maxillary incisors by means of a panoramic x-ray. Since the mandibular extraction spaces were closed, we could use all the teeth from second premolar to second premolar, including the canines, as anchorage for the mesial movement of the lower first molars.
The aligner margins were trimmed about 3 mm to accommodate direct-bonded hooks on the upper first canines. Lingual buttons were bonded to the distobuccal edges of the lower first molars, and class II elastics (0.25 in, 6 oz) were prescribed to be worn 20 hours per day. To prevent the mesial tipping of the lower first molars, vertical rectangular attachments were added to their mesiobuccal edges (Fig. 8.6).
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