Sample Principles and Biomechanics of Aligner Treatment [PDF]

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Principles and Biomechanics of Aligner Treatment Ravindra Nanda BDS, MDS, PhD Professor Emeritus, Department of Orthodontics, University of Connecticut Health Center, Farmington, Connecticut, USAProfessor Emeritus, Department of Orthodontics, University of Connecticut Health Center, Farmington, Connecticut, USA

Tommaso Castroflorio DDS, PhD, Ortho. Spec. Department of Surgical Sciences, Postgraduate School of Orthodontics, Dental School, University of Torino, Torino, ItalyDepartment of Surgical Sciences, Postgraduate School of Orthodontics, Dental School, University of Torino, Torino, Italy

Francesco Garino MD, Ortho. Spec. Private Practice, Torino, ItalyPrivate Practice, Torino, Italy

Kenji Ojima DDS, MDSc Private Practice, Tokyo, JapanPrivate Practice, Tokyo, Japan

Table of Contents Cover image Title page Copyright Dedication Contributors Foreword 1. Diagnosis and treatment planning in the three-dimensional era Introduction Intraoral scans and digital models 3D imaging References 2. Current biomechanical rationale concerning composite attachments in aligner orthodontics Introduction Geometry (active surface orientation) Location Size

Functions Basic attachment configurations in current aligner orthodontics References 3. Clear aligners: Material structures and properties Introduction Polymer molecular structure and thermal properties Physical and chemical aging of aligner polymers Conclusions and outlook References 4. Influence of intraoral factors on optical and mechanical aligner material properties Introduction Water absorption Optical changes Short-term mechanical loading of aligner materials Long-term loading Clinical loading patterns of aligner materials References 5. Theoretical and practical considerations in planning an orthodontic treatment with clear aligners Introduction Theoretical and practical considerations in CAT Biologic considerations in aligner orthodontics Patient compliance CAT fundamentals recap

References 6. Class I malocclusion Introduction Diagnostic reference Treatment plan Class I conditions References 7. Aligner treatment in class II malocclusion patients Introduction The clinical protocol Maxillary distalization case reports References 8. Aligners in extraction cases Introduction Diagnosis and treatment plan Treatment progress Treatment results Discussion Conclusion References 9. Open-bite treatment with aligners Diagnosis of anterior open bite Biomechanics for anterior open-bite correction

Aligner protocols for open-bite treatment Case report 1 Case report 2 References 10. Deep bite Introduction Leveling of the curve of spee Leveling the upper incisors Case report 1 Case report 2 References 11. Interceptive orthodontics with aligners Introduction Maxillary expansion Expansion case reports Class II malocclusion Mandibular advancement case reports Conclusions References 12. The hybrid approach in class II malocclusions treatment Introduction Tooth-borne hybrid approach with distalizing device Case report 1

Case report 2 References 13. Aligners and impacted canines Introduction Early diagnosis and treatment Late diagnosis Treatment planning and orthodontic management Labial impactions Palatal impactions Clinical case References 14. Aligner orthodontics in prerestorative patients Introduction Space management in the anterior region Case study Space management in the posterior region Management of posterior overerupted molars Management of patients with a history of temporomandibular disorders Case study References 15. Noncompliance upper molar distalization and aligner treatment for correction of class II malocclusions Upper molar distalization in aligner treatment Clinical procedure and rational of the Beneslider

Clinical case Clinical considerations Conclusions References 16. Clear aligner orthodontic treatment of patients with periodontitis Malocclusions related to periodontal disease Orthodontic treatment in patients with periodontal disease Diagnosis and treatment planning Orthodontic movements Retention Conclusions Clinical case References 17. Surgery first with aligner therapy Historic background Splint-aided maxillary and mandibular fixation without labial fixed appliances Transitioning into and out of surgery with clear aligners Surgery first and cat Case study Conclusions References 18. Pain during orthodontic treatment: Biologic mechanisms and clinical management The importance of orthodontic pain

Biologic mechanisms of orthodontic pain and clinical correlates Orthodontic tooth pain in clear aligner therapy Modulators of pain: Psychological factors Clinical considerations for the management of orthodontic pain References 19. Retention and stability following aligner therapy Retention and stability in orthodontic treatment Retention protocols and the choice of retention appliance References 20. Overcoming the limitations of aligner orthodontics: A hybrid approach Introduction Transverse expansion of the posterior teeth Canine and premolar rotation Extrusion, intrusion, and overbite control Molar distalization Conclusions References Index

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 archlength 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).

(A) Smile appearance of the patient. (B) Frontal picture at rest. (C) Three-quarter picture at rest. (D) Three-quarter smile appearance. (E) Profile smiling. (F) Profile at rest. FIG. 8.1

FIG. 8.2

Initial intraoral pictures.

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.

FIG. 8.3

(A) Initial orthopantomography. (B) Initial lateral x-ray.

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.

ClinCheck initial stage. (A) Frontal view. (B) Right view. (C) Left view. (D) Upper arch view. (E) Lower arch view. FIG. 8.4

Schematic representation of vertical orthodontic tooth movement design in the frontal plane (A). Amount of vertical movements for upper canines and central incisors (B). FIG. 8.5

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).

Schematic representation of attachments and auxiliaries required in extraction cases. FIG. 8.6

Improvement was seen in the anteroposterior relationship after use of the class II elastics, and a class I relationship was established in the buccal segments. The next phase involved the retraction of the upper anterior teeth. After 8 months of treatment, the first ClinCheck phase was finished (Figs. 8.7 and 8.8).

(A) Initial smile esthetic analysis. (B) ClinCheck simulation into the smile frame of the Digital Smile Design software. FIG. 8.7

FIG. 8.8

Treatment progresses in the frontal view.

The distalization of the upper first molars was complete, with space visible at the mesial edge of the upper left first molar. The movement of the lower second premolars and canines had closed all the mandibular spaces. The shapes and positions of the attachments were modified for the refinement phase. The crown positions were considered together with the root positions to decide the optimal conditions. After 9 months of treatment, the aligner compatibility and the crown and root positions were all consistent with the computer-simulated predictions (Figs. 8.9 and 8.10).

FIG. 8.9

Treatment progresses in the right view.

FIG. 8.10

Treatment progresses in the occlusal views.

In the final stages of refinement, the occlusal contact of all upper and lower molars and a one-to-two-tooth occlusal relationship in the buccal segments were confirmed. Both the overbite and overjet were 1 mm. After a total 10 months of treatment, all buttons, hooks, and attachments were removed (Fig. 8.11). The patient was instructed to wear class II elastics at night for an additional 10 months.

FIG. 8.11

Posttreatment pictures.

Treatment results The patient’s chief complaint—the infralabioversion of the canines—was resolved, and the improvement in gingival esthetics yielded a pleasant smile (Figs. 8.12, 8.13, and 8.14). Due to the retraction of the maxillary incisors, the upper lip was particularly natural and relaxed, and the lips were positioned appropriately in relation to the E-line. A class I molar relationship with symmetric arches was achieved, and all spaces were closed (Fig. 8.15). The physiologically correct overbite and overjet were coincident with the dental and facial midlines.

FIG. 8.12

Final smile esthetic analysis.

FIG. 8.13

(A) Final orthopantomography. (B) Final lateral x-ray.

FIG. 8.14

Posttreatment extraoral pictures.

FIG. 8.15

Final stage of the ClinCheck refinement.

The posttreatment protrusive and lateral movements of the mandible were smooth and linear. It is likely that the patient was using considerable force when biting in centric occlusion due to nervousness during the initial examination. Panoramic x-rays confirmed that there was no change in the level of the alveolar bone, which remained stable and in a healthy condition. No signs of root resorption were noted. A cephalometric analysis indicated that the mandibular plane angle was slightly reduced. Superimpositions showed that while the upper and lower incisors were retruded, their axes were upright and closer to the norm.

Discussion Aligners appeal to adults because of their pleasing aesthetics and their ability to produce gradual tooth movements with light forces over the course of time. The focus of previous reports has been on cases that did not require extractions or those with only partial extractions. This is perhaps due more to the difficulty of closing spaces without crown tipping than to the difficulty of moving teeth. When extraction spaces are closed with aligners, a bowing effect is often caused by the sagging of the plastic around the extraction sites. This effect can be prevented by using class II elastics to enhance intermaxillary anchorage. If an elastic is attached directly to an aligner, however, the plastic will separate from the teeth, making it more difficult to maintain control over mesial and distal tooth movements. In the case shown here, direct-bonded hooks were attached to the upper canines to allow the teeth to rotate both mesially and distally within the aligners, leaving a margin of more than 2 mm between the incisal edges and the aligners. Rather than attach the elastics in the mandibular arch (which was serving as anchorage) directly to the aligners, they were attached to buttons on the buccal surfaces of the first molars. This kept the aligners from lifting off the teeth, while vertical rectangular attachments on the mesial edges of the molars prevented mesial angulation. This avoided the tipping of the teeth adjacent to the mandibular extraction sites.

Because the patient found the original predicted length of treatment unacceptable, OrthoPulse33-35 was used in conjunction with the aligners to possibly accelerate treatment time. Despite the lack of published accounts of the effectiveness of this device beyond its application to fixed appliances, the patient was instructed to use it for 10 minutes every evening. We were able to shorten the interval between aligner changes to 3 days, resulting in a remarkable reduction in the treatment time to just 10 months. The patient experienced no discomfort from the OrthoPulse device or from the faster aligner changes. She finished treatment with no interferences in protrusive or lateral mandibular movements and no esthetic concerns.

Conclusion Not only are aligners aesthetically pleasing to adult patients, but the ease with which they can be removed makes them extremely safe. In the future, aligners are likely to be used in more complex cases involving rotations, deep overbites, open bites, and unusual extractions. Further clinical investigations into the effects of accelerated tooth movement in such cases are required.

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