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Treatment of an anterior open bite, bimaxillary protrusion and mesiocclusion by the extraction of premolars and the use of clear aligners

Treatment of an anterior open bite, bimaxillary protrusion and mesiocclusion by the extraction of... IntroductionIntroduced in 1999 by Align Technology (Santa Clara, CA, USA), the Clear Aligner System has become a popular treatment choice for adult orthodontic patients who reject traditional visible appliances. The technique was initially introduced by Kesling1 and improved by Ponitz2 and others.3 The current clear aligner technique (CAT) is used to treat malocclusions through a series of sequential removable trays.4 Earlier studies5–10 have shown significant limitations of using the clear aligner to treat complex malocclusions. However, several clinical case reports using CAT have revealed better vertical control due to recent appliance design improvements.11,12 Studies initially reported the development of posterior open bites as a result of CAT treatment,13,14 and demonstrated no correlation between measured and planned molar intrusion in the treatment plan.15,16 Recently, clinicians have claimed that CAT can effectively treat cases of anterior open bite, especially those with an increased mandibular plane angle.17,18The traditional mechanical orthodontic technologies, including multiloop edgewise arch wires, straight wires, and implant anchorage, present many challenges for patients and clinicians in correcting an anterior open bite.19–21 The multiloop edgewise arch wire is difficult to bend, uncomfortable to wear, and compromises aesthetics due to anterior vertical traction. Straight wire technology using reverse-curve arch wires, combined with anterior vertical traction, presents the same disadvantages. Micro-implant technology requires surgery and damages the mucosa and the alveolar bone. However, since the advent of CAT, the appliances have gained popularity, given their advantages over conventional fixed appliances regarding aesthetics, oral hygiene, patient comfort, a lighter level of force, shorter chair time,22,23 and provide a convenient solution for anterior open bite patients.18 Despite the advantages, CAT is challenging for orthodontists when extractions are part of the treatment plan. Therefore, a case of the successful correction of a skeletal anterior open bite, bimaxillary dentoalveolar protrusion, mesiocclusion and other issues through the extraction of four premolars and the use of clear aligners, is presented.Diagnosis and aetiologyA 24-year-old female patient presented with a history of tongue thrust and mouth breathing but without a history of maxillofacial trauma or a non-nutritive sucking habit. The diagnostic records revealed that, based on the E line, the patient had a convex profile with a long face, a decreased nasolabial angle, a protrusive lower lip, and a shallow mentolabial sulcus. Further, the patient had incompetent and protruded lips at rest and in contact but with mentalis strain upon forcible closure. There was also a low smile line, and the smile arc was not consonant with the curvature of the lower lip (Figure 1). An intraoral examination showed an anterior open bite with no occlusal contact from the right first premolar to the left first premolar, a bilateral Class III molar relationship, and a Class III canine relationship on the right side but a Class I relationship on the left side. An analysis of the initial study models revealed that there was an anterior dental open bite of 6 mm, a decreased overjet (the overjet and overbite were measured on digital dental models using 3-shape software), a 3 mm curve of Spee, a mandibular midline deviation (1.5 mm to the left), and arch-length discrepancies of 5 mm in the maxilla and 3 mm in the mandible. The anterior and overall Bolton ratios were compatible. The maxillary dental arch was narrow, and the upper and lower arches were unmatched. A crossbite from the upper left canine to the second premolar was also noted during the examination. The maxillary right second molar was in scissor-bite with the mandibular right second molar (Figure 2). A cephalometric analysis revealed a skeletal open bite (SN/GO-GN 48°), an increased mandibular plane angle, a counter-clockwise rotation of the ANS-PNS plane (S-N/ANS-PNS 6°), proclination of the upper incisors (UI/ANS-PNS 129°), an interincisal angle of 108°, excessive lower anterior facial height and a short upper anterior facial height (Table I). A computed tomography scan of the anterior teeth revealed adequate labial and lingual bone volumes (Figure 3A). In addition, the initial panoramic radiograph and the radiographic and clinical examinations of the temporomandibular joints revealed no obvious abnormalities (Figure 4 and 3B). The patient was diagnosed with a Class III malocclusion (S-N/ANS-PNS 6°) and skeletal open bite (SN/GO-GN 48°) with an increased mandibular plane angle, a long face, a convex profile, and lip incompetence with mentalis strain. There was also proclination of the upper incisors, a crossbite, scissor-bite, mild crowding and midline deviation.Figure 1.Pre-treatment extraoral and intraoral photographs.Figure 2.Initial study models.Figure 3.The pre-treatment labial and lingual bone volume of anterior teeth (A) and temporomandibular joint radiograph (B).Figure 4.Pre-treatment panoramic radiograph (A) and lateral cephalometric radiograph (B).Table I.Pre-treatment and post-treatment cephalometric analysis.MeasurementMean ± SDPre-treatmentPost-treatmentSagittal skeletal relations    S-N-A82° ± 3.5°76°72°    S-N-PG80° ± 3.5°73°70°    A-N-PG2° ± 2.5°3°2°Vertical skeletal relations    S-N/ANS-PNS8° ± 3.0°6°11°    S-N/GO-GN33° ± 2.5°48°48°    ANS-PNS/GO-GN25° ± 6.0°32°27°Dento-basal relations    UI/ANS-PNS110° ± 6.0°129°118°    LI/GO-GN94° ± 7.0°91°82°    LI/A-PG (mm)2 ± 2.04.42.7Dental relations    Overjet (mm)3.5 ± 2.52.22.6    Overbite (mm)2 ± 2.5-2.81.2    Interincisal angle UI/LI132° ± 6.0°108°133°A, point A; ANS, anterior nasal spine; GN, gnathion; GO, gonion; LI, lower incisor; N, nasion; PG, pogonion; PNS, posterior nasal spine; PO, porion; S, sella; SD, standard deviation; UI, upper incisor.Treatment objectivesThe primary treatment objectives were (1) partly closing the anterior open bite by a combination of retraction and extrusion of the upper incisors; (2) further closure of the anterior open bite by intrusion of the posterior maxillary dentition enabling a subsequent counter-clockwise rotation of the mandible and a reduction in facial height; (3) levelling and aligning the upper and lower dentition; (4) achieving Class I molar and canine relationships and an ideal overbite and overjet; (5) improving the facial profile and obtaining natural lip competence without mentalis and lip strain; (6) expanding the upper dental arch to improve the aesthetics of the smile; (7) moving the lower teeth to the right side to correct the midline deviation using the extraction space; and (8) correcting the crossbite and the scissor-bite of the maxillary right second molar.Treatment alternativesGiven the mild skeletal discrepancy and the strong opposition of the patient to the orthodontic and orthognathic surgical treatment program, camouflage treatment with fixed appliances and TAD skeletal anchorage was considered. However, the patient again refused because of aesthetic and comfort concerns. Finally, clear aligner appliances were chosen.Maxillary arch expansion and interproximal reduction (IPR) were additional considerations to relieve the crowding, develop a rounded arch form, and co-ordinate the maxillary and mandibular arches. IPR was also indicated to assist alignment of the lower arch and a combination of anterior extrusion and posterior intrusion to manage the anterior open bite. However, this approach did not adequately address the patient’s concerns, especially the bimaxillary dentoalveolar protrusion and mesiocclusion. Therefore, an alternative approach was selected to correct all of the issues, which involved the extraction of the maxillary second and mandibular first premolars, followed by mechanics using clear aligners, which have gained popularity in the treatment of an anterior open bite malocclusion.24–27Treatment progressBefore treatment, polyvinyl siloxane (DGM, Germany) impressions were taken to develop a ClinCheck treatment plan (Align Technology, Santa Clara, CA, USA). The digital plan was used to determine the number of aligners needed and the treatment duration and to visualise the required biomechanics of tooth movement. The treatment involved three phases:Initial treatment phaseThe treatment commened by extracting the four premolars. The goals of the initial phase were to align and level the dental arches, close the extraction spaces, and close the open bite. In the upper arch, 14, 24, 13, and 23 were retracted, leaving a space at the mesial area of 13 and 23. The anterior teeth were aligned, and 8° of lingual root torque was added prior to en-masse retraction. The teeth 16 and 26 were moved first, allowing further mesialisation of 17 and 27, until 16 and 26 contacted 14 and 24, respectively. Optimised retraction attachments were applied to the upper canines, as well as optimised anchorage attachments and vertical rectangular attachments on the upper posterior teeth. An extrusion attachment was designed and placed on the upper right incisor through an automated process. In the lower arch, the treatment plan was to retract 33 and 43, thereby leaving space mesial to 33 and 43 (which improved aligner grip), adding 10° of lingual root torque before en-masse retraction of the incisors. The G628 solution for optimised retraction attachments was used on the canines and optimised anchorage attachments on the lower posterior teeth. The patient wore bilateral Class III, 3.5-ounce elastics, full time throughout the treatment phase. It was planned to intrude the upper posterior teeth by approximately 2 mm, extrude the upper anterior teeth by approximately 1.5 mm, and finally achieve an overbite of roughly 3 mm. In addition, it was planned to expand the maxillary arch in order to co-ordinate the arch forms. Palatal crown torque of 17 was necessary to achieve a normal buccal overjet of the right posterior teeth. The pre-treatment ClinCheck treatment plan is presented in Figure 5.Figure 5.Pre-treatment ClinCheck treatment plan (Align Technology, Santa Clara, CA, USA).Fifty sets of Invisalign aligners were designed for the patient. However, the treatment had to be restarted due to poor engagement of the 31st aligners. During the following process, a ‘frog’ pattern of movement of the lower anterior teeth was designed, while the other plans remained unchanged. A ‘frog’ pattern is a staggered staging technique: the canines are first retracted for 10 stages, together with some mesialisation of the molars, and then stopped. Then the incisors are retracted for 10 stages and then stopped. The canine movement is restarted for another 10 stages and stopped, followed by further incisor retraction. This pattern is repeated until the extraction spaces are closed and the incisors fully retracted. The aligners were used for 9 months, changed every 10–14 days during the 3 months of initial treatment and changed every 7 days thereafter. The patient was seen at monthly intervals to check aligner fit, attachment stability, and compliance without using remote dental monitoring during the treatment period.Progress treatment phasePolyvinyl siloxane (DGM, Germany) impressions were obtained to assess the progress stage of the ClinCheck treatment plan and to complete the unfinished goals of the first phase. The treatment process continued and followed that established in the first stage. The open bite correction occurred during the second phase of 50 aligners.Refinement phaseThe final sets of aligners underwent improvements to correct the anterior overbite and mild posterior open bite that developed during treatment. During refinement, 15 upper and 10 lower aligners were worn for 9 months and were changed every 14–30 days. The patient’s overbite decreased by attaching power ridges and the subsequent intrusion of the anterior teeth. The posterior open bite was corrected by placing button cutouts in the maxillary and mandibular aligners for attaching vertical elastics. The ClinCheck treatment plan for the refinement stage is presented in Figure 6. While additional improvements may have been possible, the patient was satisfied with the results at the end of this stage; therefore, the treatment was terminated. At the outset, it was considered that the difference in the alignment and position of the anterior teeth before and after treatment was large, and so Hawley retainers combined with bonded lingual wires for retention were provided. However, the patient was unable to adapt to these retainers because of her occupation and socialising, so vacuum-formed and transparent full-arch wraparound retainers were supplied to maintain the treatment results.Figure 6.Refinement stage: ClinCheck treatment plan (Align Technology, Santa Clara, CA, USA).Treatment resultsAfter 33 months of therapy, the treatment objectives established in the pre-treatment plan were achieved, which improved aesthetics and the intercuspation of teeth (Figures 7 and 8). The treatment retracted and uprighted the patient’s incisors (Figures 9 and 10), which improved her lip profile and facial appearance producing a harmonious straight-type of profile. The nasolabial and mentolabial angles increased, and the lips closed naturally without lip or mentalis strain. The treatment completely closed the open bite, corrected the overbite and overjet, aligned the upper and lower dental midlines with the facial midline, and established Class I molar and canine relationships (Figure 7). Based on panoramic radiographs (Figures 4 and 11) and the relative positions of the teeth before and after treatment, standard root length, sufficient root parallelism, a tight occlusal relationship, and adequate posterior anchorage were maintained. The thickness of the labial and lingual bone volume over the anterior tooth roots before and after treatment was within normal limits (Figure 12). The temporo-mandibular joint radiographs before and after treatment revealed no significant changes (Figures 3 and 12). Unfortunately, the objective of the counter-clockwise rotation of the mandible to reduce facial height was not achieved; however, the pretreatment facial height was preserved.Figure 7.Post-treatment extraoral and intraoral photographs.Figure 8.Final study models.Figure 9.Two-dimensional (2D) superimposed cephalometric tracings.Figure 10.Three-dimensional (3D) superimpositions (pre-treatment and post-treatment). (A) the anterior teeth; (B–D) the posterior teeth.Figure 11.Post-treatment panoramic radiograph (A) and lateral cephalometric radiograph (B).Figure 12.The post-treatment labial and lingual bone volume of anterior teeth (A) and temporomandibular joint radiograph (B).DiscussionPrevious research has suggested that the aetiology of an anterior open bite is complicated and includes genetic and environmental factors (i.e., unfavourable growth patterns and parafunctional habits), which are difficult to completely differentiate.29,30 Therefore, an accurate diagnosis and causative determination are the best guides to establish appropriate objectives, ideal treatment plans and definitive corrective procedures31. According to the initial examinations, the patient was diagnosed with a Class III malocclusion and mild skeletal open bite with an increased mandibular plane angle and unmatched dental arches (Figures 1–4; Table I). Dentoalveolar or mild skeletal open bite patients generally exhibit normal craniofacial morphology and skeletal facial shapes but are characterised by proclined incisors, insufficiently erupted anterior teeth, and normal or slightly extruded molars. The anterior open bite is commonly associated with parafunctional habits.30,32 Orthodontics can treat a dentoalveolar or mild skeletal open bite to intrude the posterior teeth, extrude the anterior teeth, or both.33 The required techniques include the “pendulum effect” (Figure 13) of the anterior teeth relatively extruding during retraction; the “fulcrum effect” of the posterior teeth intruding or mesial migration to eliminate the occlusal fulcrum and move the occlusal contact point forward;34 uprighting mesially-tipped posterior teeth and correcting the occlusal plane inclination, not only to reduce the level of the open bite but also to provide space for anterior tooth retraction.35 A counter-clockwise mandibular rotation (Figure 14) is based on studies12,25 suggesting that significant molar intrusion, particularly of the maxillary molars, favours mandibular rotation in a similar fashion to high-pull headgear.Figure 13.The ‘pendulum effect’ of the retraction of the anterior teeth.Figure 14.Counter-clockwise rotation of the mandible.Contemporary orthodontics emphasises the accurate control of three-dimensional tooth movement, and CAT illustrates the advantages of this concept. CAT has unique features related to three-dimensional tooth control for patients with anterior open bite deformities, especially those with an increased mandibular plane angle.13,36,37 Traditional fixed appliances tend to extrude the posterior teeth and increase the mandibular plane angle when inter-arch elastics are used, especially in non-growing individuals, which leads to adverse vertical effects and a worsening of the anterior open bite.36,37 In contrast, even when Class II and Class III elastics are used, clear aligners may prevent extrusion or aid in the intrusion of the posterior teeth due to a “bite-block effect” of the two layers of the aligners covering the posterior teeth, combined with the patient’s natural masticatory intrusive forces.11–13,18,25,38 Additionally, based on Newton’s third law, the extrusive force placed on the anterior part of the aligner for anterior extrusion simultaneously causes a reciprocal intrusive force on the posterior part of the aligner, which is favourable for posterior intrusion (Figure 15). Some researchers24 believe that posterior intrusion using aligners must be programmed. However, evidence supporting this opinion is lacking. A recent study5 has found that the amount of intrusion of the maxillary mesiobuccal cusps can reach 0.47 mm, while others15 have determined that 0.6 mm is possible.Figure 15.The extrusive force and intrusive force generated by reciprocal anchorage.Besides molar intrusion, CAT can be designed to extrude the anterior teeth. In the presented patient, the “pendulum effect” of anterior tooth retraction and the “fulcrum effect” of posterior tooth intrusion and advancement were used to correct the anterior open bite. The radiographic superimpositions revealed that the aligners intruded the maxillary and mandibular molars no more than 1 mm and that the correction of the anterior open bite was primarily achieved by anterior tooth extrusion accompanying a small amount of molar intrusion (Figures 9 and 10). This may cause the mandible to rotate counter-clockwise. The entire treatment process sequentially involved an anterior open bite, deep overbite, and finally, a normal overbite, indicating that the anterior retraction using CAT can easily lead to extrusion of the anterior teeth. Therefore, the design of the ClinCheck plan should reduce the anterior extrusion to strengthen vertical control. In open bite cases with a large anterior facial inclination, relative extrusion may be planned during anterior tooth retraction, followed by the use of optimised extrusion attachments to produce absolute extrusion. ‘Absolute extrusion’ indicates a tooth or a group of teeth that have been extruded (relative to the alveolar bone). The mild posterior open bite may result from two factors, one of which is the intrusive effect of the aligners, and the other is the occlusal interference caused by torque loss of the upper anterior teeth. The former could be adjusted by vertical traction or self-adjustment, while the latter requires torque correction.Transversely, most open bite deformities have narrow dental arches. The wrap-around design of the aligners can effectively widen the dental arches, obtain appropriate arch forms, and digitally match the width of the upper and lower arches, which is more accurate than traditional fixed orthodontics. In the present case, clear aligners were used to widen the narrow maxillary dental arch, correct the posterior crossbite and scissor-bite and establish a normal posterior overbite and overjet. Correcting a buccal scissor-bite is difficult using fixed orthodontics. While applying CAT, the “bite-block effect” of the aligner presented a significant advantage related to opening the occlusion and avoiding occlusal interference, thereby facilitating the palatal movement of 17 and correcting the scissor-bite occlusal relationship (Figure 5). In addition, the premise was that the movement of 16 provided space for the palatal repositioning of 17. Sagittally, in order to achieve Class I molar relationships, the treatment plan involved the mesial movement of upper molars and the retraction of lower anterior teeth. Compared to traditional orthodontics, the mesial movement of posterior teeth with clear aligners is more difficult to perform as the molars tend to tip mesially9. To counteract the mesial tipping, it is possible to keep the crown tipped distally, design step-by-step molar mesial movement, and add attachments. The treatment with 5° of root movement (for 16 and 26) towards the extraction space was incorporated at the start. For every 1 mm of mesialisation of 16, 26, 17, and 27, 2° of mesial root tip was added, thereby keeping the crowns inclined distally (Figure 16). Concurrently, a vertical rectangular attachment was used to assist the long-distance mesial movement of the molars. To control anchorage and torque, a stepwise retraction mode and lingual root torque of the incisors were adopted to facilitate retraction of the anterior teeth. Simultaneously, the patient used Class III elastics to reinforce lower posterior anchorage. Before orthodontic treatment, the patient received lip training and a tongue crib to stop mouth breathing and tongue-thrusting habits.11 The clear aligner has also been reported as a useful device to aid in modifying habits like tongue-thrusting because the plastic covers the anterior teeth.14,25,39Figure 16.Overcorrection to keep the crowns inclined distally. (A-B) during treatment. (C-D) before treatment.Contemporary orthodontics also seeks to improve facial aesthetics and soft tissue profiles40,41. The current treatment visibly improved the nasolabial angle, lip protrusion, and mentolabial angle. Consistent with previous studies42 describing the retraction of incisors, the inclination of the protruded incisors reduced, and the nasolabial angle and upper lip length increased. Based on Ricketts’ aesthetic E-line,43 the patient attained better lip retraction and improved the everted lips.42 A previous study has revealed that the lower incisor provides support for the lower lip and that any movement of the incisor will affect the spatial position of the lip to some extent.42 In addition, mentolabial sulcus depth changes coincide with lower lip protrusion and E-plane changes.44 In the present patient, the retraction of the lower incisor passively retracted the lower lip, and the mentolabial sulcus depth became shallower.Studies have also shown that the mouth and teeth are the basis of facial aesthetics.44 The aligner treatment achieved a perfect smile and co-ordinated the relationship between the lips and teeth. The midline of the upper and lower dental arches matched the midline of the face, and the edges of the maxillary incisors at rest were close to the lower lip (Figure 7). According to Machado et al.,45 this ideal position of the maxillary incisors is associated with beauty, youth, etc. In addition, an ideal smile arc (i.e., maxillary incisal edges slightly contoured to the lower lip) was achieved for the patient. The anterior extrusion helped obtain a consonant smile line, which is rated as more aesthetic,45,46 and dental expansion improved the substantially reduced buccal corridors. Additionally, retraction of the incisors facilitated retraction of the upper and lower lips, increased exposure of the anterior teeth, and reduced the inter-labial gap. These changes improved the soft tissue appearance of the lower third of the face and substantially improved the patient’s aesthetics and facial profile.The ClinCheck plan is a graphic representation of the forces being applied to the teeth.47 Based on the digital methods and orthodontic biomechanical principles, clinicians formulate a desired individualised plan to achieve three-dimensional controlled and sequential tooth movement from the beginning to the end of treatment. In 2012, Align Technology announced multitooth anterior extrusive attachments for anterior open bite correction associated with their G4 innovation. These attachments are placed on the incisors when the software detects the need for pure extrusion of 0.5 mm or more.11,16,18 The size and shape of the attachments are designed directly by the ClinCheck software based on the biomechanical request.25 This movement requires ‘grip’, especially on the central and lateral incisors, which have smooth surfaces and minimal undercuts.48 In addition, the intramaxillary and intermaxillary elastics can be designed in the ClinCheck plan during the early stages of treatment in patients who need programmed extrusion.49 No attachments are required on a posterior tooth to be intruded, whereas adjacent teeth (functioning as anchorage units) require attachments. In cases of open bite, directions for the future development of the software include simulation of the progressive rotation of the mandible caused by the molar intrusion, which is similar to the sagittal occlusal jump in Class II patients.25 More research is needed on the biomechanical feasibility and effectiveness of the clear aligner system.50Summary and conclusionsThe present case report demonstrated the successful clear aligner treatment of an adult patient who complained of a protrusive profile, an anterior open bite and inefficient masticatory function. At the completion of treatment, the patient’s protrusive profile had improved, and the anterior open bite, mesiocclusion and other problems were corrected. The limitation of this study was that it only presents one case, and the guiding significance of CAT in patients with these characteristics is therefore limited. In the future, more in-depth research is necessary to provide stronger evidence and appropriate guidelines for clinical CAT decision-making. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Australasian Orthodontic Journal de Gruyter

Treatment of an anterior open bite, bimaxillary protrusion and mesiocclusion by the extraction of premolars and the use of clear aligners

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Publisher
de Gruyter
Copyright
© 2023 Xiaosong Xiang et al., published by Sciendo
eISSN
2207-7480
DOI
10.2478/aoj-2023-0007
Publisher site
See Article on Publisher Site

Abstract

IntroductionIntroduced in 1999 by Align Technology (Santa Clara, CA, USA), the Clear Aligner System has become a popular treatment choice for adult orthodontic patients who reject traditional visible appliances. The technique was initially introduced by Kesling1 and improved by Ponitz2 and others.3 The current clear aligner technique (CAT) is used to treat malocclusions through a series of sequential removable trays.4 Earlier studies5–10 have shown significant limitations of using the clear aligner to treat complex malocclusions. However, several clinical case reports using CAT have revealed better vertical control due to recent appliance design improvements.11,12 Studies initially reported the development of posterior open bites as a result of CAT treatment,13,14 and demonstrated no correlation between measured and planned molar intrusion in the treatment plan.15,16 Recently, clinicians have claimed that CAT can effectively treat cases of anterior open bite, especially those with an increased mandibular plane angle.17,18The traditional mechanical orthodontic technologies, including multiloop edgewise arch wires, straight wires, and implant anchorage, present many challenges for patients and clinicians in correcting an anterior open bite.19–21 The multiloop edgewise arch wire is difficult to bend, uncomfortable to wear, and compromises aesthetics due to anterior vertical traction. Straight wire technology using reverse-curve arch wires, combined with anterior vertical traction, presents the same disadvantages. Micro-implant technology requires surgery and damages the mucosa and the alveolar bone. However, since the advent of CAT, the appliances have gained popularity, given their advantages over conventional fixed appliances regarding aesthetics, oral hygiene, patient comfort, a lighter level of force, shorter chair time,22,23 and provide a convenient solution for anterior open bite patients.18 Despite the advantages, CAT is challenging for orthodontists when extractions are part of the treatment plan. Therefore, a case of the successful correction of a skeletal anterior open bite, bimaxillary dentoalveolar protrusion, mesiocclusion and other issues through the extraction of four premolars and the use of clear aligners, is presented.Diagnosis and aetiologyA 24-year-old female patient presented with a history of tongue thrust and mouth breathing but without a history of maxillofacial trauma or a non-nutritive sucking habit. The diagnostic records revealed that, based on the E line, the patient had a convex profile with a long face, a decreased nasolabial angle, a protrusive lower lip, and a shallow mentolabial sulcus. Further, the patient had incompetent and protruded lips at rest and in contact but with mentalis strain upon forcible closure. There was also a low smile line, and the smile arc was not consonant with the curvature of the lower lip (Figure 1). An intraoral examination showed an anterior open bite with no occlusal contact from the right first premolar to the left first premolar, a bilateral Class III molar relationship, and a Class III canine relationship on the right side but a Class I relationship on the left side. An analysis of the initial study models revealed that there was an anterior dental open bite of 6 mm, a decreased overjet (the overjet and overbite were measured on digital dental models using 3-shape software), a 3 mm curve of Spee, a mandibular midline deviation (1.5 mm to the left), and arch-length discrepancies of 5 mm in the maxilla and 3 mm in the mandible. The anterior and overall Bolton ratios were compatible. The maxillary dental arch was narrow, and the upper and lower arches were unmatched. A crossbite from the upper left canine to the second premolar was also noted during the examination. The maxillary right second molar was in scissor-bite with the mandibular right second molar (Figure 2). A cephalometric analysis revealed a skeletal open bite (SN/GO-GN 48°), an increased mandibular plane angle, a counter-clockwise rotation of the ANS-PNS plane (S-N/ANS-PNS 6°), proclination of the upper incisors (UI/ANS-PNS 129°), an interincisal angle of 108°, excessive lower anterior facial height and a short upper anterior facial height (Table I). A computed tomography scan of the anterior teeth revealed adequate labial and lingual bone volumes (Figure 3A). In addition, the initial panoramic radiograph and the radiographic and clinical examinations of the temporomandibular joints revealed no obvious abnormalities (Figure 4 and 3B). The patient was diagnosed with a Class III malocclusion (S-N/ANS-PNS 6°) and skeletal open bite (SN/GO-GN 48°) with an increased mandibular plane angle, a long face, a convex profile, and lip incompetence with mentalis strain. There was also proclination of the upper incisors, a crossbite, scissor-bite, mild crowding and midline deviation.Figure 1.Pre-treatment extraoral and intraoral photographs.Figure 2.Initial study models.Figure 3.The pre-treatment labial and lingual bone volume of anterior teeth (A) and temporomandibular joint radiograph (B).Figure 4.Pre-treatment panoramic radiograph (A) and lateral cephalometric radiograph (B).Table I.Pre-treatment and post-treatment cephalometric analysis.MeasurementMean ± SDPre-treatmentPost-treatmentSagittal skeletal relations    S-N-A82° ± 3.5°76°72°    S-N-PG80° ± 3.5°73°70°    A-N-PG2° ± 2.5°3°2°Vertical skeletal relations    S-N/ANS-PNS8° ± 3.0°6°11°    S-N/GO-GN33° ± 2.5°48°48°    ANS-PNS/GO-GN25° ± 6.0°32°27°Dento-basal relations    UI/ANS-PNS110° ± 6.0°129°118°    LI/GO-GN94° ± 7.0°91°82°    LI/A-PG (mm)2 ± 2.04.42.7Dental relations    Overjet (mm)3.5 ± 2.52.22.6    Overbite (mm)2 ± 2.5-2.81.2    Interincisal angle UI/LI132° ± 6.0°108°133°A, point A; ANS, anterior nasal spine; GN, gnathion; GO, gonion; LI, lower incisor; N, nasion; PG, pogonion; PNS, posterior nasal spine; PO, porion; S, sella; SD, standard deviation; UI, upper incisor.Treatment objectivesThe primary treatment objectives were (1) partly closing the anterior open bite by a combination of retraction and extrusion of the upper incisors; (2) further closure of the anterior open bite by intrusion of the posterior maxillary dentition enabling a subsequent counter-clockwise rotation of the mandible and a reduction in facial height; (3) levelling and aligning the upper and lower dentition; (4) achieving Class I molar and canine relationships and an ideal overbite and overjet; (5) improving the facial profile and obtaining natural lip competence without mentalis and lip strain; (6) expanding the upper dental arch to improve the aesthetics of the smile; (7) moving the lower teeth to the right side to correct the midline deviation using the extraction space; and (8) correcting the crossbite and the scissor-bite of the maxillary right second molar.Treatment alternativesGiven the mild skeletal discrepancy and the strong opposition of the patient to the orthodontic and orthognathic surgical treatment program, camouflage treatment with fixed appliances and TAD skeletal anchorage was considered. However, the patient again refused because of aesthetic and comfort concerns. Finally, clear aligner appliances were chosen.Maxillary arch expansion and interproximal reduction (IPR) were additional considerations to relieve the crowding, develop a rounded arch form, and co-ordinate the maxillary and mandibular arches. IPR was also indicated to assist alignment of the lower arch and a combination of anterior extrusion and posterior intrusion to manage the anterior open bite. However, this approach did not adequately address the patient’s concerns, especially the bimaxillary dentoalveolar protrusion and mesiocclusion. Therefore, an alternative approach was selected to correct all of the issues, which involved the extraction of the maxillary second and mandibular first premolars, followed by mechanics using clear aligners, which have gained popularity in the treatment of an anterior open bite malocclusion.24–27Treatment progressBefore treatment, polyvinyl siloxane (DGM, Germany) impressions were taken to develop a ClinCheck treatment plan (Align Technology, Santa Clara, CA, USA). The digital plan was used to determine the number of aligners needed and the treatment duration and to visualise the required biomechanics of tooth movement. The treatment involved three phases:Initial treatment phaseThe treatment commened by extracting the four premolars. The goals of the initial phase were to align and level the dental arches, close the extraction spaces, and close the open bite. In the upper arch, 14, 24, 13, and 23 were retracted, leaving a space at the mesial area of 13 and 23. The anterior teeth were aligned, and 8° of lingual root torque was added prior to en-masse retraction. The teeth 16 and 26 were moved first, allowing further mesialisation of 17 and 27, until 16 and 26 contacted 14 and 24, respectively. Optimised retraction attachments were applied to the upper canines, as well as optimised anchorage attachments and vertical rectangular attachments on the upper posterior teeth. An extrusion attachment was designed and placed on the upper right incisor through an automated process. In the lower arch, the treatment plan was to retract 33 and 43, thereby leaving space mesial to 33 and 43 (which improved aligner grip), adding 10° of lingual root torque before en-masse retraction of the incisors. The G628 solution for optimised retraction attachments was used on the canines and optimised anchorage attachments on the lower posterior teeth. The patient wore bilateral Class III, 3.5-ounce elastics, full time throughout the treatment phase. It was planned to intrude the upper posterior teeth by approximately 2 mm, extrude the upper anterior teeth by approximately 1.5 mm, and finally achieve an overbite of roughly 3 mm. In addition, it was planned to expand the maxillary arch in order to co-ordinate the arch forms. Palatal crown torque of 17 was necessary to achieve a normal buccal overjet of the right posterior teeth. The pre-treatment ClinCheck treatment plan is presented in Figure 5.Figure 5.Pre-treatment ClinCheck treatment plan (Align Technology, Santa Clara, CA, USA).Fifty sets of Invisalign aligners were designed for the patient. However, the treatment had to be restarted due to poor engagement of the 31st aligners. During the following process, a ‘frog’ pattern of movement of the lower anterior teeth was designed, while the other plans remained unchanged. A ‘frog’ pattern is a staggered staging technique: the canines are first retracted for 10 stages, together with some mesialisation of the molars, and then stopped. Then the incisors are retracted for 10 stages and then stopped. The canine movement is restarted for another 10 stages and stopped, followed by further incisor retraction. This pattern is repeated until the extraction spaces are closed and the incisors fully retracted. The aligners were used for 9 months, changed every 10–14 days during the 3 months of initial treatment and changed every 7 days thereafter. The patient was seen at monthly intervals to check aligner fit, attachment stability, and compliance without using remote dental monitoring during the treatment period.Progress treatment phasePolyvinyl siloxane (DGM, Germany) impressions were obtained to assess the progress stage of the ClinCheck treatment plan and to complete the unfinished goals of the first phase. The treatment process continued and followed that established in the first stage. The open bite correction occurred during the second phase of 50 aligners.Refinement phaseThe final sets of aligners underwent improvements to correct the anterior overbite and mild posterior open bite that developed during treatment. During refinement, 15 upper and 10 lower aligners were worn for 9 months and were changed every 14–30 days. The patient’s overbite decreased by attaching power ridges and the subsequent intrusion of the anterior teeth. The posterior open bite was corrected by placing button cutouts in the maxillary and mandibular aligners for attaching vertical elastics. The ClinCheck treatment plan for the refinement stage is presented in Figure 6. While additional improvements may have been possible, the patient was satisfied with the results at the end of this stage; therefore, the treatment was terminated. At the outset, it was considered that the difference in the alignment and position of the anterior teeth before and after treatment was large, and so Hawley retainers combined with bonded lingual wires for retention were provided. However, the patient was unable to adapt to these retainers because of her occupation and socialising, so vacuum-formed and transparent full-arch wraparound retainers were supplied to maintain the treatment results.Figure 6.Refinement stage: ClinCheck treatment plan (Align Technology, Santa Clara, CA, USA).Treatment resultsAfter 33 months of therapy, the treatment objectives established in the pre-treatment plan were achieved, which improved aesthetics and the intercuspation of teeth (Figures 7 and 8). The treatment retracted and uprighted the patient’s incisors (Figures 9 and 10), which improved her lip profile and facial appearance producing a harmonious straight-type of profile. The nasolabial and mentolabial angles increased, and the lips closed naturally without lip or mentalis strain. The treatment completely closed the open bite, corrected the overbite and overjet, aligned the upper and lower dental midlines with the facial midline, and established Class I molar and canine relationships (Figure 7). Based on panoramic radiographs (Figures 4 and 11) and the relative positions of the teeth before and after treatment, standard root length, sufficient root parallelism, a tight occlusal relationship, and adequate posterior anchorage were maintained. The thickness of the labial and lingual bone volume over the anterior tooth roots before and after treatment was within normal limits (Figure 12). The temporo-mandibular joint radiographs before and after treatment revealed no significant changes (Figures 3 and 12). Unfortunately, the objective of the counter-clockwise rotation of the mandible to reduce facial height was not achieved; however, the pretreatment facial height was preserved.Figure 7.Post-treatment extraoral and intraoral photographs.Figure 8.Final study models.Figure 9.Two-dimensional (2D) superimposed cephalometric tracings.Figure 10.Three-dimensional (3D) superimpositions (pre-treatment and post-treatment). (A) the anterior teeth; (B–D) the posterior teeth.Figure 11.Post-treatment panoramic radiograph (A) and lateral cephalometric radiograph (B).Figure 12.The post-treatment labial and lingual bone volume of anterior teeth (A) and temporomandibular joint radiograph (B).DiscussionPrevious research has suggested that the aetiology of an anterior open bite is complicated and includes genetic and environmental factors (i.e., unfavourable growth patterns and parafunctional habits), which are difficult to completely differentiate.29,30 Therefore, an accurate diagnosis and causative determination are the best guides to establish appropriate objectives, ideal treatment plans and definitive corrective procedures31. According to the initial examinations, the patient was diagnosed with a Class III malocclusion and mild skeletal open bite with an increased mandibular plane angle and unmatched dental arches (Figures 1–4; Table I). Dentoalveolar or mild skeletal open bite patients generally exhibit normal craniofacial morphology and skeletal facial shapes but are characterised by proclined incisors, insufficiently erupted anterior teeth, and normal or slightly extruded molars. The anterior open bite is commonly associated with parafunctional habits.30,32 Orthodontics can treat a dentoalveolar or mild skeletal open bite to intrude the posterior teeth, extrude the anterior teeth, or both.33 The required techniques include the “pendulum effect” (Figure 13) of the anterior teeth relatively extruding during retraction; the “fulcrum effect” of the posterior teeth intruding or mesial migration to eliminate the occlusal fulcrum and move the occlusal contact point forward;34 uprighting mesially-tipped posterior teeth and correcting the occlusal plane inclination, not only to reduce the level of the open bite but also to provide space for anterior tooth retraction.35 A counter-clockwise mandibular rotation (Figure 14) is based on studies12,25 suggesting that significant molar intrusion, particularly of the maxillary molars, favours mandibular rotation in a similar fashion to high-pull headgear.Figure 13.The ‘pendulum effect’ of the retraction of the anterior teeth.Figure 14.Counter-clockwise rotation of the mandible.Contemporary orthodontics emphasises the accurate control of three-dimensional tooth movement, and CAT illustrates the advantages of this concept. CAT has unique features related to three-dimensional tooth control for patients with anterior open bite deformities, especially those with an increased mandibular plane angle.13,36,37 Traditional fixed appliances tend to extrude the posterior teeth and increase the mandibular plane angle when inter-arch elastics are used, especially in non-growing individuals, which leads to adverse vertical effects and a worsening of the anterior open bite.36,37 In contrast, even when Class II and Class III elastics are used, clear aligners may prevent extrusion or aid in the intrusion of the posterior teeth due to a “bite-block effect” of the two layers of the aligners covering the posterior teeth, combined with the patient’s natural masticatory intrusive forces.11–13,18,25,38 Additionally, based on Newton’s third law, the extrusive force placed on the anterior part of the aligner for anterior extrusion simultaneously causes a reciprocal intrusive force on the posterior part of the aligner, which is favourable for posterior intrusion (Figure 15). Some researchers24 believe that posterior intrusion using aligners must be programmed. However, evidence supporting this opinion is lacking. A recent study5 has found that the amount of intrusion of the maxillary mesiobuccal cusps can reach 0.47 mm, while others15 have determined that 0.6 mm is possible.Figure 15.The extrusive force and intrusive force generated by reciprocal anchorage.Besides molar intrusion, CAT can be designed to extrude the anterior teeth. In the presented patient, the “pendulum effect” of anterior tooth retraction and the “fulcrum effect” of posterior tooth intrusion and advancement were used to correct the anterior open bite. The radiographic superimpositions revealed that the aligners intruded the maxillary and mandibular molars no more than 1 mm and that the correction of the anterior open bite was primarily achieved by anterior tooth extrusion accompanying a small amount of molar intrusion (Figures 9 and 10). This may cause the mandible to rotate counter-clockwise. The entire treatment process sequentially involved an anterior open bite, deep overbite, and finally, a normal overbite, indicating that the anterior retraction using CAT can easily lead to extrusion of the anterior teeth. Therefore, the design of the ClinCheck plan should reduce the anterior extrusion to strengthen vertical control. In open bite cases with a large anterior facial inclination, relative extrusion may be planned during anterior tooth retraction, followed by the use of optimised extrusion attachments to produce absolute extrusion. ‘Absolute extrusion’ indicates a tooth or a group of teeth that have been extruded (relative to the alveolar bone). The mild posterior open bite may result from two factors, one of which is the intrusive effect of the aligners, and the other is the occlusal interference caused by torque loss of the upper anterior teeth. The former could be adjusted by vertical traction or self-adjustment, while the latter requires torque correction.Transversely, most open bite deformities have narrow dental arches. The wrap-around design of the aligners can effectively widen the dental arches, obtain appropriate arch forms, and digitally match the width of the upper and lower arches, which is more accurate than traditional fixed orthodontics. In the present case, clear aligners were used to widen the narrow maxillary dental arch, correct the posterior crossbite and scissor-bite and establish a normal posterior overbite and overjet. Correcting a buccal scissor-bite is difficult using fixed orthodontics. While applying CAT, the “bite-block effect” of the aligner presented a significant advantage related to opening the occlusion and avoiding occlusal interference, thereby facilitating the palatal movement of 17 and correcting the scissor-bite occlusal relationship (Figure 5). In addition, the premise was that the movement of 16 provided space for the palatal repositioning of 17. Sagittally, in order to achieve Class I molar relationships, the treatment plan involved the mesial movement of upper molars and the retraction of lower anterior teeth. Compared to traditional orthodontics, the mesial movement of posterior teeth with clear aligners is more difficult to perform as the molars tend to tip mesially9. To counteract the mesial tipping, it is possible to keep the crown tipped distally, design step-by-step molar mesial movement, and add attachments. The treatment with 5° of root movement (for 16 and 26) towards the extraction space was incorporated at the start. For every 1 mm of mesialisation of 16, 26, 17, and 27, 2° of mesial root tip was added, thereby keeping the crowns inclined distally (Figure 16). Concurrently, a vertical rectangular attachment was used to assist the long-distance mesial movement of the molars. To control anchorage and torque, a stepwise retraction mode and lingual root torque of the incisors were adopted to facilitate retraction of the anterior teeth. Simultaneously, the patient used Class III elastics to reinforce lower posterior anchorage. Before orthodontic treatment, the patient received lip training and a tongue crib to stop mouth breathing and tongue-thrusting habits.11 The clear aligner has also been reported as a useful device to aid in modifying habits like tongue-thrusting because the plastic covers the anterior teeth.14,25,39Figure 16.Overcorrection to keep the crowns inclined distally. (A-B) during treatment. (C-D) before treatment.Contemporary orthodontics also seeks to improve facial aesthetics and soft tissue profiles40,41. The current treatment visibly improved the nasolabial angle, lip protrusion, and mentolabial angle. Consistent with previous studies42 describing the retraction of incisors, the inclination of the protruded incisors reduced, and the nasolabial angle and upper lip length increased. Based on Ricketts’ aesthetic E-line,43 the patient attained better lip retraction and improved the everted lips.42 A previous study has revealed that the lower incisor provides support for the lower lip and that any movement of the incisor will affect the spatial position of the lip to some extent.42 In addition, mentolabial sulcus depth changes coincide with lower lip protrusion and E-plane changes.44 In the present patient, the retraction of the lower incisor passively retracted the lower lip, and the mentolabial sulcus depth became shallower.Studies have also shown that the mouth and teeth are the basis of facial aesthetics.44 The aligner treatment achieved a perfect smile and co-ordinated the relationship between the lips and teeth. The midline of the upper and lower dental arches matched the midline of the face, and the edges of the maxillary incisors at rest were close to the lower lip (Figure 7). According to Machado et al.,45 this ideal position of the maxillary incisors is associated with beauty, youth, etc. In addition, an ideal smile arc (i.e., maxillary incisal edges slightly contoured to the lower lip) was achieved for the patient. The anterior extrusion helped obtain a consonant smile line, which is rated as more aesthetic,45,46 and dental expansion improved the substantially reduced buccal corridors. Additionally, retraction of the incisors facilitated retraction of the upper and lower lips, increased exposure of the anterior teeth, and reduced the inter-labial gap. These changes improved the soft tissue appearance of the lower third of the face and substantially improved the patient’s aesthetics and facial profile.The ClinCheck plan is a graphic representation of the forces being applied to the teeth.47 Based on the digital methods and orthodontic biomechanical principles, clinicians formulate a desired individualised plan to achieve three-dimensional controlled and sequential tooth movement from the beginning to the end of treatment. In 2012, Align Technology announced multitooth anterior extrusive attachments for anterior open bite correction associated with their G4 innovation. These attachments are placed on the incisors when the software detects the need for pure extrusion of 0.5 mm or more.11,16,18 The size and shape of the attachments are designed directly by the ClinCheck software based on the biomechanical request.25 This movement requires ‘grip’, especially on the central and lateral incisors, which have smooth surfaces and minimal undercuts.48 In addition, the intramaxillary and intermaxillary elastics can be designed in the ClinCheck plan during the early stages of treatment in patients who need programmed extrusion.49 No attachments are required on a posterior tooth to be intruded, whereas adjacent teeth (functioning as anchorage units) require attachments. In cases of open bite, directions for the future development of the software include simulation of the progressive rotation of the mandible caused by the molar intrusion, which is similar to the sagittal occlusal jump in Class II patients.25 More research is needed on the biomechanical feasibility and effectiveness of the clear aligner system.50Summary and conclusionsThe present case report demonstrated the successful clear aligner treatment of an adult patient who complained of a protrusive profile, an anterior open bite and inefficient masticatory function. At the completion of treatment, the patient’s protrusive profile had improved, and the anterior open bite, mesiocclusion and other problems were corrected. The limitation of this study was that it only presents one case, and the guiding significance of CAT in patients with these characteristics is therefore limited. In the future, more in-depth research is necessary to provide stronger evidence and appropriate guidelines for clinical CAT decision-making.

Journal

Australasian Orthodontic Journalde Gruyter

Published: Jan 1, 2023

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