ABSTRACT
A bone-borne full-arch vertical control strategy using miniscrews was deployed with aligners to treat a case of skeletal hyperdivergent Class II malocclusion with bimaxillary protrusion. Miniscrews were inserted in the posterior buccal and palatal regions and the anterior buccal region of the maxilla to distribute vertical intrusive force through the upper arch by anchoring vertical elastics from the miniscrews to the aligners. Synergetic lower anterior intrusion was completed using bilateral posterior miniscrews to counteract the extrusive force generated. Substantial full upper arch and lower anterior vertical intrusion was achieved. In conjunction with en masse anterior-posterior retraction, synergetic posterior and anterior vertical intrusion facilitated counterclockwise rotation of the mandible, creating significant esthetic improvement. Anterior vertical elastics also provided flaring of the anterior teeth, reducing the side effect of lingual tipping from en masse retraction, while successfully controlling overbite and incisor torque during space closure. The bone-borne full-arch vertical intrusion strategy can work well with aligners to address hyperdivergent skeletal Class II malocclusion with bimaxillary protrusion.
INTRODUCTION
Among the Asian population, protrusion is commonly complicated by a hyperdivergent Class II skeletal pattern,1–4 which is characterized by excessive alveolar bone development. For such patients, facial esthetics are compromised, both by proclined anterior teeth and a prognathic maxilla, and aggravated by a retrognathic mandible and increased lower facial height.1,2 Although it is relatively reliable to perform orthognathic surgery, there are still debates on the effectiveness of skeletal pattern correction5,6 and reluctance to undergo major surgical intervention.4,7
Miniscrews have been shown to be a reliable anchorage device in sagittal profile reduction and are regularly used in practice.2,8–11 For vertical reduction, use of miniscrews has been effective in open-bite correction.10,12 However, achieving significant synergetic true intrusion of a full arch, which is necessary for substantial mandibular rotation and improvement of the facial profile required in correction of a hyperdivergent skeletal pattern, is difficult to implement in fixed orthodontics.9,13
Previous studies have suggested that clear aligners can be an effective treatment option for open bite with a high mandibular plane angle by using bone-borne posterior intrusion without anterior extrusion.11,14,15 This indicates that appropriate combined application of miniscrews and aligners may potentially deliver promising results in treating bimaxillary protrusion in patients with a hyperdivergent skeletal pattern.
In this patient, miniscrews were used with aligners for synergetic intrusion and en masse retraction for the upper and lower arches with torque control of the anterior teeth, in expectation of achieving a harmonious profile in both the sagittal and vertical dimensions.
Diagnosis and Etiology
A 24-year-old female presented with complaints of dentoalveolar protrusion, retrusion of the chin, and a gummy smile. Clinical examination showed a convex facial profile with protruded teeth and retrusive mandible, accompanied by excessive lower facial height. In addition to an acute nasolabial angle and lip incompetence, moderate muscular tension (mentalis strain) was indicated by a shallow labiomental groove and chin fossa (Figure 1). The upper and lower dental midlines were coincident with the facial midline. Both arches were well aligned in ovoid arch forms with mild dental discrepancies of 3.5-mm crowding in the upper arch and 3 mm in the lower arch. Lingual inclination of #16 and #26 teeth was noted. Class I molar and canine relationships were noted on the right side with mild distal deviation, while an end-to-end Class II relationship was observed on the left (Figure 2). Overjet was 4 mm, and overbite was1 mm. There was 4 mm of gingival exposure during dynamic smile.
The panoramic radiograph showed horizontal impaction of the third molars (Figure 3). Lateral cephalometric radiography in maximum intercuspation exhibited a hyperdivergent profile (FH-MP = 42.4°, MP-SN = 48.3°), with a skeletal Class II relationship (ANB = 8.0°, Wits = 7.3 mm) and mandibular retrognathia (SNB = 73.5°, soft tissue facial angle G-Sn-Pg′ = 23.8°; Figure 4; Table 1). Bimaxillary protrusion was also indicated by a decreased interincisal angle (U1-L1 = 113.6°), with exaggerated labial proclination of the upper (U1-NA = 6.0 mm) and lower incisors (L1-NB = 12.2 mm).
Cephalometric radiograph and tracing (A, Pretreatment. B, Miniscrews installed. C, Posttreatment).
Cephalometric radiograph and tracing (A, Pretreatment. B, Miniscrews installed. C, Posttreatment).
Treatment Objectives
The treatment objectives were to achieve alignment and leveling of both arches, improve overjet and overbite, establish Class I relationships, attain optimal profile improvement, and avoid development of an open bite and prevent temporomandibular joint (TMJ) problems during synergistic full-arch intrusion.
Treatment Alternatives
Although it was recommended to perform orthognathic surgery, decision making became complicated when dealing with the hyperdivergent Class II skeletal pattern with bimaxillary protrusion.6,16,17 Considering the patient’s esthetic concerns and reluctance to accept surgery, a nonsurgical camouflage plan was chosen, therefore, to reduce protrusion and improve the lateral profile by extraction of four first premolars and use of miniscrews as skeletal anchorage devices. Miniscrews were planned for use primarily during maxillary sagittal retraction. Then to improve the vertical hyperdivergent skeletal pattern, a strategy of miniscrew placement would be used in both arches for vertical intrusion, by which substantial intrusion could be achieved to allow counterclockwise rotation of the mandible, in the hope of accomplishing vertical reduction and mandibular advancement.
Camouflage could have been achieved by using the edgewise appliance. However, full-arch vertical control is probably limited in transferring vertical force to the full arch through an edgewise system, and it is also a less esthetic treatment system.9,18,19
Therefore, the treatment agreed on was to camouflage the hyperdivergent Class II skeletal pattern using the Invisalign® Comprehensive Package (Align Technology, Santa Clara, California), using miniscrews in both the maxilla and mandible, which involved using six miniscrews in the anterior and posterior maxilla, and two in the posterior mandibular region. Synergetic intrusion was designed between anterior and posterior teeth in both the upper and lower dental arches to achieve anticlockwise rotation of the mandible.
Treatment Progress
For the first stage, the G6 attachment system was used with 47 aligners (Figure 5). At the early third step, two 2 × 10-mm miniscrews (Ormco, Brea, Calif) for the maxilla and two 1.4 × 8-mm miniscrews for the mandible were placed buccally between the first molar and second premolar roots, designated for anterior retraction. The lower right miniscrew was relocated between the molars after it loosened. Palatal miniscrews (2 × 12 mm) were placed between the first and second molar roots (Figure 6) by which initial vertical intrusion was initiated by using cross-aligner surface elastics anchored between the upper posterior miniscrews and the palatal miniscrew, delivering intrusive force to the posterior teeth. Anterior intrusion miniscrews (1.4 × 8 mm) were not inserted on the labial aspect between lateral incisor and canine roots until step 15, while retraction did not start until aligning and leveling was completed.
By tray 25, there was anticlockwise rotation of the mandible by full-arch intrusion and improved molar relationship bilaterally. However, retraction also resulted in premature contacts of the anterior teeth, which made continuing space closure inadvisable until further leveling was achieved. Thereby, a timely refinement was scheduled.
For the first refinement, 38 aligners were prescribed. Horizontal attachments were bonded to improve retention and counteract the extrusive force generated from anterior intrusion. To control torque of the anterior teeth, overcorrection was planned for torque and tip of the anterior teeth, while a 1-mm open bite was designed for deep bite overcorrection (Figure 7). To continue vertical intrusion, anterior elastics were attached, switching from a direct bonded resin button to an aligner half-cut bubble (Figure 8), which also helped torque control of the anterior teeth. Horizontal elastics continued to the end of space closure, while a direct bonded resin button was placed on the buccal surface to attach elastics and maintain uprighting of the lower canines.
After space closure, a final stage (Figure 9) with 33 aligners was planned for refinement. Conventional attachments were used to facilitate the refinement, and intrusive elastics were maintained for final intrusion and leveling. For the last steps, light vertical elastics were applied between the upper and lower posterior teeth to achieve intercuspation and occlusal contact. Complete correction of posterior overintrusion in the upper arch was intentionally not achieved and left to compensate for potential vertical relapse during retention.
For all stages, the patient was required to change aligners every 10 days. At the end of treatment, maxillary and mandibular aligner retainers were used to stabilize the occlusion.
Treatment Results
Upon final refinement, bilateral Class I molar and canine relationships were achieved, accompanied by ideal intercuspated occlusion with normal overbite and overjet (Figures 10 and 11). By using skeletally anchored full-arch intrusion and sagittal retraction of the anterior teeth, the extent of the anticipated resultant anticlockwise rotation of the mandible and reduction of dental protrusion was achieved. Ultimately, the mandible advanced, and balanced facial esthetics were established. Muscle tension, lip incompetence, and the gummy smile were markedly corrected (Figure 12).
Cephalometric analysis (Figure 13; Table 1) showed notable vertical skeletal improvement of MP-SN and FH-MP by 6.1° and 5.9, respectively. Vertical intrusion allowed mandibular advancement, as denoted by the decrease of ANB from 8.0° to 4.9° and an increase of SNB from 73.5° to 75.8°, with the Wits appraisal decreased by 5.8 mm. Dental movement also resulted in a 1.5° change in OP-SN, denoting that equilibrium was reestablished between the dental arches following intrusion and retraction. Similarly, the proclination of incisors was also reduced to normal levels, as indicated by a 6.1° angular and 5.1-mm linear decrease in U1-NA as well as 8.8° and 8.0 mm, respectively, in L1-NB.
Cephalometric superimposition between pretreatment (red) and posttreatment (blue).
Cephalometric superimposition between pretreatment (red) and posttreatment (blue).
As a result, the soft tissue profile exhibited significant improvement in both the sagittal and vertical dimensions. This was shown in cephalometric superimpositions by a 10.6° decrease in facial angle (G-Sn-Pg′) and a 13.4-mm advancement of soft tissue Pogonion in G-Pg′ (HP).
The condyles were distalized to centric relation after mandibular rotation, thereby reestablishing centric occlusion in accordance with the change in the occlusal plane (Figure 14).
Superimposition of pretreatment and posttreatment models (Figure 15; Table 2) showed an average of 3.7 mm of intrusion of the upper incisors and 4.2 mm of the posterior teeth, with 7.9 mm of sagittal retraction of the anterior teeth. Similarly, the lower incisors were retracted by 6.3 mm and intruded 3.1 mm.
Superimposition of pretreatment and posttreatment digital models (central incisor median point of cut edges before/after treatment; first molar mesial buccal cups tip points before/after treatment).
Superimposition of pretreatment and posttreatment digital models (central incisor median point of cut edges before/after treatment; first molar mesial buccal cups tip points before/after treatment).
Follow-up conducted 1.5 years after treatment revealed the overbite and overjet as well as molar and canine relationships being maintained and consistency of esthetics. The patient continues to wear clear retainers every day and only removes them at night (Figure 16).
DISCUSSION
Conventional fixed orthodontics is not considered capable of reducing a high mandibular plane angle and, most of the time, causes steepening of the mandibular plane.8,9,18 Full-arch vertical control with miniscrews was shown in recent years to decrease the vertical dimension; however, limited change can be achieved.8,9,19 Different from controlling individual teeth using fixed appliances, clear aligners encase the teeth of each arch within a single orthodontic appliance, which enables control of arch position and the teeth together and can probably be more effective in achieving substantial intrusion to facilitate dramatic anticlockwise rotation of the mandible. This case serves as an important reminder of the potential benefits of using a combination of treatment modalities to achieve optimal results. Approximately 6° of reduction in MP-SN was achieved, which created significant advancement of the mandible and chin in the sagittal dimension. In addition to sagittal retraction of the anterior teeth, soft tissue esthetics was significantly improved.
In this patient, the substantial intrusion and sagittal retraction achieved should be attributed primarily to the use of skeletal anchorage in both the maxillary and mandibular arches. Using multiple miniscrews allowed vertical force to be applied on both the anterior and posterior teeth simultaneously, achieving coordinated and synchronized equivalent intrusion of both the anterior and posterior teeth. Synergetic intrusion of the lower anterior teeth was also made possible using miniscrews inserted in the posterior region, which was achieved by uprighting the anterior teeth during en mass retraction and counteracted extrusion of the posterior teeth during leveling and anterior intrusion.
In addition, substantial intrusion should be attributed to the combination usage of clear aligners. The unique nature of aligners allows application of intrusive force by elastics to the occlusal surface using labial and palatal miniscrews. Also, coverage by the aligners of the full arch allows elastic force to be distributed and extended over at least three teeth by staggering posterior miniscrews on the buccal and palatal aspects for one tooth. By using elastics anchored from anterior miniscrews to the anterior labial aspect of the aligners, vertical intrusive force was distributed to the full arch by the aligners. Also, labially anchored anterior vertical force delivered a labial moment to help control the torque of anterior teeth, while also achieving significant vertical intrusion of the anterior teeth during their retraction.10,20,21
Miniscrews were inserted both on the buccal and lingual sides of the maxillary posterior teeth to facilitate intrusive force applied to the occlusal surfaces.8,9 As there was an expectation for significant intrusion designed into the treatment plan, the apical region between the first molar and second premolar labially, first and second molar palatally, as well as the canine and lateral incisor labially were selected for insertion to leave enough interroot space to protect the roots from resorption.17 These locations were also favorable due to bone quality, quantity, and thickness to achieve good primary stability of miniscrews, as reported in the literature.1,8,17,20
Although the G6 system was developed by Invisalign for use in extraction cases, especially for specific types of movement like tipping and inclination, its performance was questionable for substantial retraction as reported.21 A deep curve of Spee and exaggerated overbite prompted the use of conventional attachments in this case to provide more rigid control of teeth. The need for refinement and timely refinement is inevitable and critical when using aligners, as accuracy of tooth movement can be between 30% and 65% for different types of movement.10,15,20,21 In this case, conventional attachments provided enough extrusive force to resist anterior intrusion in the lower arch, which was neutralized by posterior intrusive force created from the lower miniscrews, as shown by superimpositions.
It has been widely believed that the treatment period using aligners is longer than that of fixed orthodontics, especially for complex cases. However, recent studies have challenged this notion, and treatment of patients with high difficulty may not necessarily be prolonged, despite a probable increase in the need for refinement restarts.10,14,22 This case may serve as a good example. Extraction of premolars requires good control of retraction as well as comprehensive vertical control throughout the process, which significantly increases treatment complexity. However, with a multidimensional design and sequencing of tooth movements, after two refinements, teeth were effectively controlled, and treatment time was appropriately compressed, resulting in a total active treatment time of 29 months. Proper treatment design, appropriate sequencing, and timely restarts can effectively improve treatment efficiency, and aligner treatment can achieve treatment times comparable with fixed orthodontic treatment, even in cases with high difficulty and complexity.
Despite limited literature supporting a causal relationship between malocclusion and TMJ dysfunction (TMD) in recent years, the impact of a hyperdivergent skeletal pattern has long been discussed.23,24 As seen in the current patient, excessive vertical growth of the posterior dental arch can result in passive mandibular clockwise rotation and a decrease in overbite, leading to a lack of vertical overlap anteriorly and resultant dysfunction of incisor and canine guidance. In addition, forward displacement of the coronoid processes could possibly take on more force than they are designated to handle, leading to joint problems. Therefore, a comprehensive evaluation of all factors contributing to TMD was necessary, which influenced the decision to conduct full-arch vertical intrusion to cause distal relocation of coronoid process to a more normal position. Finally, by ensuring proper occlusion and tooth alignment, the risk of joint problems can be minimized or even avoided altogether by orthodontic treatment in certain cases.
CONCLUSIONS
Using aligners and miniscrews, full-arch vertical control can achieve significant synergetic intrusion to achieve mandibular anticlockwise rotation, improve skeletal relationships, reestablish intermaxillary balance, and avoid TMJ problems for hyperdivergent Class II malocclusion.
Proper design, appropriate sequencing, and timely restarts can help aligners achieve treatment durations comparable with fixed orthodontics, even in such complex cases.
The treatment results and a 19-month follow-up period confirmed the effectiveness of treatment and stability in the patient presented.
ACKNOWLEDGMENT
This report was supported by Shenzhen Clinical Research Center for Oral Disease (20210617170745001).
REFERENCES
Author notes
Clinical Assistant Professor, Department of Orthodontics, Stomatology Center of Peking University Shenzhen Hospital; Shenzhen Division of National Stomatological Clinical Research Center, Stamotology Clinical Research Center of Shenzhen, Shenzhen, China.
Clinical Professor, Department of Orthodontics, Stomatology Center of Peking University Shenzhen Hospital; Shenzhen Division of National Stomatological Clinical Research Center, Stomatology Clinical Research Center of Shenzhen, Shenzhen, China.