Clear aligner mandibular advancement in growing patients with Class II malocclusion

Abstract

Treatment effects occurring during Class II malocclusion treatment with the clear aligner mandibular advancement protocol were evaluated in two growing patients: one male (12 years, 3 months) and one female (11 years, 9 months). Both patients presented with full cusp Class II molar and canine relationships. Intraoral scans and cone-beam computed tomography were acquired before treatment and after mandibular advancement. Three-dimensional skeletal and dental long-axis changes were quantified, in which the dental long axis was determined by registering the dental crowns obtained from intraoral scans to the root canals in cone-beam computed tomography scans obtained at the same time points. Class II correction was achieved by a combination of mandibular skeletal and dental changes. A similar direction of skeletal and dental changes was observed in both patients, with downward and forward displacement of the mandible resulting from the growth of the mandibular condyle and ramus. Dental changes in both patients included mesialization of the mandibular posterior teeth with flaring of mandibular anterior teeth. In these two patients, clear aligner mandibular advancement was an effective treatment modality for Class II malocclusion correction with skeletal and dental effects and facial profile improvement.

The role of dentofacial orthopedics and orthodontic growth modification in treating Class II malocclusion remains controversial.^1–3 Removable functional appliances often are bulky, have costly laboratory fabrication, and must be worn for 9–18 months to fully correct Class II malocclusions by dentoalveolar effects and increases in mandibular length.^3–8 Fixed Class II correctors such as the Herbst appliance,⁸ the mandibular anterior repositioning appliance (MARA)⁹ and Forsus appliance¹⁰ do not require excellent patient compliance. However, these appliances limit the range of mandibular motion and can be prone to breakage. In addition, undesirable dental compensations (eg, excessive flaring of the mandibular incisors) have been reported.^11,12

Conventional fixed appliances combined with intermaxillary Class II elastics correct the Class II malocclusion primarily by dentoalveolar compensation rather than skeletal changes.^13,14 The Carriere Motion 3D device improves the occlusal relationship by distalizing the maxillary dental arch with heavy intermaxillary elastics.¹⁵ Recent studies have reported clear aligner mandibular advancement (MA) treatment effects using 2-dimensional (2D) cephalometry and digital dental models.^14,16,17 However, no previous study of clear aligner MA has evaluated the 3-dimensional skeletal effects and the changes in the dental long axis after this novel treatment modality. Therefore, this report presents the 3-dimensional (3D) effects of clear aligner MA therapy in two growing patients with a Class II relationship.

DIAGNOSIS AND ETIOLOGY

A male patient aged 12 years, 3 months, physically healthy with a noncontributory medical history, presented the chief complaints of “crooked teeth” and “I don’t like my smile.” Radiographic examination of the cervical vertebrae^18,19 revealed a cervical vertebral maturation (CVM) stage 3, indicating that the patient was in the ascendant part of his pubertal growth spurt. The extraoral examination showed a slightly convex facial profile, vertical proportions within normal limits, and lip competency (Fig 1, A). The intraoral examination revealed a full cusp Class II molar and canine relationship with increased overjet (3.6 mm), a deepbite (7.8 mm, 94%), an accentuated curve of Spee, and moderate maxillary and mandibular crowding (Fig 2). Figure 3, A and B show pretreatment panoramic and lateral cephalometric radiographs. The ANB angle was increased (5.6°), whereas the SNB angle was decreased, indicating a skeletal Class II malocclusion with mandibular retrusion (Table I).

Fig 1.

Patient 1: A, A male patient aged 12 years, 3 months before clear aligner MA treatment; B, Treatment progress after 9 months, 2 weeks of mandibular advancement; C, Skeletal changes before (blue) and after (gray) the mandibular advancement. The top row shows the cranial base superimposition, the middle row shows the maxillary superimposition, and the bottom row shows mandibular regional superimposition. Arrows indicate the direction of displacements, and measurements are shown in millimeters; D, Cephalometric tracing with pretreatment (black) and posttreatment (red) superimpositions. The top row shows the cranial base superimposition, the middle row shows maxillary superimposition, and the bottom row shows mandibular regional superimposition; E, Posttreatment records.

Fig 2.

Patient 1: Intraoral photographs before clear aligner MA treatment, after mandibular advancement and at the end of treatment. CBCT/IOS merged superimpositions before and after the MA. The side views of the IOSs highlight the initial full Class II occlusion.

Fig 3.

Patient 1: A, Pretreatment panoramic radiograph; B, Pretreatment lateral cephalogram; C, Posttreatment panoramic radiograph; D, Posttreatment lateral cephalogram.

Table I.

Skeletal measurements before and after MA treatment

		Patient 1			Patient 2
Measurements		Pretreatment	Posttreatment	Changes	Pretreatment	Posttreatment	Changes
Skeletal (°)
Maxillary position	SNA	82.5	83.9	1.4	78.8	78.0	−0.8
Mandibular position	SNB	76.8	80.0	3.2	74.3	75.0	0.7
Maxillomandibular relation	ANB	5.6	3.8	−1.8	4.5	3.0	−1.5
Cranial base	Ba-S-N	127.5	127.5	0.0	133.4	133.7	0.3
Mp-SN	SN-GoGn	32.2	29.8	−2.4	33.5	33.9	0.4
Gonial angle	Co-Go-Me	125.8	124.1	−1.7	117.5	117.7	0.2
Skeletal (mm)
Posterior cranial base anteroposterior	Ba-S	22.1	23.6	1.5	22.7	22.9	0.2
Anterior cranial base anteroposterior	S-N	67.5	68.4	0.9	67.1	67.1	0.0
Maxilla length anteroposterior	PNS-ANS	54.2	58.9	4.7	52.5	53.7	1.2
Mandible length 3D scalar	Co-Pog 3D	106.4	114.5	8.1	115.0	117.6	2.6
Mandibular ramus superoinferior	Co-Go	43.6	50.6	7.0	56.4	58.3	1.9
Mandibular body anteroposterior	Go-Me	57.1	63.1	6.0	62.0	65.1	3.1

A female patient aged 11 years, 9 months with a chief complaint of “my top teeth stick out” was referred for orthodontic treatment. The patient presented with CVM stage 4 at or just after her peak pubertal growth spurt, and she did not present any contributory medical history. A slightly convex facial profile, normal vertical facial proportions, lip competency, and gummy smile were identified in the extraoral assessment (Fig 4, A). In the intraoral evaluation, the patient showed a full cusp Class II molar and canine relationship with moderate crowding in the maxillary arch and mild crowding in the mandibular arch, increased overjet (6.9 mm), deepbite (6.4 mm, 93%), and accentuated curve of Spee (Fig 5). Figure 6, A and B show pretreatment panoramic and lateral cephalometric x-rays. An increased ANB angle of 4.5° and a decreased SNB angle of 74.3° indicated a mild skeletal Class II malocclusion with mandibular retrognathism (Table I).

Fig 4.

Patient 2: A, A female patient aged 11 years, 9 months before clear aligner MA treatment; B, Treatment progress after 7 months, 3 weeks of mandibular advancement; C, Skeletal changes before (blue) and after (gray) indicate the amount of mandibular advancement. The top row shows cranial base superimposition, the middle row shows maxillary superimposition, and the bottom row shows mandibular regional superimposition. Arrows indicate the direction of displacements, and measurements are shown in millimeters; D, Cephalometric tracing with pretreatment (black) and posttreatment (red) superimpositions; The top row shows the cranial base superimposition, the middle row shows maxillary superimposition, and the bottom row shows mandibular regional superimposition; E, Posttreatment records.

Fig 5.

Patient 2: Intraoral photographs before clear aligner MA treatment, after mandibular advancement and at the end of treatment. CBCT/IOS merged superimpositions before and after the MA. The side views of the initial IOSs highlight the initial full Class II occlusion.

Fig 6.

Patient 2: A, Pretreatment panoramic radiograph; B, Pretreatment lateral cephalogram; C, Posttreatment panoramic radiograph; D, Posttreatment lateral cephalogram.

TREATMENT OBJECTIVES

The main treatment objectives for the two patients included: (1) improvement of the maxillomandibular sagittal relationship and facial profile; and (2) correction of the Class II malocclusion, maxillary and mandibular crowding, deepbite, and overjet.

TREATMENT ALTERNATIVES

Four treatment options were considered: (1) Twin-block and full-fixed appliances, (2) Herbst and full-fixed appliances, (3) Class II Carriere and full-fixed appliances, and (4) clear aligner MA therapy. After explaining the advantages, disadvantages, and need for compliance with each treatment, the patients and their parents chose the clear aligner MA option because of esthetics.

TREATMENT PROGRESS

For both patients, extraoral and intraoral photographs, cone-beam computed tomography (CBCT), and iTero intraoral scans (IOS) were performed. The clear aligner (Invisalign; Align Technology, Santa Clara, Calif) MA therapy comprised two bilateral pairs of inclined planes (precision wings) to guide the mandible in a forward position (Fig 7). After analyzing the patient’s clinical records and craniofacial parameters, the initial treatment plan was established with 61 aligners for patient 1 and 44 for patient The initial leveling phase consisted of 23 aligners for patient 1 and 13 aligners for patient 2. The MA phase with precision wings consisted of 38 aligners for patient 1 (9 months, 2 weeks) and 31 for patient 2 (7 months, 3 weeks).

Fig 7.

A, The clear aligner MA appliance; B, IOS with digital precision wings in the treatment plan for patient 1; C, IOS with digital precision wings in the treatment plan for patient 2.

The patients were instructed to switch aligners every 7 days. The MA was performed gradually with increments of 2 mm every 8 weeks¹⁶ until overcorrection of the overjet was achieved (ie, incisal edge-to-edge relationship) without any planned incisal crown or root torque. At the end of active Class II correction with the clear aligner MA protocol, progress records, including a second CBCT, IOS, and extraoral and intraoral photographs, were acquired. Both patients had a refinement phase to close the temporary posterior open bite (14 aligners in patient 1 and 20 aligners in patient 2). Afterward, final photographs were taken. The retention protocol for both treatments included maxillary and mandibular Essix (invisible) retainers worn full-time for 6 months. After the first 6 months of retention, the patients were instructed to wear retainers only at night-time.

Before obtaining the quantitative measurements, the CBCT images were processed using the following steps: anonymization, compression, segmentation, orientation, and registration.^20,21 Pretreatment and Posttreatment with clear aligner MA IOSs were registered to the corresponding CBCT scans (Fig 8).^{18,20,22–24} After the registration, the IOSs were processed with an automated cloud-based tool in the Data Storage for Computation and Integration platform to merge the detailed crowns from the IOS with the root canals obtained by the CBCT segmentation, allowing precise dental long-axis assessments (Fig 9).^25,26 The skeletal and dental 3D landmarks were defined in Tables II and III, respectively. All measurements were performed using the Slicer software, specifically the Q3DC tool.^11,18,27,28

Fig 8.

Three-dimensional reconstruction of the digital dental model registration to oriented CBCT scans.

Fig 9.

Data Storage for Computational and Integration open-access platform tools.

Table II.

Cranial base, maxilla, and mandible landmarks

	Scan space axis
Landmarks	Sagittal	Axial	Coronal
Nasion (Na)	Most anterior point of frontomaxillary suture	Most anterior and central point of frontomaxillary suture	Most central point of frontomaxillary suture
Sella (S)	Most central point of sella turcica	Most central point of sella turcica	Most central point of sella turcica
Basion (Ba)	Most inferior point of foramen magnum anterior margin	Most anterior and central point of foramen magnum	Most inferior and central point of foramen magnum
A-point (A)	Most posterior point of anterior concavity of maxilla	Deepest point along anterior concavity of maxilla	Deepest point along anterior concavity of maxilla
Posterior nasal spine (PNS)	Most posterior point of hard palate	Most posterior and central point of hard palate	Most posterior and central point of hard palate
Anterior nasal spine (ANS)	Most anterior point of nasal spine	Most anterior and central point of nasal spine	Most anterior point of nasal spine
Right condylion (RCo)	Most superior point of right condyle contour	Most superior and central point of right condyle contour	Most superior point of right condyle contour
Left condylion (LCo)	Most superior point of left condyle contour	Most superior and central point of left condyle contour	Most superior point of left condyle contour
Right gonion (RGo)	Most inferior and posterior point of mandibular right angle	Most inferior, posterior, and central point of mandibular right angle	Most inferior, posterior, and central point of mandibular right angle
Left gonion (LGo)	Most inferior and posterior point of mandibular left angle	Most inferior, posterior, and central point of mandibular left angle	Most inferior, posterior, and central point of mandibular left angle
B-point (B)	Deepest point the anterior portion of the symphysis	Deepest point of the symphysis	Deepest point along anterior concavity of mandible
Pogonion (Pog)	Most anterior point of the symphysis	Most anterior and central point of the symphysis	Most anterior point of the symphysis
Gnation (Gn)	Most anterior and inferior point of the symphysis	Most anterior, inferior, and central point of the symphysis	Most anterior, inferior and central point of the symphysis
Menton (Me)	Most inferior point of the symphysis	Most inferior and central point of the symphysis	Most inferior and central point of the symphysis

Table III.

Root canal (CBCT segmentation) and crown (dental digital model) landmarks

Landmarks	3D location
Root canal
Maxillary and mandibular molars	Center of floor of the pulp chamber
Maxillary and mandibular single-rooted premolars	Center of the root canal at the same axial level of the pulp chamber floorof the first molar
Maxillary and mandibular multi-rooted premolars	Center of floor of the pulp chamber
Incisors and Canines	Center portion of the root canal, at the axial level of the cementoenamel junction
Crown
Maxillary and mandibular molars	1. Most buccal superior point of the distal margin ridge 2. Most buccal superior point of the mesial margin ridge 3. Most central point of occlusal surface of the crown
Maxillary and mandibular premolars	1. Most buccal and superior point of the distal margin ridge 2. Most buccal and superior point of the mesial margin ridge 3. Most central point of occlusal surface of the crown
Canines	1. Most buccal and superior point of the distal margin ridge 2. Most buccal and superior point of the mesial margin ridge 3. Canine cusp tip
Incisors	1. Middle of the mesial portion of the incisal edge 2. Middle of the distal portion of the incisal edge 3. Center of the incisal edge

TREATMENT RESULTS

The total treatment time considering the refinements was 2 years, 3 months. At the end of active Class II correction with the clear aligner MA protocol, the patient had increased SNA and SNB angles, whereas the ANB angle was decreased. The gonial angle demonstrated overall minimal changes. All the skeletal linear measurements increased, including a 7-mm increase in the mandibular ramus height (Co-Go) (Fig 1, B and C; Table I). At the end of treatment, as shown by the final photographs, the patient showed a balanced profile, a symmetrical facial appearance, and an esthetic smile (Fig 1, E). The final panoramic x-ray shows no root resorption or root parallelism, and the final cephalometry shows that this patient finishes the treatment at CVM stage 5 (Fig 3, C and D).

The cranial base superimposition showed a slight clockwise rotation in the palatal plane (PNS-ANS) and a discrete counterclockwise rotation of the mandibular plane (Go-Gn). Anterior (1 mm) and inferior (4.4 mm) maxillary displacements were identified after the clear aligner MA treatment. Point B (4.3 mm) and pogonion (5.7 mm) were displaced anteriorly, improving the mandibular sagittal position relative to the cranial base. Three-dimensional mandible regional and cephalometric superimpositions illustrate a significant posterosuperior mandibular growth (Fig 1, C and D; Table IV).

Table IV.

Skeletal measurements values before and after MA treatment in the cranial base and mandibular regional superimpositionss

Measurements	Patient 1	Patient 2
Cranial base superimposition
Planes (°)
Mandibular plane angle (Go-Gn)	−2.0	0.0
Palatal plane angle (PNS-ANS)	2.6	1.1
A-point displacement (mm)
Anteroposterior	1.0	−0.1
Superoinferior	−4.4	—0.1
3D scalar displacement	4.7	0.3
B-point displacement (mm)
Anteroposterior	4.3	1.7
Superoinferior	−5.5	—1.8
3D scalar displacement	7.1	3.0
Pog displacement (mm)
Anteroposterior	5.7	1.7
Superoinferior	−7.1	−3.0
3D scalar displacement	9.2	3.8
Mandibular regional superimposition
Co displacement (mm)
Anteroposterior	−2.6	—1.3
Superoinferior	10.8	3.4
3D scalar displacement	11.3	4.0

Note. Positive values indicate clockwise rotation in angular measurements, anterior displacement in linear anteroposterior measurements, and superior displacement in linear superoinferior measurements. In contrast, negative values indicate counterclockwise rotation in angular measurements, posterior displacement in linear anteroposterior measurements, and inferior displacement in linear superoinferior measurements.

In the maxillary superimposition, the maxillary molars and premolars showed distal and buccal changes in long-axis angulation and distal, buccal and intrusion displacements measured at the molar crowns. The maxillary central incisors showed mainly buccal long-axis angulation and intrusion. In the mandible, the mandibular molars and premolars showed mesial and buccal angulation with mesial, buccal and extrusion movements, as measured at the molar crowns. In the mandibular incisors, mesial and buccal angulation and intrusion were evident (Fig 2; Table V). The excessive overjet and overbite were corrected with final values of 1.4 mm and 2 mm (24%), respectively.

Table V.

Angular and linear tooth movement changes in patient 1 before and after MA based on digital dental models and CBCT regional superimpositions

D, Distal; M, Mesial; B, Buccal; L, Lingual; MR, Mesial rotation; DR, Distal rotation.; I, Intrusion; E, Extrusion.

The total treatment time considering the refinements was 1 year, 7 months. At the end of active Class II correction with the clear aligner MA protocol, the SNA angle slightly decreased, whereas the SNB angle increased. A decrease in the ANB angle was observed as well. Most of the skeletal linear measurements increased, including an increase of 1.9 mm in the mandibular ramus (Co-Go) (Fig 4, C and D; Table I). At the end of treatment, the final photographs show a proportional vertical profile, with improved chin prominence, associated with facial symmetry and a harmonic smile. The final panoramic x-ray showed no root resorption or parallelism, and the final cephalometry showed that this patient finished the treatment at CVM stage 6 (Fig 6, C and D).

Minimal changes in the palatal (PNS-ANS) and mandibular (Go-Gn) planes were observed in the cranial base 3D and cephalometric superimposition. In addition, minor maxillary sagittal and vertical displacements were observed. Point B and pogonion moved 1.7 mm anteriorly and inferiorly (1.8 and 3.0 mm, respectively).

The regional and cephalometric superimpositions indicated that the mandible had a posterosuperior growth pattern, with 4 mm of 3D displacement at condylion because of condylar and ramal growth (Fig 4, C and D; Table IV).

In the maxillary superimposition, the maxillary first molars demonstrated lingual long-axis angulation and mesial, buccal, and intrusion displacements measured at the molar crowns. The maxillary incisors showed mainly buccal long-axis angulation. The mandibular first molars showed mesial and buccal angulation with mesial and extrusion movements measured at the molar crowns. In the mandibular incisors, buccal angulation and intrusion were shown (Fig 5; Table VI). The excessive overjet and overbite were corrected, with final values of 2.4 mm and 2.4 mm (35%), respectively.

Table VI.

Angular and linear tooth movement changes in patient 2 before and after MA based on digital dental models and CBCT regional superimpositions

D, Distal; M, Mesial; L, Lingual; B, Buccal; MR, Mesial rotation; DR, Distal rotation; E, Extrusion; I, Intrusion.

DISCUSSION

Clear aligner MA was offered as a treatment option because patients did not present severe space discrepancy, skeletal vertical problems, or perioral muscular imbalance.²⁹ Both patients presented mild to moderate maxillary and mandibular crowding, increased overjet, deep overbite but not skeletal deepbite, vertical facial proportions within normal limits, accentuated curve of Spee and lip competence. The clear aligner MA treatment corrected the Class II malocclusion in both patients, improving the maxillomandibular anteroposterior relationship with posttreatment SNA, SNB and ANB angles close to the populational norm. The chin point at the pogonion was displaced in an anterior and inferior direction in both patients.

These findings corroborate those from a recent study³⁰ that found that the sagittal SNB and ANB relationships were significantly improved with clear aligner MA treatment. Although the pubertal growth period may influence the long-term stability of the treatment response, the clear aligner MA played an important role in the patients’ full cusp Class II correction and the skeletal measurements.³¹ Lux et al³² investigated longitudinal growth changes in 2-year intervals in nontreated patients aged 7–15 years with Class II malocclusion. Those authors concluded that differences between patients with Class II malocclusion and control subjects present at 15 years old were already established at 7 years old but were less pronounced. These findings indicate that pubertal growth without orthodontic intervention does not self-correct Class II malocclusions. Moreover, compared with the control patients, it has been shown that early functional intervention has significantly interfered with the mandible length, vertical increase and overjet improvement compared with nontreated patients.³³ Therefore, the marked mandibular skeletal growth with minor dental changes observed in these two patients were likely clear aligner MA treatment effects during the pubertal growth.

The treatment results showed an anteroinferior displacement of the mandible during treatment and the pubertal growth spurt (Table IV). The mandibular regional superimposition revealed that the anteroinferior displacement of the mandible resulted from growth in the posterior region of the mandible (ramus and condyle) that occurred in an upward and backward direction rather than a temporary postural change. Both patients showed greater ramus vertical growth compared with anteroposterior development. This finding is similar to previous 3D studies quantified with comparable image analysis methods of Class II correction using Herbst appliances associated with full-fixed appliances.^12,34,35 The Class II correction with removable functional appliances, such as Twin-block and Fränkel II, in 2D cephalometric studies also identified increased length in the mandible, significant vertical increase, as well as a significant decrease in overbite and overjet compared with untreated patients with a Class II malocclusion.³³

The skeletal changes observed for the two patients at the end of clear aligner MA treatment denote variability in the amount of skeletal response. Patient 1 presented remarkable ramal growth and a 3D condylar displacement of 11.3 mm. At the beginning of treatment, this patient was in the ascendant part of the pubertal growth spurt (CVM stage 3).³⁶ Patient 2 showed a smaller amount of mandibular growth and was in cervical vertebra maturation CVM stage 4. Patients 1 and 2 finished the treatment at CVM stages 5 and 6, respectively. Table I shows that the maxillomandibular skeletal discrepancy was greater in patient 1 than in patient 2 (ANB of 5.6° and 4.5°, respectively). Figure 2 shows that patient 1 presented upright maxillary central incisors at the beginning of treatment, masking the greater maxillomandibular skeletal discrepancy. Leveling the maxillary central incisors before clear aligner MA allowed flaring of the maxillary central incisors for proper mandibular advancement in patient 1, although the initial overjet was only 3.6 mm. Only minor mandibular incisor flaring occurred in patient 1 (<5°). The anteroposterior skeletal changes were 1 mm for the maxilla at A-point, 4.3 mm at B-point, and 5.7 mm at pogonion, whereas the overall increase in mandibular length was 8.1 mm. Patient 2 had a more severe overjet at the beginning and presented greater mandibular incisor proclination of up to 9.8° after treatment, with skeletal changes anteroposteriorly at A-point of —0.1 mm, B-point of 1.7 mm, and pogonion of 1.7 mm, with an overall increase in mandibular length of 2.6 mm.

Enlow et al³⁵ described that an indirect growth displacement occurs because of the posterosuperior growth of the mandible. This observation may explain our findings that in the two patients in this report, the amount of condylar and ramal oblique 3D growth and bone apposition did not correspond directly to the amount of anteroposterior and vertical displacements of the chin. The increment in mandibular growth also is evident in the increase in mandibular length (Co-Gn). Patient 1 (Figs 1–3) showed the most remarkable skeletal response, whereas the ramal and condylar growth was less remarkable in patient 2 (Figs 4–6).

Regarding the maxillary dentoalveolar movements, both patients demonstrated mainly a distal and buccal long-axis angulation of the molars and premolars, with minor buccal movement and intrusion. The intrusion may be explained by restricting the passive eruption of the maxillary molars by wearing clear aligners with precision wings, resulting in a posterior open bite. This treatment effect also has been reported by Patterson et al³¹ for Class II treatment with Invisalign and Class II elastics.

The clear aligner MA treatment also demonstrated an intrusion and buccal angulation of the incisors, which contributed to the correction of the overjet and overbite. In patient 1, the long axis of the maxillary incisors showed greater buccal angulation and protrusion. This finding may be explained by the original Class II, Division 2 malocclusion in this patient and the efficacy of the clear aligner MA in controlling a common adverse effect in Class II correction (ie, lingual tipping of maxillary incisors for anteroposterior dental compensation).

The posterior teeth showed mesial long axis angulation changes with treatment in the mandible. Molars and premolars demonstrated mainly buccal long-axis angulation and extrusion. The changes in buccal angulation of the molars and premolars may be explained by correcting their initial lingualized position (curve of Wilson). In both patients, the mandibular incisors demonstrated buccal angulation, intrusion and buccal displacement of the incisal edge (<3 mm). The combination of those movements contributed to correcting the dental Class II relationship and deepbite.

The differences in mandibular incisor angulation observed in these two patients compared with previous studies may be explained by the degree of crowding and leveling of the curve of Spee. In the studies to which these two patients were compared, the angulation of the mandibular incisors was measured in 2D cephalograms rather than in 3D CBCT images used in this present study.^14,16,17 Both patients maintained a balanced mentolabial sulcus profile after MA, with increased soft-tissue chin prominence. In these two patients, the maxillary premolars and molars were intruded, whereas the mandibular premolars and molars were extruded. This may be explained by restricting the passive eruption of the maxillary posterior teeth while wearing clear aligners with precision wings and mandibular posterior teeth extrusion and leveling the curve of Spee.

It is important to highlight the baseline and treatment progress assessments in this patient report followed the imaging selection recommendations for using CBCT in orthodontics by the American Academy of Oral and Maxillofacial Radiology.³⁷ The consensus recommendation of the American Academy of Oral and Maxillofacial Radiology is that pretreatment and posttreatment acquisition of CBCT scans is possibly indicated for dental and skeletal anteroposterior discrepancies. For these two patients with full cusp Class II malocclusions, the CBCT scans were acquired at baseline for improved diagnosis and treatment plan and at follow-up for 3D craniofacial superimposition to assess skeletal and dental contributions to the malocclusion correction.

Although the clear aligner MA requires compliance for successful outcomes, as with any removable appliance, the clear aligner MA is a more comfortable treatment alternative. The esthetic characteristics of this appliance also play an important role in the patient’s compliance. Because of its ability to perform alignment and Class II correction simultaneously, this therapy can provide good control of undesirable dental effects and a favorable condition for mandibular growth and vertical correction in 1-phase treatment, especially considering patients with Class II, Division 2 malocclusion.¹⁷ Interestingly, the discrete variation in the Mp-SN angle demonstrated clear aligner MA efficiency in controlling the vertical pattern, as reported previously.^17,38 The two patients considered in this report did not show a vertical growth pattern before treatment, which was favorable to the observed treatment results.

Limitations of this therapy in these two patients were the flexibility of the wings, which may now have been solved by newer enhanced precision wings released after these patients were treated,³⁴ and patients had to be frequently instructed to posture the mandible forward to engage the wings. In addition, a posterior open bite was developed, which required occlusal refinements after the MA phase. In the other patient, the refinement phase with the set of aligners without the wings may also require using Class II lastics to maintain the mandible position and final intercuspation.

CONCLUSIONS

The two patients presented in this article demonstrated favorable skeletal and dental changes with successful Class II malocclusion correction using clear aligner MA therapy. The Class II relationship was corrected by mandibular ramus and condylar growth that led to the anterior and inferior displacement of the mandible and mesialization of the mandibular posterior teeth with flaring of the mandibular anterior teeth in both patients.