Evaluation of clear aligner treatment for early permanent dentition Angle Class II Division 1 malocclusion in adolescents

Introduction

Angle Class II Division 1 malocclusion is a prevalent orthodontic condition among adolescents, with a reported prevalence rate of up to 19.41% (1,2). This condition is characterized by the labial inclination of the upper anterior teeth, maxillary protrusion, mandibular retrusion, deep anterior overbite, excessive anterior overjet, and lip incompetence—all of which can adversely affect oral health, masticatory function, facial aesthetics, and psychological well-being (3). The primary treatment objectives for adolescents with early permanent dentition Angle Class II Division 1 malocclusion include retraction of the protrusive upper anterior teeth and upper lip, promotion of mandibular forward development, and improvement of the nasolabial-chin relationship. Traditional orthodontic management involves the use of fixed appliances to correct the spatial relationship between the maxilla, mandible, and dental arches (4).

Clear aligners present advantages over fixed orthodontic devices in terms of aesthetics, comfort, ease of maintaining oral hygiene, and preservation of periodontal health. However, clinical evidence regarding their efficacy in managing this malocclusion remains limited. This study analyzes pre- and post-treatment cephalometric X-ray measurements in 30 adolescents to evaluate the clinical efficacy of clear aligner therapy combined with Class II intermaxillary traction for the treatment of early permanent dentition Angle Class II Division 1 malocclusion. The findings aim to provide a clinical reference for similar cases. We present this article in accordance with the STROBE reporting checklist (available at https://tp.amegroups.com/article/view/10.21037/tp-2025-373/rc).

Methods

Sample selection

This retrospective study analyzed a cohort of patients with early permanent dentition Angle Class II Division 1 malocclusion treated at the Department of Stomatology of Tianjin First Central Hospital between January 2017 and June 2024. As an exploratory investigation into the efficacy of clear aligners for this specific malocclusion, a formal a priori sample size calculation was not feasible due to the lack of prior data. Therefore, the sample size was determined based on clinical feasibility and is consistent with similar preliminary clinical studies (5,6). Ultimately, 30 patients who met the inclusion criteria were enrolled. The cohort included 14 males and 16 females, with a mean age of 12.6 years. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. This study was approved by the Ethics Committee of Tianjin First Central Hospital (approval No 20240122-1). Written informed consent was obtained from all participants’ legal guardians.

Inclusion criteria

Participants were included in the study based on the following criteria:

• Age between 12 and 15 years, permanent dentition occlusion, with second molars erupted and bilateral molars showing mild or complete distal relationship.
• Presence of deep anterior overbite and anterior overjet with mild crowding in the upper and lower dental arches.
• Skeletal class II malocclusion with a point A-nasion-point B angle (ANB) angle exceeding 5°.
• Absence, underdevelopment, or extraction of third molars.
• Demonstrated good compliance with treatment protocols.

Exclusion criteria

Participants were excluded if they met any of the following conditions:

• Previous history of orthodontic treatment.
• History of periodontal disease.
• History of temporomandibular joint disorders.
• Significant labial inclination of the lower incisors.

Treatment plan

All patients received non-extraction treatment using Invisalign clear aligners (Align Technology Co., Ltd., Tempe, AZ, USA). Class II intermaxillary traction with a force of approximately 50 g was applied to enhance the anchorage of maxillary anterior teeth. Sequential molar distalization in a V-pattern was employed to move the upper molars posteriorly, aiming to achieve a neutral molar relationship and normal coverage. The target anterior overbite was set at 0.5 mm, primarily accomplished by elevating the posterior teeth and coordinating the intrusion of both upper and lower anterior teeth to establish a normal overjet.

Intrusion of the upper anterior teeth was performed as a single unit, while the mandibular anterior teeth were intruded in two stages. The first stage involved intrusion of half the incisor height, followed by half the canine height; the second stage completed the remaining intrusion for both incisors and canines. Maxillary expansion was applied to facilitate mandibular development, while Class II intermaxillary traction was used to promote forward mandibular teeth growth and correct mandibular retrusion.

The entire treatment process was conducted exclusively using clear aligners in combination with Class II intermaxillary traction to achieve clinical correction of malocclusion.

Measurement methods

Lateral cephalometric radiographs were obtained for each patient both prior to and following treatment. All landmark identification and measurements were performed by a single operator on three separate occasions, with intervals of one week between measurements. The average values of these three assessments were utilized for analysis. The cephalometric parameters measured are detailed in Table 1.

Statistical analysis

Data processing and analysis of pre- and post-treatment measurements were performed using SPSS statistical software version 23.0. All measurement data conformed to normal distribution and homogeneity of variance and were expressed as x¯±s. Comparisons between pre- and post-treatment measurements were conducted using paired t-tests. A two-tailed P value <0.05 was considered statistically significant.

Results

Skeletal cephalometric measurements before and after treatment

No statistically significant differences were identified in the SNA angle, MP-FH angle, or MP-SN angle between pre- and post-treatment measurements (P>0.05). However, statistically significant differences were observed in the ANB angle, SNB angle, and Go-Pog distance (P<0.05). Post-treatment measurements showed an increase in the SNB angle by 2.84±1.33°, a decrease in the ANB angle by 2.71±0.94°, and an increase in the mandibular body length (Go-Pog distance) by 3.75±1.40 mm. Detailed results are presented in Table 2. SN plane overlap diagram is shown in Figure 1A.

Figure 1 Head measurement overlap diagrams before and after orthodontic treatment. (A) SN plane overlap diagram; (B) maxillary palatal plane overlap diagram; (C) mandibular plane overlap diagram. Red: before treatment; blue: after treatment. SN, sella-nasion.

Dental cephalometric measurements before and after treatment

All dental cephalometric measurements showed statistically significant differences between pre- and post-treatment (P<0.05). Post-treatment measurements showed reductions in overjet by 3.31±1.20 mm, overbite by 2.09±1.27 mm, and distal movement of maxillary first molars by 2.64±1.02 mm. The data are summarized in Table 3. The maxillary palatal plane and mandibular plane overlap diagram are shown in Figure 1B,1C.

Soft tissue cephalometric measurements before and after treatment

Statistically significant differences were noted in all soft tissue cephalometric measurements between pre- and post-treatment (P<0.05). Post-treatment measurements showed reductions in the distance of the upper and lower lip points to the esthetic plane by 2.21±0.69 and 0.48±0.68 mm, respectively, an increase in the nasolabial angle by 10.85±5.60° and a decrease in the facial contour angle by 2.91±3.40°. These findings are detailed in Table 4.

Overall results

The average treatment duration across the 30 patients was 28.6 months. All patients achieved satisfactory outcomes, including proper overjet, overbite, and neutral molar occlusion, with well-aligned upper and lower dental arches. Additionally, significant improvements were observed in the maxillary protrusion and mandibular retrusion morphology.

Typical case

Clinical examination

A 13-year-old female patient presented with a chief complaint of protruding upper teeth, seeking an improvement in her facial profile. Clinical examination revealed symmetrical facial features in the frontal view, with maxillary protrusion and mandibular retrusion on the profile view. Mild crowding was observed in both upper and lower dental arches, with significant labial inclination of maxillary anterior teeth, deep overbite, and pronounced overjet. The upper and lower dental midlines were aligned with the facial midline, and bilateral molars exhibited a complete distal relationship. The temporomandibular joints were asymptomatic, with no tenderness or clicking.

Panoramic X-ray revealed undeveloped roots in teeth 18, 28, 38, and 48, with no notable structural or periodontal abnormalities in the remaining teeth. The condylar processes appeared symmetrical with intact cortical bone, and no significant pathology was noted in the maxillary sinus, alveolar bone, or jawbone. Lateral cephalometric X-ray and associated measurements indicated skeletal Class II with a low mandibular angle (Figure 2).

Figure 2 Pre-treatment facial photographs, intraoral photographs, and X-ray images. This image is published with consent from the participant’s legal guardian.

Treatment plan

A non-extraction treatment plan was developed for this patient. Class II intermaxillary traction was applied to enhance anchorage of the maxillary anterior teeth. Sequential molar distalization in a V-pattern was employed to move upper molars posteriorly, aiming to achieve a neutral molar relationship and normal overjet. A normal overbite was primarily achieved through extrusion of the posterior teeth and coordinated intrusion of both the maxillary and mandibular anterior teeth.

The intrusion of maxillary anterior teeth was performed as a single unit. For the mandibular anterior teeth, intrusion was carried out in two steps: the first stage involved partial intrusion of the incisors and canines, followed by a second phase to complete the intrusion. Maxillary expansion was employed to relieve mandibular development, along with Class II intermaxillary traction to promote forward mandibular teeth growth and enhance the mandibular profile by addressing retrusion.

The specific methods of tooth movement are as follows: (I) Sagittal direction: For the II-class inter-jaw traction, the anterior teeth of the maxilla are reinforced with a support system. The molars are moved backward in a sequential manner (V-pattern mode) to achieve a neutral and normal overbite relationship. (II) Vertical direction: The normal overjet relationship is achieved mainly by elevating the posterior teeth and depressing the anterior teeth of the upper and lower jaws. The anterior teeth of the maxilla are depressed as a whole, while the anterior teeth of the mandible are depressed in two steps. (III) Lateral direction: the maxillary expansion arch is used to release the locking effect on the mandibular development, which is beneficial for the forward growth of the mandible and the improvement of the posteriorly protruding mandible appearance.

Treatment process

After two weeks of wearing the first aligner, attachments were bonded, and follow-up appointments were scheduled every three months. The treatment involved a total of 58 aligners, each worn 20 to 22 hours daily in combination with Class II intermaxillary traction. Aligners were replaced every 7 to 14 days. After using 25 aligners, there was a significant improvement in the anterior deep overbite, and the bilateral molar relationship shifted from a complete distal to nearly neutral alignment (see Figure 3).

Figure 3 Facial and intraoral photographs after using 25 aligners. This image is published with consent from the participant’s legal guardian.

After wearing 58 aligners, satisfactory outcomes were achieved, including proper anterior overjet and overbite, bilateral neutral molar relationships, well-aligned upper and lower dental arches, and notable improvement in maxillary protrusion and mandibular retrusion profile (see Figure 4). The total treatment duration was approximately 29 months.

Figure 4 Post-treatment facial photographs, intraoral photographs, and X-ray images. This image is published with consent from the participant’s legal guardian

The treatment was completed with the removal of attachments, tooth surface polishing, and retention using a clear vacuum-formed retainer. The patient demonstrated good compliance, and the treatment progressed smoothly without the need for mid-course refinement or additional adjustments. Both the clinician and the patient were satisfied with the treatment outcomes.

Discussion

Although adolescents with early permanent dentition are past the optimal window for functional orthodontic interventions, adolescents with early permanent dentition and Angle Class II Division 1 malocclusion still possess residual mandibular growth potential. Prior to age 16 in males and 14 in females, the mandibular bone is estimated to increase by approximately 1.5 mm per side annually (2). Treatment in this age group should therefore aim to harness this remaining mandibular growth potential to encourage forward mandibular development and improve profile morphology, alongside achieving dental alignment.

In this study, all patients received Class II intermaxillary traction from the beginning of treatment to enhance anchorage, enabling posterior movement of maxillary molars and encouraging mandibular teeth forward. Angle Class II Division 1 malocclusion in adolescents typically presents with narrow upper and lower dental arches. The early treatment plan in this study included maxillary arch expansion to alleviate mandibular development restrictions and guide its forward growth.

Clear aligners were used for molar distalization, a key advantage of this appliance system (7-11). The full-coverage design of clear aligners can fully encase the crown, facilitating molar distalization (12-14). When combined with intermaxillary traction for enhanced anchorage, bracketless clear aligners can achieve good results in single-jaw molar distalization (15). In this study, post-treatment measurements revealed significant distalization of the maxillary first molars, averaging 2.64±1.02 mm, compared to pre-treatment (P<0.05), demonstrating that clear aligners combined with Class II intermaxillary traction effectively achieved maxillary molar distalization with enhanced anchorage.

Skeletal improvements were also observed, including a significant increase in SNB angle by 2.84±1.33°, a decrease in the ANB angle by 2.71±0.94°, and an increase in mandibular body length (Go-Pog) by 3.75±1.40 mm (all P<0.05), indicating forward mandibular growth and correction of retrusive profiles. These results suggest the combined impact of residual mandibular teeth growth and stimulation from intermaxillary traction.

Notably, no significant differences were found in MP-FH or MP-SN angles pre- and post-treatment (P>0.05), suggesting that molar distalization did not increase the mandibular plane angle. This aligns with findings by Ravera et al. (16) and Caruso et al. (17), who also reported that distalization using clear aligners results in molar intrusion but no significant alteration in facial length or mandibular plane angle.

Analysis suggests that clear aligners function similarly to a bite plane, producing some intrusion effect on posterior teeth. Furthermore, the application of excessive occlusal force in the posterior region may contribute to posterior teeth intrusion.

In this study, post-treatment overbite decreased by 2.09±1.27 mm, and overjet decreased by 3.31±1.20 mm, both showing statistically significant differences compared to pre-treatment (P<0.05). These findings indicate significant improvement in deep overbite and overjet. Additionally, post-treatment reductions in the U1-SN angle, U1-NA angle, and U1-NA distance were observed, all of which demonstrated statistically significant differences compared to pre-treatment values (P<0.05). These results reflect significant improvements in the labial inclination and protrusion of the upper central incisors.

Post-treatment measurements also revealed increases in the L1-MP angle (1.68±2.87°), L1-NB angle (1.62±2.62°), and L1-NB distance (0.60±0.93 mm), all of which were statistically significant compared to pre-treatment (P<0.05). These changes suggest mild labial inclination of the lower anterior teeth after treatment. The observed labial inclination may be attributed to the effects of Class II traction, which promotes lower incisor labial inclination, as well as the treatment design that incorporated lingual root torque to ensure that the tooth intrusion occurred within the cancellous bone.

The research results suggest that caution is warranted when using Class II traction for patients with significant pre-treatment lower incisor labial inclination. Preventive measures may be necessary to mitigate further labial inclination in such cases. This study also observed a decrease in the L1-MP distance of 1.60±0.86 mm post-treatment (P<0.05), indicating that lower anterior teeth intrusion resulted from a combination of true intrusion and labial inclination.

Similarly, a reduction in U1-PP distance of 0.42±0.75 mm post-treatment (P<0.05), alongside significant palatal inclination of the maxillary anterior teeth, suggests true intrusion of the maxillary anterior teeth. Previous studies have reported variable success rates for anterior tooth intrusion using clear aligners. Haouili et al. reported a 35% success rate for lower incisor intrusion, while Al-Balaa et al. found the efficiency of anterior teeth intrusion with clear aligners to be 51.19% (18,19). Shi et al. discovered that greater designed incisor intrusion amounts result in increased vertical forces on incisors (20). These findings underscore the need for clinical overcorrection in the design of anterior tooth intrusion using clear aligners.

In this study, the treatment goal for anterior overbite correction was designed at 0.5 mm. It is suggested that clear aligners can achieve effective anterior tooth intrusion when designed appropriately, ensuring that tooth intrusion occurs within the cancellous bone with adequate spacing and using a step-by-step intrusion approach. The amount of overcorrection design depends on bone density, as individuals with lower alveolar bone density in early permanent dentition require conservative overcorrection to avoid complications.

Facial soft tissue aesthetics is a crucial objective in orthodontic treatment planning. In this study, post-treatment measurements indicated reductions in the distances from the upper and lower lip points to the esthetic plane by 2.21±0.69 and 0.48±0.68 mm, respectively, while the nasolabial angle increased by 10.85±5.60° and the facial contour angle decreased by 2.91±3.40°. All these changes were statistically significant compared to pre-treatment values (P<0.05). The protrusion of the upper and lower lips and the protrusion of the soft tissue surface were both improved. The lateral facial shape has become more inclined towards a straight face type. Analyzing the reasons, due to the significant tongue-inward and inward retraction movement of the anterior teeth with a lip inclination, the position of the upper lip has shifted backward, and the nasolabial angle has increased. Meanwhile, the mandible has grown forward, the chin point moved forward, and the aesthetic plane has undergone a reverse rotation, thereby making the lower lip protrusion point closer to the aesthetic plane and reducing the facial angle.

The observed changes can be attributed to several factors. The significant lingual tipping movement and retraction of previously labially inclined upper anterior teeth contributed to posterior movement of the upper lip and an increase in the nasolabial angle. Furthermore, forward mandibular growth and anterior displacement of the pogonion point caused counter-rotation of the esthetic plane, drawing the lower lip point closer to the esthetic plane and reducing the facial contour angle. These structural and positional changes collectively enhanced the soft tissue profile aesthetics.

However, the sample size utilized in this study is relatively limited, which may impact the generalizability of the findings. In addition, the study lacks a control group, and follow-up data after treatment to evaluate the stability of occlusion and soft tissue changes. Future research efforts should aim to include a larger cohort to facilitate more robust validation of the results.

Conclusions

In conclusion, the findings of this study indicate that clear aligner treatment combined with Class II intermaxillary traction is an effective approach for managing early permanent dentition Angle Class II Division 1 malocclusion in adolescents. This treatment modality not only achieves dental correction but also enhances soft tissue profile morphology. A key advantage of this technique is the application of Class II intermaxillary traction from the initiation of treatment, which optimizes anchorage to facilitate maxillary molar distalization and correct molar distal relationships. Additionally, this method promotes forward mandibular growth, leveraging the residual growth potential of the mandibular bone in early permanent dentition, thereby reducing the risk of jawbone deformities.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://tp.amegroups.com/article/view/10.21037/tp-2025-373/rc

Data Sharing Statement: Available at https://tp.amegroups.com/article/view/10.21037/tp-2025-373/dss

Peer Review File: Available at https://tp.amegroups.com/article/view/10.21037/tp-2025-373/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://tp.amegroups.com/article/view/10.21037/tp-2025-373/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. This study was approved by the Ethics Committee of Tianjin First Central Hospital (approval No 20240122-1). Written informed consent was obtained from all participants’ legal guardians.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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