Management of bilateral molar deep overbite with buccal crossbite using bracket-free clear aligners: a case description

Introduction

Buccal crossbite is a common form of malocclusion, often involving the second molars (1). Deep overbite is a type of malocclusion resulting from abnormal development of the maxillary and mandibular dental arches or discrepancies in maxillomandibular skeletal growth (2). These conditions are associated with reduced masticatory efficiency, restricted mandibular range of motion, and facial asymmetry (3,4). Simultaneous correction of buccal crossbite and posterior deep overbite presents notable clinical challenges and often requires adjunctive anchorage, such as temporary anchorage devices (TADs), to ensure treatment stability (5). Although TADs provide effective anchorage, their use carries potential complications, including infection, loosening, displacement, and patient discomfort, which may lead to treatment refusal. Achieving effective correction of buccal crossbite and posterior deep overbite using clear aligners alone may simplify the treatment process and enhance patient comfort, offering practical value in clinical settings. This report presents a recent case in which bilateral second molar deep overbite and buccal crossbite were successfully corrected using a clear aligner-based approach without adjunctive skeletal anchorage, yielding favorable clinical outcomes and informing orthodontic practice.

Case data

General information

A 38-year-old female patient presented with impaired masticatory function, specifically reporting difficulty in chewing with the posterior teeth.

All procedures performed in this study were in accordance with the Declaration of Helsinki and its subsequent amendments. This study was conducted with approval from the Ethics Committee of Tianjin First Central Hospital (No. 20240122-1). Written informed consent was obtained from the patient for publication of this article and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Clinical examination

Clinical evaluation revealed a generally symmetrical facial appearance in the frontal view and a near-straight lateral profile. Both the maxillary and mandibular arches exhibited dental crowding, accompanied by a pronounced anterior deep overbite and increased overjet. The maxillary dental midline was coincident with the facial midline, while the mandibular dental midline demonstrated a 1 mm deviation to the right.

Occlusal assessment revealed a distal molar relationship on the right side and a neutral molar relationship on the left. The maxillary anterior teeth were labially inclined. Bilateral occlusal locking of the second molars was observed. In maximal intercuspation, the palatal cusp of tooth 17 impinged upon the buccal gingiva of tooth 47, and the palatal cusp of tooth 27 was in close proximity to the buccal gingival margin of tooth 37 (Figure 1).

Figure 1.

Pre-treatment cephalometric radiographs and panoramic radiograph. These images are published with the patient’s consent.

Periodontal health was stable, with no clinically significant restriction in mandibular range of motion. The bilateral temporomandibular joints exhibited no tenderness, joint sounds, or functional limitation.

Model analysis

Dental model analysis demonstrated maxillary crowding of 2.9 mm and mandibular crowding of 7.3 mm. The observed deep overbite and overjet were consistent with characteristics of Angle Class II malocclusion. Bolton analysis revealed an anterior tooth size ratio of 77.8% and an overall ratio of 90.2%, indicating tooth size discrepancies. The curve of Spee exhibited a depth of 3.6 mm. Additionally, teeth 17 and 47 were in a locked occlusion with a vertical overbite of 5.25 mm, while teeth 27 and 37 demonstrated a similar occlusal locking pattern, with a vertical overbite of 4.93 mm.

Imaging assessment

Panoramic radiographic imaging confirmed prior extraction of teeth 18, 28, and 48, and vertical impaction of tooth 38. No radiographic abnormalities were noted in the crowns, roots, or periodontal structures of the remaining dentition. The bilateral condyles exhibited symmetrical morphology and structure, with intact and continuous cortical bone. The maxillary sinuses, alveolar bone, and jaw structures appeared radiographically normal (Figure 1).

Lateral skull radiography and cephalometric analysis identified a skeletal Class II relationship with an average mandibular plane angle. Cone-beam computed tomography (CBCT) showed the root of tooth 17 centrally located within the cancellous bone. The palatal root apex of tooth 27 was adjacent to the palatal cortical plate, while the root apices of teeth 37 and 47 were positioned near the buccal cortical plate (Figure 2).

Figure 2.

Coronal cone-beam computed tomography images showing the bilateral second molars prior to orthodontic treatment.

Diagnosis

The patient was diagnosed with skeletal Class II malocclusion; Angle Class II Division 1, subclass malocclusion; bilateral occlusal locking of the second molars; and an obtuse mandibular angle.

Orthodontic design

Tooth 38 was extracted prior to initiating treatment. Orthodontic therapy was performed using Invisalign clear aligners following a two-phase treatment protocol. Superimposed digital models of pre-treatment and post-treatment occlusion are presented in Figure 3. All attachments were configured using conventional rectangular shapes. The patient was instructed to wear the aligners for 20–22 hours per day, with a replacement interval of 7–10 days per aligner.

Figure 3.

Digitally superimposed models illustrating pre-treatment and post-treatment changes in tooth position and arch alignment.

Initial treatment phase

The primary objective of the initial phase was to eliminate interocclusal interference in the segments affected by buccal crossbite and to establish proper buccal occlusion. Correction of the buccal crossbite was achieved through precise, segmented tooth movements as follows:

• ❖ Teeth 17 and 27 were subjected to buccal root torque, lingual crown translation, and palatal cusp intrusion.

• ❖ Teeth 47 and 37 were subjected to lingual root torque, buccal crown translation, and buccal cusp intrusion.

• ❖ To minimize occlusal interference during movement, contact between the lingual surfaces of teeth 17 and 27 and the buccal surfaces of teeth 47 and 37 was intentionally avoided. The treatment goal for the affected molars was to create an overcorrected open bite in the crossbite regions while maintaining a normal horizontal overlap of the mandibular molars. Once interocclusal clearance and partial horizontal overlap were achieved, correction of the buccal crossbite enabled progression to the second treatment phase.

Second treatment phase

The aim of the second phase was to optimize occlusal relationships through coordinated alignment of both arches, midline adjustment, and improvement of overbite and overjet. Tooth movements included horizontal and vertical repositioning of teeth 17, 27, 37, and 47. Sequential distalization of the molars facilitated anterior-posterior space creation, which supported dental alignment, midline correction, overjet enhancement, and progression toward a bilateral Class I molar relationship. Reduction of the deep overbite was accomplished via vertical intrusion of both the maxillary and mandibular anterior teeth.

Treatment protocol

Tooth 38 was extracted prior to the initiation of orthodontic treatment. Two weeks after the patient began wearing the initial set of clear aligners, attachments were placed. The first treatment phase comprised 24 aligner sets, during which inter-arch resistance at the bilateral second molars was reduced, resulting in an open-bite configuration. This facilitated the successful correction of the buccal crossbite and allowed progression to the second phase of treatment (Figure 4).

Figure 4.

Bilateral occlusal views following the 24th aligner set during the initial treatment phase, showing resolution of occlusal interference.

The second treatment phase involved the use of 48 aligner sets. This phase achieved coordinated alignment of the maxillary and mandibular dental arches, establishment of a stable posterior occlusion, and improvement in both overbite and overjet. Treatment outcomes were consistent with both clinical objectives and the patient’s expectations.

At the conclusion of active treatment, attachments were removed, tooth surfaces were polished, and retention was maintained with a clear thermoplastic retainer. The entire course of treatment was completed without the use of adjunctive measures such as TADs or intermaxillary elastics, relying exclusively on clear aligner therapy.

Correction outcomes

The total treatment duration was approximately 24 months. Correction of the buccal crossbite involving teeth 17, 47, 27, and 37 was successfully achieved, resulting in the establishment of a functional and stable posterior occlusion. The maxillary and mandibular dental arches were properly aligned, with notable improvement in both the deep overbite and anterior overjet. Post-treatment evaluation showed alignment of the dental midlines with the facial midline and a straight facial profile.

Lateral cephalometric radiography demonstrated parallel root alignment, with no significant evidence of root resorption or alveolar bone loss (Figure 5). CBCT confirmed that the roots of teeth 17, 47, 27, and 37 were centrally located within the alveolar cancellous bone (Figure 6). Pre-treatment and post-treatment cephalometric measurements are summarized in Table 1, with corresponding cephalometric superimpositions presented in Figure 7.

Figure 5.

Post-treatment cephalometric radiographs and panoramic radiograph. These images are published with the patient’s consent.

Figure 6.

Coronal CBCT images of the bilateral second molars following completion of orthodontic treatment. CBCT, cone-beam computed tomography.

Table 1. Cephalometric measurements before and after treatment.

Measurement items	Normal value, $\overline{x}\pm s$	Before treatment	After treatment
SNA (°)	82.8±4	84.88	85.12
SNB (°)	80.1±3.9	78.88	79.45
ANB (°)	2.7±2.0	6	5.67
U1-NA (°)	22.8±5.7	22.48	15.72
L1-NB (°)	30.3±5.8	33.73	35.21
U1-L1(°)	125.4±7.9	117.79	123.4
U1-NA (mm)	5.1±2.4	5.39	5.11
L1-NB (mm)	6.7±2.1	8.61	9.87
U6-PP	22.0±2.0	24.95	22.51
L6-MP	33.0±2.0	34.03	33.88
MP-SN (°)	32.5±5.2	33.1	32.92
MP-FH (°)	31.1±5.6	27.25	27.07
PTM-U6 (mm)	16.0±3.0	18.87	17.06
Overjet (mm)	2.0±1.0	6.32	3.97
Overbite (mm)	3.0±2.0	3.32	1.22
UL-EP (mm)	−1.4±0.9	0.12	0.18
LL-EP (mm)	0.6±0.9	1.63	2.2
NLA (°)	85.7±19.2	92.23	92.75
FCA (°)	6.4±8.8	11.83	11.81

U1-NA: the angle between the upper central incisor and the NA plane. L1-NB: the angle between the lower central incisor and the NB plane. U1-L1: the interincisal angle between the upper and lower central incisors. U1-NA: the vertical distance from the cutting edge of the upper central incisor to the NA plane. L1-NB: the vertical distance from the cutting edge of the lower central incisor to the NB plane. L6-MP: vertical distance from the buccal cusp tip of the mandibular first molar to the mandibular plane. PTM-U6: the distance between the laceration point of the upper wing and the point near the middle buccal sulcus of the first molar of the upper jaw on the orbital and auricular plane. U6-PP: vertical distance from the buccal cusp tip of the maxillary first molar to the palatal plane. ANB, A point-nasion-B point angle; FCA, facial convexity angle; LL-EP, lower lip to esthetic plane; MP-FH, mandibular plane to Frankfort horizontal plane angle; MP-SN, mandibular plane to sella-nasion plane angle; NLA, nasolabial angle; SNA, sella nasion A point angle; SNB, sella nasion B point angle; UL-EP, upper lip to esthetic plane.

Figure 7.

Cephalometric superimpositions comparing pre-treatment (red) and post-treatment (blue) measurements. (A) SN plane. (B) Maxillary palatal plane. (C) Mandibular plane. SN, sella nasion.

At the 1-year follow-up, post-treatment stability was confirmed, with no signs of occlusal relapse (Figure 8).

Figure 8.

Cephalometric radiographs obtained one year post-treatment, confirming stability and absence of relapse. These images are published with the patient’s consent.

Discussion

Buccal crossbite is a common and functionally disruptive form of malocclusion that requires timely diagnosis and management to prevent long-term complications. Current evidence indicates a strong correlation between posterior locked occlusion and posterior dental arch crowding (6). Unilateral posterior locked occlusion is frequently associated with mandibular asymmetry, facial imbalance, and mandibular deviation. In contrast, bilateral second molar locked occlusion is more often linked to mandibular retrusion, molar displacement, and increased severity of anterior deep overbite and overjet.

A previous study suggests that bilateral second molar locked occlusion may hinder the development of mandibular length and restrict basal bone arch width in the affected region (7). Treatment selection is typically guided by the specific characteristics of the occlusion and may include occlusal pads to facilitate bite opening and unlock posterior teeth, combined with inter-arch traction. Additional interventions may involve TADs, second molar extraction in severe cases, repositioning of third molars to support eruption and alignment, and comprehensive restoration of functional occlusion. These approaches aim to reestablish a balanced occlusal relationship while supporting coordinated skeletal and dental development.

Compared to fixed appliances, bracket-free clear aligners offer distinct advantages, including improved aesthetics, increased patient comfort, enhanced oral hygiene, and favorable periodontal outcomes (8). The full-coverage design of clear aligners enhances control over tooth movement and may be particularly effective in managing complex cases such as molar displacement (9,10). Numerous studies have confirmed the effectiveness of clear aligners in the correction of malocclusions (11,12).

In the present case, treatment complexity was heightened by the coexistence of a buccal crossbite and a deep overbite, both contributing to significant interocclusal resistance. A targeted movement protocol was developed to resolve the interocclusal interference associated with the buccal crossbite. Pre-treatment CBCT imaging revealed that the root apices of teeth 37 and 47 were in proximity to the buccal cortical plate, the apex of tooth 27 was adjacent to the palatal cortical plate, and the root of tooth 17 was centered within the cancellous bone.

To correct the crossbite while preserving favorable root positioning, distalization of the affected molars was employed. Teeth 17 and 27 underwent buccal root torque, lingual crown translation, and palatal cusp intrusion, while teeth 37 and 47 underwent lingual root torque, buccal crown translation, and buccal cusp intrusion. Occlusal interference was mitigated by ensuring no contact occurred between the lingual surfaces of teeth 17 and 27 and the buccal surfaces of teeth 47 and 37 during movement.

This protocol effectively reduced interocclusal resistance by the 24th aligner set, resulting in the development of an open bite configuration and resolution of the crossbite. At this stage, horizontal overlap had been partially corrected, facilitating the subsequent alignment and finishing phase. The non-contact design of the involved teeth also contributed to increased patient comfort and reduced post-treatment interference. At follow-up, the corrected molars maintained their position with no relapse observed.

Post-treatment evaluations demonstrated an increase in the interincisal angle between the upper and lower central incisors (U1-L1), indicating improved incisor positioning. Measurements such as upper lip to esthetic plane (UL-EP), lower lip to esthetic plane (LL-EP), nasolabial angle (NLA), and facial convexity angle (FCA) exhibited no significant changes, suggesting preservation of the soft tissue profile.

Arch space for alignment was achieved primarily through molar distalization. Skeletal parameters such as mandibular plane to sella-nasion plane angle (MP-SN) and mandibular plane to Frankfort horizontal plane angle (FH-MP) remained unchanged, suggesting that the distalization process did not increase the mandibular plane angle. Reductions in vertical distance from the buccal cusp tip of the maxillary first molar to the palatal plane (U6-PP) and vertical distance from the buccal cusp tip of the mandibular first molar to the mandibular plane (L6-MP) confirmed vertical molar intrusion post-treatment.

These findings are consistent with prior studies. Caruso et al. reported that clear aligner-based molar distalization led to significant molar intrusion without changes in mandibular plane inclination or vertical facial dimensions (13). Similarly, Ravera et al. demonstrated that bracket-free clear aligners facilitated distal molar movement while maintaining mandibular plane stability, supporting the outcomes observed in this case (14). The effectiveness of this approach may be attributed to the 0.75 mm thickness of each aligner, providing a combined occlusal thickness of 1.5 mm when upper and lower aligners are worn simultaneously, functioning analogously to occlusal pads and promoting posterior intrusion. Additionally, posterior bite forces contribute to molar depression.

Further improvements in molar distalization outcomes can be achieved with optimized attachment design to minimize anchorage loss (15). In this case, conventional rectangular attachments were used, which have been shown to support effective maxillary molar distalization in clear aligner therapy (16,17).

Conclusions

In this case, the establishment of clear treatment objectives and the application of a targeted, biomechanically guided protocol for buccal crossbite correction enabled the successful management of bilateral second molar deep overbite and locked occlusion using Invisalign aligners alone. The treatment approach achieved favorable clinical outcomes without the use of adjunctive measures such as TADs or intermaxillary traction. This simplified protocol enhanced patient comfort, reduced procedural complexity, and contributed to a positive overall treatment experience.

Supplementary

The article’s supplementary files as

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. All procedures performed in this study were in accordance with the Declaration of Helsinki and its subsequent amendments. This study was conducted with approval from the Ethics Committee of Tianjin First Central Hospital (No. 20240122-1). Written informed consent was obtained from the patient for publication of this article and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.