Skeletal Class III malocclusion is commonly characterized by a retrognathic and narrow maxilla, a prognathic and wider mandible, or a combination of both [1, 2]. Growth modification, orthodontic camouflage, or orthognathic surgery are main treatment choices to achieve a normal occlusion and improve facial aesthetics for skeletal Class III malocclusion. However, growth modification should be initiated before the pubertal growth spurt; beyond this stage, only orthodontic camouflage or orthognathic surgery are viable [3].
Patients with skeletal Class III malocclusion generally exhibit dentoalveolar compensation, accompanied with proclination of the maxillary incisors and retroclination of the mandibular incisors [4], to adapt their craniofacial skeletal patterns and to achieve occlusal function [5]. For Class III malocclusion with severe skeletal discrepancies, the optimal treatment is generally orthodontics combined orthognathic surgery. While for those who reject surgery and show a mild to moderate skeletal discrepancy with acceptable facial profile can benefit from compensatory orthodontic treatment by establishing an acceptable occlusion, allowing teeth displacement based on their supporting bone, and masking the underlying skeletal discrepancy [6, 7]. The treatment targets of presurgical orthodontic therapy and orthodontic camouflage treatment for nongrowing skeletal discrepancies are completely different, in which orthodontic decompensation and proper dentoalveolar compensation are crucial steps leading to successful treatment outcome respectively [8, 9].
The objectives camouflage treatment encompass achieving acceptable occlusion, functionality, and aesthetic results by strategically using dentoalveolar compensation to address skeletal discrepancies [10]. The extent of dentoalveolar compensation is limited by the anatomic features of alveolar bone and remodeling potential of targeted teeth [11]. Overly compensatory proclination or retroclination of anterior teeth with insufficient alveolar bone would result in undesired fenestration or dehiscence. A reduced lower anterior facial height or a deep overbite can improve the prognosis in camouflage treatment for skeletal Class III malocclusion. This is because clockwise rotation of the mandible helps to mask a prognathic mandible and enhances the concave profile, contributing to a more favorable overall outcome [12]. Therefore, when choose camouflage orthodontic therapy for skeletal Class III malocclusion, the following must be cautiously considered: (1) the severity of skeletal discrepancy and patients’ complaints; (2) vertical dimension; (3) the anatomic features of dentoalveolar bone.
The primary factors involved in the dental equilibrium are resting pressure from lip and tongue, extrinsic forces from habits or orthodontic appliances, dental occlusal forces, and eruption forces from periodontal membrane [13]. Due to tooth extraction, arch expansion, and the removal of oral bad habits during orthodontic treatment, the original equilibrium of the patient's stomatognathic system is broken, and the remaining dentition will naturally shift to establish a new dental equilibrium.
Physiologic drift was first proposed by Bourdet [14], which referred to the natural physical movement of other teeth in the dental arch after tooth extraction. And the improved condition in tooth alignment resulted from spontaneous drift was called “physiological driftodontics” [15]. In some orthodontic techniques, physiologic drift was used to simplify the treatment. Alexander [16] straight wire technique suggested that after the extraction of four first premolars, maxillary teeth should be performed first, while mandibular teeth were supposed to bond brackets after natural adjustment for a period of time. The potential benefits of this period time of physiologic drift includes better occlusal relationship, increased dentoalveolar support, and a shorter overall time of orthodontic therapy owing to spontaneous realignment of the dentition [17].
This case report presents extraction camouflage orthodontic treatment using miniscrews and driftodontics to correct a skeletal Class III malocclusion with anterior crossbites and severe crowding. The treatment results were clinically acceptable, leading to enhanced smile aesthetics.
Diagnosis and etiology
An 18-year-old Chinese woman presented to our hospital with primary concerns of dental crowding and mild mandibular prognathism. She reported no history of trauma or previous orthodontic treatments, no family history or bad oral habits.
Pre-treatment facial photographs revealed a slightly concave profile, a protruded chin, and increased lower anterior facial height (Fig. 1). Nasolabial angle was acute (NLA, 79.3°), and both the upper and lower lips located behind the E-line (UL-EL, 3mm; LL-EL, 2mm). Mild facial asymmetry and decreased upper incisor exposure were observed. The maxillary dental midline was aligned with the facial midline, whereas the mandibular dental midline was shifted 1 mm to the right. The intraoral examination and study casts (Fig. 2) exhibited Class III molar and canine relationships with anterior crossbites and severe crowding. The mandibular right second premolar was impacted, and the deciduous mandibular right second molar was retained. Gingival redness and swelling were observed, especially in anterior region. Cast analysis revealed a narrow maxillary dental arch, a mild curve of Spee (2.8 mm at right and 3.2 mm at left), severe crowding (9.7 mm of maxillary arch and 10.5 mm of mandibular arch), and normal value of Bolton index analysis (79.2% of anterior ratio and 91.1% of overall ratio).
Panoramic and cephalometric radiographs were obtained prior to the initiation of treatment (Fig. 3). Panoramic radiograph showed impacted mandibular right second premolar, retained deciduous teeth, and the presence of the maxillary and mandibular third molars. The lateral cephalometric analysis and tracing showed a mild skeletal Class III relationship characterized by a slightly prognathic mandible (ANB, -0.1°; SNA, 84.9°; SNB, 85.3°) and average mandibular plane angle (SN-MP, 31.8°). The inclination of the maxillary incisors was within the normal range (U1-SN, 106.4°), while the mandibular anterior incisors exhibited compensatory retroclination (IMPA, 72.8°). The cephalometric measurements are listed in the Table 1. The temporomandibular joint (TMJ) evaluation (Fig. 3D) revealed no symptoms indicative of TMJ dysfunction, such as pain, joint noise, restricted jaw movement, or any other related issues. Mesial proximal caries of maxillary right lateral incisor was observed in the cone-beam computed tomography (CBCT) image.
Table 1
Pretreatment and posttreatment cephalometric analysis
| measurement | norm | pretreatment | posttreatment |
|---|
| SNA° | 83.13 ± 3.6 | 84.9 | 85.2 |
| SNB° | 79.65 ± 3.2 | 85.3 | 85.1 |
| ANB° | 3.48 ± 1.69 | -0.4 | 0.1 |
| SN-MP° | 32.85 ± 4.21 | 31.8 | 30.9 |
| Y-axis° | 63.54 ± 3.23 | 56.0 | 61.1 |
| S-Go/N-Me | 65.85 ± 3.83 | 68.4 | 68.6 |
| ANS-Me/N-Me | 53.32 ± 1.84 | 58.3 | 57.0 |
| U1—L1° | 126.96 ± 8.54 | 151.6 | 153.1 |
| U1—SN° | 104.62 ± 6.02 | 106.4 | 105.1 |
| Ul—NA° | 21.49 ± 5.92 | 20.6 | 19.5 |
| Ul—NA (mm) | 4.05 ± 2.32 | 3.7 | 1.8 |
| Ll—NB° | 28.07 ± 5.58 | 15.3 | 6.9 |
| Ll—NB (mm) | 5.69 ± 2.05 | 1.1 | 1.0 |
| L1-MP° | 95.42 ± 4.69 | 72.8 | 71.8 |
| UL—EP (mm) | 71.22 ± 4.76 | 89.8 | 85.2 |
| LL—EP (mm) | -0.46 ± 1.92 | -3.4 | -2.7 |
The patient was diagnosed with a mild skeletal Class III malocclusion, accompanied by dental Class III malocclusion, dental crowding, anterior crossbites, impaction of the mandibular right second premolar, and a retained deciduous mandibular right second molar.
Treatment objectives
The treatment objectives were to (1) align and level the upper and lower dentine; (2) correct anterior crossbites; (3) coordinate the width of the upper and lower dental arch; (4) correct the midline of the lower dental teeth; (5) establish Class I occlusal relationship with appropriate anterior overjet and overbite.
Treatment alternatives
Two treatment options were provided to the patient. The first option was miniscrews-assisted camouflage orthodontic treatment with extraction of the maxillary first premolars, mandibular left first premolar, impacted mandibular right second premolar, retained deciduous mandibular right second molar and mandibular third molars. Miniscrews were designed as absolute anchorage to help retraction of mandibular teeth, and appropriate Class III traction was used to adjust molar relationship. The second option was orthodontic combined orthognathic treatment, with setback of mandible to correct the skeletal discrepancy and achieve maximum improvement of the facial esthetics. After careful consideration, the patient desired for non-invasive approach and chose camouflage orthodontic treatment.
Treatment progress
Prior to bracket bonding, pulp treatment was first performed on the maxillary right lateral incisor. Then, maxillary first premolars, mandibular left first premolar, impacted mandibular right second premolar, retained deciduous mandibular right second molar and mandibular third molars were extracted. Self-ligation brackets (Damon-Q; Ormco Co, Brea, Calif) were bonded to the maxillary arch, and bite turbos were placed on the occlusal surfaces of the mandibular first molars to unlock the bite. The lower arch treatment was deferred until sufficient physiologic drift occurred in the mandibular teeth, alleviating the severe anterior crowding to some extent [16]. Both arches were aligned and leveled by sequenced 0.012, 0.014, 0.016, 0.016 × 0.022, 0.018 × 0.025-in nickel titanium archwires and 0.018 × 0.025-in stainless steel archwires.
On account of mandibular anterior crowding, brackets were bonded on mandibular teeth except incisors after six months of physiologic drift. To provide maximum anchorage for retraction of mandibular anterior teeth, at 9th month of treatment, two miniscrews (12 mm, VectorTAS; Ormco Co, Brea, Calif) were inserted into the buccal alveolar bone bilaterally at the height of external obilque line positioned distally to the second molars in mandibular arch [18]. Two weeks after insertion, passive ligation was applied from mandibular right first premolar or left canine to the miniscrew respectively. Active space closure on both arches was commenced initially on 0.018 × 0.025-in stainless steel archwires. At 15th month of treatment, a retraction force was applied from mandibular canines to the miniscrews for distal movement of mandibular canines with maximum anchorage. At 21st month of treatment, mandibular canines moved into proper position without remaining space in buccal segment. Mandibular incisors were bonded with brackets and integrated into active alignment. At 25th month of treatment, bite turbos were removed bilaterally after occlusal interference was missing. In the 27th month of treatment, light Class III elastics were employed to achieve mesial movement of the maxillary molars, thereby coordinating the molar relationship.
The overall duration of active treatment was 31 months (Fig. 4). The miniscrews were extracted, and brackets were debonded. Then, both clear retainers and Hawley retainers were provided, and the patient was instructed to wear clear retainers during the day and switch to Hawley retainers at night. And she was advised to wear the retainers full-time for the first year, and then only at night thereafter.