Class III malocclusion: a challenging treatment using miniscrews for extra anchorage
Article Category: research-article
Online veröffentlicht: 12. Okt. 2021
Seitenbereich: 227 - 236
DOI: https://doi.org/10.21307/aoj-2021.024
© 2021 Mirian Aiko Nakane Matsumoto et al., published by Sciendo
This work is licensed under the Creative Commons Attribution 4.0 International License.
A Class III malocclusion invariably shows skeletal and dentoalveolar components. Genetic and environmental factors act as positive stimuli regulating mandibular growth, related to mandibular functional anterior deviation or mouth breathing.1–4 A Class III phenotype is commonly associated with craniofacial characteristics displaying a sharp cranial base angle, a retrusive maxilla, and a protrusive mandible. Subjects with a retrusive maxilla are more likely to present with a hyperdivergent facial pattern, demonstrating vertical growth as a potential compensation mechanism.1 Dentoalveolar compensations are frequently observed in Class III patients and, in addition to maintaining function, the compensations mask the underlying skeletal discrepancy.
Treatment is often challenging as the diagnosis and prognosis are complex and difficult to establish, especially in malocclusions with associated asymmetries.2 In the nongrowing Class III malocclusion patient, it is essential to evaluate the magnitude of skeletal involvement, the facial profile and the patient’s goals. The treatment options are limited to either orthognathic surgery or a nonsurgical compensatory approach.1–3 Nongrowing patients presenting with a mild to moderate Class III malocclusion with an acceptable facial profile can be successfully treated by dental extractions and dentoalveolar compensation. However, in order to achieve functional and facial aesthetic improvements, surgical orthodontic treatment is recommended for severe malocclusions.
The aim of the present article is to discuss an orthodontic treatment approach using miniscrews for anchorage, in an adult skeletal Class III malocclusion, who refused an orthognathic surgical procedure.
A male (17 years 11 months) sought orthodontic treatment due to dissatisfaction with the aesthetics of his smile. The patient presented with a Class III malocclusion displaying an anterior cross bite, mild upper and moderate lower anterior crowding and an absent maxillary left canine.
The patient’s face was oval and no facial asymmetry was detected. Paranasal depression and a relatively long lower face was noted. The facial profile was slightly concave due to a prognathic mandible, and featured a long anterior facial height and an obtuse nasolabial angle. Although the patient had a slightly protrusive chin and a mild midface deficiency, the facial appearance was accepted without aesthetic complaint (Figure 1).
Figure 1.
Extra- and intra-oral pretreatment photographs.
The intraoral photographs and dental casts revealed a full unit Class III molar relationship on both sides, a lateral open bite, involving the left lateral incisors, canine and premolars, a negative overjet (0.5 mm), a transverse skeletal constriction and a reduced overbite. Posterior and anterior crossbites were evident. The upper dental midline was not coincident with the face and the maxillary and mandibular midline had shifted 1.5 mm and 1.0 mm to the left, respectively. The upper arch form was asymmetric, as the left upper first molar was 3.0 mm mesially displaced relative to the upper right first molar. There was a negative tooth-size discrepancy of 2.0 mm in the maxillary arch and 4.5 mm in the mandibular arch, and it was noted that a canine was absent in the upper arch. A mesial inclination of mandibular premolars and molars was also recorded (Figure 1).
Dental radiography showed no root length abnormalities and alveolar bone loss was not detected. The third molars were unerupted and impacted (Figure 2).
Figure 2.
Pretreatment records.
The pretreatment lateral cephalometric tracing and analysis (Figure 2 and Table I) indicated a maxillary deficiency (SNA, 78.0°) and mandibular protrusion (SNB, 81.0°), indicating a skeletal Class III malocclusion (ANB, −3.0°, Wits, −5.0 mm). The mandible exhibited a downward and backward rotation characteristic of a hyperdivergent skeletal pattern (SN. GoGn, 36.0o; FMA, 34.0o; SN.Y-axis, 57o; Facial angle, 87o). The maxillary incisors were proclined (U1 to NA, 28o; 1-NA, 8.0 mm), the mandibular incisors were upright (FMIA, 68.0o; IMPA, 78.0o; L1 to NB, 16.0o; 1-NB, 3.0 mm) and the interincisal relationship was 139.0o. Conventional orthodontic therapy was possible as there was good alveolar bone support. The skeletal and facial profile were concave (NA-Pog −9°, S-LS, −3.0 mm; S-LI, −2.0 mm) therefore the diagnosis was a Class III skeletal malocclusion due to mandibular protrusion in company with a hyperdivergent skeletal pattern and an upper and lower midline deviation.
Initial and final cephalometric measurements.
| Measurements | Average | Initial pretreatment | Final posttreatment |
|---|---|---|---|
| Sagital skeletal relationships | |||
| SNA (o) | 82.0 | 78.0 | 78.0 |
| SNB (o) | 80.0 | 81.0 | 81.0 |
| SND (o) | 76.0 | 80.0 | 80.0 |
| ANB (o) | 2.0 | −3.0 | −3.0 |
| Wits (mm) | −1.0 | −5.0 | −5.0 |
| SNPg (o) | 83.0 | 84.0 | |
| ANPg (mm) | −9.0 | −13.5 | |
| Vertical skeletal relationships | |||
| SN.GoGn (o) | 32.0 | 36.0 | 40.0 |
| SN.y-axis (o) | 59.0 | 57.0 | 58.0 |
| FMA (o) | 25.0 | 34.0 | 35.0 |
| Facial angle (o) | 87.9 | 87.0 | 89.0 |
| Dental relationships | |||
| 1. NA (o) | 22.0 | 28.0 | 27.0 |
| 1-NA (mm) | 4.0 | 8.0 | 7.0 |
| 1. NB (o) | 25.0 | 16.5 | 11.0 |
| 1- NB (mm) | 4.0 | 3.0 | 0.5 |
| 1.1 (o) | 131.0 | 139.0 | 146.0 |
| IMPA (o) | 90.0 | 78.0 | 68.0 |
| Occl plane.SN (o) | 14.0 | 19.0 | 15.0 |
| Overjet (mm) | −1.0 | 1.0 | |
| Overbite (mm) | 0.0 | 3.0 | |
| Soft tissues | |||
| Z-angle | 80.0 | 95.0 | 90.0 |
| Pog-NB (mm) (o) | – | 5.0 | 7.0 |
| S line-lower lip (mm) | 0.0 | −3.0 | −3.0 |
| S line-upper lip (mm) | 0.0 | −2.0 | −3.0 |
| Nasolabial angle (o) | 100.0 | 121.0 | 112.0 |
The treatment goals intended to (1) establish an acceptable overbite and overjet; (2) correct the dental posterior crossbite by expanding the maxilla; (3) improve the dental and smile aesthetics; (4) correct the mandibular arch crowding and the lateral open bite; (5) correct the dental midline deviation; (6) achieve acceptable and a stable occlusal relationship with a favourable functional occlusion; and (7) maintain the pre-treatment facial profile.
The treatment plan considered the extraction of teeth in the lower arch to facilitate the retraction of the incisors and to correct the dental asymmetries and midline deviation. Edgewise brackets incorporating a 0.022-inch slot were planned to treat the malocclusion.
Because no future growth was expected to influence the treatment goals,5 two alternative options (with or without orthognathic surgery) were considered.
The patient, however, did not want orthognathic surgery due to social and psychologic reasons, and current satisfaction with his facial profile and appearance. Therefore, orthodontic camouflage with the extraction of the lower first premolars and third molars, and dentoalveolar compensation using miniscrew anchorage was planned to correct the mandibular dental asymmetries and the occlusal relationship.
A non-surgical orthodontic treatment option would reduce the risk of morbidity; however, there would be greater demands related to time and patient compliance.6
The mandibular first premolars and third molars were removed before appliance treatment. A Hyrax expander (0.9 mm, Morelli, São Paulo, Brazil) was placed to correct the posterior crossbite. It was activated by turning the screw twice a week (0.2 mm per turn) for 3 months. Once sufficient transverse expansion had been obtained, the appliance was stabilised in place for approximately 3 months for retention. A standard orthodontic edgewise appliance (0.022 × 0.028-inch slot; Generus, GAC, Dentsply) was subsequently placed.
Initial levelling and alignment followed a sequence of co-ordinated archwires of 0.016- to 0.020-inch stainless steel. To enhance anchorage, two miniscrews (diameter, 1.5 mm; length, 8 mm; ref. 37.10.202; Morelli, São Paulo, Brazil) were placed between the mandibular second premolar and first molar. The lower left first molar was distalised using a sliding archwire jig with a long arm placed mesial to the first molar and associated elastic chains to provide a distalising force. The extraction space was used to relieve the crowding and correct the midlines.7
The mandibular incisors were retracted using a 0.018
A maxillary wrap-around retainer was worn full time for 12 months and then at night for a further 12 months. In addition, a 0.028-inch stainless steel lower lingual retainer was anteriorly bonded from canine-to-canine.
The nonsurgical orthodontic results achieved the treatment goals. The post-treatment extraoral photographs showed that the patient’s facial profile was mostly unchanged. The patient still exhibited Class III facial characteristics mildly affected by a slight clockwise rotation of the mandible. The dental relationships improved along with retraction of the lower lip and an increase of the inferior labial sulcus (Figure 3).
Figure 3.
Extra- and intra-oral posttreatment photographs.
The post-treatment intraoral photographs showed a functional occlusal relationship. Despite the missing left maxillary canine, the patient appeared to exhibit a natural intact dentition. The anterior and posterior crossbites were corrected, the dental midlines were coincident with the facial midline and the maxillary and mandibular arches were well aligned and levelled. Good intercuspation, interproximal contacts, and an ideal incisor relationship were established. The maxillary right canine was in a Class I relationship, and the occlusion was well interdigitated. As planned, the maxillary left second premolar occluded with the mandibular first molar, and the maxillary left first molar occluded with the mandibular left second molar. The maxillary left third molar had no antagonist and was planned for extraction (Figure 4).
Figure 4.
Posttreatment records.
The post-treatment panoramic radiograph showed good overall root parallelism and confirmed that no pathosis or root resorption was present. The maxillary right third molar was well developed and still unerupted; this molar was also to be extracted (Figure 4).
The post-treatment cephalometric radiograph and tracing (Figure 4 and Table I) illustrates the dental and skeletal treatment outcomes. The interincisal angle increased from 139° to 146°. The lower incisor was uprighted and retracted over basal bone during space closure as shown by the FMIA angle (from 68° to 77°), IMPA angle (from 78° to 68°), L1 to NB angle (from 17° to 11°), and 1-NB distance (from 3 to 1 mm). The upper incisor position remained stable as shown by U1 to NA angle and 1-NA distance. The maxilla remained relatively stable (SNA 78°), as did the mandible (SNB 81°; SND 80°). The ANB angle and Wits appraisal remained unchanged. The vertical cephalometric values were increased as shown by the SN-GoGn, FMA, SN-Y-axis, facial angle measurements, which increased facial height and helped to improve the Class III appearance. An increase in the nasolabial angle was observed (Table I).
The maxillary superimposition revealed maintenance of incisor position. The mandibular molars were uprighted without extrusive side effects and the lower incisors were retracted. No maxillomandibular growth was observed (Figure 5).
Figure 5.
Superimposition of initial and final tracings at SN, maxilla and mandible, respectively.
Five years after the completion of active treatment, the occlusion remained stable with an acceptable incisor relationship, and good posterior intercuspidation. The periodontal health of the teeth was maintained without bone loss (Figures 6 and 7).
Figure 6.
Extra- and intra-oral photographs after 5 year retention.
Figure 7.
Records after 5 year of retention.
For adults presenting with a class III malocclusion, two treatment approaches are possible: orthognathic surgical treatment or orthodontic camouflage and factors related to individual patterns of growth, the magnitude of the skeletal discrepancy, the facial profile, patient expections,4,8 root parallelism, the functional occlusion, patient compliance, and the duration of treatment,2,9–11 need to be taken into full consideration.
After the treatment options were discussed with the patient, the orthognathic surgical approach was refused because of the surgical risks and likely post-operative discomfort. A viable approach was to perform dentoalveolar compensation without correcting the underlying skeletal deformity.10
The patient presented with a significant skeletal discrepancy (ANB −3.0o), but the presence of a functional deviation and an end-to-end incisor relationship in centric relation (CR) made nonsurgical orthodontic treatment possible. An acceptable facial profile and functional occlusion could be achieved with mandibular extractions instead of orthognathic surgery. Although the maxillo-mandibular relationship was not corrected, and the facial profile remained concave, a genioplasty procedure to reduce the prominence of the chin and achieve a more uniform and aesthetic facial profile was also declined.8
The compensatory orthodontic treatment for a nongrowing Class III patient includes extraction decisions. A lower incisor may be removed in moderate cases expressing an edge-to-edge relationship or anterior crossbite.8,12 Its success depends on the extent of anterior crowding, the Bolton’s ratio, and the overjet and overbite. An alternative treatment possibility includes lower premolar extractions to provide space to retract the mandibular incisors, to improve the anterior crossbite and the AP relationship.11
In the presented case, the lower first premolars and third molars were removed to assist delivery of a Class I canine relationship, to allow incisor retraction, to align the teeth, and to correct the midline deviation and the negative overjet. The third molar extraction facilitated distalisation of the mandibular posterior teeth.8 The Class III mechanics corrected the anterior crossbite, achieved a positive overjet and overbite and eliminated the functional mandibular deviation. The retroclination of the mandibular anterior teeth (by 5°) produced an overcorrected overjet. The orthodontic camouflage masked the skeletal discrepancies, by virtue of intense linguoversion of the lower incisors6 and the labial inclination of the upper incisors. It might be argued that such tipping of the mandibular incisors, although essential for the crossbite correction, could lead to gingival recession.11 However, no recession was seen five years later (Figure 3).
It has been stated that anteroposterior intermaxillary elastics may produce significant adverse vertical effects.2,8,11 The effects can be minimised by using appropriate mechanics involving an 0.018 × 0.025-in stainless archwire as integrated anchorage opposing Class III elastic forces. The results show that the torque maintained maxillary incisor position. However, despite the compensating lingual torque applied to the mandibule incisors, the Class III elastic force still caused uprighting of these teeth (Figures 3 and 4 and Table I).
The achieved occlusal and aesthetic results were due to significant dentoalveolar compensation and excellent patient elastic compliance. The lingual cusp of the maxillary left first premolar required equilibration to avoid premature contact in excursive movements. The right molars were in a Class III relationship and the canines were in a Class I relationship, but on the left side, the first premolar was substituted for the canine. The lingual cusp of the maxillary left first premolar required equilibration to avoid interfering contact in excursive movements. lncisal and canine guidance and group function in lateral excursions can also be achieved.
The sliding jig mechanics attached to the archwire together with elastic chains to the miniscrew provided specific tooth movements and allowed control of the occlusal plane.2,6,10 The miniscrew anchorage provided stability of the occlusal plane and uprighting of the entire mandibular posterior dentition without side effects affecting the maxillary teeth. The third molars were removed and contributed to the control of the vertical dimension in a patient who had a clinically long face.9
A backward rotation of the mandible is sometimes useful to improve a concave profile in Class III patients.7,13 However, in the presented case, a clockwise rotation of the mandible could not be performed because of the lateral open bite (Figure 1). Therefore, it was important to consider the direction of the retracting force delivered from the miniscrews. A retraction force was applied in a distal and downward direction7 and, as a result, the lower molars were distally inclined without extrusion, and the mandibular plane angle did not change throughout the treatment period.7
The orthodontic treatment of non-growing patients requires realistic objectives to be established and followed.5 The present case achieved an excellent final result that met the patient’s needs. The functional occlusion was stable 5 years after appliance removal, orthognathic surgery was avoided and the patient’s quality of life was greatly improved.
A nonsurgical orthodontic treatment approach involving dental extractions and dentoalveolar compensation can be a successful orthodontic treatment strategy to manage a Class III malocclusion by creating an acceptable aesthetic functional occlusion without orthognathic surgery. However, it is important that anchorage considerations in the mandibular arch are efficient to enable maximum retraction of the lower incisors.
The authors declare no conflict of interest.