Class III malocclusion: a challenging treatment using miniscrews for extra anchorage

Mirian Aiko Nakane Matsumoto,* Patrícia Maria Monteiro,* Wendes Dias Mendes,† José Tarcísio Lima Ferreira,* Fábio Lourenço Romano* and Maria Bernadete Sasso Stuani* Department of Pediatric Dentistry, Orthodontics, School of Dentistry of Ribeirão Preto – University of São Paulo, Ribeirão Preto, São Paulo, Brazil* Department of Basic and Oral Biology, School of Dentistry of Ribeirão Preto – University of São Paulo, Ribeirão Preto, São Paulo, Brazil†


Introduction
A Class III malocclusion invariably shows skeletal and dentoalveolar components. Genetic and environ mental factors act as positive stimuli regulating mandibular growth, related to mandibular functional anterior deviation or mouth breathing. [1][2][3][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 pro gnosis 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][2][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 treat ment 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.

Diagnosis and etiology
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) .   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 toothsize 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 ab normalities and alveolar bone loss was not detected. The third molars were unerupted and impacted ( Figure 2).
The pretreatment lateral cephalometric tracing and analysis ( Figure 2 and Table I)

Treatment objectives
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 pretreatment 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 0.022inch slot were planned to treat the malocclusion.

Treatment alternatives
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 ancho rage was planned to correct the mandibular dental asymmetries and the occlusal relationship.
A nonsurgical orthodontic treatment option would reduce the risk of morbidity; however, there would be greater demands related to time and patient compliance. 6 Table I. Initial and final cephalometric measurements.

Measurements
Average

Treatment progress
The mandibular first premolars and third molars were removed before appliance treatment. 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 × 0.025inch rectangular closing loop archwire and Class III elastic wear. Patient compliance was very good and at the end of treatment after 38 months, occlusal interdigitation had been achieved and the miniscrews were removed.
A maxillary wraparound retainer was worn full time for 12 months and then at night for a further 12 months. In addition, a 0.028inch stainless steel lower lingual retainer was anteriorly bonded from caninetocanine.

Treatment results
The nonsurgical orthodontic results achieved the treatment goals. The posttreatment extraoral photo graphs 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).
The posttreatment 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).
The posttreatment 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 posttreatment 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 1NB distance (from 3 to 1 mm). The upper incisor position remained stable as shown by U1 to NA angle and 1NA 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 SNGoGn, FMA, SNYaxis, 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).

Superimpositions results
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).

Assessment after retention
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).

Discussion
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 −3.0 o ), but the presence of a functional deviation and an endtoend 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 maxillomandibular 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 non growing Class III patient includes extraction decisions. A lower incisor may be removed in moderate cases expressing an edgetoedge 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 devi ation. 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 incisors 6 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 × 0.025in 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 direction 7 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 nongrowing 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.

Conclusion
A nonsurgical orthodontic treatment approach in volving dental extractions and dentoalveolar com pensation 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.