Treatment of facial asymmetry and severe midline deviation with orthodontic mini-implants

This case report describes the treatment of a 29-year-old woman with facial asymmetry and 2 hopeless teeth. Her lower dental midline was shifted to the left side, and the mandibular left second molar would need to be extracted because of severe caries. The maxillary right second premolar was root rest, and the upper dental midline was shifted to the right side. Because of the patient’s asymmetry and Class III skeletal pattern, a severe Class III relationship in the right canine region and lingual crossbite in the left side was observed. She did not want jaw surgery. The mandibular right first premolar, 2 hopeless teeth, and maxillary left second premolar were extracted, and orthodontic mini-implants were used to correct the dental midline, crossbite, and crowding. The mandibular left third molar was moved to the second molar extraction space by using orthodontic mini-implant anchorage. Adequate functional and esthetic results were obtained. Correction of the crossbite on the left side could improve facial asymmetry by changing the drape of the overlying lips.

Highlights

  • Third molars were moved to the second molar extraction space using mini-implants.

  • Correcting the crossbite in the buccal segment improved facial asymmetry.

  • Archwire width and torque and molar tube prescriptions differed side to side.

Asymmetry is a common finding in the craniofacial region and often causes occlusal problems like midline deviation and crossbite. If the degree of facial asymmetry is severe, it is better to improve the problem through orthodontic decompensation and asymmetric jaw surgery. In comparison, if the asymmetry is mild, it may be difficult for the patient to agree to surgery, and occlusal problems may need to be corrected through orthodontic treatment alone. To achieve proper occlusion while conducting the necessary asymmetrical movement, anchorage control is very important. In most patients, it is difficult to improve facial asymmetry without orthognathic surgery, but in some patients, it can be improved significantly by orthodontic treatment alone. ,

Some orthodontic patients have a missing second molar because of severe caries. If the patient’s third molar is healthy, protraction of the third molar into the missing space may be considered rather than implant placement and third molar extraction. In such a case, particularly when the retraction of anterior teeth is not required, anchorage becomes a significant problem.

The introduction of orthodontic mini-implants (OMIs) made it possible to obtain absolute anchorage. Asymmetric tooth movement or molar protraction can be achieved without patient cooperation, , and the scope of orthodontic treatment has become much wider.

This case report describes asymmetric mandibular tooth movement in a patient with facial asymmetry who was treated with OMIs to improve the midline deviation and crossbite. The hopeless mandibular left second molar was extracted, the third molar was protracted, and the patient’s occlusal problem was successfully corrected with adequate OMI anchorage.

Diagnosis and etiology

A 29-year-old woman sought treatment for her chief complaints of facial asymmetry and poor occlusion. Her chin was deviated to the left side because of overgrowth of the right side, and lip canting was observed ( Figs 1-3 ). In the posteroanterior (PA) cephalogram, based on the crista galli–anterior nasal spine line, menton was located to the left of the midline about 4.7 mm ( Table I , Fig 4 , B ). The mandibular ramus and body lengths were significantly different from one another, but the occlusal plane canting was mild (0.5°; Fig 4 , B ). The interpupillary line and commissure line were not parallel to each other ( Fig 4 , C ).

Fig 1
Pretreatment photographs.

Fig 2
Pretreatment dental casts.

Fig 3
Pretreatment radiographs.

Table I
Pretreatment posteroanterior cephalometric measurements
Pretreatment
Rt Co-Ag 72.6
Lt Co-Ag 67.5
Rt Ag-Me 60.1
Lt Ag-Me 52.9
Rt Ag-MSL 49.2
Lt Ag-MSL 49.0
MSL-Me 4.7

Rt , right; Lt , left; Co , condylion; Ag , antegonial notch; Me , menton; MSL , midsagittal line (crista galli–anterior nasal spine).

Fig 4
A, Tracing of pretreatment lateral cephalogram. B, Tracing of posteroanterior cephalogram. The mandibular ramus (Co, condylion; Ag, antegonion) and body (Ag; menton, Me) length, the distance from Ag to the midsagittal reference line (MSL; CG, crista galli; ANS, anterior nasal spine), and MSL to Me distance were measured (Table I). C, The angle between soft tissue nasion–subnasale line (NSL, red ) and interpupillary line ( yellow ) was 92.0°. The angle between NSL and commissure line ( blue ) was 87.4°. D, Upper dental midline was located 1.5 mm to the right side of NSL ( blue ).

Lingual crossbite was observed in the left premolar area because of jaw asymmetry and Class III tendency. As the mandibular left first molar was tilted lingually by natural dental compensation, there was no crossbite in the left first molar area. Because of the patient’s asymmetry and Class III skeletal pattern, a severe Class III relationship in the right canine region was also observed. In the right molar area, the Class I molar relationship was shown because of the forward movement of the maxillary right first molar toward the second premolar space. The patient did not have any temporomandibular joint symptoms. The bilateral manual manipulation technique was used to evaluate condyle position, and the incisor relationship did not show significant lateral deviation during the manipulation procedure.

The maxillary right second premolar and mandibular left second molar were root rest because of severe caries. In the maxillary right second premolar area, the alveolar bone recession was observed on the panoramic radiograph. The upper dental midline was shifted to the right side because the anterior teeth were moved toward the root rest. Separately, the lower midline was shifted to the left because of mandibular asymmetry. The nose dorsum was slightly curved. In addition, nasion, subnasale, and labrale superius were not on a straight line, and it was difficult to evaluate the amount of lateral displacement of the dental midline. In a frontal facial photograph with the soft tissue nasion–subnasale line, the upper dental midline was located 1.5 mm to the right side ( Fig 4 , D ). But in a PA cephalogram with a crista galli–anterior nasal spine line, it was located about 0.8 mm to the right side ( Fig 4 , B ).

The upper midline was located at the interproximal surface of the mandibular right central and lateral incisors. Overbite and overjet were within normal limits (2.5 mm and 2.5 mm), and a mild to moderate degree of crowding was observed in both arches. The patient did not have any specific medical or dental history.

Her vertical skeletal pattern was normal (Bjork sum, 399.1°; Facial height ratio, 60.5) ( Table II ), and her sagittal pattern was mild Class III (ANB, 0.6°). Maxillary and mandibular incisors showed a slight lingual inclination. Mild lower lip protrusion with lip incompetency was noted on the facial photograph (lower lip to the esthetic line, 2.1 mm).

Table II
Changes in cephalometric measurements
Pretreatment Posttreatment Postretention
Bjork sum (°) 399.1 397.3 397.6
Facial height ratio (%) 60.5 61.7 61.6
ANB (°) 0.6 −0.6 −0.5
A to N perpendicular (mm) −1.6 −1.6 −1.6
Pog to N perpendicular (mm) −2.9 −1.2 −1.2
U1 to FH (°) 109.8 105.7 105.7
U1 to SN (°) 100.1 96.0 95.9
L1 to A pog (mm) 4.1 0.2 0.3
IMPA (°) 83.2 79.7 79.5
Interincisal angle (°) 135.9 145.7 145.8
Nasolabial angle (°) 102.2 103.5 103.8
Upper lip to Esthetic line (mm) −0.5 −3.1 −3.4
Lower lip to Esthetic line (mm) 2.1 −1.4 −1.4
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Aug 14, 2021 | Posted by in Orthodontics | Comments Off on Treatment of facial asymmetry and severe midline deviation with orthodontic mini-implants
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