Chin remodeling in a patient with bimaxillary protrusion and open bite by using mini-implants for temporary anchorage

Patients with bimaxillary protrusion may have an unattractive profile with a retruded chin contour. Correction of the severely protrusive anterior alveolar bone and teeth combined with a moderate open bite without orthognathic surgery can be challenging. This case report describes the orthodontic treatment of a woman with severe bimaxillary protrusion and a moderate open bite. Excellent chin morphology and facial appearance were obtained with the extraction of 4 first premolars and 4 third molars, and total distalization of both arches with 4 mini-implants, one in each quadrant between the second premolar and the first molar. The total treatment time was 30 months.

Highlights

  • A patient with bimaxillary protrusion and a retruded chin wanted to improve her profile.

  • Good chin morphology was obtained without surgery.

  • Treatment included premolar extractions and entire dentition distalization.

  • Relocation of anterior teeth and soft tissue tension around mouth led to good outcome.

  • Inclination and rotation of mandibular plane were also important.

The chin plays an important role in the overall harmony of the facial profile. It has been generally suggested that when evaluating facial esthetics, the public mostly considers the lower third of the face rather than the other facial structures. Patients with bimaxillary dentoavelolar protrusion usually have a retrusive chin contour, occasionally combined with a mild to severe open bite. These patients are often treated with a combination of orthodontics and orthognathic surgery to improve their facial esthetics.

A common treatment approach for bimaxillary protrusion patients is to extract 4 premolars and then retract the anterior teeth. However, 1 premolar space is usually not enough to alleviate the dentoalveolar protrusion, especially when patients have an open bite as well. Some authors have reported that extracting second molars or both premolars in the same quadrant could generate enough space to retract the anterior teeth and create an acceptable facial profile. However, these tooth extraction patterns might lead to loss of molar and premolar function and cause disturbance of the occlusion.

Currently, implants are widely used to help retract the anterior teeth, and some authors have used them to distalize the whole arch. In addition, mechanical analysis related to full-arch distalization with a temporary anchorage device has been elucidated. However, when using skeletal anchorage to treat bimaxillary protrusion, some patients obtain good chin morphology and a good lateral profile, but others do not; this is always perplexing to orthodontists.

Here we report on a patient with severe bimaxillary protrusion and moderate open bite treated by extraction of 4 first premolars and 4 third molars, and retraction of the anterior teeth and the full arches distally with mini-implants. See Supplemental Materials for a short video presentation about this study.

Diagnosis

A woman, aged 24 years 3 months, was referred for an orthodontic consultation in Department of Orthodontics, West China Hospital of Stomatology, Sichuan University, Chengdu, China. Her chief complaints were self-consciousness about her lip protrusion and lack of contact of her anterior teeth. Her lips were incompetent because of the severe proclination of her anterior teeth and open bite at rest.

The clinical examination showed a symmetric face, incompetent lips, acute nasolabial angle, and convex lateral profile without a chin contour ( Fig 1 ). She had a 5-mm overjet and a 4-mm open bite, with a Class I molar relationship on both sides. The maxillary and mandibular anterior teeth were significantly proclined, but there was almost no crowding in either arch ( Fig 2 ). She had caries on the maxillary second molars and silver amalgam fillings in her 4 first molars. The 4 third molars had erupted, and the mandibular right third molar was mesially and horizontally impacted. A panoramic radiograph showed that the mandibular right first molar had received root canal treatment ( Fig 3 , A ).

Fig 1
Pretreatment facial and intraoral photographs.

Fig 2
Pretreatment dental models.

Fig 3
Pretreatment radiographs: A, panoramic radiograph; B, cephalometric radiograph; C, cephalometric tracing.

The lateral cephalometric analysis showed a skeletal Class I jaw relationship (ANB, 4.4°) with a hyperdivergent growth pattern (SN-MP, 39.7°). The maxillary and mandibular anterior teeth were severely proclined (U1-SN, 64.2°; L1-MP, 106.9°; U1-L1, 95.3°). Her lips were protrusive, with upper lip to E-line at 2.5 mm and lower lip to E-line at 6.1 mm ( Table ; Fig 3 , B and C ).

Table
Cephalometric measurements
Measurement Normal Pretreatment Posttreatment Difference
SNA (°) 81.69 ± 4.7 83.7 82.2 −1.5
SNB (°) 78.94 ± 3.4 79.3 78.9 −0.4
ANB (°) 2.75 ± 1.5 4.4 3.3 −1.1
SN-MP (°) 32.85 ± 6.0 39.7 39.6 −0.1
y-axis (°) 60.3 ± 3.4 69.5 69.8 0.3
S-Go/N-Me (%) 65.85 ± 4.0 60.6 61.3 0.7
ANS-Me/N-Me (%) 53.32 ± 3.0 56.5 56.1 −0.4
U1-L1 (°) 123.22 ± 6.0 95.3 130.8 35.5
U1-SN (°) 74.94 ± 5.5 64.2 80.5 16.3
Ul-NA (mm) 5.56 ± 2.7 9.7 3.3 −6.4
Ul-NA (°) 23.26 ± 5.7 32.1 17.5 −14.6
Ll-NB (mm) 5.76 ± 1.8 12 5.9 −6.1
Ll-NB (°) 27.38 ± 6 42.2 28.5 −13.7
L1-MP (°) 95 ± 7 106.9 89.4 −17.5
U6-PP (mm) 22 ± 2 21 20 −0.1
L6-MP (mm) 35 ± 3 30 29 −0.3
UL-EP (mm) −0.46 ± 2 2.5 −0.7 −3.2
LL-EP (mm) 1.31 ± 2 6.1 1.3 −4.8
Pog-Pog’ (mm) 9.96 ± 2.06 4.19 5.67 1.48
Gn-Gn’ (mm) 6.01 ± 2.23 2.18 4.36 2.18
Me-Me’ (mm) 6.52 ± 2.14 2.53 5.32 2.79
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Dec 12, 2018 | Posted by in Orthodontics | Comments Off on Chin remodeling in a patient with bimaxillary protrusion and open bite by using mini-implants for temporary anchorage
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