Alternative approach using miniscrew-anchored sliding jig to correct maxillary midline deviation in a patient with unilateral missing premolar

INTRODUCTION

Treating midline deviation without tooth extraction is a challenging problem in orthodontics. When correcting midline deviation, it is important to determine the etiology and to evaluate the effects on occlusion.^[1] Interarch elastics, symmetrical extraction, and unilateral distalization are the recommended treatments for midline deviation. However, unilateral distalization is challenging in patients with asymmetric molar relationships. Multiple treatment methods and appliances for molar distalization have been described.^[2,3]

The use of miniscrews to obtain an absolute anchorage in other applications has recently been shown to optimize orthodontic mechanics, minimize unwanted reciprocal movement of other teeth, and require minimal patient cooperation.^[4,5] Some reports have described the successful use of miniscrews with a sliding jig (SJ) to distalize the posterior teeth both unilaterally^[6] and bilaterally.^[7]

In this case report, we describe simultaneous unilateral distalization to correct maxillary midline deviation and full-arch mandibular distalization using miniscrew-anchored SJs.

CASE REPORT

A 41-year-old female presented with the chief complaints of uncentered maxillary dental midline and crowding of the mandibular anterior teeth. She had previously undergone 4 years of unsuccessful orthodontic treatment involving the extraction of the maxillary left first premolar.

The patient had facial symmetry and a straight profile. Her upper and lower lips were anterior to the E-line by 0.5 mm and 2.5 mm, respectively. The maxillary and mandibular dental midlines were coincident, although both were 2.5 mm to the left of the midsagittal plane, with the maxillary central incisors tipped to the left. The right molar relationship was Class I, whereas the left molar relationship was Class II because of the missing maxillary left first premolar [Figure 1].

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Figure 1

Pretreatment facial and intraoral photographs and lateral cephalometric and panoramic radiographs.

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Cephalometric analysis indicated a slight skeletal Class II tendency with an SNA angle of 79.7°, an SNB angle of 75.2°, and a high mandibular plane angle of 39.0°. Labial inclinations of the maxillary incisors (U1 to FH) and mandibular incisors (L1 to occlusal) were 118.2° and 34.2°, respectively.

On the basis of these findings, the patient was diagnosed with Angle Class II subdivision malocclusion, skeletal Class II relationship, a large mandibular plane angle, midline deviation toward the left, and mild mandibular anterior crowding.

Treatment progress

Before orthodontic treatment, the right maxillary third molar was extracted and the orthodontic miniscrews (Dual top; Jeil Medical, Seoul, Korea) were inserted between the mandibular second premolar and first molar bilaterally to serve as an abutment for SJs fabricated of 0.032-inch wire. Orthodontic tooth movement at all stages was performed with 0.018 × 0.025-inch slot preadjusted brackets (Dentsply- Sankin and Tomy International, Tokyo, Japan) and 0.016 × 0.022-inch improved superelastic nickel-titanium alloy wire (L and H Titan; Tomy International, Tokyo, Japan).

Multibracket appliances and an SJ were placed for distalization of the mandibular arch prior to the backward- left movement of the maxillary arch [Figure 2a]. After the space had been opened mesial to the first molar, an elastomeric chain was placed from the first molar to the premolar and canine to move distally. Anterior retraction and intrusion of the mandibular incisors was performed concurrent with alignment of the dental midline to the facial midline [Figure 2b].

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Figure 2

Progressive intraoral photographs.

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In the maxilla, unilateral distalization of the right posterior segment was performed with an SJ [Figure 2c]. After molar distalization, anterior retraction toward the right side progressed with the alignment of the midline of the maxillary incisors with the facial midline.

The duration of active treatment was 32 months. After all the appliances were removed, a Hawley-type retainer was placed for the retention.

Treatment results

The patient’s facial esthetics improved with correction of dental midline discrepancies and repositioning of the incisors without additional premolar extraction, which maintained profile esthetics [Figures 3 and 4]. Class I molar and canine relationships were achieved on the right side, and full-cusp Class II molar and Class I canine relationships were achieved on the left side. The overjet was corrected, adequate overbite was maintained, the mandibular molars were uprighted, and the proper contact points were obtained.

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Figure 3

Post-treatment facial and intraoral photographs and lateral cephalometric and panoramic radiographs.

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Figure 4

Tracing of pretreatment and post-treatment posteroanterior cephalometric radiographs. Abbreviations: (Lo) Right latero-orbitale. (Lo') Left latero-orbitale. (CG) Crista gali. (Me) Lowest point on the midline curve of the symphysis.

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Cephalometric superimposition showed molar distalization of both the maxilla and mandible [Figure 5a] except for the left maxillary molars [Figure 5b].

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Figure 5

Superimposition of pretreatment and post-treatment lateral cephalometric radiographs. (a) Superimposition of right molars. (b) Superimposition of left molars.

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Twenty-nine months after completion of active treatment, occlusion remained good and stable [Figure 6].

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Figure 6

Facial and intraoral photographs after 29 months of retention.

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DISCUSSION

Midline deviation can be isolated or can occur in combination with dental factors, skeletal asymmetry, or functional shifts of the mandible.^[8] Asymmetrical midlines in nongrowing patients are commonly treated with premolar extractions.^[9] However, our patient’s previous orthodontic extraction made this case more complicated. The development of skeletal anchorage devices provides new treatment options, particularly in adults.^[10] Previous reports have described the successful use of an SJ, which combines the benefits of skeletal anchorage with a simply designed, versatile distalizing appliance. Pithon^[6] described correction of dental asymmetry with SJs. Lim et al.^[7] reported a method for full-arch distalization with SJs. In our patient, the use of orthodontic miniscrews made it possible to deliver consistent low force levels with SJs for molar distalization without proclination of the incisors. Their use enabled the maxillary dental midline to be moved 2.5 mm to the right and prevented unwanted arch deformity.

CONCLUSION

In this case, midline correction and alignment were obtained with unilateral maxillary distalization and full- arch mandibular distalization without additional premolar extraction. SJs provided efficient unilateral or bilateral molar distalization mechanics in both arches and facilitated midline coordination without requiring patient’s cooperation.