Molar uprighting using a newly designed segmental wire: a case report

The ectopic eruption of permanent molars occurs with a prevalence of 0.06–6%.^1–5 The prevalence of a first molar eruption disturbance is higher in the maxilla compared with that in the mandible, and the prevalence of second molar problems is higher in the mandible compared with the maxilla.^2–5 An incorrect eruptive path can result in incomplete eruption through interference by an adjacent tooth, which is often accompanied by distal root resorption and/or early loss of a primary second molar. This circumstance also can lead to an arch length discrepancy.^6–8

An ectopic eruption of a first molar has been categorised as reversible or irreversible depending on the severity of the disturbance and second primary molar resorption.⁷ If the ectopic eruption does not self-correct, consideration should be given to first molar distalisation using a fixed or removable appliance. An array of appliances for molar distal uprighting has been introduced, including Humphrey-type and Halterman appliances.^9–12 However, due to the relatively narrow intraoral space for insertion and application, particularly in growing patients, it is clinically useful to determine the appropriate appliance that can be easily placed for the most effective delivery of a corrective force. In addition, for fully impacted molars, access to bond a molar attachment and the appropriate application of force is more challenging, even after surgical exposure.¹³

A newly designed appliance for the distal uprighting of an ectopically erupting molar is presented. A small-dimensional segmental wire incorporating double-sided hooks plays a key role in transferring an uprighting force to the molar (Figure 1). An elastomeric thread is attached from a mesial hook to an anchor tooth, and a distal hook is used to engage an attachment on the ectopic molar. Molar uprighting begins when the elastomeric force is applied between the mesial hook of the wire and the bracket of the anchor tooth. The applied force is transferred to the attachment of the ectopic molar and supported by the distal hook of the wire. The applied elastomeric thread is used anterior to the impacted molar and so the application of the distalising and uprighting force is simple and changing the elastomeric thread is effortless.

Figure 1.

The following cases show the distal uprighting of ectopic molars using small-scale segmental wires. The simplicity and effectiveness of this clinical technique are demonstrated.

Case 1

A 7-year-old male patient presented with bilateral ectopically erupting maxillary first molars (Figures 2A, B). Asymptomatic resorption of the distal surface of the second primary molars was noted. Immediate distal uprighting of the permanent molar was implemented to prevent further root resorption and eruption disturbance.

Figure 2.

The right first permanent molar was surgically exposed using a laser and a button was bonded to its occlusal surface (Figure 2C). The second primary molar on the right side was used as an anchor unit, and a 0.018-inch standard bracket (with no torque and no angulation) was bonded onto the buccal surface. To apply a molar uprighting force, a 0.016-inch segmental stainless steel wire incorporating double-sided hooks was prepared. The distal hook was engaged to the button of the first molar, and a light force (of approximately 50 g) was applied by an elastomeric thread (Super thread, T-45, Rocky Mountain Orthodontics, Denver, CO, USA) between the bracket of the second primary molar and the mesial hook of the wire.

Distal uprighting of the right first molar was fully corrected two months after treatment began, and the force application was discontinued (Figure 2D). Distal uprighting of the left first molar commenced using the same technique. After both of the molars were in favourable positions and mesial surface contact against the primary second molars was attained, the brackets and buttons were removed. After 24 months of follow-up observation without retainers, the corrected molar positions were maintained with no apparent further adverse resorption of the primary molars (Figures 2E, F).

Case 2

A 15-year-old female patient presented with an anterior edge-to-edge bite and a Class III canine and molar relationship. Comprehensive treatment for tooth alignment and distalisation of the entire mandibular dentition was planned after full eruption of the permanent teeth. However, mesially angulated mandibular second molars were also noted on the right and left sides at the beginning of treatment (Figure 3A). Therefore, the uprighting of the ectopic mandibular second molars was included in the treatment plan. At the beginning of treatment, 0.022-inch pre-adjusted brackets were bonded to both arches, except for the unerupted second molars. Levelling and alignment began with the insertion of a 0.014-inch nickel-titanium arch wire. After 4 months, a 0.016 × 0.022-inch stainless steel arch wire was inserted, the mandibular second molars were surgically exposed by partial gingival excision, and buttons were bonded to their mesiobuccal surface (Figure 3B). A segmental 0.016-inch stainless steel wire incorporating double-sided hooks was ligated onto the bracket of the mandibular second premolar, and the distal hooks were engaged to the buttons on the second molars. After appropriately placing both segmental wires, a light force (approximately 50 g) was applied by the elastomeric threads (Super thread, T-45, Rocky Mountain Orthodontics, Denver, CO, USA) from the first molar tube to the mesial hook of the segmental wire to commence distal uprighting of the second molars. After 3 months, the mandibular second molars were sufficiently corrected to bond buccal tubes and insert a 0.016-inch nickel-titanium arch wire. The overall treatment was completed in 24 months, resulting in a well-interdigitated Class I occlusion and appropriate angulation of both mandibular second molars (Figure 3C).

Figure 3.

After 26 months of retention using ‘wraparound’ retainers in both arches, the overall result was stable along with maintenance of the favourable position of the second molars (Figure 3D).

Correcting the ectopic eruption path of permanent molars is an important treatment aim and so various appliances have been described in previous studies and case reports.^9–12 However, inserting appliances and applying an uprighting force is difficult for clinicians and patients due to relatively complicated appliance designs. In practice, applying a precise force to activate helical springs, such as the Humphrey-type appliance, is not simple in the confined intraoral space. Additionally, the limited space around the molar can restrict the distal extension of wires for molar uprighting thereby reducing the level of force or activation.¹²

In the described novel technique, a distal uprighting force to the molar was effectively applied using a small-sized segmental wire incorporating double-sided hooks. By using the mesial hook, the force application of this appliance was more anterior to the molar than that produced by previous appliances. Therefore, the appliance was more accessible when force delivery was adjusted by changing the elastomeric thread. The current technique required minimal space for an attachment to be bonded to the molar. Therefore, the use of this appliance was highly feasible even for molars that are only partially exposed. In addition, the amount and direction of force could be precisely adjusted and tooth movement predicted because the uprighting force was managed by changing the elastic thread instead of activating a helical loop or other mechanism. This result mirrors previous studies which highlight the advantages of sliding mechanics, and which include ease of wire fabrication, no requirement for activation space, and better force control compared with loop mechanics.^14,15 Consequently, the mesially angulated molars were efficiently corrected over a short time period (2–3 months after beginning force application), as illustrated in the presented cases.