Navigating 2 x 4 Appliance in Modern Orthodontics: A Case Report and Review

 Introduction

The mixed dentition stage represents the gradual transition from primary to permanent dentition. This transition highlights the distinction between malocclusions that require intervention and those that are likely to self-correct, which needs to be emphasized. Common malocclusions observed at this stage include anterior and posterior crossbites, dental crowding, tooth rotations, midline diastema, and spacing issues.¹

Interceptive orthodontic therapy is often carried out to minimize the intensity of malocclusion since it influences the jaw growth and development.²

A significant number of malocclusions can be treated non-surgically without necessitating extraction of permanent teeth and this represents the primary benefit of interceptive treatment.² It can also enhance the child's self-esteem and prevent the need for future orthodontic treatment.

The 2 x 4 Appliance

The appliance includes bands cemented to the first permanent molars on both sides to provide anchorage, along with brackets attached to the erupting permanent incisors.² Hence, it is vital to consider the eruption of permanent molars and incisors. Continuous arch wires are introduced into the molar tubes to maintain proper arch form and regulate tooth movement.

This fixed appliance is used during the early mixed dentition phase to align malpositioned permanent incisors and improve occlusion within a short treatment period. The 2 × 4 appliance approach effectively controls anterior tooth movements by managing force magnitude and direction across all three dimensions, including tipping, root torque, and rotations, while maintaining the integrity of the arch form.³

Applications of 2 x 4 Appliance

Correction of rotated teeth

Early intervention in cases of dental rotation may significantly reduce the necessity for comprehensive orthodontic treatment in later stages, can help enhance function, and positively impact an individual’s psycho-logical well-being. A lingual button is bonded on the rotated tooth and elastomeric chain is attached to the button to derotate using couple force.²

Management of anterior/ posterior crossbites & mild crowding

An old orthodontic maxim states, ‘The best time to treat a crossbite is the first time it is identified’.⁴ Early correction of an anterior crossbite is highly recom-mended to prevent its progression into a true Class III malocclusion later in life.⁵ To align teeth, NiTi arch wire is initially applied, followed by a 0.016 or 0.018-inch stainless steel archwire with omega loops placed in front of the first molars to procline the anterior teeth.5 To increase space for incisor proclination, a compressed NiTi push coil spring can be inserted between the molars and incisors.⁶ Expansion appliances like quad helix can also be soldered to the bands in cases with constricted arch requiring expansion. Class III elastics can be used along with a 2 x 4 appliance to produce proclination of the maxillary anteriors and to retrocline the mandibular anterior teeth, thereby correcting the anterior crossbite.⁶

Ectopic/impacted upper permanent central incisors

To maintain the arch shape and preserve space for the impacted incisor, a heavy gauge stainless steel archwire can be placed, along with a push coil spring shortly before traction. Traction may then be applied using an elastomeric chain, ligature wire, supplementary archwire, or a piggyback technique.⁷

Closure of midline diastemas or abnormal spacing

Treatment options depend on factors such as incisor angulation, the presence of the ugly duckling stage, overjet, and overbite. To reduce the risk of root resorption during gap closure, it is advisable to bypass the brackets on the lateral incisors, facilitating mesial movement of their roots.⁸ A push coil spring (extending from the lateral incisor brackets and molar bands or between the lateral incisor brackets and a metal or plastic sheet) is recommended to close anterior spacing with minimal or negative overjet.9 For increased overjet, a power chain is a better option. Double-helical loops in a 0.017 × 0.025- inch steel or beta titanium archwire, with or without a step, can effectively handle situations with spacing, increased overjet, and/or increased overbite.⁹

Vertical control of the anterior teeth for deep bite/ open bite correction

Vertical control of anterior teeth can be achieved using 2 × 4 appliances such as the utility arch, continuous intrusion arch and Connecticut intrusion arch.¹⁰

Case Report

An 11-year-old boy reported to the Department of Pediatric & Preventive Dentistry with the chief complaint of deposits on his tooth surface and a desire to have them cleaned. No significant medical history was noted. The dental history revealed that the child had visited a dentist two years ago for the extraction of a carious tooth. Extra-oral examination revealed a convex profile with an apparently symmetrical face and competent lips. On intra-oral examination, transitional dentition was observed with an Angle’s Class I molar relationship on the left side, with 3 mm of overbite, and 3 mm of overjet, ectopic eruption in relation to 16, transpositioned 42, clinically missing 84, gingival recession in relation to 41 along with a midline deviation of 2 mm to the left compared to the facial midline (Figure 1).

To evaluate the association between the transpositioned lateral incisor and permanent canine, cone beam computed tomography images were obtained. Cone beam computed tomography revealed the positioning of permanent right mandibular lateral incisor crown in between the primary canine and primary second molar. The roots of permanent mandibular lateral incisor remained in their usual position, and therefore no contact was present between the permanent canine and premolar roots. The crown of 44 was located approximately 5.2 mm below the alveolar crest (Figure 3).

An appropriate treatment plan was developed based on the clinical and radiographic findings. Given that the patient was in the mixed dentition phase, a removable appliance was recommended to manage the trans-position and correct the improper axial angulation of the lateral incisor. The primary treatment objective was to intercept and guide the ectopic eruption of tooth 16 and to achieve a Class I occlusion with ideal overjet and overbite.

Treatment Progress

Oral prophylaxis was done initially, followed by the bilateral extraction of retained primary canines. An alginate impression was made one-week after the extraction procedure to facilitate healing. A modified lingual arch appliance with a hook like extension was constructed to engage the e-chain.

A 0.022-inch standard edgewise bracket was bonded to the buccal surface of the right mandibular lateral incisor, and 1/8-inch light elastics were applied between the bracket and a hook to guide the lateral incisor mesially. This was achieved using a light, continuous force generated from the hook soldered onto the anterior segment of the lingual holding arch. However, after one week, due to breakage of the appliance and patient discomfort, a 2 x 4 appliance was bonded to the mandibular arch and a NiTi open coil spring was used between the deciduous second molar & the transposed lateral incisor. The treatment involved a sequential progression through various NiTi and stainless-steel round archwires .014 and .016 inch for the initial leveling and alignment of the lower incisors. Following the successful uprighting of the lateral incisor, an elastic chain (e-chain) was applied to the mandibular incisor segment for four weeks to stabilize the anterior alignment (Figure 4).

Haltermann’s appliance was initially employed to correct the ectopic eruption of the molar. However, due to the failure of the lingual button attachment on the permanent maxillary first molar, proximal stripping of the deciduous second molar was carried out to facilitate the proper eruption of the permanent first molar (Figure 4).

Although the permanent canine is likely to erupt into its proper position due to the uprighting and mesial movement of the permanent mandibular lateral incisor, additional orthodontic intervention using fixed appliances is planned to correct the lower midline deviation and moderate crowding.

Discussion

Ectopic eruption is a broad category defined as ‘any abnormal or aberrant eruptive position taken by a tooth’.¹¹ All transpositions are considered as ectopic eruptions. Transposition is defined as the interchange of positions between two adjacent permanent teeth within the same quadrant of the dental arch.¹¹ The incidence of transposition was estimated as 0.2% to 0.38%, while an incidence ranging between 2% and 6% was reported for ectopic eruption of maxillary first molars. In the presented case, the clinical and radiographic features were consistent with the classic characteristics of mandibular lateral-canine (Mn.I2.C) transposition as outlined by Peck.¹¹ Transposition is considered complete when the positions of the affected teeth are fully transposed. The transposition is considered incomplete when only the crowns are displaced, and the roots retain their normal anatomical positions.¹²  

In the above case, the mandibular lateral incisor had migrated distally, but the roots of the teeth stayed in their normal position. Hence, it was considered as an incomplete transposition. The most common etiologies of transposition include trauma, premature loss of primary teeth, failure of resorption of root of primary canine, and variations in genes affecting the positioning of newly formed tooth buds.^2,10,12 In our case, no familial history of ectopic eruption was noted. Early loss of primary tooth caused the transposition leading to the deflection of permanent canine and premolar from their path of eruption.

The primary objective of treatment in all the trans-position cases is to rectify the aesthetic and functional abnormalities of occlusion. Treatment options for this patient included orthodontic movement of teeth into their normal anatomic positions in the arch, extraction of deciduous tooth, and alignment of the teeth involved in transposition. Primary treatment should be based on careful consideration of multiple factors, including occlusion, patient cooperation, treatment length, periodontal support, position of the root apices, patient’s age, and aesthetics.

Early detection of ectopic eruption is crucial and greatly influences treatment outcomes. Transposition anomalies are typically diagnosed using conventional panoramic radiography.2 In this case, ectopia was identified prior to the eruption of the permanent mandibular canine through a standard radiograph. To further assess the positional relationship among the lateral incisor, permanent canine, and premolars, a CBCT scan was performed. The imaging revealed that although the crown of the lateral incisor was transposed, the roots remained correctly positioned. Consequently, the primary mandibular canines were extracted bilaterally, and the inclination of the transposed permanent mandibular lateral incisor was corrected before the eruption of the permanent canine. Additional orthodontic treatment was advised to manage midline deviation and space deficiencies.

The 2 x 4 appliance is essential considering its versatility, easy of use, and ability to effectively treat dental malocclusions in a short period, while maintaining strong control over tooth movements.^2,13,14 Removable appliances have certain limitations such as need for multiple visits, limited control over tooth movement patterns, the risk of unintentional movements, and the requirement of patient cooperation, in contrast to fixed appliance treatment.^12,13 McKeown et al., reported that using a 2 x 4 appliance early can effectively correct malocclusion in a span of weeks to months, as opposed to traditional fixed appliance therapy.¹⁴

However, this does not eliminate the need for a second phase of orthodontic treatment in the future. Placement of bands can be challenging in partially erupted permanent teeth and in such instances, buccal tubes can be utilised.^14,15 Also, this method does not address skeletal malocclusions.^2,14

General practitioners and pediatric dentists should understand the biomechanics of using 2 × 4 appliance to correct malocclusions in basic cases, while orthodontists are better equipped to handle more complex cases.^13,16

Conclusion

Early diagnosis of ectopia and timely intervention are essential to prevent future aesthetic concerns and occlusal issues. The 2 × 4 appliance serves as an efficient treatment option for managing mild to moderate  malocclusions during the mixed dentition phase. It delivers light, continuous, and precisely controlled forces, making it particularly advantageous in cases where removable appliances are not feasible. Moreover, it can be easily adapted to various clinical situations and generally presents fewer limitations compared to conventional removable appliances.

Conflict of Interest

Nil