Introduction
The mandibular second molar plays a critical role in establishing posterior occlusion, maintaining masticatory function, and ensuring dental arch stability. Eruption disturbances occur more frequently with mandibular second molars than with maxillary molars and commonly present unilaterally[1]. If not properly resolved, these disturbances may lead to various adverse consequences, such as supraeruption of the opposing teeth, compromised periodontal health, and caries in the impacted teeth. Therefore, early diagnosis and therapeutic intervention are recommended[2].
Eruption disturbances of the mandibular second molars have diverse etiologies, making an accurate evaluation of the causative factors essential for formulating effective treatment plans[3]. Common causes include insufficient arch length, abnormal inclination of the tooth germ, lack of root guidance from the first molar, spatial competition with adjacent teeth, and the presence of supernumerary teeth or tumors. In particular, mandibular second molars tend to incline mesially when they lack sufficient guidance from the first molar during development or when excessive space exists between their crowns and the first molars[4,5]. Therefore, radiographic examinations, especially three-dimensional cone beam computed tomography (CBCT)-based analyses, are important for comprehensively evaluating the eruption direction, angulation, and relationships with adjacent anatomical structures[6].
The treatment for impacted mandibular second molars varies depending on the severity. Mild impactions can be managed by inducing spontaneous eruptions using interproximal separators, whereas moderate to severe cases often require surgical exposure combined with orthodontic traction, surgical uprighting, or extraction, followed by autotransplantation. Treatments for impacted mandibular second molars have relatively high success rates (66.7 - 100.0%), although outcomes vary depending on the treatment approach[7]. For example, surgical uprighting and autotransplantation have limitations, including invasiveness and the risk of root damage, whereas conventional orthodontic appliances may be affected by biomechanical constraints, such as limited traction directions, anchorage instability, and unintended tooth movements[8,9].
Miniscrews, which provide a more stable and predictable anchorage, have been recently introduced, and their use has become widespread owing to their advantages, such as minimizing the need for complex mechanical devices, enabling efficient traction, and overcoming the limitations associated with traditional dental anchorage[10,11]. A previous study reported that miniscrews placed in the retromolar area enable vertical control by applying traction posterior to the center of resistance[12], a biomechanical principle similar to that of miniscrew placement in the mandibular ramus. Ramus miniscrews offer effective anchorage for molar traction without negatively affecting the adjacent teeth[3]. Anatomically, the ramus provides abundant cortical bone and maintains a relatively safe distance from major nerve structures, offering biomechanical advantages favorable for traction[13,14]. Previous studies have reported orthodontic traction of mandibular second molars using ramus miniscrews[3,14]; however, the present case report aimed to provide clearer clinical evidence regarding mini-screw placement and traction vectors by performing an additional three-dimensional evaluation using CBCT.
This report presents the treatment process, clinical outcomes, and significance of orthodontic traction using ramus miniscrews in two cases: one with mesially inclined impaction accompanied by root curvature, cortical bone interference, and odontoma and the other with horizontal impaction positioned close to the mandibular canal and in contact with the roots of the adjacent teeth.
Case Reports
The patients’ legal guardians provided consent for publication of this case report and the associated clinical and radiographic images.
Case 1
A 15-year-old boy presented with bilateral mandibular second molar impaction. Intraoral examination revealed complete impaction of the right mandibular second molar, and only a portion of the crown of the left mandibular second molar was clinically visible (Fig. 1). Panoramic radiography indicated partial eruption of the mandibular left second molar with a mesial inclination, whereas the right second molar was horizontally impacted inferior to the mandibular first molar (Fig. 2). Three-dimensional reconstructed images generated by segmentation using Medical Design Studio in Invivo 6 (version 6.0; Anatomage, San Jose, CA, USA) based on CBCT revealed that the mandibular right second molar was closely positioned against the distal root of the adjacent first molar. This resulted in an S-shaped deformation and thinning of the distal root. Although clear root resorption was not observed, the distobuccal root appeared relatively thinner compared to the mesial root. Additionally, the third molar was impacted lingually and superiorly to the mesially inclined second molar root. The patient was diagnosed with skeletal Class II malocclusion accompanied by mandibular retrognathism (Table 1). Clinical examination revealed Class II canine and molar relationships, along with large overbite and overjet.
A treatment plan was established to correct the skeletal Class II malocclusion, which involved extracting both the maxillary second molars, distalization of the maxillary arch molars, and substituting the extracted teeth with the third molars. To guide the eruption of the mandibular second molars, extraction of the bilateral mandibular third molars and traction using a miniscrew placed in the mandibular right ramus area were planned. Distal traction and uprighting using a Halterman appliance were planned on the left side. Subsequently, full orthodontic bonding of the upper and lower arches was performed, and comprehensive orthodontic treatment was initiated.
Initially, the mandibular third molars were extracted bilaterally to secure an eruption space for the mandibular second molars. An orthodontic miniscrew (1.8 × 10.0 mm; Ortholution, Seoul, Korea) was then placed in the mandibular right ramus region. The miniscrew was inserted approximately 4 - 6 mm superior to the occlusal plane at an angle of 25 - 30° relative to the sagittal plane and 25 - 30° superior to the occlusal plane[14,15]. The button connected to the wire was bonded to the distal surface of the right mandibular second molar. Previous studies have reported no significant differences in miniscrew stability or clinical outcomes between immediate loading and delayed loading following miniscrew insertion[16]. To minimize patient discomfort, a short waiting period was allowed before initiating orthodontic traction, considering soft tissue healing at the surgical site. Two weeks after miniscrew placement, traction was initiated in the posterosuperior direction by connecting a lingual button to the miniscrew using an elastic chain. Fig. 3 schematically illustrates the biomechanical force system applied during this traction procedure. The elastic chain was connected from a miniscrew placed in the posterosuperior region of the mandibular ramus to a button bonded to the distobuccal surface of the mandibular second molar. This configuration generated a traction force composed of vector components in the occlusal, buccoposterior, and linguoposterior directions, resulting in an overall posterosuperior force. The direction of this force was intentionally designed to approximate the line of action through the estimated center of resistance of the tooth, aiming to facilitate controlled uprighting and eruption without inducing undesirable mesial tipping or excessive extrusion.
Fig. 4 shows a clinical photograph taken at the time of miniscrew placement and a panoramic radiograph obtained two months after initiating traction. (A) shows an intraoral photograph demonstrating a 1 cm incision along the external oblique ridge, extending posterosuperiorly from the occlusal plane level, for miniscrew insertion. The impacted mandibular second molar was exposed superiorly using electrocautery (bovie), and a lingual button was attached to its distal surface. Subsequently, the wire connecting the miniscrew was exposed, and suturing was performed. Additionally, bands with triple tubes were placed on the maxillary first molars to facilitate distal movement using headgear after extraction of the second molars. Furthermore, a lingual arch (LA) was initially applied to the mandibular arch to prevent distal tipping of tooth #46; however, it was later replaced with a band fitted with a twin tube to allow the application of a box loop for uprighting.
Eight months after the start of traction, the crown was intraorally exposed. The lingual button was repositioned onto the occlusal surface, and a 0.017 × 0.025- inch TMA box loop was applied to adjust the traction direction toward the bucco-occlusal side (Fig. 5). After 11 months of treatment, the right mandibular second molar reached the occlusal plane (Fig. 6). Fig. 7 shows a clinical photograph and panoramic radiograph taken after the completion of orthodontic treatment, demonstrating the complete eruption of the mandibular left and right second molars as well as a stable posterior occlusal relationship. In addition, the forward mandibular growth observed during the treatment period contributed to the improvement of the anteroposterior skeletal relationship, thereby facilitating the establishment of a Class I molar relationship.
The final clinical evaluation was performed 13 months after initiating traction. The right mandibular second molar was fully positioned in the occlusal plane, and tooth axis inclination improved by approximately 70°. Root resorption was not observed during the treatment, although soft tissue overgrowth around the miniscrew site occurred and was surgically removed. Alveolar bone height recovered to normal levels. Gingival health and functional occlusion remained stable throughout the treatment. The patient reported restoration of masticatory function without pain or discomfort during bilateral mastication. Table 1 presents the pre- and post-treatment cephalometric measurements. Skeletal Class II discrepancy was improved through mandibular growth and distalization of the maxillary first molars, accompanied by a reduction in upper and lower lip protrusion.
Case 2
A 14-year-old boy presented with impaction of the right mandibular second molar. An anterior crossbite was observed in the left maxillary lateral incisor, and the mandibular right second molar was completely impacted with no visible crown (Fig. 8). Panoramic radiography showed a mesially inclined impaction of the mandibular right second molar, with an odontoma superiorly positioned and a developing third molar posterior to it. Three-dimensional reconstructed images generated by segmentation using Medical Design Studio in Invivo 6 (version 6.0; Anatomage) based on CBCT clearly demonstrated the positional relationship and angulation between the impacted mandibular second molar and the adjacent first molar (Fig. 9). The crown of the mandibular right second molar was positioned lingually and inferiorly to the mandibular right first molar. Radiographic evaluation revealed no root resorption of the first molar. However, all three roots of the impacted second molar exhibited distal curvature, and the apex of the lingual root was in close proximity to the lingual cortical bone, creating an abnormal anatomical position extraosseously, thus making spontaneous eruption unlikely. Additionally, the third molar was impacted posterior to the second molar with a more severe lingual inclination. The patient was diagnosed with skeletal Class III malocclusion accompanied by mandibular prognathism (Table 2). Clinical examination revealed lingual tipping of the anterior mandibular teeth, indicating dental compensation due to skeletal disharmony. The canine relationship was Class I, and the molar relationship was Class III.
Due to skeletal limitations, it was difficult to achieve complete correction of the overall malocclusion. Therefore, after thorough consultation with the patient and guardian, a limited orthodontic treatment goal was established, focusing on the eruption of the mandibular right second molar and the correction of the anterior crossbite of the maxillary left lateral incisor. Accordingly, the anterior crossbite was planned to be corrected through segmental orthodontic treatment involving only the maxillary arch. Conventional orthodontic appliances have limited ability to generate adequate posterosuperior traction for the right mandibular second molar. Therefore, a miniscrew was placed in the mandibular ramus to effectively control and adjust the traction pathway. Considering the curvature of the root apex, the initial traction was planned in the buccal and posterior directions, followed by traction toward the occlusal plane. First, an incision was made distal to the right mandibular first molar to remove the odontoma located superior to the impacted second molar. An orthodontic button with an attached wire was bonded to the buccal side of the occlusal surface. To secure the eruption pathway, the mandibular right third molar was extracted. Subsequently, an orthodontic miniscrew (1.8 × 10.0 mm; Ortholution) was placed in the mandibular ramus region, approximately 4 - 5 mm superior to the occlusal plane, and inclined at 30 - 35° relative to the sagittal plane and 10 - 15° superiorly relative to the occlusal plane. However, to minimize patient discomfort and facilitate soft tissue healing, traction was initiated 2 weeks after miniscrew placement in the present cases. Two weeks after the miniscrew placement, traction was initiated in the buccal and posterior directions by connecting the miniscrew and button to an elastic chain (Fig. 10). However, the patient returned one month after insertion with the miniscrew dislodged. This was attributed to insufficient insertion depth and the presence of residual unhealed space following the extraction of the third molar. Therefore, the miniscrew was reinserted at a slightly more horizontal angle, approximately 1 mm superior to the originally planned location.
Three months after the start of traction, the button was repositioned at the center of the occlusal surface to adjust the traction direction occlusally (Fig. 11). After six months of traction, the mandibular second molar successfully erupted into the occlusal plane. For retention purposes, the miniscrew and tooth were passively connected for an additional month and subsequently removed, at which time the soft tissue overgrowth around the miniscrew site was surgically excised. Fig. 12 demonstrates a stable posterior occlusion. Although the crossbite of the maxillary left lateral incisor was resolved, residual mandibular asymmetry and crowding resulted in some occlusal spacing. No significant skeletal changes were observed after orthodontic treatment; however, lingual inclination of the maxillary anterior teeth was noted.
The final clinical evaluation was conducted eight months after initiating traction. The mandibular right second molar moved by approximately 9.0 mm, and the tooth axis inclination improved by approximately 30°. Radiographic evaluation confirmed that the tooth had reached an appropriate occlusal position and that axial alignment had improved. Additionally, alveolar bone height recovered to normal levels. Clinically, gingival health and functional occlusion remained stable. The patient reported normal masticatory function without pain or discomfort during bilateral mastication. Table 2 presents the pre- and post-treatment cephalometric measurements. While no substantial skeletal changes were observed, a mild lingual inclination of the mandibular incisors was evident, suggesting limited dentoalveolar adaptation during the course of treatment.
Discussion
These cases demonstrate successful orthodontic traction of mandibular second molars presenting with complex anatomical impactions, including severe horizontal impaction, root curvature, and cortical bone interference, using miniscrews placed in the mandibular ramus area. Both cases successfully achieved the common goal of orthodontically erupting the impacted mandibular second molars; however, due to differences in skeletal characteristics and initial conditions, the degree of skeletal improvement and the scope of orthodontic objectives varied between the two cases. In Case 1, although the orthodontic objectives of eruption and proper occlusal alignment of the impacted mandibular second molars were successfully accomplished, cephalometric analysis indicated favorable mandibular growth, which contributed to a slight improvement in the ANB angle (from 6.1° to 4.8°), thereby facilitating skeletal correction and supporting the overall orthodontic treatment. This limited improvement likely reflects the difficulty in resolving established skeletal discrepancies through orthodontic treatment alone. Nevertheless, partial improvement in molar relationships and reduction of upper lip protrusion resulted in meaningful clinical improvements in aesthetics and function. In Case 2, significant mandibular growth and existing dental compensation in the mandibular dentition posed limitations for fully correcting the skeletal malocclusion through orthodontics alone. Therefore, orthodontic objectives were set in consultation with the patient and guardians from the beginning of treatment, specifically targeting proper occlusal alignment of the impacted mandibular right second molar and resolution of the crossbite of the maxillary left lateral incisor, both of which were successfully achieved.
Given the difficulties in precisely controlling the direction and magnitude of orthodontic forces when performing traction or uprighting of impacted second molars, conventional orthodontic appliances alone are often insufficient. Therefore, previous studies have proposed alternative approaches, such as surgical uprighting or third molar substitution[9,10,17]. In these cases, surgical uprighting was also considered; however, concerns regarding potential root resorption or a poor prognosis arose because of anatomical factors, such as root curvature, cortical bone contact, and severe horizontal impaction.
Traditional non-invasive orthodontic appliances (e.g., lingual arch or modified lingual arch) typically utilize the first molars as additional anchorage to guide the eruption of mandibular second molars. However, in cases where the second molars are severely mesially inclined or horizontally impacted, these methods rely on tooth-borne anchorage, potentially resulting in anchorage loss or unwanted movements of adjacent teeth. Furthermore, complicated force delivery pathways make it challenging to precisely control the direction and magnitude of traction. In the present cases, miniscrews placed in the mandibular ramus were employed as direct anchorage to overcome these limitations. Traction using miniscrews can be performed by directly connecting NiTi closed-coil springs or cantilever mechanics to the miniscrews and impacted teeth. Cantilevers provide a simple, statically determined force system and effectively control side effects commonly observed with tooth-borne anchorage[ 18]. However, activation and re-adjustment become challenging when there is limited space available for appliance placement. Additionally, NiTi closed-coil springs can also be difficult to manage, particularly when soft tissue overgrowth and bleeding around miniscrews obscure visibility, further complicating the activation or re-adjustment process. In contrast, closed traction using elastomeric chains and lingual buttons enables intuitive and precise control over the magnitude and direction of traction forces, with the added advantage of delivering gradual and gentle forces. Furthermore, elastomeric chains are easily activated and replaced, allowing clinicians to manage the appliance effectively even under conditions of limited visibility due to soft tissue proliferation. A previous study also reported no significant differences between NiTi closed-coil springs and elastomeric chains regarding tooth movement rate, tipping, rotation, and root resorption[19]. Therefore, traction using elastomeric chains and lingual buttons was adopted in the present cases.
Another important consideration in miniscrew-assisted traction is the choice between open and closed surgical exposure. A previous randomized controlled trial reported that patients treated with closed exposure experienced more pain and discomfort during active orthodontic traction; however, there were no clinically significant differences between open and closed exposure techniques in terms of total treatment duration, final tooth alignment, or periodontal outcomes[20]. Accordingly, in the present report, open exposure was selected in Case 1 because the impacted tooth was positioned relatively less deeply, facilitating surgical access and clear visibility, while closed exposure utilizing miniscrew-assisted traction was performed in Case 2. Miniscrew anchorage methods can be classified as direct or indirect. Indirect anchorage, in which force is transmitted indirectly through the intermediate teeth, can complicate force delivery pathways, resulting in difficulties in controlling the direction and magnitude of traction. Previous studies have reported potential unintended occlusal changes due to the movement of indirect anchorage teeth[21]. Therefore, we selected direct anchorage for these cases.
The ideal placement site for ramus miniscrews is the midpoint between the external and internal oblique ridges on the ascending ramus, approximately 5 - 8 mm superior to the occlusal plane. This position provides sufficient depth and thickness for the ramus bone, enabling straight-line traction without occlusal interference[3]. Anatomically, this region offers suitable conditions for miniscrew placement owing to its abundant cortical bone and its adequate distance from the major neural structures[13]. Such anatomical characteristics provide clinically favorable conditions for stable anchorage and control of the traction direction, making ramus miniscrews particularly effective for the orthodontic traction of deeply and horizontally impacted mandibular second molars. For successful tooth uprighting, accurate identification and removal of interfering factors, such as third molar pressure or cortical bone obstacles, which commonly cause impaction, must precede treatment[3]. Therefore, in both cases, the third molars were extracted before orthodontic traction to effectively remove these obstructions and facilitate efficient traction using miniscrews.
Objective and quantitative analytical tools are required for accurately evaluating treatment outcomes. Three-dimensional CBCT-based analyses can effectively visualize and confirm positional relationships of teeth, and accurately evaluate specific anatomical factors, such as root morphology of adjacent teeth, cortical bone thickness, and proximity to vital anatomical structures, including the mandibular canal, during miniscrew placement[6]. In particular, in Case 1, although no radiographic signs of root resorption were observed in the adjacent mandibular first molar, the segmented three-dimensional image showed a relatively thin distobuccal root, suggesting that the severe impaction of the mandibular second molar might have influenced the root morphology or development of the adjacent tooth. This highlights the importance of carefully evaluating the potential anatomical influence of impacted teeth on adjacent teeth during treatment planning. Similarly, in Case 2, segmented three-dimensional images revealed that the presence of an odontoma and the lingual curvature of the second molar root might have significantly contributed to the impaction. In addition, CBCT analysis was utilized to determine the appropriate miniscrew insertion site and depth, optimal insertion angles relative to the sagittal and occlusal planes, and the direction of traction forces, as well as to evaluate cortical bone thickness at the insertion site and proximity to critical anatomical structures such as the mandibular canal. Thus, three-dimensional CBCT-based analyses are particularly useful for accurately identifying the spatial relationships of complex anatomical factors, such as odontomas and root curvature, and for determining optimal miniscrew insertion sites, angles, and traction directions.
In the present cases, segmentation-based three-dimensional reconstruction using in vivo software facilitated a clear understanding of the spatial relationships between the impacted teeth and adjacent anatomical structures, such as the tooth roots and cortical bone, which helped determine the traction direction and anchorage positions. Meanwhile, the clinical application of ramus miniscrews requires consideration of the insertion site, the biomechanical characteristics, and soft-tissue management[9]. Miniscrews in the ramus area were inserted perpendicularly (90°) to the bone surface[22], and the traction angle between the miniscrew and button was set at 110 - 120° to minimize mechanical stress during traction and prevent anchorage failure[16]. Additionally, to minimize soft-tissue irritation and facilitate oral hygiene management, maintaining a minimum clearance of 5 mm between the screw head and the surrounding soft tissue is recommended. Each miniscrew should have a minimum diameter of 1.5 mm, and early management of gingival inflammation is advised[12].
In both cases presented in this report, inflammatory soft tissue overgrowth occurred around miniscrews and adjacent orthodontic appliances. Such soft tissue overgrowth can adversely affect the long-term stability of miniscrews, increase patient discomfort, and reduce overall treatment efficiency. In these cases, inflammatory soft tissue overgrowth was managed by periodic soft tissue trimming using electrocautery and meticulous oral hygiene care. Previous studies have identified bacterial plaque accumulation and local irritation caused by orthodontic appliances as major aggravating factors of soft tissue overgrowth, emphasizing that eliminating these factors is critical for alleviating and preventing inflammatory soft tissue symptoms[23]. Standardized protocols for soft tissue management include periodic soft tissue trimming using electrocautery or diode lasers, individualized oral hygiene instruction, and plaque control programs. Additionally, special caution is required during orthodontic treatment in patients taking medications such as cyclosporin, nifedipin, and phenytoin, as these medications significantly increase the risk of gingival overgrowth. Therefore, clinicians need to apply such protocols systematically, tailored to the individual patient’s clinical situation and medication history, to effectively manage soft tissue overgrowth and associated inflammation.
Opinions regarding orthodontic anchorage using miniscrews in adolescent patients vary; however, previous studies have reported high success rates and excellent anchorage stability of miniscrews, even in adolescents, and differences in orthodontic force loading timing did not significantly influence miniscrew stability[24]. Moreover, the mandibular ramus area, characterized by thicker cortical bone that enhances primary stability[19] and maintains a safe anatomical distance from vital nerve structures[13,14], may further reduce risks such as insufficient anchorage or premature loss of miniscrews associated with lower bone density in growing patients. In addition, the potential risks and anatomical considerations associated with miniscrew placement were thoroughly explained to the patient and guardian in advance, and the procedure was performed with their full understanding and consent. Therefore, as demonstrated in these cases, ramus miniscrews can be considered clinically effective and safe anchorage options for adolescent patients requiring orthodontic traction of impacted second molars.
Nonetheless, for the successful clinical application of ramus miniscrews, it is essential to accurately determine the appropriate insertion site and traction direction based on precise radiographic assessments and have a thorough understanding of the anatomical structures prior to treatment. Additionally, more stable clinical outcomes can be anticipated when proper management practices are implemented, such as considering soft tissue interactions, maintaining oral hygiene, ensuring adequate miniscrew insertion depth to prevent loosening or failure, periodically evaluating anchorage stability, and meticulously adjusting the magnitude and direction of the orthodontic force.
Summary
These cases suggest that orthodontic traction using miniscrews placed in the mandibular ramus region can be an effective clinical approach for managing anatomically complex impactions of the mandibular second molars. By leveraging the anatomical characteristics of the ramus area, miniscrews can overcome limitations related to anchorage stability and traction direction, thereby facilitating efficient tooth movement and appropriate tooth axis uprighting. However, precise anatomical evaluation before treatment and careful management throughout the treatment process are essential to maximize the therapeutic effectiveness and minimize potential complications.
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