Distalization Methods for Maxillary Molars Utilizing Temporary Anchorage Devices (TADs): A Narrative Review

Abstract

Class II malocclusions, characterized by the mesial positioning of the maxillary molars relative to the mandibular molars, are among the most frequently encountered orthodontic issues. One of the widely adopted non-extraction approaches for addressing this malocclusion is maxillary molar distalization, which has been utilized for decades to create space within the dental arch. Historically, extraoral appliances such as headgear were commonly employed. However, with technological advancements, intraoral distalization devices, particularly those incorporating temporary anchorage devices (TADs), have gained prominence due to their compact size, not being visible externally, and improved patient acceptance. These appliances offer significant advantages, including being less invasive compared with extraction-based camouflage treatments, being more readily accepted by patients due to the absence of extraction spaces, and not requiring the complex biomechanical principles involved in extraction-based methods. TADs have revolutionized distalization techniques by providing superior anchorage control, reducing treatment duration, and offering a straightforward, patient-friendly application. The purpose of this comprehensive narrative review is to focus specifically on intraoral distalization techniques utilizing TADs, summarizing their efficacy and outcomes in the management of Class II malocclusions as reported in clinical studies over the past three decades.

1. Introduction

According to Angle [1], normal occlusion is characterized by the arrangement of the upper and lower teeth in a smooth curve that is in harmonious alignment. Angle identified the first molars as the most reliable reference points for classification, basing sagittal relationships on their positions. Class II malocclusion is defined as the condition where the lower first molar is positioned more distally relative to the upper first molar [1]. In Graber’s approach [2], the treatment of Class II malocclusions is guided by fundamental principles: the severity of the malocclusion, the patient’s growth stage, and the etiology of the condition. Treatment options include growth modification, orthognathic surgery, and camouflage therapy.

Contemporary orthodontic treatment approaches for sagittal discrepancies in the dental arches, particularly Class II malocclusions, prioritize noninvasive orthodontic methods that can be executed without the necessity for permanent tooth extractions [3]. In this regard, the utilization of various orthodontic appliances through different methods that diminish or even eliminate the need for tooth extractions is a noteworthy phenomenon [4]. Camouflage treatment is a therapeutic approach aimed at achieving acceptable occlusion and aesthetic appearance without inducing skeletal changes in the patient. This treatment can be performed with or without tooth extraction [5]. In non-extraction camouflage treatments, distalization of the molars can be employed to create the necessary space [5].

Maxillary molar distalization (MMD) has been recognized as an alternative non-extraction treatment option in cases of mild to moderate sagittal discrepancies [6,7]. Although the intraoral appliances traditionally used for MMD eliminate the need for patient compliance, they may also lead to undesirable effects such as distal tipping, crown rotation, and anchorage loss, resulting in mesial movement of the premolars, flaring of the maxillary incisors, and increased overjet [8]. It has been reported that the use of skeletal temporary anchorage devices (TADs) during MMD provides resistance to reactive forces [9] and that achieving direct anchorage with these devices eliminates the adverse effects, such as mesial tipping and anterior tooth proclination, caused by the loss of anchorage due to the reactive forces generated during MMD [6,10]. Miniscrews, when used as TADs, have gained widespread acceptance due to their ease of placement and removal, their ability to be loaded immediately, and their cost-effectiveness [11].

Although numerous studies have reported the efficacy of TADs, which can be placed in interradicular alveolar areas such as buccal or palatal regions or in extra-radicular areas such as the infrazygomatic region, providing three-dimensional tooth movement with minimal anchorage loss, clinical evidence regarding the treatment effects of these mechanics remains unclear [12,13]. Consequently, conventional intraoral molar distalization appliances such as the Distal Jet [14] and pendulum [15], which provide effective distalization while replacing headgear that requires patient compliance, raise aesthetic concerns, and have been used for many years [13,16], continue to be utilized for the purpose of distalizing maxillary molars.

A review of the literature reveals that, in response to increasing aesthetic demands and the necessity for effective and stable outcomes, various intraoral molar distalization appliances have evolved over time [17,18], while technological advancements have further introduced the use of clear aligners produced through three-dimensional printing for distalization [19], thereby providing orthodontists with a wide array of treatment options for achieving molar distalization. To the best of our knowledge, there is no study in the literature that comprehensively addresses the numerous MMD appliances that have been developed with various biomechanical design approaches and reported using different application methods.

We believe that the complexities arising from this versatility in MMD may be the reason for the unresolved issues mentioned. In light of the above, this study provides a comprehensive overview of all reported appliances used in MMD, along with an analysis of their various methods of application. Thus, this narrative review aims to provide orthodontists with valuable clinical insights to guide their selection of the appropriate method and appliance when planning for MMD.

2. Materials and Methods

2.1. Literature Search

A literature review was conducted to prepare this study, utilizing databases such as PubMed, Scopus, and Google Scholar. Searches were performed using specific keywords, including “Class II malocclusion”, “extraoral molar distalization”, “intraoral molar distalization”, “skeletal anchorage”, “TADs”, “camouflage treatment”, “distalization appliances”, and “tooth-tissue-supported”. To illustrate the development of distalization techniques over time, appliances were organized and discussed under appropriate headings in accordance with our classification.

2.2. Study Selection

Articles not meeting inclusion and exclusion criteria were excluded from the review. Of the articles initially screened, a total of 24 articles met the inclusion criteria and were incorporated into the study.

Inclusion criteria were as follows: (1) prospective cohort studies, randomized controlled trials, and non-randomized controlled trials conducted within the last 20 years and (2) studies reporting clinically significant outcomes. Exclusion criteria were as follows: (1) non-clinical studies; (2) retrospective studies; (3) case reports; and (4) articles lacking information on parameters such as the distalization pattern in molar teeth, treatment duration, applied force, and anchorage loss.

Maxillary molar distalization methods are generally divided into two categories: extraoral and intraoral mechanics. In this narrative review, extraoral appliances are briefly discussed, while the primary focus is on intraoral distalization methods. These intraoral approaches are categorized into two main types: tooth tissue-supported appliances and skeletal anchorage-supported appliances, each reviewed in detail under specific headings and subheadings.

3. Extraoral Molar Distalization Methods

In the United States, headgear appliances were commonly used in the mid-1940s. The effects of headgear on the craniofacial complex were intended to both inhibit maxillary growth and distalize upper molars [20].

Headgear is categorized into three groups: occipital, cervical, or a combination of both based on their points of support (Figure 1). The cervical headgear, also known as the Kloehn type headgear, after its developer, is the most commonly used type. The molar distalization achieved with this appliance results in extrusion and posterior rotation of the mandible. This extraoral appliance is particularly suitable for cases of skeletal deep bite [21]. In patients with a vertical growth pattern and posterior mandibular rotation, occipital headgear is recommended [22].

Occipital headgear is associated with distalization and intrusion of the molars, cervical headgear with distalization and extrusion of the molars, and combined headgear with distalization without vertical movement of the molars [22].

Headgear has been an effective treatment for the correction of Angle Class II malocclusions. The cooperation of children and adolescents plays a major role in achieving the desired results, but cooperation is often difficult to verify [23].

4. Intraoral Molar Distalization Methods

Intraoral distalization methods were developed to overcome the disadvantages of extraoral molar distalization techniques. The primary advantages of these appliances are that they do not rely on patient compliance and they minimize aesthetic concerns [24].

Intraoral distalization methods are divided into two main groups, tooth tissue supported and skeletal supported, according to the anchorage area.

4.1. Tooth Tissue-Supported Intraoral Molar Distalization Methods

In tooth tissue-assisted intraoral distalization methods, the posterior teeth are typically distalized using the support of the premolar teeth and an acrylic Nance button positioned on the anterior palate.

4.1.1. Acrylic Cervical Occipital (ACCO) Appliance

The ACCO appliance, designed by Bernstein [25], is a removable molar distalization device. It is supported by Adams clasps attached to an acrylic plate for retention, along with a labial arch. Two spring systems, known as finger springs, are bent around the molars and activated to apply a force [26].

4.1.2. Super-Elastic Nickel–Titanium (Ni-Ti) Open Coil Springs

Ni-Ti open coil springs have gained large popularity for distalization purposes due to their good spring-back action and light continuous force delivery. They produce about 100 gm of force when they are compressed by 10 mm between the first premolars and first molars on a 0.016 × 0.022 inch stainless steel wire [27].

Öztürk et al. [28] showed that compressed Ni-Ti coil springs were effective in moving maxillary first molars distally, particularly in the treatment of noncooperative patients with Class II molars malocclusion. However, molar distalization occurred at the expense of increased crown tipping and anchorage loss at the anterior dental region [28].

4.1.3. Transpalatal Arch

The transpalatal arch (TPA) is a widely used appliance in orthodontic treatments and, in addition to several other functions, including stabilization and anchorage, correction of molar rotation, vertical molar control, and treatment of unilateral molar crossbites, it is also an alternative to the other treatment regimen for the correction of the molar relationship when the maxillary molars present a slight unilateral Class II discrepancy [29].

An intraoral occlusal view of the transpalatal arch is shown in Figure 2.

4.1.4. Jones Jig Appliance

The Jones Jig appliance is inserted buccally and acts through a nickel–titanium spring anchored in the second premolars. Patel et al. [30] compared the dentoalveolar changes in Class II patients treated with Jones Jig and pendulum appliances. In conclusion, the Jones Jig group showed greater mesial inclination and extrusion of the maxillary second premolars. The mean amounts and monthly rates of first molar distalization were similar in both groups [30].

4.1.5. Distal Jet Appliance

The Distal Jet appliance was developed to prevent the rotational and tipping movements often observed in molars during intraoral distalization methods. The Nance appliance serves as the anchorage unit. Distalization is achieved through Ni-Ti springs attached to a thick wire, which is embedded on one side in the Nance acrylic and on the other side in the palatal tube of the molar band. Activation is performed by compressing the Ni-Ti springs toward the first molar. Pereira et al. [31] compared the maxillary dentoalveolar changes in patients treated with three distalization force systems (Jones Jig, Distal Jet and First Class appliances) using digitized models. The Distal Jet appliance promoted smaller mesial displacement of the premolars and greater expansion of the posterior teeth [31].

An intraoral occlusal view of the Distal Jet appliance is shown in Figure 3.

4.1.6. First Class Appliance

The First Class appliance was developed by Fortini et al. [32] to address the issue of anchorage loss associated with the Distal Jet appliance. This device comprises two components, palatal and buccal, which are connected by Ni-Ti springs positioned between the premolars and molars. Pereira et al. [31] compared the maxillary dentoalveolar changes in patients treated with three distalization force systems (Jones Jig, Distal Jet, and First Class appliances) using digitized models. In conclusion, similar amounts of distalization were promoted, with some degree of undesirable effects. The First Class promoted the smallest rotation of maxillary molars and had the shortest treatment time.

4.1.7. K-Loop Appliance

The K-Loop was constructed according to the description by Kalra [33] for upper molar distalization. The K-Loop is made from 0.017” × 0.025” TMA wire and located between the upper first molar and the first premolar. Marure et al. [34] used K-Loop, pendulum, and Distal Jet appliances to evaluate the skeletal, dental, and soft-tissue changes produced. The K-Loop was activated to produce 200 g of force. After placement of the appliances, patients were monitored every 4 weeks, and the K-Loop was activated every 6 weeks. When the molars achieved a Class I occlusion, the appliance was replaced with a Nance button for retention. In conclusion, all three distalization techniques in growing children produced significant effects on the anchor unit. There was a significant bite opening, proclination of the maxillary incisors, and increase in the cant of the upper lip [32]. To prevent anchorage loss, the use of cervical or occipital headgear was recommended. The K-Loop appliance offers advantages such as ease of fabrication, hygienic design, and patient comfort [32].

An illustrated model of the K-Loop appliance is shown in Figure 4.

4.1.8. Wilson 3D Bimetric Molar Distalization Arch

Wilson [35] introduced the 3D bimetric molar distalization arch, which combines a 3D lingual arch with Class II elastics. The maxillary arch wire, measuring 0.022 inches in thickness, is passively inserted into the bracket slot. Hooks are positioned posteriorly for attaching the elastics, and omega bends are located at the entrance of the molar tube. An opening spring is placed between the omega bends and the molar tube to facilitate molar distalization. Class II elastics are employed to prevent the protrusion of the anterior teeth. Altug-Atac et al. [36] compared the dentofacial effects of an intraoral technique, the three-dimensional bimetric maxillary distalizing arch, with an extraoral technique, cervical headgear, in subjects requiring maxillary molar distalization. The result showed that while the techniques are both effective in distalizing the maxillary molar teeth, the distalization time was significantly shorter with the 3D bimetric molar distalization arch [36].

4.1.9. Veltri Appliance

The Veltri appliance was first introduced by Veltri [37] in 1999. This appliance uses an expansion screw placed in the palatal region to exert an active distalization force. The screw arms are soldered to the bands on the molars and first premolars. To enhance anchorage, acrylic is added in the palatal region between the palatal bar and the premolar bands. Screw activation is recommended at a rate of two half-turns per week. Oruç et al. [38] examined the clinical efficacy of Veltri and First Class appliances. In conclusion, although Veltri and First Class appliances provided a similar amount of distalization in a similar amount of time, recurrence was observed in the Veltri group during the reinforcement period. In addition, a loss of anchorage was observed more in the Veltri group [38].

4.1.10. Frog Appliance

The Frog appliance was designed by Walde [39] in 2003. In this appliance, the anterior arms of an expansion screw placed in the palatal region are soldered to the bands on the first premolars, while the acrylic Nance appliance provides anchorage support. The posterior arms of the screw consist of two springs that exert an active force and are inserted into the molar tubes. Burhan et al. [40] evaluated the efficiency of the Frog appliance (FA) alone or in combination with headgear for distalizing the maxillary molars. In conclusions, the Frog appliance can effectively distalize the maxillary molars, but this distalization is associated with some unfavorable changes. Nighttime use of high-pull headgear combined with the Frog appliance can reduce these unfavorable changes and improve treatment outcomes [40].

4.1.11. Carriere Distalizer

Luis Carriere [41] introduced the Carriere Distalizer in 2004, later renaming it the Carriere Motion 3D. The appliance consists of two rigid rods attached bilaterally to the maxillary canine and first molar teeth. Its primary objective is to establish a Class I molar relationship in highly cooperative patients who initially present with a Class II molar relationship, prior to beginning leveling and alignment with fixed appliances [41].

Yin et al. [42] evaluated the treatment effectiveness of the Carriere Distalizer in comparison with Class II intermaxillary elastics and Forsus. In conclusion, there was no clinically significant skeletal correction induced by the Carriere Distalizer in growing patients. The Carriere Distalizer can be applied to treatment of mild to moderate Class II dental malocclusion over 6 months on average, although the total treatment time may be prolonged due to various side effects [42].

An intraoral view of the Carriere Distalizer is shown in Figure 5.

4.1.12. Intraoral Bodily Molar Distalizer

The intraoral bodily molar distalizer appliance was introduced in 2000 by Keleş and Sayinsu [43]. The anchorage unit was provided by a Nance appliance, while the distalization unit consisted of springs made from 0.032 × 0.032-inch TMA wire. One of the loops in the springs generated the force required for distalization, while the other loop applied a counterforce to prevent distal tipping of the tooth.

Ijaz et al. [26] compared the clinical dental effects of two different molar distalization devices (the intraoral bodily molar distalizer and the ACCO), involving 29 patients having Class II malocclusion with low angle or normal angle. The appliances were used for the mean period of 11 months and 7.2 months respectively. Measurements were made from the lateral cephalogram tracings before and after molar distalization. The results showed that with I.B.M.D maxillary first molar distalized bodily on an average of 4.5 mm and the mean anchorage loss was 4.75 mm. In I.B.M.D the distalization spring being composed of square sectioned TMA wire distalized the maxillary first molar bodily without any rotation. With A.C.C.O mean distal movement of the maxillary first molar was 4.38 mm with mesial tip of 3.03 degree. However, anchorage loss with A.C.C.0 appliance was less being 2.11 mm on an average due to the use of the headgear [26].

4.1.13. Pendulum Appliance

The pendulum appliance is used for the treatment of Class II malocclusions, utilizing the Nance button for anchorage. The pendulum employs two hoops made from 0.032-inch diameter round TMA wire capable of applying a continuous, light force. The pendulum springs are used parallel to the palatal midline, with a mean force of about 250 g. Patel et al. [30] compared the dentoalveolar changes in Class II patients treated with pendulum and Jones Jig appliances. As a result, the maxillary first molars showed distal tipping, distal movement, and a slight intrusion in both groups. The mean amount of distalization and the monthly rate of distal molar movement were statistically similar in the two groups [30].

An intraoral occlusal view of the Pendulum appliance is shown in Figure 6.

4.1.14. Keles Slider Appliance

Keles [43] introduced the Keles Slider, a parallel molar distalization appliance, in a study. To ensure force application close to the center of resistance, tubes were soldered over the molar bands and aligned parallel to the occlusal plane. Open Ni-Ti springs placed on the wire extending between the acrylic part and the tube generated a distalization force in the molars. Sayınsu et al. [44] utilized the Keles Slider in 17 patients to achieve unilateral molar distalization, observing an average distalization rate of 0.48 mm per month, totaling 2.85 mm. The first premolars exhibited 2 mm of mesial movement and 2.03 mm of extrusion, while the anterior teeth showed 1.32 mm of protrusion and 1.12 mm of extrusion. The mandibular incisors and mandibular molars erupted 0.83 and 0.95 mm, respectively. The Keles Slider distalized molars successfully to a Class I molar relationship [44].

4.2. Skeletal Anchorage-Assisted Distalization Methods

Anchorage loss is a common issue in intraoral molar distalization studies [45]. To address this, the use of miniscrews for anchorage support has gained prominence [46]. Miniscrews can be placed in various anatomical regions of the buccal and palatal areas to facilitate distalization.

4.2.1. Palatinal Miniscrew-Assisted Distalization Applications

The palatal region offers several advantages over other anatomical sites for miniscrew placement in the maxilla. These include the keratinized surface of the palate, the absence of frenulum attachments and mobile tissues, and a reduced risk of root contact [47]. To prevent anchorage loss during molar distalization, miniscrews have been incorporated into distalization appliances, either by modifying existing devices or by being included in original appliance designs.

Beneslider Appliance

Wilmes et al. [48] introduced the ‘Beneslider’ appliance for molar distalization, describing it as a modification of the miniscrew Keles Slider and Distal Jet appliances. In this appliance, anchorage is achieved using miniscrews placed in the palatal region in either an anteroposterior or right-left orientation. Stainless steel (SS) wire ‘Beneplates’ are passed through the grooves of the ‘Benetubes’, which are attached to the molar bands, allowing the applied force to pass through the molars’ centers of resistance. The appliance can apply a force ranging from 200 to 500 g, generated by compressing Ni-Ti springs using activation locks.

An intraoral occlusal view of the Beneslider appliance is shown in Figure 7.

Modified Lokar Appliance

Kaan [49] used a modified mini-implant-anchored Lokar appliance on 20 patients to evaluate its effectiveness. An activator tube soldered to the Lokar was positioned on the buccal side and attached to the molar band to ensure the force passed as close as possible to the center of resistance. Mini-implants were placed between the first molar and second premolar, serving as anchors, while the Ni-Ti coil springs on the Lokar appliance were activated to generate the distalization force. After 10.8 months of treatment, the results indicated a 3.28 mm distal movement and a 5.48° distal tipping of the molars. The author also noted that the distal movement of the upper incisors was insignificant and that the overjet values decreased due to a 0.93° distal tipping.

Miniscrew-Assisted Frog Appliance

Ludwig et al. [50] redesigned the modified Nance appliance, which serves as the anchorage unit in the Frog appliance, by incorporating miniscrews, and introduced this modification in 2011. Anchorage was achieved using two screws placed on either side of the median palatal suture, posterior to the intersection of the line connecting the distal contact points of the canine crowns in the rugae region with the midline. Aside from the modified anchorage unit, the rest of the appliance was constructed similarly to the conventional Frog appliance. It can be activated with a force of 200 g, and it has been reported that turning the Frog screw 3–5 times over a 4–5-week period results in an average distalization of 1–2 mm per month.

Modified Distal Jet Appliance

Cozzani et al. [17] investigated and compared the efficiency of two appliances for molar distalization, the modified Distal Jet and the traditional tooth-supported Distal Jet, for molar distalization and anchorage loss. In conclusion, the modified distal is an adequate compliance-free distalizing appliance that can be used safely for the correction of Class II malocclusions. In comparison with the traditional Distal Jet, the modified distal enables not only a good rate of molar distalization, but also a spontaneous distalization of the first premolars [17].

Modified Pendulum Appliance

Kircelli et al. [51] used a bone-supported modified pendulum appliance for molar distalization in 10 patients, placing an osseointegrated implant 7–8 mm posterior to the foramen incisivum for skeletal anchorage. After 7 months of treatment, the upper first molars exhibited 6.4 mm of distal movement and 10.9° of distal tipping, with distal movement also observed in the premolars, while no forward movement was noted in the incisors.

Similarly, Escobar et al. [52] applied a modified pendulum appliance supported by two miniscrews in the palatal region in 15 patients. After 7–8 months of distalization, they reported that the first molars demonstrated 6 mm of distal movement and 11.3° of distal tipping, the second premolars showed 4.85 mm of distalization and 8.6° of distal tipping, and the upper incisors exhibited 0.5 mm of retrusion and 1.27° of palatal tipping.

The modified pendulum appliance is shown in Figure 8.

Modified Palatal Anchorage Plate

The modified palatal anchorage plate was introduced to the literature by Kook et al. [53] in 2010. The modified palatal anchorage plate appliance was introduced to effectively distalize maxillary molars in adolescents [53]. It functions by rigidly attaching a palatal plate adapted to the curve of the palatal region in the transverse direction to the palatinal process of the maxilla, with one minivail on one side of the median palatal suture and two minivails on the other side. With three notches on the palatal plate, the direction of the vector that creates the distalization force can be adjusted differently. In this way, the distalization pattern can be modified according to the desired movement. Kook et al. [53] evaluated the treatment effects of maxillary posterior tooth distalization performed by a modified palatal anchorage plate appliance with cephalograms derived from cone-beam computed tomography. In conclusion, the maxillary first molar was distalized by 3.3 mm at the crown and 2.2 mm at the root level, with distal tipping of 3.4° [53].

Modified Keles Slider

The Keles Slider appliance was employed by Keles et al. [43] bilaterally with support from a palatal implant. An 8 mm long and 4.5 mm diameter osseointegrable titanium implant was placed in the palatal region for anchorage. Özdemir et al. [54] performed three-dimensional comparisons of changes occurring after maxillary first molar distalization with modified and tooth tissue-supported Keles Slider appliances. They reported that only dentoalveolar changes and maxillary first molar distalization were obtained in both appliance groups. Maxillary first molars moved more parallelly with the bone-supported Keles Slider appliance. Retraction of upper incisors and distalization of the upper canine and premolar teeth was observed in the skeletal anchorage group while distalization of the upper second premolars, protrusion of the upper incisors, and mesialization of the canine and first premolars were seen in the Keles Slider group. Significant increases in vertical dimension were observed in both groups.

The occlusal view of the modified Keles Slider appliance is shown in Figure 9.

4.2.2. Buccal Miniscrew-Assisted Distalization Applications

Distalization methods using miniscrews placed in the buccal interradicular area (Figure 10) result in less soft tissue irritation and greater patient comfort compared with applications in the palatal region [55]. However, placing miniscrews between the tooth roots introduces the risk of root contact during distalization in the sagittal direction, posing a potential disadvantage of the buccal position [56]. To minimize this risk, it has been suggested that miniscrews be placed at a 30°–40° angle to the long axis of the tooth [50]. Additionally, due to this concern, molar distalization with buccally applied miniscrews is recommended for Class II molar relationships requiring less distalization, typically up to 3 mm [57].

Bechtold et al. [58] studied to determine the effects of linear force vector(s) from interradicular miniscrews on the distalization pattern of the maxillary arch in adult Class II patients. Either single or dual miniscrews were inserted in the posterior interradicular area to deliver a distalizing force to the main archwire. The displacement patterns of the maxillary incisors and molars were measured and compared. As a result, significant distalization in the molars and incisors was shown in both groups. Significantly greater distalization and intrusion of the first molar and intrusive displacement of the incisor, together with significant reduction in the mandibular plane, were noted in the dual screw group, in contrast with the rotation of the occlusal plane in the single screw group [58].

4.2.3. Infrazygomatic Miniscrew-Assisted Distalization Applications

The infrazygomatic crest region (IZC) is a suitable anatomical site for the placement of miniscrews and mini-plates in the maxilla. It features the thickest cortical bone in the maxilla, second only to the mandible. Clinically, the IZC is palpable between the alveolar bone of the maxilla and the zygomatic process. In young individuals, it is typically located at the level of the second premolars and first molars, while in adults, it is generally found at the level of the first molars [59].

Maxillary molar distalization using the zygomatic plate as an anchorage unit provides a stable and effective method for the simultaneous distalization of both the first and second molars. The literature suggests that this approach minimizes undesirable dental side effects and achieves distalization without anchorage loss [60]. However, due to the anatomical location of the zygomatic region, the surgical procedure for mini-plate placement is more complex than that for other skeletal anchorage devices and should be performed by an experienced surgeon.

The IZC screw was first introduced in 2003 and was applied using a self-drilling method to the attached gingiva and the mobile mucosa border between the first and second maxillary molars. Since then, numerous researchers have proposed modifications to this technique [61].

Wu et al. [59] placed stainless steel IZC screws (Bioray, Taiwan) with a diameter of 2 mm and a length of 10 mm in the infrazygomatic region of 20 patients (16 female and 4 male) with a mean age of 12 ± 5 years. They used 0.019 × 0.025-inch stainless steel archwires between the lateral incisors and canines, with 4 mm high retraction hooks positioned in the same region. A force of 300 g was applied using Ni-Ti springs anchored to the IZC screws. This method enabled the distalization of the entire maxillary dentition [58,59].

Chang et al. [62] assessed the 6-month success rate of infrazygomatic crest bone screws relative to patient age, insertion angle, sinus penetration, and terminal insertion torque. In conclusion, both sinus penetration and IZC bone quality increased with age. Sinus penetration did not significantly affect the 6-month survival rate of the IZC TADs because the loss of bone quantity at the interface was offset by the age-related increase in bone quality at the IZC site.

An infrazygomatic mini-screw-assisted distalization applications are illustrated in Figure 11.

4.2.4. Maxillary Tuber Miniscrew-Assisted Distalization Applications

Maintaining anchorage in orthodontic treatments has always been a challenging objective. To address this, miniscrews are placed in various anatomical locations within the jawbones, one of which is the maxillary tuberosity (MT) [63]. The MT is the posterior extension of the maxillary bone, bordered mesially by the last molar tooth and the maxillary sinus and distally by the pterygopalatine fissure and the pyramidal process of the palatine bone [64]. While the cortical bone in this region is thinner and bone density is lower compared with other maxillary sites, it offers advantages such as a minimal risk of damage to the molar roots, a wide range of orthodontic tooth movements, and the possibility of en masse retraction of the upper teeth [65,66].

A sufficient number of prospective and randomized controlled clinical studies on distalization methods using maxillary tuberosity screws is lacking in the existing literature.

4.3. Distalization with Clear Aligner Systems

In recent years, aesthetics has become a significant requirement in orthodontic treatments due to the increasing number of adult orthodontic patients. Clear aligner technology was developed to meet this demand and has become highly popular. Today, there are numerous clear aligner manufacturers. Effective molar distalization can be achieved with clear aligner systems. Simon et al. [67] reported an 87% success rate for maxillary molar distalization with clear aligners, while Rossini et al. [68] also noted that maxillary molar distalization with clear aligners is among the most reliable movements, with an 88% success rate. When greater distalization is needed beyond the movement capacity of aligners alone, auxiliary elements should be added, as aligners may not suffice independently. Attachments, Class II elastics, and TAD support are examples of such auxiliaries.

Ravera et al. [69] conducted a retrospective study evaluating the effects of bilateral maxillary molar distalization with Class II elastics and attachment support in 20 adult patients. The average treatment duration was found to be 24.3 ± 4.2 months, with the first molars distalized by an average of 2.25 mm without tipping or vertical movement.

Figure 12 illustrates the use of Class II elastics with skeletal anchorage support for distalization with clear aligners.

5. Results

For intraoral MMD appliances, the type of anchorage used, the name of the appliance, the applied force, the duration and amount of distalization, the amount of anchorage loss, and recommendations are summarized in

Table 1. Intraoral distalization applications.

Study	Anchorage Type	Appliance Name	Movement Type of First Molars and Anterior Teeth	Force (g) (Unilateral)	Treatment Duration of Molar Distalization	Anchorage Loss (Measured as the Amount of Mesialization in the Upper Premolars Corresponding to Each 1 mm of Distalization in the First Molar)	Authors’ Recommendations
Ijaz et al. (2004) [26]	Tooth tissue-supported	ACCO appliance	4.38 mm distal movement of first molars and 2.2 mm protrusion of anterior teeth	300 g	11 months	0.5 mm of premolars	The face bow can also be bent to reduce extrusion in the molar tooth.
Öztürk et al. (2005) [28]	Tooth tissue-supported	Super-elastic Ni-Ti open coil springs	4.59 mm distal movement of first molars and 2.22 mm protrusion of anterior teeth	250 g	6.95 months	0.62 mm of premolars	The use of Class II elastics is recommended to support anchorage anteriorly.
Eyüboğlu et al. (2004) [29]	Tooth tissue-supported	Transpalatal arch	2.06 mm distal movement of first molars and 2.22 mm protrusion of anterior teeth	150 g	5 months	0.36 mm of premolars	TPA can be used in the unilateral distalization of maxillary molars.
Patel et al. (2009) [30]	Tooth tissue-supported	Jones Jig appliance	3.12 mm distal movement of first molars and 1.11 mm protrusion of anterior teeth	100 g	10.9 months	0.81 mm of premolars	Caution should be exercised as the appliance is prone to anchorage loss.
Pereira et al. (2021) [31]	Tooth tissue-supported	Distal Jet appliance	3.32 mm distal movement of first molars and 0.56 mm protrusion of anterior teeth	240 g	11.4 months	0.47 mm of premolars	Care should be taken to ensure that it expands the posterior teeth.
Pereira et al. (2021) [31]	Tooth tissue-supported	First Class appliance	2.98 mm distal movement of first molars and 0.51 mm protrusion of anterior teeth	240 g	8.2 months	0.55 mm of premolars	Orthodontic mechanics should be applied to correct the undesirable effects inherent in the use of conventional anchorage.
Marure et al. (2016) [34]	Tooth tissue-supported	K-Loop appliance	2.2 mm distal movement of first molars and 4.1 mm protrusion of upper anterior teeth	200 g	5 months	1.8 mm of premolars and protrusion of upper anterior teeth	The conventional distalization appliances can be substituted by TAD to prevent maxillary incisors proclination.
Altug-Atac et al. (2007) [36]	Tooth tissue-supported	Wilson 3D bimetric molar distalization arch	3.55 mm distal movement of first molars, 0.06 mm protrusion of upper anterior teeth, and 2.82 mm protrusion of mandibular anterior teeth	180 g	3.4 months	0.79 mm of premolars and anchorage loss in the mandibular dental arch due to Class II elastics	To achieve successful results, the effects of treatment modality on dentofacial structures need to be taken into consideration for each individual patient.
Oruç et al. (2024) [38]	Tooth tissue-supported	Veltri appliance	2.16 mm distal movement of first molars and 4.39 mm protrusion of anterior teeth	Distalization of the first molar by 0.5 mm per week was achieved by turning the screw twice per week.	4.2 months	2.28 mm of premolars	Anchorage loss should be considered in the clinical application.
Burhan et al. (2013) [40]	Tooth tissue-supported	Frog appliance	5.51 mm distal movement of first molars and 1.78 mm protrusion of anterior teeth	Distalization of the first molar by 0.5 mm per week was achieved by turning the screw twice per week.	7.4 months	0.49 mm of premolars	Nighttime use of high-pull headgear should be combined with the Frog appliance.
Yin et al. (2019) [42]	Tooth tissue-supported	Carriere distalizer	3.5 mm distal movement of first molars and 3 mm protrusion of upper anterior teeth	150–200 g from the Class II elastics	6.3 months	0.62 mm of premolars and anchorage loss in the mandibular dental arch due to Class II elastics	There is no clinically significant skeletal correction caused by the Carriere distalizer in growing patients.
Ijaz et al. (2004) [26]	Tooth tissue-supported	Intraoral bodily molar distalizer	4.5 mm distal movement of first molars and 3.85 mm protrusion of anterior teeth	230 g	7.5 months	1.05 mm of premolars	Demands anchorage reinforcement.
Patel et al. (2009) [30]	Tooth tissue-supported	Pendulum appliance	3.51 mm distal movement of first molars and 1.47 mm protrusion of anterior teeth	250 g	14.1 months	0.63 mm of premolars	Caution should be exercised as the appliance is prone to anchorage loss.
Sayinsu et al. (2006) [44]	Tooth tissue-supported	Keles Slider appliance	2.85 mm distal movement of first molars and 1.32 mm protrusion of anterior teeth	150 g	6 months	0.70 mm of premolars	Patients with palatally inclined maxillary incisors should be selected for treatment with distalization devices.
Wilmes et al. (2010) [48]	Skeletal supported (palatinal)	Beneslider appliance	4.6 mm distal movement of first molars	240 g	8 months	No anchorage loss	The benefit system is more secure and more comfortable for the clinician than the spider screw system.
Kaan (2007) [49]	Skeletal supported (palatinal)	Modified Lokar appliance	3.28 mm distal movement of first molars and 0.23 mm retrusion of anterior teeth	240 g	10.8 months	No anchorage loss (1.83 mm distalization of upper second premolar)	Transverse evaluation showed significant distopalatal rotation of the upper first molar. Caution should be exercised.
Shah et al. (2016) [70]	Skeletal supported (palatinal)	Miniscrew-assisted Frog appliance	3 mm distal movement of first molars	200 g	5 months	No anchorage loss	The Frog appliance is an effective, noninvasive, and compliance-free intraoral distalization appliance for achieving maxillary molar distalization.
Cozzani et al. (2014) [17]	Skeletal supported (palatinal)	Modified Distal Jet appliance	4.7 mm distal movement of first molars	240 g	9.1 months	No anchorage loss (2.1 mm distalization of upper second premolar)	The modified Distal Jet is a compliance-free distalizing appliance that can be used safely for the correction of Class II malocclusions.
Kircelli et al. (2006) [51]	Skeletal supported (palatinal)	Modified pendulum appliance	6.4 mm distal movement of first molars	250 g	7 months	No anchorage loss (5.4 mm distalization of upper second premolar)	The modified pendulum appliance is an effective, minimally invasive, and compliance-free intraoral distalization appliance for achieving both molar and premolar distalization without any anchorage loss.
Kook et al. (2014) [53]	Skeletal supported (palatinal)	Modified palatal anchorage plate	3.3 mm distal movement of first molars and 3.0 mm retrusion of anterior teeth	300 g	12.5 months	No anchorage loss (3.05 mm distalization of upper second premolar)	It is recommended that clinicians should consider using the modified palatal anchorage plate appliance in treatment planning for patients who require maxillary total arch distalization.
Özdemir (2013) [54]	Skeletal supported (palatinal)	Modified Keles Slider	3.58 mm distal movement of first molars and 0.53 mm retrusion of anterior teeth	300 g	10.5 months	No anchorage loss (3.42 mm distalization of upper second premolar)	The maxillary first molars can be moved in parallel without any anchorage loss using the bone-supported appliances.
Bechtold et al. (2013) [58]	Skeletal supported (buccal)	Buccal miniscrew	2.91 mm distal movement of first molars and 2.41 mm retrusion of anterior teeth	200 g	10.1 months	No anchorage loss	The dual-screw group demonstrated significantly greater molar distalization and intrusion, as well as incisor retraction, compared with the single-screw group.
Wu et al. (2018) [59]	Skeletal supported (infrazygomatic)	IZC screw	3.15 mm distal movement of first molars and 4.3 mm retrusion of anterior teeth	300 g	8 months	No anchorage loss	The anchorage of miniscrews implanted in the IZ crest is an efficient device for maxillary dentition distalization. Therefore, it is recommended that clinicians consider using the method in treatment planning for adult patients who require maxillary total dentition distalization.
Ravera et al. (2016) [69]	Clear aligner technique	Clear aligner technique	2.25 mm distal movement of first molars and 2.23 mm retrusion of anterior teeth	130 from the Class II elastics	24.3 months of total orthodontic treatment	No anchorage loss	Clinicians may consider incorporating Invisalign aligners into treatment plans for adult patients requiring 2 to 3 mm of maxillary molar distalization.

based on the available literature.

6. Discussion

Class II malocclusions can be subdivided into skeletal and dental subtypes. In skeletal Class II malocclusion, orthopedic and orthodontic corrections are typically pursued before growth and development are complete, while surgical approaches or camouflage treatments may be considered, depending on the severity of the malocclusion after growth has ceased [71,72]. In cases of dental Class II malocclusion, where no skeletal discrepancy is present, orthodontic correction is required to address the malocclusion. One of these corrective methods involves the distalization of the upper molars.

In orthodontics, the distalization of the upper molars is primarily achieved through extraoral and intraoral methods. Extraoral appliances such as headgear have been utilized in orthodontic practice for many years and have demonstrated effective results. However, in contemporary settings, the acceptability of extraoral appliances has declined due to aesthetic concerns [24]. One study reported complications associated with headgear use, including skin irritation, abnormal tension in neck muscles, and injuries to the face and eyes [73]. Beyond aesthetic concerns, these appliances rely on patient compliance, which can negatively impact treatment effectiveness from a clinician’s perspective. Consequently, challenges such as patient cooperation, associated complications, and difficulty in achieving a Class I molar relationship as patients age have led researchers to develop intraoral distalization methods [74]. Unlike headgear, these systems do not require extraoral support for distalization; rather, they apply continuous force while relying on adjacent teeth and tissues for support. As a result, anchorage loss in premolars and incisors is common. Furthermore, when the mesially shifted premolars and incisors are subsequently distalized, additional disadvantages, such as anchorage loss and time inefficiency, may arise [75].

To ensure the permanence of results and prevent relapse after molar distalization, it is recommended that molars not be used as support for any orthodontic movement for at least 4–5 months following the completion of distalization. Given these requirements, intraoral molar distalization methods, which allow for rapid distalization, may actually prolong the overall treatment duration when the necessary retention period is considered [75]. Consequently, when tooth tissue-supported appliances are used, treatment duration may increase, and anchorage loss may develop in the supporting teeth. To address this anchorage loss, researchers have sought to utilize direct bone support. Initially, osseointegrated implants were employed [76], but their primary drawbacks include the need for surgical placement and removal, an average postoperative healing period of three months, and relatively large size [77]. Another technique for providing direct skeletal anchorage is the use of titanium mini-plates, which, despite requiring surgical placement and having limited application sites, offer the significant advantages of eliminating the need for osseointegration and allowing the application of heavy forces [78]. In recent years, miniscrews have become increasingly popular, as they help overcome the disadvantages of surgical stages and osseointegration requirements [79]. In addition to their small size, which enables their use for distalization in the oral cavity, skeletal anchorage distalization mechanics are frequently noted in the literature to have minimal complications [48,51].

Due to these advantages, the use of orthodontic miniscrews has become widespread, and miniscrew-supported molar distalization methods have gained popularity as a means of minimizing anchorage loss. The primary advantage of miniscrew-supported molar distalization is that it does not require other dental structures to serve as anchorage units. Consequently, reciprocal forces are avoided, and unwanted movements in the premolar and incisor regions are minimized, which not only shortens the treatment duration but also provides the clinician with a more predictable treatment outcome [55,80].

With the increasing use of miniscrew-supported molar distalization systems, these screws have started to be used in modified forms alongside traditional distalization appliances [81]. However, these appliances still require laboratory procedures, occupy space in the oral cavity that may cause patient discomfort, and impose additional financial costs for clinicians. For these reasons, distalization methods that utilize screws independently of appliances—such as those placed in the buccal, infrazygomatic crest, and maxillary tuberosity regions—are gaining prominence. Among these, the use of extra-alveolar screws, which has gained popularity in recent years, offers clinicians a new perspective. Extra-alveolar screws are less limited by anatomical constraints, resulting in a lower risk of root damage and a safer working environment. Compared with intra-alveolar screws, extra-alveolar screws can be used with larger diameters and lengths. Additionally, since they do not require surgical procedures, they can be placed by orthodontists in the clinic with local anesthesia. Using an infrazygomatic crest screw, a variety of malocclusions can be corrected in the sagittal, vertical, and horizontal planes. If distalization with an infrazygomatic screw proves as effective as anticipated, it could replace hybrid distalization devices that require extensive laboratory procedures.

In this narrative review, the effectiveness of appliances used for maxillary molar distalization over the past two decades has been examined, with an emphasis on identifying the most effective methods for current clinical practice. The primary limitation of this study is the lack of comprehensive research in the existing literature directly comparing all appliances, which restricts the objective evaluation of their relative effectiveness. Nevertheless, through an extensive literature review, the clinical advantages and limitations of tooth tissue-supported and skeletal anchorage distalization methods have been systematically analyzed. This review aims to serve as a valuable resource for clinicians in selecting the most appropriate distalization method on a patient-specific basis and to lay the groundwork for future comparative studies.

7. Conclusions

Intraoral MMD methods generally offer several advantages over extraoral methods, including greater comfort and ease of use, improved aesthetics and patient acceptance, and shorter treatment times due to the continuous force application that does not rely on patient compliance. However, these methods also present drawbacks such as undesirable tooth movements resulting from anchorage loss, including distal tipping and rotation of the molars, mesialization of the premolars, and proclination of the incisors. To address these issues, miniscrew applications have been incorporated into distalization mechanics in orthodontic treatments in recent years. When applied in a controlled manner, these miniscrews can help achieve treatment goals more effectively by mitigating the disadvantages of intraoral molar distalization.

In distalization methods that utilize miniscrews in regions such as the buccal area, infrazygomatic crest (IZC), and maxillary tuberosity, these approaches are considered preferable due to the absence of anchorage loss, lack of laboratory requirements, reduced intraoral bulk compared with other methods, and improved patient comfort. However, more comprehensive studies are needed to further elucidate the advantages and disadvantages of these distalization techniques in clinical case selection and to effectively compare them with one another.