A narrative review of orthodontic treatment modalities

Introduction

There are several treatment modalities within the realms of orthodontics. The choice of treatment largely depends on both clinical and radiographic examination involving soft tissue, dental and skeletal parameters (1). Patient needs and expectations are also taken into account in order to provide the best care tailored to each patient (2). Traditional fixed appliance systems have been used for over a century to provide successful outcomes for patients. This has been complemented but not superseded by the use clear aligner systems (3) and has led to orthodontic treatment evolving with a larger emphasis being placed on aesthetic treatment options and a larger rise in patient expectations. It is important to note that both fixed and removable appliance systems each have their own merits. The perception of orthodontic treatment by patients is also important when deciding on the merits of each appliance system. Whilst orthodontists focus on the clinical aspects of an appliance system, for patients the main drivers are quality of life and comfort (4). Patient expectations of treatment can also uncover their initial motivation for seeking treatment such as gaining an improved aesthetic outcome or enabling better cleaning between teeth (5). In some cases, there can be a knowledge gap for orthodontists when making treatment decisions due to the large amount of information and occasional misinformation in the literature. In a study by Barber et al., one knowledge gap that has been highlighted is in shared decision making within orthodontics. Concerns surrounding shared decision making proves that further understanding is required in order to provide comprehensive patient care (6). Another area with a knowledge gap in orthodontics as demonstrated in a study by Mishra et al. is in the understanding of genomics within precision orthodontics (5). There are several knowledge gaps within orthodontics and the aim of scientific studies is to reduce the knowledge gap, allowing orthodontists to make sensible and safe decisions for patient care.

This paper aims to reduce the knowledge gap of orthodontic appliance systems by giving a narrative review of the various treatment modalities in orthodontics. This will help clinicians to choose the most suitable orthodontic appliance for a patient in order to provide comprehensive evidence-based care.

This paper will discuss the scientific literature for different types of fixed and removable appliances including their main indications and success in terms of health, stability and aesthetics. We present this article in accordance with the Narrative Review reporting checklist (available at https://fomm.amegroups.com/article/view/10.21037/fomm-25-7/rc).

Methods

A literature search was carried out for this narrative review. The search was carried out by author A.H. Table 1 describes the method for this narrative review. The following section of this narrative review will discuss and appraise the evidence surrounding each orthodontic treatment modality.

Fixed appliances

The term ‘fixed appliance’ refers to orthodontic appliances that are bonded to teeth and cannot be removed by a patient. There are typically 3 main categories: the straight-wire appliance (SWA), lingual appliances and self-ligating appliances.

The SWA

The SWA was invented by Lawrence Andrews in 1979 (7). At the time, this was a novel approach to solving the challenges of difficult three-dimensional control with both Begg and Tip-Edge appliances (8). A bracket prescription was developed by Andrews that provided first (in-out), second (tip) and third (torque) order bends which alleviated the need for copious amounts of wire bending (9). The main indications for the SWA are for aligning mal-aligned teeth, using the benefits incorporated into the appliance of sliding mechanics producing lighter forces and less friction than traditional closing loops (10). It has proven to be a reliable method of fixed appliance treatment, with the mechanics still being adopted by orthodontists today. Figure 1 demonstrates an example of the SWA.

Figure 1 Straightwire appliance. This has been used for simple alignment of teeth. This image is published with the patient/participant’s consent.

Self-ligating bracket (SLB) systems

Whilst the SWA has several benefits, one major criticism is the amount of frictional resistance it can generate, leading to slower tooth movement (11). An alternative that was developed is the SLB appliance. The definition of a self-ligating appliance is as thus ‘A bracket that utilises a permanently installed moveable component to entrap the archwire’ (12). Whilst this is not a new technique, their use in the early 20^th century was limited. However, in later years, self-ligating appliances underwent several improvements which has led to a popularity in their use. This technique was first pioneered in 1935 by Dr. Jacob Stolzeberg with the Russell Lock Edgewise appliance. The technique was further improved in the 1970s whereby the ’speed’ SLB system was developed by Hanson. By the 1980s another SLB system was created by Johnson and Johnson termed ‘Activa’ brackets. They provided a different type of self-ligating system by using cylindrical brackets whereas the ’speed’ SLB system used a spring to constantly activate the archwire (10).

By the 1990s, Damon SL5 brackets were developed. This system was marketed by describing the lowering of frictional resistance of during tooth movement. Several Damon systems were then created including Damon 2, Damon 3MX, Damon Q (13). Figure 2 demonstrates the use of a self-ligating appliance.

Figure 2 Self-ligating appliance used to aid derotation of the lower right lateral incisor (LR2). This image is published with the patient/participant’s consent.

A SLB system is hinged upon using lighter forces to provide a more natural and efficient movement of teeth whilst protecting the periodontal health of teeth (12). However, even though SLBs have gained popularity, a systematic review carried out by Fleming et al. demonstrated that there is insufficient high-quality evidence to propose that SLBs are advantageous over conventional orthodontic systems, i.e., the SWA (14). The majority of studies within this systematic review were randomised or controlled clinical trials. This was advantageous as the studies relied on prospective rather than retrospective data. However, in terms of sample size calculation, only six studies used a priori sample size calculations leading to an increased risk of a type II error. It is also important to note that for the randomised controlled studies, often the methods of allocation and concealment were poorly reported.

Lingual appliances

With aesthetic demands having increased over recent years, popularity in using ‘invisible’ lingual appliances has become very evident. Laboratory improvements in creation of these appliances has demonstrated the effectiveness of their use. First created by Dr. Fujita and Dr. Kurz, these appliances are bonded to the inner surfaces of teeth, leading to the appearance of seemingly not wearing any orthodontic appliances (15). Dr. Fujita began to create the appliance in 1979 using a mushroom shaped archwire to successfully treat patients on both an extraction and non-extraction basis (16). A little earlier in 1975, Dr. Kurz in the USA used plastic brackets on the lingual surfaces of anterior teeth and metal brackets on the lingual surfaces of posterior teeth (17). The main reason for using plastic was to create a better fit to the lingual surfaces of anterior teeth, avoiding an occlusal interference with the opposing arch. He subsequently went on to create a patented lingual bracket system sold by Ormco in 1979. However, due to difficulties with bonding and archwire placement, lingual appliances were not very popular until more sophisticated designs were developed (17). The current software used to create lingual appliances relies on a computer-aided design and computer-aided manufacturing (CAD-CAM) system.

A systematic review carried out demonstrated that lingual appliances have several benefits such as a decrease in decalcification, improved aesthetics and better achievement of personal treatment objectives (14).

However, some issues that can occur with lingual appliances include having a reduced inter-bracket distance and a marked in-out discrepancy on the labial face due to the lingual bonding. In order to overcome this, some wire bending is required and the archwire can be placed above the bracket to increase the inter-bracket distance (18).

In terms of patient factors, lingual appliances can cause difficulties with speech, particularly ‘s’ and ‘t’ sounds and greater tongue soreness compared to patients wearing labial appliances (19). In terms of outcomes using the Peer Assessment Rating (PAR) index, it has been found in one study that lingual and labial appliances have a similar reduction in PAR scores. However, this study had a small sample size which reduces its generalisability and the fact it was conducted retrospectively can lead to an increased risk of bias (20). Figure 3 demonstrates the use of a lingual appliance.

Figure 3 A maxillary lingual appliance in situ. This image is published with the patient/participant’s consent.

In summary, fixed appliances provide three-dimensional control of tooth movement, which allows the operator to provide optimal results whilst underpinning the mechanics of the case on health, stability and aesthetics.

Removable appliances

Removable appliances are those that are not fixed in the mouth and can be removed by a patient. Removable appliances were first developed in 1836 by Friedrich Christoph Kneisel in Germany (21). Early appliances were made of ivory baseplates or precious metals which were soon superseded by cheaper Vulcanite appliances made of vulcanised rubber. In the 1930s this was finally replaced with acrylic which is still used today. Removable appliances create primarily tipping movements and require compliance in order to achieve the desired objectives (22).

There are three main types of removable appliances: upper removable appliances (URAs), lower removable appliances and removable functional appliances. Removable appliances are commonly used as a method of interceptive orthodontic treatment to correct anterior crossbites, unilateral buccal crossbites with displacement, traumatic overbites and for growth modification. They can also be used with a split screw in the acrylic baseplate to distalise a maxillary molar, i.e., when the Leeway space has been lost. Following early loss of the second deciduous molar. Expansion using a removable appliance is known as ’slow expansion’ (23). Figure 4 shows the use of a URA to correct an anterior crossbite.

Figure 4 An occlusal view of an upper removable appliance used for correction of an anterior crossbite with displacement. There is a recurved palatal spring to procline the upper labial segment with Adams cribs on all first premolars and first permanent molars. This image is published with the patient/participant’s consent.

URAs

A URA is a versatile treatment modality. It contains both active and passive components. The passive components of a URA are Adams cribs or ball ended claps of 0.7 mm stainless steel. They are used for retention of the appliance by engaging in the undercuts of the teeth. They are usually cribbed to the first permanent molar and the first premolar. However, if used in the mixed dentition they can also be cribbed to deciduous molars (24,25).

The baseplate is made from polymethylmethacrylate (PMMA) resin and provides anchorage through contact with the hard palate. The active components of a URA include the use of a midline screw if expansion is needed through tipping movements and the use of springs. The most common spring types include: T-spring, Z-spring and a palatal recurved spring. Each type of spring has its own merits. The anchorage of the appliance must be adequate enough so that when the springs are activated, it does not cause the appliance to dislodge posteriorly. The springs are typically made of between 0.5 to 0.7 mm stainless steel (24,25). Figure 4 shows the use of a URA to correct an anterior crossbite.

One of the most common uses of a URA is for treatment of a posterior crossbite. In terms of posterior crossbites, the prevalence varies depending on the stage of development. In the primary dentition the prevalence of a posterior crossbite is between 2.4–18%. In the mixed dentition, the prevalence of a posterior crossbite based on evidence is between 5–18% and in permanent dentition between 8.5–15% (26). If a posterior crossbite is present in the primary dentition, it rarely self corrects and therefore will be present in the permanent dentition (27).

A posterior crossbite with displacement, can lead to a facial asymmetry as differential mandibular growth can occur. This is due to the fact that is causes greater growth on the non-affected side (28). Condylar positioning can also be affected due to different occlusal and muscular forces. In a systematic review by Agostino et al., it was found that there is only an 83% reliability of correcting a crossbite using a removable appliance compared to using a quadhelix in the mixed dentition with children between 8–10 years old [risk ratio (RR) 1.20; 95% confidence interval (CI): 1.04 to 1.37]. Most of the studies in this systematic review had a low risk of selection and performance bias and there were clear outcomes to evaluate crossbite correction. It was found that a quadhelix appliance achieves faster correction and greater intermolar expansion than a URA with a midline expansion screw. However, some of the included trials barely met the target sample size, reducing the statistical power of the studies. There was also heterogeneity across the studies such as differences in activation protocols, measurement methods and follow up periods (29).

Lower removable appliances

Lower removable appliances are less commonly used but can be a method of disclusion for patients with a deep anterior crossbite that prevents placement of a fixed appliance on the upper labial segment. They require excellent patient compliance and must be worn full time including when eating (30). Figure 5 shows an example of a lower removable appliance in situ, to avoid debonding of the upper labial metal brackets whilst correcting an anterior crossbite.

Figure 5 Images showing a lower removable appliance in situ. (A) Frontal view of a lower removable appliance in situ. The lower removable appliance is passive. This image is published with the patient/participant’s consent. (B) A right buccal view of a lower removable appliance in situ. It is being used to disclude the occlusion to allow for bond up of the upper arch without the deep reverse overbite causing breakages and loss of the upper incisor brackets. These images are published with the patient/participant’s consent.

Removable functional appliances

For growth modification, removable appliances are often used. They are termed ‘functional appliances’ and are defined by Mills as ‘fixed or removable orthodontic appliances that use the forces from muscles of mastication and the periodontal ligament to change tooth and/or jaw positions in an actively growing patient’ (31). Removable functional appliances can be tooth or soft tissue borne, each having its own merits. Tooth borne appliances include a modified Twin-block appliance, Dynamax appliance and a medium open activator. The modified Twin-block appliance developed by Clark, in particular is most commonly used in the UK and has been shown to provide 30% skeletal change and 70% dental change (32).

The Dynamax appliance and medium open activator are both useful for those with a dolichocephalic facial form as they provide less occlusal opening (33). However, no expansion can be carried out with a medium open activator which may not be suitable for all cases (34). Figure 6 demonstrates the use of a modified Twin-block appliance.

Figure 6 A front (A) and right buccal (B) view of a modified Twin-block appliance. These images are published with the patient/participant’s consent.

Furthermore, for patients exhibiting a dolichocephalic facial form, removable functional appliances including the van Beek and Teuscher Appliance can be used in conjunction with high pull headgear. This delivers forces through the centre of resistance of the maxilla (apical to the premolars) aiming to restrict anterior and vertical development of the maxilla and encourage a more horizontal vector of mandibular growth (35). Whilst these appliances are used rarely in today’s society due to the advent of temporary anchorage devices, a study by Singh and Thind found that patients who work a Teuscher appliance in combination with high pull headgear had antero-posterior maxillary restraint and improvements in mandibular position and soft tissue profile (36).

A further study comparing both van Beek and Teuscher appliances, showed that overbite reduction in patients using a Teuscher appliance was mainly due to molar extrusion, whereas with a van Beek appliance, this was mainly due to incisor intrusion. It was also found that more favourable mandibular growth was found in the van Beek group compared to the Teuscher group. However, both appliances worked well when combined with high pull headgear for patients exhibiting a dolichocephalic facial form (37).

Aligners

Another removable appliance that has become very popular is the use of clear aligners. Various aligner systems exist each with their own merits. All aligner systems use the concept of ‘push’ rather than ‘pull’ mechanics. The first initial idea for this came from Kesling in 1946 to use thermoplastic aligners to move teeth (38). However, it wasn’t until in 1997, two Stanford University students (Kelsey Wirth and Zia Chishti) introduced clear aligners using the brand Invisalign (39). At this point, aligners were seen to be an alternative to fixed appliances with minor space closure and mild crowding cases (3).

Since then, several companies have developed different clear aligners systems including Angel, Spark and Smartee Aligner systems. Composite attachments bonded to the teeth are used for retention and to enhance specific tooth movements (40). Figure 7 demonstrates the use of aligners to correct a Class 2 Division II malocclusion.

Figure 7 A front view of aligners in situ for correction of a Class 2 Division II malocclusion. This image is published with the patient/participant’s consent.

The types of composite attachments used vary between the different aligner companies. They form a crucial part of the aligner system as they aid in expression of the desired orthodontic tooth movements. However, it is still a challenge to express these movements. A systematic review in 2023 revealed that the site of attachment placement can influence how well a desired tooth movement is carried out (40). By using attachments tooth movements are better controlled as teeth as pushed in various directions. They increase the contact area and localise the position of force closer to the centre of resistance, achieving bodily movement of the teeth rather than tipping movements (41). In a recent randomised controlled trial, it has been found that the transfer trays used to apply the attachments to the teeth can influence the accuracy of the attachment placement. Those with thicker and stiffer transfer trays provide a greater degree of accuracy of placing attachments and this therefore leads to more predictable outcomes for the desired tooth movements (42).

When comparing fixed and aligner treatments, in a randomised controlled trial by Jaber et al., they found no difference between in terms of PAR treatment outcomes with premolar extraction cases. There was also no difference in treatment duration between aligners and fixed appliances (43). However biomechanically, aligners are still inferior to fixed appliances. When looking at occlusal outcomes of aligner treatment, most evidence looks at non randomised controlled trials with only a few randomised controlled trials being available in the literature. In a study by Papageorgiou et al., the overjet root angulation, occlusal contacted and buccolingual inclination all had poorer outcomes with aligner treatment compared to fixed appliance treatment. They used the ABO Index (American Board of Orthodontics Discrepancy Index) which scored at 9.9 (95% CI: 3.6–16.2), indicating treatment with aligners had worse ABO scores than with fixed appliances. However, six of the studies were at serious risk of bias and so the results of this systematic review should be treated with caution (44).

In terms of the differences in periodontal outcomes when using fixed appliances and aligners, the evidence is extremely limited. A systematic review and meta-analysis found that patients with aligners and no attachments had better oral hygiene compared to those wearing fixed appliances. The plaque scores of those wearing aligners were less, although the indices used to detect inflammation showed no differences between the two groups (45). Further research in this area is required, in order to understand the impact of wearing aligners and fixed appliance on periodontal health.

With aligners, the five main tooth movements (tipping, torque, extrusion, intrusion rotation) have varying degrees of success. Due to this, overcorrection of some tooth movements is often required. It has been shown that the most difficult tooth movement with aligners is incisor extrusion. The accuracy of this tooth movement was approximately 30% in aligner cases (46). This is due to the fact that there is lack of an undercut and the fact that using aligners is a closed system therefore interproximal binding can occur as vertical contact points overlap. Due to the lack of an undercut, horizontal attachments are better (47). Interproximal enamel reduction is also required to clear the overlapping vertical contact points.

In a study by Kravitz et al., it was found that when looking at the aligner system Invisalign in isolation, there was a 41% accuracy of tooth movements. Similar to Rossini et al. (46), they found that maxillary incisor extrusion was the least accurate tooth movement at 18.3% (48). The most predictable tooth movement is tipping. The accuracy of this tooth movement is 73% with mesiodistal tipping being the most successful given the accuracy of this tooth movement being 82.5% (49).

In further research, a systematic review by Yassir et al. in 2022 came to the conclusion that aligner treatment is inferior to conventional fixed appliance treatment for severe crowding and more complex cases. They also found that there is little evidence comparing aligner and fixed appliance treatments when looking at orthodontic induced root resorption (50). However, it must be taken into account that there was low quality primary evidence in this systematic review with many studies having a moderate to high risk of bias. There was also a lack of randomised controlled trials in this review and due to significant heterogeneity, a limited meta-analysis was carried out. The current evidence states that aligners cause less root resorption; however, as aligners move teeth less than fixed appliances, this is likely the reason as to why less root resorption is caused with aligners.

In terms of quality of life, a study by Zhang et al. in 2023 demonstrated that patients have less discomfort and functional difficulties, i.e., chewing with aligners compared to fixed appliance treatment (51). It is also important to note, that when using aligners to correct a malocclusion, refinements are often required and some orthodontists will still use fixed appliances to achieve a perfect finish.

Expansion appliances

Expansion is often a desired objective for malocclusions with either a unilateral or bilateral crossbite with or without displacement. The type of expansion and rate of expansion depends upon the following factors: age, periodontal health, severity of the transverse discrepancy and if a detectable displacement is present (52).

There are two main types of expansion; rapid and slow. The different types of appliances for each type of expansion can be seen below in Table 2. Slow maxillary expansion uses primarily tipping movements to correct a transverse discrepancy that is aetiologically dental rather than skeletal in nature. This type of crossbite is usually accompanied by a displacement that can be eliminated with the correct amount of expansion. A quadhelix or tri-helix are both expanded to one molar width for 4–6 months or longer, until a crossbite is corrected. When using a URA, the screw is turned one quarter turn per week which equates to 0.25 mm of movement, Over the course of four weeks, this leads to 1 mm expansion per month (53).

In terms of the stability of using a URA compared to a quadhelix in crossbite correction, a randomised controlled trial by Petren et al. found that the long stability of correction of unilateral crossbite was similar when using a quadhelix or a URA (54). Figure 8 demonstrates the use of a quadhelix for correction of a unilateral posterior crossbite with a displacement.

Figure 8 An occlusal view of a removable quadhelix used for correction of a posterior crossbite with a lateral displacement. This image is published with the patient/participant’s consent.

On the other hand, rapid maxillary expansion (RME), as the name assumes, leads to crossbite correction in a faster fashion compared to using slow expansion devices. These devices are mainly used to correct a crossbite that is skeletal rather than dental in nature. There is greater bodily movement and less tipping movements of teeth due to force being dissipated over the maxilla, leading to splitting of the mid-palatal suture with a force of 900–4,500 g (55). This skeletal effect allows for more controlled bodily tooth movement in the ratio of 80:20 with respective to skeletal and dental changes. RME works effectively up to the age of 14 years old as it only works reliably until fusion of the palatal suture which occurs post puberty (56). Figure 9 demonstrates a bonded RME appliance.

Figure 9 An occlusal view of a bonded RME appliance with a hyrax screw used to correct a bilateral posterior crossbite. This image is published with the patient/participant’s consent. RME, rapid maxillary expansion.

The rate of screw expansion to maxillary expansion is not a 1:1 ratio due to resistance from the zygomatic buttress. There is more expansion anteriorly than posteriorly. The rate of screw expansion to maxillary expansion is more of a ratio of 3:1 (57). The relapse rate of RME is in the region of 22% as shown in a long-term study over 7 years by Gurel et al. (58).

Traditionally RME is used in order to correct a skeletal transverse discrepancy in patients up to the age of 14 years old. In recent years, miniscrew-assisted rapid maxillary expansion (MARPE) has been popularised. In a study by Bazargani et al. in 2023 they found no difference in outcomes from using MARPE compared to RME in children up to age 11 years old (57). However, parallel opening of mid palatal suture is 2 mm greater at the first maxillary molar region compared to RME (59). The main advantages of using MARPE compared to RME has been described in a systematic review and meta-analysis. The salient points have been summarised below in Table 3 (60).

In non-growing patients, surgically assisted rapid maxillary expansion (SARPE) is mainly used when 5 mm and above of expansion are needed to correct a true skeletal transverse discrepancy (61). The aim is to release osseous articulations of the maxilla. Careful assessment of the arch form is required as well as measuring the width of the buccal corridors and the bucco-palatal inclination of the posterior teeth. The soft tissue thickness and gingival biotype should also be assessed.

For SARPE to occur, a maxillary expansion device is cemented pre-surgery. This can be a bonded or banded device. It has been suggested that bone borne expansion devices can lead to more asymmetric expansion and should be used primarily when there are less teeth than needed for banded RME or periodontal cases (62). Pre-surgery, from an orthodontic perspective the central incisors must be moved apart to reduce the risk of damage to the roots of these teeth.

During the operation surgical cuts are made and the RME is widened during the operation then narrowed to the start position. There is a latency period by which no expansion is carried out (usually 1 week is sensible to allow osteoid to fill the midline cut as this is reported to increase stability) before asking a patient to turn the screw twice once per day (63).

At subsequent follow up visits, it is important to measure the amount of expansion occurring, ensure there is a midline diastema and ensure the expansion is not asymmetric. It is also important to ensure there is no significant pain on turning the screw. In order to know how much expansion is required, for Class II malocclusions a patient can posture the mandible forwards to a Class I position. For those with a Class III malocclusion, it isn’t possible for a patient to ’setback’ their mandible or advance their maxilla and so it can be challenging to estimate how much expansion is needed. In order to overcome this, the use of a ‘Powerbite’ provides an easy way of checking the amount of expansion required. Some overcorrection is advised in order to take into account the amount of relapse that can occur (64).

Once the desired amount of expansion has been achieved usually over the course of 3–4 weeks, the screw can be cemented and a continuous rectangular nickel-titanium archwire placed. There is often spontaneous closure of the midline diastema with no active treatment due to trans-septal fibres being pulled together, but if not then the diastema should be left to close on its own for 3 months with bony infill of the palatal suture. Attempting to orthodontically mesialise the upper central incisors into the space before bony infill is present can lead to the risk of devitalisation of upper centrals (65).

A literature review has found that expansion is greatest at molars and this diminishes progressively anteriorally with SARPE (62). They found a reported rate of relapse to be 0.5–1 mm one year after completion of orthodontic treatment. There was a significantly lower relapse rate by 63% of SARPE compared to RME. Chamberland and Proffit in 2008 found a 30% relapse rate overall with SARPE and discussed the maximum amount of expansion to be 3.49±1.37 mm. They recommended overcorrecting by 2 mm to account of relapse (63).

A recent study has reported that the most immediate effect of SARPE is molar expansion rather than skeletal transverse widening of the maxilla. Whilst the evidence in this study is low to moderate, it is an interesting finding (66,67).

Table 4 illustrates a summary of all of the different types of appliances discussed in this paper with their indication, advantages and disadvantages for their use.

Implications for clinical practice and research

Fixed and removable orthodontic appliances each have a specific time and place in treatment planning. Their selection is guided by the complexity of the malocclusion, patient compliance and overall treatment goals. The aim of the paper was to reduce the knowledge gap for clinicians making treatment decisions and as evidenced there are an array of appliances available to use. Reducing the knowledge gap among clinicians when choosing between orthodontic appliances is essential for delivering personalised evidence-based care.

As treatment options expand with advancements in clear aligner technology and improvements in fixed appliance systems, it becomes increasingly important for clinicians to stay updated on the indications, limitations and outcomes associated with each modality. Continued professional development through workshops, clinical trials and comparative research can help clinicians understand when and how to use different appliances effectively.

With newer technology being available, i.e., aligner-based systems, there is a lot more choice when deciding on the best appliance to treat a particular malocclusion. The evidence base for aligner-based systems is different to fixed appliances in both quantity and scope. Fixed appliances have been studied extensively over decades with a large body of long-term high-quality research supporting their effectiveness for various malocclusions. In contrast, whilst the evidence for aligners is growing, much of it is recent and often limited to specific case types, i.e., mild to moderate crowding. Aligner studies often lack long-term outcome data and therefore this disparity in evidence can make direct comparisons between aligners and fixed appliances challenging. There is a definite need for further research to fully establish the efficacy and limitations of aligner therapy across a broader range of clinical scenarios.

Conclusions

Fundamentally, the choice of which appliance to choose depends upon operator experience, patient factors and the current evidence base for the use of each appliance. A thorough clinical assessment by an orthodontist is essential to determine the most suitable option, ensuring optimal outcomes and patient satisfaction. Ultimately, we aim to provide predictable and stable treatment. The type of appliance used can determine this. Therefore, as each appliance has its own merits, they should be carefully chosen in order to provide the most predictable outcome for patients.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the Narrative Review reporting checklist. Available at https://fomm.amegroups.com/article/view/10.21037/fomm-25-7/rc

Peer Review File: Available at https://fomm.amegroups.com/article/view/10.21037/fomm-25-7/prf

Funding: None.

Conflicts of Interest: Both authors have completed the ICMJE uniform disclosure form (available at https://fomm.amegroups.com/article/view/10.21037/fomm-25-7/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All clinical procedures described in this study were performed in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patients for the publication of this article and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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