1 Definition of orthodontic aligners
The term ‘orthodontic aligner’ most commonly refers to clear, remov- able, plastic appliances that can produce small tooth movements (Fig. 21.1). The name aligner reflects the origin of the appliances in correction of mild irregularity, often in cases where post-orthodontic relapse had occurred. Contemporary aligner treatment usually refers to the process of providing a series of aligners to deliver comprehensive treatment for a range of malocclusions.
The term ‘orthodontic aligner’ most commonly refers to clear, remov- able, plastic appliances that can produce small tooth movements (Fig. 21.1). The name aligner reflects the origin of the appliances in correction of mild irregularity, often in cases where post-orthodontic relapse had occurred. Contemporary aligner treatment usually refers to the process of providing a series of aligners to deliver comprehensive treatment for a range of malocclusions.
Removable appliances were first used in orthodontics in Europe in the nine- teenth century as a method for straightening teeth. Later advances in enamel bonding technology and recognition of better results with fixed appliances resulted in greater use of fixed appliances with removable appliances becoming a largely adjunctive treatment. The discovery of vacuum-formable thermoplastic sheets in the 1980s led to a resurgence in the popularity of removable appliances as a stand-alone treatment in the form of aligners.
2.1 Thermoplastic aligners
2.1 Thermoplastic aligners
Initially aligners were used in cases where one or two teeth required a small amount of movement. These aligners were referred to as ‘positioners’.
The aligners were constructed by laboratory technicians, who sectioned and repositioned any teeth, usually with a maximum tooth movement of approximately 0.2 mm. The teeth were secured in the new position and the subsequent cast was used to construct the aligner using thermoplastic vacuum-formed sheets (Fig. 21.2).
The Hilliard thermoforming pliers were later developed to enable tooth-moving forces to be added to the aligner by the clinician at the chair-side. The pliers were used to create a projection in the appliance which then applied force to the tooth as the plastic returned to its origi- nal state. Various pliers were designed to apply different forces to the teeth and to modify the projections as the teeth moved.
Even with the introduction of pliers to create projections, individual thermoplastic aligners had limited ability to move teeth due to the stiff- ness of the material. To overcome this, sequential aligners were used to incrementally move the teeth and achieve greater overall tooth move- ment. Using the method previously described, laboratory technicians would perform multiple incremental tooth movements, producing an aligner at each stage. The considerable time requirements and technical difficulties associated with modifying multiple casts to produce a series of aligners by hand limited the scope of this method.
The Hilliard thermoforming pliers were later developed to enable tooth-moving forces to be added to the aligner by the clinician at the chair-side. The pliers were used to create a projection in the appliance which then applied force to the tooth as the plastic returned to its origi- nal state. Various pliers were designed to apply different forces to the teeth and to modify the projections as the teeth moved.
Even with the introduction of pliers to create projections, individual thermoplastic aligners had limited ability to move teeth due to the stiff- ness of the material. To overcome this, sequential aligners were used to incrementally move the teeth and achieve greater overall tooth move- ment. Using the method previously described, laboratory technicians would perform multiple incremental tooth movements, producing an aligner at each stage. The considerable time requirements and technical difficulties associated with modifying multiple casts to produce a series of aligners by hand limited the scope of this method.
2.2 Spring aligners
The spring aligner was developed as an alternative method for align- ing anterior teeth. These appliances employ two opposing nickel- titanium sprung bows, which straighten teeth by applying reciprocal force labially and palatally (Fig. 21.3). The appliances are designed to provide a short course of treatment (usually less than 4 months) and are limited to mild crowding of rotated or labiolingually displaced inci- sors. The most common commercially manufactured spring aligner is the Inman Aligner™, but most laboratory technicians can produce a spring aligner from a standard appliance prescription.
2.3 Contemporary aligners
Contemporary orthodontic aligner treatment has been driven by the research and development arising from the Invisalign® system, which was introduced by Align Technology (San Jose, California, USA) in 1998. Invisalign® is a proprietary orthodontic technique that uses sequential computer-generated plastic aligners to deliver a course of treatment. Other manufacturers have emerged to offer complete aligner treatment that follow similar principles, but Invisalign® remains the most popular system worldwide. The combined benefits of three-dimensional (3D) planning technology, improved materials, mechanics arising from under- standing of aligner tooth movement, and computer-aided manufacture of multiple aligners have led to a much broader scope for orthodontic aligner treatment. This is discussed more in the following sections.
The popularity of contemporary aligner treatment may be attributed to a number of factors (Box 21.1). Although designed for adults with fully erupted permanent dentitions, there is a growing demand for aligner treatment for teenage patients. This younger age group presents particular challenges for aligner treatment, such as changes to the dentition with continued tooth eruption, difficulties in gaining sufficient purchase on partially erupted teeth to fully control tooth movements and retain the aligners, and potential compliance issues. Manufacturers are rapidly developing solutions to address these potential difficulties and it is likely that through continued research and development, aligner treatment will evolve further and become established as an adjunct or alternative to other orthodontic treatment modalities in many countries.
2.3 Contemporary aligners
Contemporary orthodontic aligner treatment has been driven by the research and development arising from the Invisalign® system, which was introduced by Align Technology (San Jose, California, USA) in 1998. Invisalign® is a proprietary orthodontic technique that uses sequential computer-generated plastic aligners to deliver a course of treatment. Other manufacturers have emerged to offer complete aligner treatment that follow similar principles, but Invisalign® remains the most popular system worldwide. The combined benefits of three-dimensional (3D) planning technology, improved materials, mechanics arising from under- standing of aligner tooth movement, and computer-aided manufacture of multiple aligners have led to a much broader scope for orthodontic aligner treatment. This is discussed more in the following sections.
The popularity of contemporary aligner treatment may be attributed to a number of factors (Box 21.1). Although designed for adults with fully erupted permanent dentitions, there is a growing demand for aligner treatment for teenage patients. This younger age group presents particular challenges for aligner treatment, such as changes to the dentition with continued tooth eruption, difficulties in gaining sufficient purchase on partially erupted teeth to fully control tooth movements and retain the aligners, and potential compliance issues. Manufacturers are rapidly developing solutions to address these potential difficulties and it is likely that through continued research and development, aligner treatment will evolve further and become established as an adjunct or alternative to other orthodontic treatment modalities in many countries.
3 Tooth movement with aligners
3.1 Understanding tooth movement with aligners
Application of force to achieve tooth movement with aligners is differ- ent to other orthodontic appliances. For aligners, the plastic enclosing the tooth has two functions: application of force for tooth movement and retention of the appliance. Tooth movement is achieved by elastic deformation of the aligner and the composition of the plastic is therefore important. The material needs to be stiff enough to deliver the correct level of force, but also highly elastic so it will return to its original shape when stretched, moving the tooth with it. Retention for the appliance is usually provided by the natural undercuts of the tooth, however, in some cases the functions of retention and elastic deformation can compete, for example, displacement of the aligner when trying to extrude teeth. This has been addressed to some extent by adding composite attachments to the teeth. Attachments provide a surface for the retainer to grip on to and prevent unwanted displacement of the aligner in addition to providing a point of force application to achieve more difficult tooth movements.
An understanding of the biomechanics of tooth movement with aligners will help clinicians to achieve more predictable results. For fur- ther information, readers are directed to the sources given in ‘Principal sources and further reading’.
3.2 Scope of tooth movement with aligners
Much like other removable appliances, early aligners were largely restricted to tipping movements of the crown due to limitations in the force vectors that could be transmitted to the teeth. The ability to apply adequate forces to correct buccolingual tip and rotational movement of flat teeth, such as incisors, allowed aligners to manage rotated, pro- clined, or retroclined anterior teeth; however, there was little scope for mesiodistal or vertical tooth movement, or root torque. Advances in understanding of tooth movement mechanics have ena- bled the development of a range of different shaped attachments that are placed on teeth to increase engagement between the aligner and tooth. These attachments have been carefully designed using biome- chanical knowledge to allow the aligner to exert a range of force vectors. Attachments, in conjunction with advanced plastic aligner materials, enable more difficult tooth movements to be achieved, such as de- rotation of round teeth (canines and premolars), relative intrusion/ extrusion of one or multiple teeth, and root torque. With appropriate understanding, planning, and use of modern aligner technologies it is possible to achieve a scope of tooth movement with aligners that is comparable to fixed appliances.
4 Clinical stages in aligner treatment
It is a common misconception that the brand of aligner is important to the eventual success of aligner treatment. The type and brand of aligner may determine the scope of potential tooth movements, however, as with all orthodontic treatment, success depends on accurate diagnosis of malocclusion, establishing patients’ expectations from treatment, careful treatment planning, and understanding of mechanics.
Application of force to achieve tooth movement with aligners is differ- ent to other orthodontic appliances. For aligners, the plastic enclosing the tooth has two functions: application of force for tooth movement and retention of the appliance. Tooth movement is achieved by elastic deformation of the aligner and the composition of the plastic is therefore important. The material needs to be stiff enough to deliver the correct level of force, but also highly elastic so it will return to its original shape when stretched, moving the tooth with it. Retention for the appliance is usually provided by the natural undercuts of the tooth, however, in some cases the functions of retention and elastic deformation can compete, for example, displacement of the aligner when trying to extrude teeth. This has been addressed to some extent by adding composite attachments to the teeth. Attachments provide a surface for the retainer to grip on to and prevent unwanted displacement of the aligner in addition to providing a point of force application to achieve more difficult tooth movements.
An understanding of the biomechanics of tooth movement with aligners will help clinicians to achieve more predictable results. For fur- ther information, readers are directed to the sources given in ‘Principal sources and further reading’.
3.2 Scope of tooth movement with aligners
Much like other removable appliances, early aligners were largely restricted to tipping movements of the crown due to limitations in the force vectors that could be transmitted to the teeth. The ability to apply adequate forces to correct buccolingual tip and rotational movement of flat teeth, such as incisors, allowed aligners to manage rotated, pro- clined, or retroclined anterior teeth; however, there was little scope for mesiodistal or vertical tooth movement, or root torque. Advances in understanding of tooth movement mechanics have ena- bled the development of a range of different shaped attachments that are placed on teeth to increase engagement between the aligner and tooth. These attachments have been carefully designed using biome- chanical knowledge to allow the aligner to exert a range of force vectors. Attachments, in conjunction with advanced plastic aligner materials, enable more difficult tooth movements to be achieved, such as de- rotation of round teeth (canines and premolars), relative intrusion/ extrusion of one or multiple teeth, and root torque. With appropriate understanding, planning, and use of modern aligner technologies it is possible to achieve a scope of tooth movement with aligners that is comparable to fixed appliances.
4 Clinical stages in aligner treatment
It is a common misconception that the brand of aligner is important to the eventual success of aligner treatment. The type and brand of aligner may determine the scope of potential tooth movements, however, as with all orthodontic treatment, success depends on accurate diagnosis of malocclusion, establishing patients’ expectations from treatment, careful treatment planning, and understanding of mechanics.
4.1 Case selection
When deciding whether alignment treatment is a viable option, it is important to elicit the patient’s key concerns and establish treatment goals. If significant tooth movement is required or there is an underlying skeletal discrepancy that requires correction, other forms of treatment may be preferable. It is essential that treatment objectives are measured against the scope of the appliance to deliver the necessary tooth movements and any biological limitations posed by the malocclusion. Advances in aligner technology have broadened the scope of treatment with aligners but this will not compensate for poor case selection by inexperienced clinicians.
4.2 Treatment planning
Regardless of the aligner system, full diagnostic records are required for treatment planning. This includes clinical information, photographs, radiographs, and detailed impressions in a stable material. Bite registra- tion is usually taken in maximum intercuspation and should be checked carefully, as errors in bite registration increase the risk of unattainable treatment plans.
A prescription is sent by the clinician with the records to the manu- facturer to allow the technician to deliver a preliminary sequence of tooth movements. In the prescription, the clinician specifies the aims of treatment, including which aspects of malocclusion are to be cor- rected or accepted. The manufacturer will usually produce a virtual set- up that reflects the desired outcome described in the prescription. The virtual set-up can often be viewed in a software program, such as the Invisalign® ClinCheck (Fig. 21.4).
Regardless of the aligner system, full diagnostic records are required for treatment planning. This includes clinical information, photographs, radiographs, and detailed impressions in a stable material. Bite registra- tion is usually taken in maximum intercuspation and should be checked carefully, as errors in bite registration increase the risk of unattainable treatment plans.
A prescription is sent by the clinician with the records to the manu- facturer to allow the technician to deliver a preliminary sequence of tooth movements. In the prescription, the clinician specifies the aims of treatment, including which aspects of malocclusion are to be cor- rected or accepted. The manufacturer will usually produce a virtual set- up that reflects the desired outcome described in the prescription. The virtual set-up can often be viewed in a software program, such as the Invisalign® ClinCheck (Fig. 21.4).
The virtual set-up is not the treatment plan but simply the technician’s 3D interpretation of the prescription provided by the clinician. It should be noted that the technician is usually not orthodontically trained and is not responsible for the treatment plan. The technician will follow the instructions on the prescription and ensure the tooth movements are within the software limits for that particular brand of aligner, but it is the clinician’s responsibility to approve the virtual set-up. The prelimi- nary set-up details the sequence of steps, the amount of movement per aligner, the use of adjunctive treatments such as attachments, elastics, and interproximal reduction. The clinician can view the virtual set-up and make adjustments to the treatment plan to ensure the treatment objectives are met.
4.3 Consent
Treatment planning and consent are covered in detail in Chapter 7; however, it is worthwhile highlighting the issues that are most perti- nent to aligners. The effectiveness of aligners is not yet established and clinicians are wise to avoid overselling the alleged benefits of aligners compared to other types of treatment. Much like fixed appliance treat- ment, the outcome of treatment is influenced by the experience of the clinician and careful treatment planning and delivery.
Patients should be aware of any potential limitations posed by the biological constraints of the malocclusion and limited treatment objectives should be clearly stated. Aligners are not able to overcome the aspects of treatment that are biologically determined, such as any limitations in the final tooth position, the rate of tooth movement, and the need for long-term retention. Treatment time depends on the extent of tooth movement needed and compliance with aligner wear and conservative estimates are advised to allow time for detail- ing the occlusion with additional aligners if needed. Adjunctive treat- ments should be described and agreed during treatment planning and consent.
Aligners have similar potential side effects as other removable appli- ances, namely effects on speech, increased salivation, discomfort, and gagging, and these may be more marked in adults than children. The patient should be warned that in most cases aligners must be removed for eating and drinking, as this can impact eating habits and the num- ber of hours of wear that are achievable. The benefit of being able to remove aligners for cleaning may be countered by the risk of non- compliance with wear and patients should be assessed on an indi- vidual basis.
4.3 Consent
Treatment planning and consent are covered in detail in Chapter 7; however, it is worthwhile highlighting the issues that are most perti- nent to aligners. The effectiveness of aligners is not yet established and clinicians are wise to avoid overselling the alleged benefits of aligners compared to other types of treatment. Much like fixed appliance treat- ment, the outcome of treatment is influenced by the experience of the clinician and careful treatment planning and delivery.
Patients should be aware of any potential limitations posed by the biological constraints of the malocclusion and limited treatment objectives should be clearly stated. Aligners are not able to overcome the aspects of treatment that are biologically determined, such as any limitations in the final tooth position, the rate of tooth movement, and the need for long-term retention. Treatment time depends on the extent of tooth movement needed and compliance with aligner wear and conservative estimates are advised to allow time for detail- ing the occlusion with additional aligners if needed. Adjunctive treat- ments should be described and agreed during treatment planning and consent.
Aligners have similar potential side effects as other removable appli- ances, namely effects on speech, increased salivation, discomfort, and gagging, and these may be more marked in adults than children. The patient should be warned that in most cases aligners must be removed for eating and drinking, as this can impact eating habits and the num- ber of hours of wear that are achievable. The benefit of being able to remove aligners for cleaning may be countered by the risk of non- compliance with wear and patients should be assessed on an indi- vidual basis.
4.4 Starting treatment
Following confirmation of the treatment plan and consent, align- ers are manufactured and dispatched to the clinician to commence treatment. The first aligner is fitted, and instructions are provided including the hours of wear needed per day, usually a minimum of 22 hours, alongside dietary and oral hygiene advice. Advocates of aligner treatment claim patients report lower pain experience than with fixed appliances, however, there is no good evidence to support this claim. Pain depends on the individual and analgesia advice is recommended, as aligners often feel tight initially.
Where a series of aligners are to be used, patients should be instructed how and when to progress to the next aligner. Teeth should be ‘tracking’ with the series of aligners, meaning the teeth move as expected to fit into the aligner, and teeth must be fully seated in the current aligner before moving to the next one.
4.5 Adjunctive treatments
Adjunctive treatments may be required to facilitate the required tooth movement. The most common adjunctive treatments are placement of attachments, interproximal reduction and use of inter- arch elastics.
Attachments are selected and located during the treatment plan- ning stage to allow force application in the desired vector or to pro- vide additional retention. The attachments are placed using a stent to allow composite to be bonded to the tooth in the correct shape and position (Fig. 21.5). There is anecdotal evidence that during treatment the attachments may be prone to some staining. Patients should be warned about this but reassured that at the end of treat- ment attachments will be removed without any permanent effect on the enamel if diet control and oral hygiene are satisfactory through- out treatment.
Interproximal reduction is often incorporated into treatment plans to provide space for alignment of teeth. The timing, location, and extent of interproximal reduction is specified in the prescription (Fig. 21.6). Usually a maximum of 0.3 mm and 0.5 mm of enamel removal is advised per interproximal surface for anterior and posterior teeth respectively, although the extent of reduction possible should be judged individu- ally for each tooth based on enamel thickness and crown morphology. Current evidence suggests that interproximal enamel reduction used in appropriate cases and within recognized limits causes no long-term detriment to dental health.
Inter-arch elastics can be applied to notches or hooks incor- porated during the aligner construction (Fig. 21.7) or by bonding metal or clear buttons directly to the tooth surface. Much like fixed orthodontics, inter-arch elastics allow correction of the anteropos- terior relationship. If the application points for elastic traction are cut into the aligner, these need to be designed to prevent displace- ment of the aligner by the elastic force.
More advanced adaptations to aligners are also possible. Aligners have been designed to incorporate interlocking blocks to apply a Class II correction, working in the same way as other types of functional appli- ances. Aligners have reportedly been used in conjunction with other orthodontic auxiliaries, for example, temporary anchorage devices (mini-screws) to correct vertical discrepancies. This type of treatment is highly complex and should only be undertaken by experienced ortho- dontists who are competent in this approach
Inter-arch elastics can be applied to notches or hooks incor- porated during the aligner construction (Fig. 21.7) or by bonding metal or clear buttons directly to the tooth surface. Much like fixed orthodontics, inter-arch elastics allow correction of the anteropos- terior relationship. If the application points for elastic traction are cut into the aligner, these need to be designed to prevent displace- ment of the aligner by the elastic force.
More advanced adaptations to aligners are also possible. Aligners have been designed to incorporate interlocking blocks to apply a Class II correction, working in the same way as other types of functional appli- ances. Aligners have reportedly been used in conjunction with other orthodontic auxiliaries, for example, temporary anchorage devices (mini-screws) to correct vertical discrepancies. This type of treatment is highly complex and should only be undertaken by experienced ortho- dontists who are competent in this approach
4.6 Monitoring progress
One potential benefit of aligner treatment is reduced chair-side time arising from patients being able to change their own aligners. The patient can be instructed how to monitor progress to determine when the next aligner can be started. However, it is still important that patients are seen regularly to allow the clinician to monitor progress and provide support. Progress is assessed by comparing actual tooth move- ment to expected tooth movement and this allows any problems to be identified and managed swiftly. The most common reasons for lack of progress are loss of tracking (Fig. 21.8) arising from insufficient wear, insufficient interproximal reduction, inadequate application of force on teeth, for example, from incorrect attachment placement, or as a result of an unfeasible plan where too much movement is planned from one aligner.
4.7 Retention
As with all forms of orthodontic treatment, retention is a key component of aligner treatment and the patient must be aware of the commitment to long-term retention from the outset of treatment. Removable, fixed, or combined retainers may be used depending on patient preference. Retention is discussed in detail in Chapter 16.
5 Digital aligner construction
Most manufacturers use their own proprietary software and process- ing equipment for computer-aided aligner construction, however, the systems tend to follow a common sequence. The key stages are sum- marized here but for further information about a specific system it is advisable to contact the manufacturer.
Firstly, a digital study model is creating using a direct scan of the impression or scan of a dental cast. The teeth are articulated using the bite registration and any obvious artefacts are removed at this stage. Some systems allow the teeth and bite to be scanned directly and trans- ferred to the manufacturer without the need for an impression and this can reduce the time required for the digitization stage.
Tooth movements are executed by the technician using instructions from the prescribing dentist. The teeth are moved incrementally to ensure the forces applied are within physiologically acceptable limits, usually around 0.25 mm and 0.33 mm per aligner for anterior and poste- rior teeth respectively. Adjunctive treatments are added as required to achieve the range of desired tooth movements. Once the full sequence of movements has been executed, the final occlusion is provided and this should correspond to the treatment objectives. At this stage, it is usual for the preliminary plan to be reviewed by the prescribing cli- nician. Ideally, software that enables 3D visualization of each aligner stage is used to allow real-time adjustments by the clinician to the tooth movements to finalize the treatment plan. Modifications can be made and rechecked until the clinician is satisfied that the treatment is feasible and will achieve the desired outcome. It is also possible to show the patient the proposed plan and expected tooth movements at this stage.
Following finalization of the treatment plan by the clinician, the digi- tal study models are transferred to cast production. Previously a series of stereolithographic models were produced and each model was used to fabricate an aligner. However, developments in 3D printing technol- ogy now mean aligners can be produced directly from the computer software by the manufacturer. It is likely that with the reducing price of 3D printers and the increasing use of aligners, in the future, in-house 3D printers will enable the manufacturer to transfer the aligner details to the clinician for printing on site.
As with all forms of orthodontic treatment, retention is a key component of aligner treatment and the patient must be aware of the commitment to long-term retention from the outset of treatment. Removable, fixed, or combined retainers may be used depending on patient preference. Retention is discussed in detail in Chapter 16.
5 Digital aligner construction
Most manufacturers use their own proprietary software and process- ing equipment for computer-aided aligner construction, however, the systems tend to follow a common sequence. The key stages are sum- marized here but for further information about a specific system it is advisable to contact the manufacturer.
Firstly, a digital study model is creating using a direct scan of the impression or scan of a dental cast. The teeth are articulated using the bite registration and any obvious artefacts are removed at this stage. Some systems allow the teeth and bite to be scanned directly and trans- ferred to the manufacturer without the need for an impression and this can reduce the time required for the digitization stage.
Tooth movements are executed by the technician using instructions from the prescribing dentist. The teeth are moved incrementally to ensure the forces applied are within physiologically acceptable limits, usually around 0.25 mm and 0.33 mm per aligner for anterior and poste- rior teeth respectively. Adjunctive treatments are added as required to achieve the range of desired tooth movements. Once the full sequence of movements has been executed, the final occlusion is provided and this should correspond to the treatment objectives. At this stage, it is usual for the preliminary plan to be reviewed by the prescribing cli- nician. Ideally, software that enables 3D visualization of each aligner stage is used to allow real-time adjustments by the clinician to the tooth movements to finalize the treatment plan. Modifications can be made and rechecked until the clinician is satisfied that the treatment is feasible and will achieve the desired outcome. It is also possible to show the patient the proposed plan and expected tooth movements at this stage.
Following finalization of the treatment plan by the clinician, the digi- tal study models are transferred to cast production. Previously a series of stereolithographic models were produced and each model was used to fabricate an aligner. However, developments in 3D printing technol- ogy now mean aligners can be produced directly from the computer software by the manufacturer. It is likely that with the reducing price of 3D printers and the increasing use of aligners, in the future, in-house 3D printers will enable the manufacturer to transfer the aligner details to the clinician for printing on site.
6 Uses for aligners
6.1 Types of cases
The type of case that can be successfully managed with orthodontic aligners depends on the tooth movements required to correct the maloc- clusion and the ability of the aligner system to achieve this movement. Different aligner systems are able to deliver different types of tooth move- ments and this, alongside clinician competence, will determine whether aligners are a suitable treatment method. More complex cases require a more sophisticated system that incorporates adjunctive treatments (Table 21.1). There is little evidence beyond the level of case reports to evaluate the efficacy of orthodontic aligners for correction of specific types of mal- occlusion and the rapid advances in technology combined with individual patient variation present challenges for generalization across cases.
Most aligner systems are suitable for simple cases where mostly tipping movements are required. Where there is moderate crowding, space for alignment is gained through interproximal reduction, expan- sion, or a combination of both. Alignment in the anterior region com- monly results in proclination of the incisors and the effect of this should be considered in relation to the overjet and overbite. If proclination or expansion is not desirable, interproximal reduction will be necessary.
For more complex cases, where tooth movement beyond tipping is required, attachments are necessary to enable appropriate force appli- cation. Attempts to close spaces without attachments to drive root movement will result in tipped crowns. For intrusive or extrusive move- ment of one or two teeth, attachments enable differential force applica- tion on adjacent teeth. On round teeth, such as premolars and canines, attachments provide a point of force application. Inter-arch elastic trac- tion may also be necessary to correct the buccal segment relationship.
Complex cases are those judged to require significant tooth move- ment, such as bodily movement of teeth over a distance after extraction (Fig. 21.9) or distalization of molars. For complex cases, the selection of an appropriately advanced aligner system and execution of treatment by an experienced clinician is essential for success.
The type of case that can be successfully managed with orthodontic aligners depends on the tooth movements required to correct the maloc- clusion and the ability of the aligner system to achieve this movement. Different aligner systems are able to deliver different types of tooth move- ments and this, alongside clinician competence, will determine whether aligners are a suitable treatment method. More complex cases require a more sophisticated system that incorporates adjunctive treatments (Table 21.1). There is little evidence beyond the level of case reports to evaluate the efficacy of orthodontic aligners for correction of specific types of mal- occlusion and the rapid advances in technology combined with individual patient variation present challenges for generalization across cases.
Most aligner systems are suitable for simple cases where mostly tipping movements are required. Where there is moderate crowding, space for alignment is gained through interproximal reduction, expan- sion, or a combination of both. Alignment in the anterior region com- monly results in proclination of the incisors and the effect of this should be considered in relation to the overjet and overbite. If proclination or expansion is not desirable, interproximal reduction will be necessary.
For more complex cases, where tooth movement beyond tipping is required, attachments are necessary to enable appropriate force appli- cation. Attempts to close spaces without attachments to drive root movement will result in tipped crowns. For intrusive or extrusive move- ment of one or two teeth, attachments enable differential force applica- tion on adjacent teeth. On round teeth, such as premolars and canines, attachments provide a point of force application. Inter-arch elastic trac- tion may also be necessary to correct the buccal segment relationship.
Complex cases are those judged to require significant tooth move- ment, such as bodily movement of teeth over a distance after extraction (Fig. 21.9) or distalization of molars. For complex cases, the selection of an appropriately advanced aligner system and execution of treatment by an experienced clinician is essential for success.
6.2 Who should provide aligner treatment?
In the UK, the General Dental Council states dental treatment can be performed by any dentist who has the necessary skills and is appropri- ately trained, competent, and indemnified. Similar guidance exists in other countries. Therefore, specialists and general dentists who have sought the appropriate training and are competent to perform the treat- ment to a satisfactory standard are generally allowed to offer ortho- dontic treatment. Competency will depend on the aligner system used, the complexity of the case, and clinician experience, so clinicians must decide on a case-by-case basis whether they feel able to offer treatment. One area of concern has arisen around manufacturer training courses which only include information about the one specific system. In these cases, clinicians may not have sufficiently broad knowledge to be able to provide all treatment options in a balanced way to allow informed decision-making. It is important that patients are informed of the quali- fications and experience of clinicians offering treatment, including any limitations in what they are able to offer, and if the patient requests additional information or a second opinion, a referral should be offered. Evidence shows treatment outcomes are improved by accurate diagnosis, careful treatment planning, and operator experience. Those at the start of their aligner journey are encouraged to select cases carefully and seek mentoring from more experienced colleagues where possible to ensure patient care is optimized
In the UK, the General Dental Council states dental treatment can be performed by any dentist who has the necessary skills and is appropri- ately trained, competent, and indemnified. Similar guidance exists in other countries. Therefore, specialists and general dentists who have sought the appropriate training and are competent to perform the treat- ment to a satisfactory standard are generally allowed to offer ortho- dontic treatment. Competency will depend on the aligner system used, the complexity of the case, and clinician experience, so clinicians must decide on a case-by-case basis whether they feel able to offer treatment. One area of concern has arisen around manufacturer training courses which only include information about the one specific system. In these cases, clinicians may not have sufficiently broad knowledge to be able to provide all treatment options in a balanced way to allow informed decision-making. It is important that patients are informed of the quali- fications and experience of clinicians offering treatment, including any limitations in what they are able to offer, and if the patient requests additional information or a second opinion, a referral should be offered. Evidence shows treatment outcomes are improved by accurate diagnosis, careful treatment planning, and operator experience. Those at the start of their aligner journey are encouraged to select cases carefully and seek mentoring from more experienced colleagues where possible to ensure patient care is optimized
7 Advantages and limitations of orthodontic aligners
Many claims have been made by supporters and manufacturers of orthodontic aligners and while the body of evidence to support these claims is growing, there are few high-quality trials to determine the effectiveness of aligners compared to other treatment methods. The most commonly proposed advantages of aligners include more aesthetic appliance, improved dental health in terms of periodontal health and reduced risk of decalcification, and a reduction in chair-side time, overall treatment time, pain experience, and root resorption. The current body of evidence for orthodontic aligners is insufficient to conclusively support or refute these claims although future high-quality randomized trials are planned.
It is generally acknowledged that aligners are more aesthetic than metal buccal fixed appliances but not as inconspicuous as lingual fixed appliances. The appearance of aligners compared to ceramic fixed appliances is more difficult to judge and depends on the particular sys- tems in use and personal preference. The ability to remove aligners for cleaning and eating might be expected to reduce the risk of periodontal problems and decalcification; however, this has not yet been substanti- ated and it is likely that the risk of treatment is related more to individual motivation than the appliance.
Many claims have been made by supporters and manufacturers of orthodontic aligners and while the body of evidence to support these claims is growing, there are few high-quality trials to determine the effectiveness of aligners compared to other treatment methods. The most commonly proposed advantages of aligners include more aesthetic appliance, improved dental health in terms of periodontal health and reduced risk of decalcification, and a reduction in chair-side time, overall treatment time, pain experience, and root resorption. The current body of evidence for orthodontic aligners is insufficient to conclusively support or refute these claims although future high-quality randomized trials are planned.
It is generally acknowledged that aligners are more aesthetic than metal buccal fixed appliances but not as inconspicuous as lingual fixed appliances. The appearance of aligners compared to ceramic fixed appliances is more difficult to judge and depends on the particular sys- tems in use and personal preference. The ability to remove aligners for cleaning and eating might be expected to reduce the risk of periodontal problems and decalcification; however, this has not yet been substanti- ated and it is likely that the risk of treatment is related more to individual motivation than the appliance.
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