Clear aligners: a good tool, but not the right one for everyone

How do clear aligners move teeth?

Each aligner is made slightly different from where the teeth currently sit, so once it is in place the elasticity of the plastic applies continuous force in a planned direction. Each aligner is generally set to deliver movement of around 0.2 to 0.25 mm or less, with the actual amount adjusted for the tooth, the direction of movement and the treatment design.

Because a smooth aligner cannot reliably control every movement, many courses of treatment need composite attachments bonded to the teeth. Attachments are small tooth-coloured bumps that help the aligner grip the tooth and direct force where it is needed.

In other words, clear aligners do not necessarily mean nothing at all on the teeth. Many treatments need attachments and some also need elastics; more complex cases may need other adjuncts. Knowing about this before starting avoids finding out later that the reality differs from what you pictured.

Why clear aligners do not suit everyone: difficulty varies widely by movement

Studies compare the tooth movement predicted by the digital treatment plan against the movement actually achieved. Earlier work recorded a mean predicted-movement accuracy of about 41%, and a more recent study of the same kind recorded about 50%. These figures do not mean that only half of a treatment succeeds. They reflect that each step the software predicts will not necessarily be realised in full. Different teeth, directions of movement and individual responses vary considerably, which is why review visits, attachments, elastics and refinement aligners are often part of the overall treatment plan.

Which movements are easier, and which are more challenging

For the same treatment goal, clear aligners can genuinely take longer than fixed appliances. In straightforward cases an aligner course can be comparable or even quicker; but where larger rotations, extrusion, root control or a complex bite are involved, fixed appliances are usually easier to control directly. Insisting on aligners throughout may extend treatment and require more refinement aligners. Put another way, a less visible appliance is sometimes paid for in time and cooperation, and that is worth understanding before starting.

20 to 22 hours a day: wear too little and the teeth fall behind the plan

Clear aligners rely on continuous, steady force to move teeth, so wear of around 20 to 22 hours a day is generally advised, with the actual instruction coming from your clinician. If aligners are out for too long too often, actual tooth movement can progressively fall behind, and later aligners begin not to seat fully.

1. Wearing them too little does not simply extend treatment a little. Once the teeth sit behind what the next aligner was designed for, the aligner can start to lift away or fail to seat completely, and every aligner after that becomes harder to fit.
2. What is most easily missed is that an aligner course can drift away from the plan without causing any obvious discomfort. On the surface the aligners still go in, while individual teeth may already have stopped moving as expected. Insufficient wear is one common reason, but the response of the teeth themselves, the attachment design and the difficulty of the movement all affect the outcome.
3. If long daily wear is hard to sustain around your routine, fixed appliances may in fact be the safer option, since there is nothing to put in and take out each day. Fixed appliances do, however, still require oral hygiene, regular review visits, and using elastics as instructed.

Regular review visits, so drift from the plan is caught early

When an aligner course drifts, it does not necessarily cause pain or obvious discomfort straight away. The aligners still go in, while individual teeth may already have stopped moving in the planned direction. A review visit is therefore not simply collecting the next set of aligners; it is checking whether actual progress still matches the plan.

1. Each review checks how well the aligners are seating, the condition of the attachments and the progress of the teeth. The earlier drift is found, the easier it usually is to deal with by extending wear, making a localised adjustment or changing what happens next.
2. If drift accumulates into the later part of treatment, a fresh scan, refinement aligners or an extension of the treatment time may be needed.
3. Refinement aligners are not unusual in clear aligner treatment and do not necessarily mean treatment has failed. What matters is recognising the gap between the actual response and the original plan in good time, and adjusting accordingly.

Clear aligners and fixed braces are not strictly either / or

Clear aligners and fixed appliances are not, in every situation, a choice of one or the other. For some patients who suit clear aligners overall but have individual movements that are harder to control, hybrid treatment can be a practical option.

1. Sectional fixed appliances with aligners: in some cases a sectional fixed appliance can be used on particular teeth for a period, to handle a rotation or extrusion an aligner controls less well, before returning to aligners for the rest of treatment. Where it is used and for how long varies from case to case.
2. Temporary anchorage devices (TADs, commonly called mini-screws) with aligners: in some cases skeletal anchorage provides a more stable point from which to apply force, helping with retraction, intrusion or the control of anchorage. Whether it is needed is assessed against the treatment goals and the condition of the mouth.
3. More advanced use of attachments and elastics: different attachment shapes and elastic configurations to improve control of individual teeth.

The key is sequencing. When designing the plan, the clinician should work out which movements are less predictable with aligners alone, whether other means are needed to support them, and when to switch tools, rather than discovering part-way through treatment that the teeth have not kept up with the plan for some time. This is also why a complete diagnosis matters more than picking an aligner brand first.

Finishing treatment is not the end: retainers are what hold the result

After orthodontic treatment, teeth can still drift as periodontal tissues reorganise and under the influence of bite forces, oral habits and natural changes with age. So whether treatment used clear aligners or fixed appliances, a retainer is generally needed as instructed once treatment finishes. Long-term studies also show that alignment can change years later, which is why a retainer is not an optional extra but part of the overall course of treatment.

1. Retainers may be removable, fixed, or a combination of both, chosen to suit the case.
2. Wear is generally more intensive in the period just after treatment and then tapers to long-term maintenance. Patients should not stop wearing a retainer without being assessed first.
3. If a retainer breaks, distorts, no longer fits, or if you notice teeth beginning to move, arrange a check early. The sooner it is dealt with, the easier it usually is to control.

Three cases we are often asked about

One: can someone with gum disease have clear aligner treatment?

Having gum disease does not necessarily rule out orthodontic treatment, but the sequence cannot be reversed: the periodontal condition has to be controlled and stable first, and only then is it assessed whether the teeth can be moved.

Gum disease can cause alveolar bone loss, reducing the support around teeth, and the front teeth may progressively develop spacing, flare outwards or shift. Starting orthodontic treatment while periodontal inflammation is still uncontrolled may increase the risk of further loss of attachment and bone support.

Once the periodontal condition is stable, clear aligners offer two practical conveniences for some patients: first, the plan can be set to move teeth in smaller staged increments; second, aligners can be taken out, so day-to-day cleaning is usually easier than with a fixed appliance. That said, an aligner does not in itself reduce periodontal risk. Whether treatment is safe still depends on the remaining bone support, control of inflammation, how the movement is designed, oral hygiene and regular monitoring.

What the literature says: some studies have observed better plaque and gingival inflammation measures among clear aligner users than in fixed appliance groups, possibly related to easier cleaning. However, the existing findings are not entirely consistent, and the actual periodontal condition still depends heavily on the patient's cleaning habits, whether the periodontal condition is already stable, and professional monitoring during treatment. So it cannot be assumed that using clear aligners necessarily means lower periodontal risk.

To be clear: orthodontic treatment addresses the position of teeth, not alveolar bone and gum tissue already lost. That loss is irreversible, so the earlier periodontal treatment begins, the greater the range within which teeth can usually be moved safely afterwards.
More on periodontal care: assessment, debridement and long-term maintenance →

Two: spacing is relatively easier to treat, but closing it completely is not necessarily ideal

Some cases of straightforward spacing are well suited to clear aligners, but the first step is establishing what is causing the spaces. Spacing can arise from narrow teeth, missing teeth, loss of periodontal support, a labial frenum, tooth position, or a mismatch in tooth size proportions, and the treatment differs by cause.

If the teeth themselves are relatively narrow, closing every space by moving teeth alone can affect the inclination of the front teeth, root parallelism or the proportions of the smile. In some cases orthodontic treatment is used first to redistribute the space, and composite bonding or porcelain veneers are then used to adjust tooth width; whether restorative treatment is needed depends on tooth form, the bite and the patient's expectations.

Three: gummy smile and facial profile — how much can change depends on the actual cause

A gummy smile can arise from tooth position, gum coverage, upper lip movement, the vertical proportions of the upper jaw, or several of these together. Where the problem relates mainly to tooth position, orthodontic treatment, with skeletal anchorage where needed, may improve it; where it is mainly a matter of the gums, the upper lip or clear skeletal factors, periodontal treatment, other non-orthodontic treatment or orthognathic surgery may be required.

Because the causes differ, so does how much clear aligners can improve. An assessment should establish where the problem comes from before setting out what orthodontic treatment can achieve and which parts cannot be changed by an aligner alone.

Changes in facial profile depend on the position of the front teeth, lip support, chin proportions and the skeletal relationship. Orthodontic treatment can influence lip support by changing tooth position, but this does not mean everyone will see a noticeable change in profile, and the result cannot be predicted from the brand of aligner.

What you pay for is more than the aligners themselves

Fees for clear aligner treatment vary widely across the market. What a patient is paying for should not be simply a set of aligners, but an assessment of whether the approach suits them, a complete diagnosis, the treatment design, monitoring through review visits, and the retention arrangements once treatment finishes.

1. Case selection and diagnosis: establishing first whether clear aligners genuinely suit the case, rather than designing a plan around an aligner the patient has already chosen.
2. Treatment design and monitoring: assessing the harder-to-control movements before starting, and checking during treatment that the aligners are seating and the teeth are moving to plan.
3. A clear scope of fees: whether refinement aligners, retainers, imaging and other adjunctive treatment are included should be set out before treatment begins, so no unexpected cost appears part-way through.

Orthodontic treatment starts from HK$30,000. The actual fee depends on case complexity, the appliances chosen, the length of treatment, and whether refinement aligners, skeletal anchorage or hybrid treatment are needed. Before treatment begins the clinic provides a quotation for the individual case, itemising what is included and what is charged separately. A consultation with a Specialist in Orthodontics is HK$400 to HK$1,500, and a general consultation is HK$180.

Want to know roughly where your case sits? WhatsApp us to book an assessment, or call 3956 9387.

Common names and cost considerations for clear aligners

Clear aligners are known by several names, and Invisalign is one brand system among them. Whatever the name, the actual cost depends on how complex the tooth movement is, the expected length of treatment and the number of aligners required; Invisalign pricing may differ from other brands. A dentist provides a specific quote after clinical assessment.

1. Kravitz ND, et al. How well does Invisalign work? A prospective clinical study evaluating the efficacy of tooth movement with Invisalign. Am J Orthod Dentofacial Orthop. 2009;135(1):27–35. (mean accuracy of planned movement about 41%; extrusion among the movements hardest to achieve accurately)
2. Haouili N, Kravitz ND, et al. Has Invisalign improved? A prospective follow-up study on the efficacy of tooth movement with Invisalign. Am J Orthod Dentofacial Orthop. 2020;158(3):420–425. (a study of the same kind recorded mean accuracy of about 50%)
3. Rossini G, et al. Efficacy of clear aligners in controlling orthodontic tooth movement: a systematic review. Angle Orthod. 2015;85(5):881–889. (good performance in alignment; extrusion, large rotations and root control more challenging)
4. Ke Y, Zhu Y, Zhu M. A comparison of treatment effectiveness between clear aligner and fixed appliance therapies. BMC Oral Health. 2019;19:24. (in some more complex cases fixed appliances offered better control)
5. Rossini G, Parrini S, Castroflorio T, Deregibus A, Debernardi CL. Periodontal health during clear aligners treatment: a systematic review. Eur J Orthod. 2015. (periodontal measures during clear aligner treatment; findings across studies are not entirely consistent)
6. Little RM, Wallen TR, Riedel RA. Stability and relapse of mandibular anterior alignment. Am J Orthod. 1981;80(4):349–365. (primarily concerns long-term stability of alignment of the lower front teeth)
7. Little RM, Riedel RA, Årtun J. An evaluation of changes in mandibular anterior alignment from 10 to 20 years postretention. Am J Orthod Dentofacial Orthop. 1988;93(5):423–428. (also confined to the lower front teeth, following changes 10 to 20 years after retention stopped)

Note: these findings reflect the average result for particular study designs, aligner systems and study populations, and cannot directly predict the outcome for an individual patient. The actual plan is decided after clinical and radiographic assessment.

Disclaimer: this page is for educational reference and does not constitute medical advice. Individual treatment outcomes vary, all treatment carries potential risk, and any plan must be decided following clinical examination by a registered dentist. Invisalign is a registered trademark of Align Technology, Inc.